CAPE BIOLOGY U2
SUMMARY/REVISION NOTES
(BY DINELL MOTILAL)
THIS SYLLABUS CONSIST OF 3 MODULES
❖MODULE 1 (Bioenergetics and Conservation) – 4 TOPICS
1. PHOTOSYNTHESIS AND ATP SYNTHESIS (Pg 2 – 23)
2. CELLULAR RESPIRATION AND ATP SYNTHESIS (Pg 24 – 38)
3. ENERGY FLOW AND NUTRIENT CYCLING (Pg 39 – 52)
4. ECOLOGICAL SYSTEMS, BIODIVERSITY AND CONSERVATIONS (Pg 53 – 65)
❖MODULE 2 (Biosystems Maintenance) – 6 TOPICS
1. THE UPTAKE AND TRANSPORT OF WATER AND MINERALS (Pg 66 – 74)
2. TRANSPORT IN THE PHLOEM (Pg 75 – 81)
3. THE CIRCULATORY SYSTEM OF MAMMALS (Pg 82 – 99)
4. HOMEOSTASIS AND HORMONAL ACTION (Pg 100 – 112)
5. THE KIDNEY, EXCRETION AND OSMOREGULATION (Pg 113 – 129)
6. NERVOUS COORDINATION (Pg 130 – 148)
❖MODULE 3 (Applications of Biology) – 4 TOPICS
1. HEALTH AND DISEASE (Pg 149 – 161)
2. IMMUNOLOGY (Pg 162 – 182)
3. SOCIAL AND PREVENTATIVE MEDICINE (Pg 183 – 207)
4. SUBSTANCE ABUSE (Pg 208 – 219)
NB you are expected to have your CSEC knowledge as well
*No form of copyright is intended; these notes are a compilation of what I used as revision*
DINELL MOTILAL CAPE BIOLOGY UNIT 2 SUMAMRY NOTES
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MODULE 1
1. PHOTOSYNTHESIS AND ATP SYNTHESIS
1.1: Relate the structure of a dicotyledonous leaf, a palisade cell and a chloroplast to their
roles in the process of photosynthesis
RE: The basic structure of a leaf and its functions
Plants are autotrophs, they make their own food. They do this by harnessing light
energy from the sun.
The leaf is the main photosynthetic part of the plant and has:
•
a broad, thin lamina – Large Surface Area: Maximum interception of light
– Thin: minimizes the distance for diffusion for gaseous exchange\
– Arrangement (Leaf Mosaic): Maximum interception of light
•
a midrib
•
a network of veins
THE BASIC STRUCTURE OF A LEAF
DINELL MOTILAL CAPE BIOLOGY UNIT 2 SUMAMRY NOTES
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What is Photosynthesis?
Photosynthesis is a process where AUTOTROPHS (or producers) take in inorganic
molecules and produce organic substances, such as CARBOHYDRATES. These
carbohydrates contain trapped energy that the organism can release and use from a molecule
called ATP. Doing so is called RESPIRATION.
What is ATP?
ATP (or adenosine triphosphate) functions as the intracellular energy currency in all
organisms. It contains a nitrogenous base (adenine), a ribose sugar and three inorganic
phosphate groups (Pi). When the bonds between these groups are broken,
energy is released.
RE: The basics about photosynthesis;
those photosynthetic organisms (such as plants) contain CHLOROPLASTS which houses
the light- capturing pigment, CHLOROPHYLL, in membranes (such as phytoplankton).
The word and chemical equations for photosynthesis in green plants can be written as:
CARBON DIOXIDE + WATER → GLUCOSE + OXYGEN
In simple terms, during photosynthesis, plants take in carbon dioxide (CO2) and water (H2O)
from the air and soil. Within the plant cell, the water is oxidized, meaning it loses electrons,
while the carbon dioxide is reduced, meaning it gains electrons. This transforms the water
into oxygen and the carbon dioxide into glucose.
Before we go further into how photosynthesis actually occurs let’s take a look at the internal
structure of a dicotyledonous leaf.
DINELL MOTILAL CAPE BIOLOGY UNIT 2 SUMAMRY NOTES
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THE STRUCTRUE OF A DICOTYLEDONOUS LEAF (internal structure)
YOU MUST BE ABLE
TO:
- Annotate
-Draw from prepared
slides
-Functions
- Descriptions
TISSUE / SEGMENT
Cuticle
Upper epidermis
Lower epidermis
Spongy mesophyll
DESCRIPTION
Waxy cuticle
FUNCTION
A water tight layer that
reduces water loss by
preventing water vapour
from escaping.
Also, protects against
microorganisms and some
insects
Thin layer of transparent
Secretes waxy cuticle. The
cells, usually coated with waxy cuticle limits water
a watertight, waxy cuticle. loss through the top
to allow maximum
of leaf; protects against
penetration of light to the insects and microbes;
lower levels.
transparent to allow
sunlight in.
Thin layer of cells
Guard cells‟ unevenly
interspersed with
thickened cell walls
GUARD CELLS, which
absorb water via osmosis
form stomata.
and „curve‟ to open
the stomata. This allows
DIFFUSION and
TRANSPIRATION to
occur.
Loosely and irregularly
Facilitates diffusion of
packed layer of cells with materials and gaseous
numerous air spaces.
exchange between the
palisade mesophyll and
stomata.
DINELL MOTILAL CAPE BIOLOGY UNIT 2 SUMAMRY NOTES
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Palisade mesophyll
Cylindrical cells arranged in an upright manner. They
contain a large number of CHLOROPLASTS to
facilitate light absorption. This type of packing creates
several long, narrow air spaces.
Contain a very LARGE VACUOLE so as to keep
chloroplasts on the outer edges of the cells (to
maximize exposure to light). They are also adjacent to
VASCULAR BUNDLES, which supply water via the
XYLEM.
Contain very THIN CELL WALLS to facilitate
efficient diffusion of gases.
The chloroplasts are MOBILE due to proteins in the
cytoplasm.
Xylem
Supply leaf with water and ions.
Phloem
Removes assimilates (such as sucrose and amino acids)
to be transported to other parts of the plant.
Chloroplast
Organelle in cell that contains chlorophyll. Allows
plant to harness light energy to make its own food.
Sub-stomatal Air Space Store CO2 when stomata are closed.
Guard Cell
Specialised cells in lower epidermis that control the
opening and closing of stomata
Stoma
Opens and closes stoma due to change in shape based
on turgidity.
Tiny holes in lower epidermis (and rarely upper
epidermis) through which CO2 enters, O2 enters and
exits and H2O exits the leaf.
Alternative Diagram:
DINELL MOTILAL CAPE BIOLOGY UNIT 2 SUMAMRY NOTES
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Prepared slides of a transverse section of a dicotyledonous leaf, and a palisade cell.
DINELL MOTILAL CAPE BIOLOGY UNIT 2 SUMAMRY NOTES
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Now we go further into the structure of a leaf where the main parts of photosynthesis
occur, The Palisade cell.
A “palisade” is a fence, so think of the arrangement as such where there are ‘pickets’
with air-filled gaps between them with long, narrow areas of contact between the air
and the cells.
They are long cylinders arranged at right-angles to the upper epidermis. This
reduces the number of light-absorbing cross walls in the upper part of the leaf
so that as much light as possible can reach the chloroplasts. On hot, bright days,
chloroplasts rearrange positions so that not all are exposed to this intense light
energy.
The cells have a large vacuole with a thin peripheral layer of cytoplasm. This
restricts the chloroplasts to a layer near the outside of the cell where light can
reach them most easily.
The chloroplasts can be moved (by proteins in the cytoplasm, as they cannot move
themselves) within the cells, to absorb the most light or to protect the chloroplasts
from excessive light intensities.
The palisade cells also show adaptations for gaseous exchange.
The cylindrical cells pack together with long, narrow air spaces between them. This
gives a large surface area of contact between cell and air.
The cell walls are thin, so that gases can diffuse through them more easily.
DINELL MOTILAL CAPE BIOLOGY UNIT 2 SUMAMRY NOTES
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Moving in further, we will now look at where photosynthesis occurs, The Chloroplast.
Chloroplasts are double-membraned
organelles that contain inner membranes
called LAMELLAE and sacs called
THYLAKOIDS, which are then stacked to
form GRANA. These are efficient at
trapping light due to their large surface
area. Thylakoid LUMENS aid in
production of ATP by holding H+ ions.
Structure:
Envelope (inner/outer membrane) –
double membrane surrounding the
organelle.
Stroma – Site of the light-independent
stage. Gel like structure that contains
enzymes, sugars and other organic
compounds
Starch Grain - small granules that store
energy (starch)
Lipid Droplet – Stores fats/oils
Ribosomes (70S) – Protein Synthesis
Stroma Lamella – Connects Grana
Thylakoid – Fluid Filled sacs and the site
of the light dependent stage.
Granum/Grana – Consist of stacks sacs
Circular DNA – Contain instructions to
make proteins in chloroplast.
MICROGHRAPH OF CHLOROPLAST
Within the chloroplast are
photosynthetic pigments such as
chlorophyll. Chlorophyll comes in
two forms, chlorophyll a and
chlorophyll b.
Chlorophyll a and b are similar, but
absorbs slightly longer
wavelengths of light.
Leaves appear green because they
absorb all colour wavelengths except
green (which they reflect). Another
pigment, CAROTENOIDS, tend to
reflect red and orange instead.
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Light, Absorption and Action Spectrum
Light
-
Visible Light
Re: ROYGBIV
Quality of Light
- The specific wavelength
necessary for photosynthesis
Absorption Spectrum
Chlorophyll A – Blue and Red
Chlorophyll B – Blue Green and Red
Carotenoids
Nb the Differences between chlorophyll A and B
Engelmann Experiment
if absorption is maximum then photosynthesis should also be maximum. This has been
interpreted as the action spectrum that was determined by Engelmann.
This experiment was done by exposing green algae in an aquatic medium to visible light.
V
I
B
G
Y
O
R
Visible Light
O O
O
O
O
O
O
Algae
Oxygen Bubbles
What was observed is that at the blue
and red regions, many bubbles were
emitted. These bubbles were the results
of a reaction taking place – this
reaction was photosynthesis where
oxygen was released as a by-product.
The more oxygen bubbles liberated
indicated that photosynthesis was high
– which occurred at the blue (B) and
red (R) regions.
The maximum reaction/action occurred
in these two regions can be represented
by an action spectrum graph;
DINELL MOTILAL CAPE BIOLOGY UNIT 2 SUMAMRY NOTES
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Last but not least, before we move into the in-depth process of photosynthesis, we would
look at a Quantasome/Antenna Complex (A collection of pigments)
Light
Other Pigments
Chlorophyll A, B, C....
Carotenoids
Chlorophyll A
Light
Reaction Center
Light
NB: A major advantage of Chlorophyll A (Ch a) being surrounded by “other pigments” is
that:
-
It acts as a barrier from UV light (Ultraviolet light)
It allows for the maximum amount of light to enter as the other pigments also absorb
light.
Some other pigments:
-
Carotenoids (Lipids)
Carotene (C40H56) (orange red in colour)
Phycobilin’s (Blue Green)
Xanthophyll’s (C40H56O2) (Yellow-ish brown in colour)
Now we will move onto how photosynthesis actually occurs;
DINELL MOTILAL CAPE BIOLOGY UNIT 2 SUMAMRY NOTES
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1.2: Explain the process of photophosphorylation with respect to photosynthetic electron
transport
Re; The overall equation for photosynthesis:
This equation shows a simplified way as to how it occurs. However, it’s a more metabolic
process and can be split up into 2 stages:
▪
▪
The light Dependent Stage
The light Independent Stage
Before jumping into the process lets understand what is Photophosphorylation.
What is Photophosphorylation?
Photo means (the use of light) and phosphorylation means (the adding of a phosphate to a
compound) in this case ATP. Hence, Photophosphorylation is a biochemical process that uses
light to attach a phosphate group to an organic compound (usually ADP to form ATP)
Overall Process
DINELL MOTILAL CAPE BIOLOGY UNIT 2 SUMAMRY NOTES
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THE LIGHT DEPENDENT STAGE
The light dependent stage, occurs on the thylakoids in the grana inside the chloroplast. Here,
light energy is captured by chloroplast pigments such as chlorophyll, carotene and
xanthophyll. There are two types of chlorophyll (a & b). Chlorophyll a absorbs slightly
longer wavelengths than b. Carotene and xanthophyll are carotenoids which are accessory
pigments that allow plants to absorb a wide range of short wavelength (blue-green) light it
would not ordinarily be able to use. The goal is to use the light energy and the splitting of
water, to make ATP and reduce NADP. The pigments in the chloroplast are arranged into
light-harvesting complexes arranged around a reaction centre. Each one is a photosystem.
There are two of these photosystems:
• photosystem I (PSI) (Location: Inter-granal lamellae)
• photosystem II (PSII) (Location: Granal lamellae
At the centre of each photosystem is a chlorophyll a molecule. In PSI this molecule has a
maximum absorption at 700 nm and in PSII it has a maximum absorption at 680 nm. The
chlorophyll molecules are often known as P700 and P680. Energy is transferred from
accessory pigments to the reaction centre.
DINELL MOTILAL CAPE BIOLOGY UNIT 2 SUMAMRY NOTES
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Light of many wavelengths is absorbed, and the energy excites an electron in the centre of the
chlorophyll molecule in PSII. This excited electron leaves and is accepted by one of the
electron carriers in the thylakoid membrane. As it passes from carrier to carrier, energy is
released in small ‘packets’ and is used by the carrier molecules to move protons from the
stroma into the thylakoid space. This is a form of active transport. The electron now has a
lower energy level when it reaches PSI. The absorption of light by this photosystem reenergises the electron and it is accepted by another electron carrier. From here it travels to
NADP, which accepts the electron and a proton from the stroma to become reduced NADP.
NADP + e- + H+ → reduced NADP
There are actually 2 pathways that the electrons can take:
Non-cyclic photophosphorylation- electrons travel from PSII to PSI and then to NADP
Hence, in summary of Non-Cyclic Phosphorylation, the products are NADPH/Reduced
NADP, ATP and Oxygen as a waste/ by-product of photosynthesis.
Therefore, Electros travel from PSII to PSI and then to NADP
Key Points of NCP;
1) Occurs in the Thylakoid.
2) Photolysis complex in found in
the inner membrane.
3) NADP reductase is found on the
outer membrane.
DINELL MOTILAL CAPE BIOLOGY UNIT 2 SUMAMRY NOTES
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Cyclic photophosphorylation- electron travels from PSI but instead of reaching NADP they
return to PS I. While it does not lead to reduced NADP, it does generate sufficient energy to
combine inorganic phosphate with ADP. (Occurs in the Stroma Lamellae)
Essentially, Cyclic Photophosphorylation can be defined as the synthesis of ATP during the
light reaction stage of photosynthesis, resulting to a ‘cyclic’ movement of electrons to and
from Photosystem I (PSI). The excited electron ‘return’ to the PSI chlorophyll, and the cycle
restarts. This usually occurs in isolated chloroplasts and photosynthetic bacteria.
Differences/Similarities between CP and NCP
Factor
Is ATP Produced?
Photosystem Involved?
Non-Cyclic
Yes
PSI and PSII
Cyclic
Yes
PSI Only
Is Reduced NADP Made?
Yes
No
PSI replacement electrons found where?
From the electron
emitted in PSII
PSII replacement electrons found where?
Predominated when?
From the Photolysis
of water
Aerobic Conditions
From the electrons
that is emitted form
itself
PSII is not involved
in Cyclic
Anaerobic Conditions
Evolution of Oxygen?
Yes
No
DINELL MOTILAL CAPE BIOLOGY UNIT 2 SUMAMRY NOTES
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The electrons lost by PSII are replaced by photolysis. This is catalysed by a water splitting
enzyme found on the inner side of the thylakoid membrane.
2 H2O → 4H+ + 4e- + O2
The accumulation of protons lowers the pH inside the thylakoid membrane thereby creating
an electrochemical gradient. The membranes are impermeable to protons except through ATP
synthetase channel proteins that span the membrane. Part of this remarkable protein spins as
protons pass through it travelling down their electrochemical gradient. As the protein spins,
the active site accepts ADP and a phosphate ion. Energy is transferred so a bond forms
between the terminal (one at the end) phosphate on ADP and the phosphate ion. This is a
phosphorylation reaction.
Proton Gradient in Non-Cyclic Photophosphorylation
To break down the above into steps/points to better understand:
•
•
•
•
Water is split into H+ ions, O2 and electrons, which are released as they become
“excited” by light.
As the electron passes from PSII to PSI, it stimulates the movement of H + ions from the
stroma to the thylakoid lumen. This establishes a proton gradient.
The proton gradient allows H+ ions to flow from the thylakoid to the stroma. These form
ATP as the H+ pass through ATP synthase enzymes embedded in the membrane.
Finally, H+ ions and electrons reduce NADP to form NADPH.
To further simplify this “Proton pump” process here is alternative explanation;
o In the electron transport chain from PSII to PSI as the electron goes through energy is
released. The energy released is used by the electron transporter “Cytochrome” to
actively pump a pair of protons (H+) into the lumen of the thylakoid.
o The photolysis complex on the inner membrane of the thylakoid allows for the
splitting of water into a pair of electrons, a pair of protons and an oxygen atom. The
pair of electrons is used to replace the electrons in PSII, the Oxygen is released as a
byproduct.
o With the pair of protons evolved from the photolysis of water and the pair of protons
that was actively pumped into the lumen, there is now a high concentraiton of protons
in the lumen. The pair of protons will move from a region of high proton
concentraiton (the lumen of the thylakoid) to a region of low proton concentraiton
(the stroma) via diffusion.
DINELL MOTILAL CAPE BIOLOGY UNIT 2 SUMAMRY NOTES
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o In order for the proton ions to leave via diffusion there are channels that proteins
(integral protein that is in the thylakoid membrane and an extrinsic protein on the
outer membrane that helps move the protons). When the protons move through these
protein channels energy is released in which the extrinsic protein acts as ATPase
which converts ADP by adding an inorganic phosphate to form ATP. Hence the
products are ATP and a pair of protons that move onto NADPH and the dark/light
independent reaction.
DINELL MOTILAL CAPE BIOLOGY UNIT 2 SUMAMRY NOTES
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1.3: Outline the essential stages of the Calvin cycle and light independent fixation of carbon
dioxide;
THE LIGHT INDEPENDENT STAGE (CALVIN CYCLE)
Re; that from the light-dependent stage of photosynthesis the products were ATP, Reduced
NADP and the by-product oxygen.
In the light-independent stage of photosynthesis also referred to as the Calvin Cycle, we need
the products from the light dependent stage (ATP and reduced NADP) together with Carbon
Dioxide from the atmosphere.
This stage occurs in the Stroma of the chloroplast and involves a series of reactions that will
occur and lead to the raw product that can be used to make glucose.
There are three main processes:
o Carbon dioxide fixation/ Carbon fixation/ Carboxylation
o Reduction (to form Carbohydrates)
o Regeneration of RuBP (the Carbon Dioxide acceptor molecule)
In the stroma there is a special enzyme called ribulose biphosphate carboxylase aka.
(RUBISCO) which catalyses a reaction to combine carbon dioxide with Ribulose
bisphosphate (RuBP). Ribulose bisphosphate is a 5C (Pentose) substance that when it reacts
with CO2 it produces an unstable intermediary 6C compound.
The unstable 6C intermediate immediately splits in two 3C compounds known as
phosphoglyceric acid (PGA) or glycerate 3-phosphate (GP). This is the first main process of
carbon fixation that occurs. PGA can be used to make glycerol, amino acids and fatty acids
(outside of the Calvin cycle process).
The ATP and reduced NADP are used to provide phosphate groups and energy to reduce and
phosphorylate the PGA to another 3C compound, triose phosphate (TP). Of the 12 TPs
produced, 10 will be recycled to RuBP (5/6) and 2 can be used to produce a hexose sugar
(glucose or fructose) or glycerol (1/6).
Hexose sugar can then be polymerised to form various polysaccharides (starch or cellulose).
NB: The entire purpose here is to create GLUCOSE which is a 6C sugar/Hexose (or fructose,
sucrose, etc.) These sugars are made from the triose phosphate (or G3P), after the reduction
of phosphoglyceric acid. G3P is a key molecule here, as it also helps re-initiate the cycle.
It takes Six (6) Calvin cycles to make 1 molecule of Glucose.
And, 18 ATP and 12 NADPH to make one molecule of Glucose.
Look at the diagram in the next page to better understand how this process works;
DINELL MOTILAL CAPE BIOLOGY UNIT 2 SUMAMRY NOTES
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THE CALVIN CYCLE
1.4: Discuss the concept of limiting factors in photosynthesis.
What is a limiting Factor?
A limiting factor is any factor that is present in the least desirable amount and limits the rate
of a process.
Recall that photosynthesis requires the presence of the following:
▪
▪
▪
▪
(Light Energy) Energy in the form of sunlight
Raw materials (carbon dioxide and water)
(Temperature) A reasonable temperature (usually around 25-35oC)
Chloroplasts and light-capturing pigments, such as chlorophyll
The limitation of any of the above will also limit the rate of photosynthesis. Hence, these are
known as LIMITING FACTORS of photosynthesis.
DINELL MOTILAL CAPE BIOLOGY UNIT 2 SUMAMRY NOTES
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The Limiting Factors of Photosynthesis
Light Intensity: As light intensity increases the rate
of photosynthesis increases. Light provides energy to
excite ELECTRONS in chlorophyll reaction centers
that eventually trigger reactions. Since there are only
a finite number of chlorophyll molecules, light stops
being a limiting factor at a certain intensity as all of
them are already „firing‟. This is called the
saturation point. Increasing light intensity after this
point does not increase rate of photosynthesis.
CO2 Concentraiton: As CO2 concentration
increases the rate of photosynthesis increases
Carbon dioxide is required in the chloroplasts to
donate carbon atoms to RuBP to produce hexose
sugars that eventually turn into glucose that is
facilitated through the enzyme, RUBISCO. If CO2
concentration is limited/low, the Calvin Cycle
process is slowed down decreasing the rate of
Photosynthesis since the rate of carboxylation
catalysed by RUBISCO will be slower than if the
concentration was higher, Increasing Carbon
dioxide which would increase the rate of
photosynthesis. Similarly, as light intensity, it
reaches saturation at a certain concentration and
plateaus.
Temperature: As temperature increase the rate of
photosynthesis increase as the reactions are
controlled by enzymes. Enzymes are globular
proteins that usually have a tertiary structure. Their
bonds can be broken if too much heat or kinetic
energy is applied causing the enzyme structure to
change. Hence, DENATURAITON. Enzymes of the
Calvin cycle are temperature dependent so at low
temperatures, the rate of the light independent stage
is low. At higher temperatures RUBISCO will sort of
malfunction and combine RuBP with Oxygen instead
of Carbon Dioxide (Wasting RuBP). This is called
photorespiration. In which the rate of photosynthesis
is reduced. Higher temperature will denature the
enzymes and the Calvin cycle Stops.
DINELL MOTILAL CAPE BIOLOGY UNIT 2 SUMAMRY NOTES
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This is not Considered as a factor but should still be mentioned;
Oxygen Concentraiton: Rubisco is an enzyme with an active site that not only accepts
Carbon dioxide but also Oxygen. This means that oxygen competes with Carbon Dioxide in
the active site; the enzyme acts as OXYGENASE and produces less fixed carbon. At low
concentrations of Carbon dioxide this effect reduces and the rate at which carbon dioxide is
fixed and TP is produced.
Experiment: Investigating the effect of Limiting Factors on the rate of Photosynthesis.
Apparatus Setup
The easiest parameter to measure is the volume of O2 given off. An Audus photosynthometer
can be set up as shown above.
Precautions:
• Ensure apparatus is airtight and that no air bubbles were introduced during set up.
• Leave apparatus in the dark for at least 2 hours after set up and before conducting
experiment to ensure photosynthesis doesn’t occur and that any oxygen produced would have
dissipated.
• Water bath is used to ensure constant temperature is maintained.
• Instead of pond water, potassium/sodium hydrogen carbonate solution can be used as a
source of carbon dioxide.
• Conduct experiment in a dark room to control light exposed to the plant.
• Use LED light source to limit excess heat affecting set up.
DINELL MOTILAL CAPE BIOLOGY UNIT 2 SUMAMRY NOTES
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Method:
Turn on light source and start stopwatch. After 30 minutes, using syringe, gently draw up air
bubble to region above scale so the size of the air bubble could be measured. Reset apparatus
and repeat 4-5 times to find average to determine the volume of oxygen produced per hour.
Limiting Factors:
Light intensity
The light intensity is changed by plugging in the lamp to a variable resistor and changing the
current flowing to the lamp, or by putting the lamp at different distances from the plant. The
actual light intensity can be measured with a light meter. When light is the limiting factor, the
rate of photosynthesis is directly proportional to light intensity. As light intensity is increased,
the volume of oxygen produced, and carbon dioxide absorbed due to photosynthesis will
increase to appoint where the oxygen absorbed and carbon dioxide The Student Hub CAPE
Biology Unit 2 Notes 5 August 2022 produced by respiration. At this point there would be no
net exchange of gases into or out of the plant. This is the light compensation point. Further
increases in light intensity will cause a proportional increase in the rate of photosynthesis and
increasing volumes of O2 will be given off and CO2 taken up.
Carbon dioxide concentration
The optimum concentration of CO2 for a consistently high rate of photosynthesis is 0.1%
(atmosphere 0.04%). Carbon dioxide concentration is changed by making up a series of
solutions of sodium hydrogen carbonate. This dissolves in water to form hydrogen carbonate
ions (HCO3-), which diffuse into cells and into chloroplasts to form carbon dioxide, which is
then fixed in the Calvin cycle. The experiment is repeated using differing concentrations of
sodium hydrogen carbonate each time.
Temperature
The experiment is repeated using different temperatures. This is easily controlled if using an
electronic water bath.
Possible sources of error:
• The rate can be underestimated as some of the oxygen produced would be used up in
respiration.
• It can also be overestimated as dissolved oxygen, nitrogen and other gases are often
released from the leaf and surrounding water and included in the gas volume measured.
DINELL MOTILAL CAPE BIOLOGY UNIT 2 SUMAMRY NOTES
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Minor Summary from The Student Hub Bio U2 Class Notes:
DINELL MOTILAL CAPE BIOLOGY UNIT 2 SUMAMRY NOTES
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1.5: discuss how knowledge of these can be applied to the improvement of plant productivity.
Photosynthesis is a major factor in crop production. The rate of photosynthesis would be
determined by the factor in shortest supply (limiting factor). Identifying and increasing this
factor would therefore increase the rate of photosynthesis and plant productivity. Determining
the limiting factor at any one time and mitigating its effects is commercially valuable to
stakeholders. Farmers and growers of protected crops (e.g., tomatoes, lettuce and cucumber)
in temperate countries have fully automated glasshouses that:
1. control light intensity with artificial lighting and shading
2. control temperature with heaters and ventilation
3. enrich the carbon dioxide concentration by burning hydrocarbons (e.g., propane)
4. supply water direct to the roots or by using sprinklers
5. supply mineral nutrients direct to roots at the concentrations appropriate to the growth
stage of the crop.
In the Caribbean, growers use plastic and mesh greenhouses to control the conditions. Plastic
protects against heavy rain and the mesh reduces light intensities so that salad crops are not
scorched. Both also protect against insect pests, so reducing costs of pesticides. Drip
irrigation is also used, reducing costs of watering as water is supplied direct to the plants.
Growers of field crops such as cereals, sugar cane, soya, yams and cassava, are not able to do
much about carbon dioxide concentration, light intensity or temperature. However, they can
provide irrigation and drainage to ensure that water is not a limiting factor for growth, and
apply fertilisers to ensure mineral nutrients do not limit growth. They can also sow their crops
at an optimum density, so the plants do not shade each other. All farmers and growers take
steps to reduce the activities of competitors (weeds), pests and diseases. Simply increasing
levels of all factors would not be practical as different crops photosynthesise at the optimal
rate at different ranges of these factors. Conditions conducive to the particular species being
grown must be set. Also, it may not be cost effective to keep all factors at high levels when it
is not necessary. Profitability is also very important to farmers and other stakeholders.
GREENHOUSES can have artificial light so that photosynthesis can continue beyond
daylight hours, or at a higher-than-normal light intensity. The use of paraffin lamps inside a
greenhouse increases the rate of photosynthesis because the burning paraffin produces carbon
dioxide as well as heat.
GROWTH CHAMBERS can also offer precise controls of environmental limiting factors
such as temperature regulation and CO2 concentration for crops sensitive to fluctuating
abiotic factors, such as groundnuts, or in areas prone to drought.
HYDROPONICS are liquid-medium, soil-less systems that plants are sometimes grown
in. Hydroponics allow the grower to optimize mineral ions given to plants. Mineral ions are
required to synthesise other essential molecules from the glucose produced during
photosynthesis.
DINELL MOTILAL CAPE BIOLOGY UNIT 2 SUMAMRY NOTES
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2. CELLULAR RESPIRATION AND ATP SYNTHESIS
2.1: Explain the sequence of steps in glycolysis.
Before we get into Respiration. The Respiration that is going to be discussed about is a
“Chemical Process” which is not to be confused with “Ventilation” the physical process.
Respiration takes a high energy molecule like glucose and turns it into low energy molecules
like carbon dioxide and water to produce energy. From glucose, only 39% of the energy is
converted to ATP whereas 61% of the energy is lost as heat.
There are two (2) types of respiration:
o Aerobic: a process that consists of a series of steps (metabolic reactions) that lead to
the breakdown of glucose (or other compounds such as fat and protein) into CO2 and
H2O in order to produce ATP
o Anaerobic: respiratory process that occurs in both prokaryotes and eukaryotes in
which cells break down the sugar molecules to produce energy without the presence
of oxygen
For now, we will focus on Aerobic Respiration (With Oxygen).
As we recall; Cellular respiration is a process that consists of a series of steps (metabolic
reactions) that lead to the breakdown of glucose (or other compounds such as fat and protein)
into CO2 and H2O in order to produce ATP.
On average 36-38 molecules of ATP can be generated from the breakdown of 1 glucose
molecule (depending on conditions).
This process can be broken down into 3
main components:
• Glycolysis,
• Krebs cycle,
• Electron transport chain and oxidative
phosphorylation.
The breakdown of glucose is an oxidationreduction (redox) reaction. Recall OiL
RiG: Oxidation is Loss of electrons and
Reduction is Gain of electrons. Conversely
the opposite is true with respect to protons
(H+). The breaking of -CH bonds lead to
release of e- and H+ that affects
compounds in different ways.
Now we will move onto the first stage of Cellular Respiration...
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What is Glycolysis?
Glycolysis translates to “breaking apart of glucose‟ and occurs in the cytosol of cells and
does not require O2 to function. It comprises of a series of steps that are catalysed by various
enzymes (the names of which you do not need to know).
This process can be summarised by the equation below:
Glucose → 2 pyruvate + 2 ATP + 2 NADH
This process can be broken down into steps (all of which you NEED!! To know):
Glucose (6C)
ATP
1
ADP
Glucose 6-phosphate (6C)
Structural
2
Isomers
Fructose 6-phosphate (6C)
3
ATP
ADP
Fructose 1,6-bisphosphate (6C)
4
Glyceraldehyde-3-phosphate (3C)
5
Pi
Glyceraldehyde-3-phosphate (3C)
NAD (Oxidised)
Pi
NADH (Reduced)
NADH (Reduced)
1,3-bisphosphoglycerate (3C)
6
1,3-bisphosphoglycerate (3C)
ADP
.
ADP
ATP
.
ATP
3-phosphoglycerate (3C)
7
3-phosphoglycerate (3C)
H2O
.
Phosphoenolpyruvate (3C)
8
NAD (Oxidised)
H2O
Phosphoenolpyruvate (3C)
ADP
.
ADP
ATP
.
ATP
Pyruvate (3C)
DINELL MOTILAL CAPE BIOLOGY UNIT 2 SUMAMRY NOTES
Pyruvate (3C)
2023/2024
1. Glucose is phosphorylated by ATP to form glucose-6-phosphate by adding a phosphate.
This uses 1 ATP. Hence, it raises the energy level of the compound so it can participate in
the subsequent steps that follow.
2. Glucose-6-Phosphate is isomerized to form Fructose-6-Phosphate. Structural Isomer
(Change in shape). Isomerisation is the reorganising of atoms in the compound. None is
added or removed.
3. Another phosphorylation reaction occurs whereby Fructose-6-Phosphate is
phosphorylated by ATP to produce Fructose-1,6-Bisphosphate. This uses 1 ATP.
4. Fructose-1,6-Bisphosphate is unstable and eventually undergoes LYSIS (catabolic
reaction) to become two 3C sugar molecules, glyceraldehyde-3-phosphate.
Glyceraldehyde 3-phosphate, also known as triose phosphate or 3-phosphoglyceraldehyde
and abbreviated as G3P, GA3P, GADP, GAP, TP, GALP or PGAL.
5. Glyceraldehyde 3-phosphate is oxidised with the help of a DEHYDROGENASE
(hydrogen-removing) enzyme. Dehydrogenase functions if an enzyme helper (coenzyme)
called NAD is present. The hydrogen removed is taken up by NAD so that it is
simultaneously reduced to NADH*. Additionally, 2Pi from the cytoplasm are added and
this leads to the formation of 1,3-bisphosphogylcerate.
6. 1,3-bisphosphogylcerate undergoes Substrate level phosphorylation. This is the formation
of ATP by enzymatic transfer of Pi (inorganic phosphate) to ADP from metabolic
intermediate. Energy for this comes from the energy originally in the glucose molecule.
Re: phosphorylation is the addition of a phosphate group. This forms 3-phosphoglycerate.
7. Oxidation reaction where water is removed to convert 2-phosphoglycerate into
Phosphoenolpyruvate
8. Same as step 6 but occurs from Phosphoenolpyruvate to finally form Pyruvate.
Note: *NAD (nicotinamide adenine dinucleotide) is a coenzyme (helps and enzyme) that is
an electron acceptor in cellular respiration. Oxidised NAD (NAD+) accepts electrons and
hydrogen and becomes reduced NAD (NADH); (Relatable to step 5)
2H (From substrate) → 2H+ + 2e2H+ + 2e- + NAD+ → NADH + H+
In the end there will be 2 Pyruvate, 2ATP and 2NADH produced.
Also note You must be able to recognise simplified structural diagrams of the intermediates.
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2.2: Describe the structure of a mitochondrion, relating its structure to its function
STRUCTURE OF A MITOCHONDRION
Outer mitochondrial membrane Composed of phospholipid bilayer and
proteins.
Inner mitochondrial membrane Phospholipid bilayer with protein
complexes of ETC and ATP synthases.
Pumps
hydrogen
ions
into
intermembranal space.
Loop of DNA - Codes for 13 proteins
used in the mitochondria genes are
transcribed as mRNA. Rest of
mitochondrial proteins coded for by
nucleic DNA.
Intermembranal space - Lower pH than
matrix due to increased concentration of
H+ ions.
Cristae/Crista - Infolding of the inner
membrane to increase surface area for
enzymes to recycle NAD quickly
through ETC ATPases.
Matrix - Protein rich and site of link
reaction Krebs cycle
Ribosome (70S) - Composed of rRNA
and proteins. Site of translationassembly of amino acids to form proteins
NB:
• More active cells like liver
and muscle cells have more
mitochondria.
• The inner and outer
membranes
of
the
mitochondrion
form
its
envelope. In general, the
mitochondrion is narrow to
keep the diffusion distances for
substances to a minimum.
• The larger surface area of
cristae means more ATP and
reduced
NAD
can
be
produced.
• Cristae from different cell
types differ: more active cells
have longer more densely
packed cristae than less active
cells.
DINELL MOTILAL CAPE BIOLOGY UNIT 2 SUMAMRY NOTES
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DINELL MOTILAL CAPE BIOLOGY UNIT 2 SUMAMRY NOTES
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2.3: State the fate of pyruvate in the cytosol when oxygen is available.
Once oxygen is available pyruvate will undergo aerobic respiration. Before this can happen,
the link reaction must take place in order to transform pyruvate into a form that can enter the
Krebs cycle. This occurs in the matrix of the mitochondrion.
The link reaction is also known as oxidative decarboxylation.
Decarboxylation is the removal of CO2. Simultaneously, hydrogen is also removed from the
pyruvate to reduce NAD to form NADH. What is left is a 2C acetyl molecule. This binds to
coenzyme A to form acetyl coenzyme A (Acetyl CoA).
Therefore;
o Glycolysis converts 6C glucose into 3C pyruvate.
o The link reaction turns 3C pyruvate into 2C acetyl coA, needed for the Krebs cycle. A
carbon leaves via creation of CO2.
o The Krebs cycle allows 2C acetyl coA to combine with 4C oxaloacetate to become 6C
citrate, which initiates steps to oxidative phosphorylation, where ATP is formed.
o The ETC also drives ATP production but also helps create water.
What is the Link Reaction?
As stated above, the link reaction is named as such as it is the intermediate step that “links‟
glycolysis (which produces pyruvate) to the Krebs cycle (which produces ATP). Another
name for it is oxidative decarboxylation (called that because carbon dioxide is removed
during this process).
THE LINK REACTION
➢ You can see pyruvate (3C) is losing a carbon due to the removal of carbon dioxide.
➢ Hydrogens are removed as this occurs, which are captured by NAD to reduce it to
NADH.
➢ An enzyme known as coenzyme A (or CoA) converts the 2C compound to Acetyl
CoA (2C). If the Krebs cycle was a car, think of Acetyl CoA as the gasoline to keep
it going…
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2.4: Explain the significance of the Krebs cycle in ATP production.
The Krebs cycle is a series of steps that occur within the MATRIX of the mitochondria.
There are two main things that happen here:
A 6C compound (citrate) is gradually turning into a 4C compound (oxaloacetate)...
While ATP is being produced once per cycle (amongst other molecules that also help
produce ATP).
Remember Acetyl CoA? This is a 2C compound. With the help of coenzyme, A once again,
this combines with a 4C compound called oxaloacetate. This creates a 6C
compound called citrate. Two carbon dioxides leave after some steps. Remember
that as this happens, hydrogens are released as well. And what „catches‟ those? NAD! So, each
time, NAD is reduced to NADH. Since two CO2’s leave, the 6C becomes a 5C, then a 4C. As
other enzymes come into play, so does another coenzyme call FAD. FAD works like NAD. It
accepts hydrogens to reduce to FADH2, which can go on to form 1.5 ATP when re-oxidized.
(NADH yields 2.5 ATP) Eventually, the 4C compound becomes oxaloacetate once again,
waiting to combine with Acetyl CoA (from the link reaction) to become citrate and restart the
cycle.
THE KREBS CYCLE
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To briefly recap the cycle;
3C pyruvate loses a CO2 to turn into 2C Acetyl CoA, with help from coenzyme A.
When CO2 is removed, NAD accepts a hydrogen and reduces to NADH.
2C Acetyl CoA combines with 4C oxaloacetate to become 6C citrate.
6C citrate becomes a 4C compound after two CO2’s are removed (which lead to two more
hydrogens being accepted by NAD and two NADH‟s being formed).
ATP is produced now. Only one ATP per cycle like this. This is substrate-level
phosphorylation.
As hydrogens are being lost from the 4C compound, FAD is reduced to FADH2. This
cycle will then restart once the 4C compound becomes oxaloacetate again.
FADH2 and NADH can yield ATP if they become FAD and NAD once again if they are
oxidized (lose their hydrogens) again. This is called oxidative phosphorylation.
2.5: Explain the process of oxidative phosphorylation with reference to the electron transport
chain
Oxidative phosphorylation can be defined simply as the use of OXYGEN to attach a
phosphate group (Pi) to ADP for it to become ATP.
This is facilitated through an electron transport chain, which is a collection of molecules (a
series of electron carriers and proteins) embedded in the inner membrane of the cristae.
NB: Details of electron carriers are not required.
Generally, in the electron transport chain, electrons are shuttled from one molecule to
another. This releases energy. This energy is used to form an electrochemical gradient and
used to make ATP.
At the end of the ETC is OXYGEN. Think of oxygen completing a “circuit‟, so if oxygen
isn’t present, the entire chain is “broken‟ and stops working, so no ATP is made (more of this
explained later on).
Recall that when NAD is “caught” by a hydrogen (accepts a hydrogen), it is reduced to form
NADH (Reduced NAD) and when NADH releases/loses a hydrogen it becomes oxidised
(Oxidised NAD)
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Now use that concept where the NADH produced form the Krebs cycle when it is oxidised it
releases 2e- ‘s, 2H+ and forms NAD+.
The NADH gives its electrons to the electron carrier and as these passes along the chain,
energy is used for proton pumping and they gradually lose energy until they are passed onto
the final electron acceptor which is O2.
Every time this happens 3 molecules of ATP is produced.
Recall FADH2 was also produced. The same occurs for FADH2 however its electrons enter
the ETC at a lower point so only 2 molecules of ATP are generated.
NADH produced in glycolysis don’t deliver electrons directly to the ETC, they are passed to
NAD/FAD from the matrix of the mitochondrion. If it passes to NAD, 3 molecules of ATP
would be generated per NAD molecule however if it is passed to FAD only 2 molecules are
generated.
Electron carriers use energy from electrons to pump hydrogen ions into the intermembranal
space.
Electron carriers are embedded/oriented in the inner membrane so that hydrogen ions are
always picked up from the matrix side.
The hydrogen or proton gradient across the inner mitochondrial membrane is established.
ATP synthase uses this to form ATP similarly as described in photosynthesis.
Oxidative phosphorylation is using that proton gradient across the inner mitochondrial
membrane to form ATP from ADP an inorganic phosphate. This is linked to the redox
reactions in the electron transport chain. This only occurs in aerobic respiration and yields a
higher amount of ATP.
To add a better understanding of this let’s look at a diagram.
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1. Electrons from split hydrogens (from reduced NADs and FADs) are being shuttled
from carrier to carrier along the ETC until they arrive at oxygen molecules, which
help form WATER. This occurs in the mitochondrial MATRIX.
2. Recall that the electron contains energy. This energy is being used to pump H + ions
across channels along the inner membrane into the intermembranal space of the
mitochondrion. These have a POSITIVE charge, of course, and create an
ELECTROCHEMICAL GRADIENT between the matrix and intermembranal space,
with the greater positive charge being in the intermembranal space.
3. H + ions diffuse from a greater to lower “concentration” in a process called
CHEMIOSMOSIS. However, this diffusion can only occur through channels which
have ATPases (or ATP synthases) attached to them. ATPases are enzymes that help
make ATP. So, the energy from this diffusion of H+ ions help convert ADP into ATP.
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To conclude the process:
1. Electrons from split hydrogen atoms contain energy and are shuttled along carriers in the
ETC.
2. Oxygen is the final receptor of the electron. The oxygen, the electron and H+ ions make
water.
3. This electron energy helps pump H+ ions through the inner membrane.
4. This creates an electrochemical gradient, where the inner membrane has greater +ve
charge than the matrix, as it now contains more H+ ions.
5. These H+ ions flow back down to the matrix but can only do so via special channels.
6. These channels have ATP synthases attached to them. The flow the H+ ions allow the
enzyme to make ATP.
7. This process CANNOT occur without oxygen, as it is the final destination of the electron.
❖ From one (1) molecule of Glucose, we need to conclude how many ATPs are produced.
NB: each NADH yields 2.5 ATP and each FADH2 yields 1.5 ATP.
Glycolysis
▪
▪
▪
▪
Produces two (2) pyruvate molecules.
Produces two (2) NADH‟s. (2 x 2.5 = 5 ATP)
Produces 2 net ATP at substrate-level phosphorylation.
Total = 7 ATP.
Link reaction (decarboxylation)
▪
▪
Produces two NADH‟s, from the two pyruvates as they convert to acetyl CoA’s.
Two NADH‟s = 2 x 2.5 = 5 ATP
Krebs cycle
▪
▪
▪
▪
▪
For both acetyl CoA’s, produces 6 NADH‟s and 2 FADH2‟s.
For both acetyl CoA’s, produces 2 molecules of ATP at substrate-level phosphorylation.
6 NADH‟s = 6 x 2.5 = 15 ATP
2 FADH2‟s = 2 x 1.5 = 3 ATP
Total = 15 + 3 + 2 = 20 ATP
Total net ATP per glucose molecule = 7 + 5 + 20 = 32 ATP
Total max ATP per glucose molecule = 32 ATP + 2 ATP (used during glycolysis) = 34 ATP
* These values will differ if NADH from glycolysis is transferred to FAD instead of NAD in
matrix and result in less molecules of ATP overall. The total amount of ATP produced must
be adjusted as ATP is used for substances to enter and leave the mitochondria during the
respiration process.
(Research labs on Respiration (Respirometers); TAKE PHOTOS OF THIS LAB IF WHEN
IT IS BEING DONE.
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Investigating Respiration
Respirometers are pieces of apparatus designed to measure the rate of respiration.
They rely on the fact that organisms absorb Oxygen and release Carbon Dioxide.
There are two (2) designs, but all respirometers have:
➢ Container for living organisms
➢ Carbon Dioxide absorbent (Soda Lime); made from Calcium hydroxide that combines
with Carbon Dioxide to form Calcium Carbonate (CaCO3).
➢ Manometer to measure the decrease in volume of air in the container.
Nb: when the CO2 is absorbed, the O2 in the air can be detected/measured.
Simple Respirometer
Steps:
-
Weigh the animal and place into a syringe
Sip the capillary tube into the manometer fluid (water with dye and a drop of detergent to
ease the movement of water in the tube) so a droplet enters the tubing.
Place respirometer on a bench
Droplet moved towards the syringe as the air decreases.
Measurements are taken from the
start and then again at a time mark.
Distance travelled and time are
recorded.
Volume of O2 can be calculated by
knowing the tubes diameter.
Precautions:
-
-
Soda lime or other absorbents are
harmful (don’t let them touch the
organisms)
Return the droplet to the end of the
tube by pushing the syringe.
Don’t leave the animal in the syringe
too long (Re-pump for fresh air)
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2.6: Compare the fate of pyruvate in the absence of oxygen in animals and yeast.
In Animals- Lactic acid fermentation
First of all, anaerobic respiration is the release of energy without the use of oxygen. Recall
that without oxygen, the ETC cannot be “completed”, and the ETC and oxidative
phosphorylation is the final step of ATP production following the link reaction and Krebs
cycle.
There is, however, another metabolic pathway that can take place during GLYCOLYSIS to
produce ATP. Remember that glycolysis breaks down glucose into a 3C compound called
PYRUVATE. In humans, pyruvate can be converted to LACTATE (or lactic acid) in the
absence of oxygen.
Therefore, when oxygen is absent or in low supply, it is no longer possible for aerobic
respiration to occur. Due to oxygen’s key role as the final electron acceptor at the end of the
ETC, its absence means a backlog for the ETC. This backlog means that the reduced NAD
cannot be oxidized. No available oxidized NAD means no H+ and electron acceptors for link
reaction and Kreb’s cycle.
Respiration is still possible, however, with much reduced efficiency. It permits the recycling
of NAD so that glycolysis could continue to make ATP.
AEROBIC RESPIRATION IN HUMANS
In the diagram shown, you can see that NAD
(oxidized) and NADH (reduced) are in a “loop”
to allow glycolysis to continue since the link
reaction and Krebs cycle cannot be initiated
without oxygen. This allows respiration to
continue but only 2 net ATP is produced per
glucose molecule (as opposed to 32 ATP during
aerobic respiration).
NB: The lactate acts as a temporary H+ acceptor.
This is likely to occur in skeletal muscles during vigorous
exercise eg 400m race. O2 used faster than blood can
supply. Lactate production is more like a loan. It builds up
in the muscle cells and diffuses into the blood. It affects
brain cells (lowers pH and reduces the efficiency of
enzymes) that leads to disorientation and nausea. After a
short while, the muscles eventually stop contracting.
Hepatocytes (liver cells) absorb and use lactate. It initially
converts it back to pyruvate, which, when oxygen is
available again can enter the mitochondria to follow the
aerobic respiration pathway. The pyruvate can also be used
to form glycogen as well if not
immediately needed for energy
production. The extra O2 the
hepatocytes need to breakdown and
metabolise all the lactate produced
is known as the oxygen debt. The
time taken to repay this debt is
known as the recovery period.
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In Plants and Fungi- Ethanol fermentation
In plants and fungi, the recycling of NAD is brought about by the formation of a different
compound.
In YEAST, the above process is similar but two different products are yielded: ETHANOL
and CO2.
Commercial uses of Yeast
o Alcoholic drinks
Depending on the substrate used for fermentation, different types of alcoholic drinks
are produced:
- Sucrose (Sugar Cane) – Rum
- Starch in Barely Grains – Beer
- Starch in potato, corn, rice, rye/wheat – Vodka
o Bread making
Anaerobic respiration produces CO2 which remains trapped in the dough causing it
to rise.
o Yoghurt making
Lactic acid fermentation of milk by bacterium Lactobacillus bulgarius (Lactobacillus
bacteria can produce lactate to produce yoghurt and also help preserve grass feed for
livestock).
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Alternate Respiratory Substrates
Other substrates can be used in the respiration pathway to obtain energy other than glucose
by some cells. These are:
Glycerol
Pyruvate
Link Reaction
Fatty Acids
Acetyl CoA
Krebs Cycle
Lipids
Pyruvate
Proteins
Link Reaction
Amino Acids
Malate
(4C Intermediate before Oxaloacetate)
Krebs Cycle
Nb. Brain cells and red blood cells can only use glucose as the substrate for respiration while
heart muscle derives most of its ATP from fatty acids.
To conclude this topic lets compare the major parts of both types of Respiration:
Aerobic
Processes Involved
Anaerobic
Glycolysis, Link rxn, Krebs cycle
Oxidative Phosphorylation
Glycolysis, Fermentation,
Decarboxylation of pyruvate
to Ethanol
Net ATP gained Per
Glucose
32
2
Max ATP gained per
Glucose
34
4
Products Formed
CO2 & H2O
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Yeast – Ethanol and CO2
Bacteria & Humans – Lactate
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3. ENERGY FLOW AND NUTRIENT CYCLING
3.1: Discuss the efficiency of energy transfer between trophic levels
Ecosystem: All the biotic (living) and abiotic (non-living) components of a particular area
interacting together to make one functional unit.
Habitat: The place where an organism usually lives and which is characterised by physical
conditions and the types of other organisms present.
Ecological niche: The role of a species within its community. It includes what the species is
like, where it occurs, how it behaves, its interactions with other species and how it responds
to the abiotic environment. (It’s impact on biotic and abiotic factors)
Food chains: The sequence of transfers of matter and energy in the form of food from
organism to organism usually starting with plants.
Food webs: Food chains intertwine locally to form a web because most organisms consume
more than one type of plant/animal.
Trophic level: Position within the food chain ie feeding level
Producer: Autotrophic organism that synthesises organic molecules from simple inorganic
ones such as carbon dioxide and water. Most producers are photosynthetic and form the first
trophic level.
Consumer: Heterotrophic organism that obtains energy by eating or decomposing other
organisms. Primary consumers (herbivores) feed on plants while secondary consumers feed
on herbivores.
Decomposer: A saprophytic/ saprotrophically (digests externally then absorbs products)
organism that breaks down the organic matter of dead organisms and waste products to form
water, carbon dioxide and inorganic ions. Their role is essential as they allow for the
recycling of nutrients within the ecosystem. Unused nutrients that are trapped in the bodies of
dead organisms would now be made accessible for use by living organisms. Of note is the
recycling of carbon and nitrogen, however, water, carbon dioxide and other compounds such
as phosphorus and calcium.
Population: A group of organisms of the same species, e.g. a group of snails.
Community: A group of organisms of multiple species, e.g. a group of snails, guppies and
tadpoles.
Niche: The role an organism plays in its environment; its impact on the living and non-living
factors.
DINELL MOTILAL CAPE BIOLOGY UNIT 2 SUMAMRY NOTES
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The collective dynamic of living (biotic) and non-living (abiotic) factors within an
environment is known as an Ecosystem. Most ecosystems are stable, unless there is some sort
of external interference.
These can include any of the following:
➢ The introduction of a disease-causing pathogen.
➢ A catastrophic shift in climate or weather, e.g. flash flooding or a hurricane.
➢ Human interference, such as urbanization, deforestation, poaching or noise pollution.
➢ The introduction of an invasive species, which can decimate a certain population.
How is Energy transferred in an ecosystem….?
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Food chains and webs consist of Trophic levels, which represent levels of energy and
feeding. In order, the trophic levels are:
➢ Producer
➢ Primary Consumer
➢ Secondary Consumer
➢ Tertiary Consumer
➢ Quaternary Consumer (or Apex Predator).
The sun is the source of energy for ecosystems. Producers capture 1-3% of the sun’s energy
available to them and as this energy is passed to subsequent levels, energy is lost at each
stage. The amount of energy stored at each level also decreases. Producers absorb much
energy as sunlight, but only a small proportion of this becomes available for primary
consumers in the form of the leaves, stems, roots, flowers and fruits that are made each year.
The energy content of this new growth is primary productivity. Producers only pass on 510% of energy in general to primary consumers.
This is due to a variety of reasons such as:
➢ Not all plant productivity is consumed each year.
➢ Plant uses energy for metabolic reactions eg. respiration
➢ Some parts are eaten but cannot be digested.
Carnivores are slightly more efficient at transferring energy available from prey into their
own bodies. Much closer to the 20% than primary consumers.
The rest is “lost” for many reasons such as:
➢ Energy used for body maintenance and movement
➢ Lost as heat during respiration
➢ Energy transferred to detritus food chains from all levels
➢ In open ecosystems, organisms and/or their waste can be lost to other ecosystems.
On the food chain shown above (Pg 39), the grass is the common
Producer (or autotroph, “self-feeding”), meaning that it can transform the electromagnetic
energy from the Sun into stored chemical energy (carbohydrates) via the process
of PHOTOSYNTHESIS. Some bacteria have this ability as well. Energy cannot be returned
to the Sun, so it is referred to as an ENERGY FLOW as it moves from organism to organism
as feeding occurs. Only an average of 10% of energy is transferred from one successive
trophic level to another, which is why there is a limit of trophic levels. The energy obtained
after quaternary consumers would be too little to sustain life in larger organisms. It is worth
noting that certain consumers can occupy various trophic levels simultaneously, e.g. if the
bluebird feeds on a fruit, it is also primary consumer (2nd Diagram Pg 39).
DINELL MOTILAL CAPE BIOLOGY UNIT 2 SUMAMRY NOTES
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The efficiency of energy flow between trophic levels can be calculated using the following
formula:
The answer is the % of energy of the energy consumed by one trophic level is available to the next.
In Food webs we would observe the interlinking of multiple food chains. It is important to
note that the arrows in both chain and web point to the organism that does the feeding.
High food web complexity is usually an indicator of high biodiversity and ecosystem
stability.
Advantages of a food web:
➢ Members of higher trophic level can feed upon many organisms of the lower trophic
level of other food chains.
➢ Presence of complex food web increases the stability of the ecosystem.
➢ It has a variety of trophic levels or populations of different species.
➢ Food web reduces risk of starvation and help in increasing the population of
endangered species. (5) It has many interconnected food chains.
Energy “losses” across trophic levels
It is important to remember that due to the law of conservation of energy, that energy cannot
be “created nor destroyed”. So energy is not actually “lost”, but instead converted and
transferred out of organisms due to metabolic processes.
The simple energy flow diagram seen
represents per 200 J of energy intake by a
caterpillar. Only 10% of that figure (20 J)
is left for energy storage in cells and only this
amount can be directly transferred into the
organism that consumes it
(e.g. a bird).
The other 180 J is transferred out into the
atmosphere and to decomposers, usually as
thermal energy released during respiration
and excretion.
You also have to take into account the following:
- Not all parts of the organism is being consumed.
- Not all molecules consumed would be digested and assimilated, e.g. humans eating
cellulose.
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Photosynthetic efficiency is another factor that has to be taken into account. Not all of the
sunlight that enters the Earth‟s atmosphere is absorbed by plants. Leaves may have
large surface areas but much of the sunlight will not be in contact with them. Energy is also
“lost” when:
➢ Sunlight is reflected from leaf surfaces.
➢ Sunlight transmits through leaves and misses
➢ chlorophyll molecules.
➢ Certain ranges of wavelength cannot be
➢ absorbed by chlorophyll.
➢ Photosynthesis itself uses energy.
Another Concept that needs to be understood is GPP and NPP
What is GPP and NPP?
If we imagine a leaf comes into contact with 100 units of solar energy, only about 40 of those
units will be absorbed by chloroplasts and chlorophyll as stored chemical energy. The „lost‟
60 units are reflected or miss the chloroplasts altogether.
Of the 40 units that are actually absorbed, about 10 units is utilized for photosynthesis to
make glucose. This is known as the leaf’s GPP or GROSS PRIMARY PRODUCTIVITY.
However, since energy is required for respiration to carry out the process of photosynthesis,
even more energy is lost (about 4 units). So only about 6 units has been converted to sugars
and stored as biomass out of that 100 that made contact with the leaf, and out of the 40 that
was absorbed by chlorophyll. These 6 units is known as the NPP or NET PRIMARY
PRODUCTIVITY.
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3.2: Discuss the concept of biological pyramids
Energy flow through an ecosystem can be represented by diagrams known as ecological
pyramids. Three main types of pyramids are:
o Pyramid of numbers- shows the relationship between the number of producers,
herbivores and carnivores at successive trophic levels.
o Pyramid of biomass- shows the relationship between the biomass of producers,
herbivores and carnivores at successive trophic levels.
o Pyramid of energy- shows the relationship between the energy successive trophic
levels.
Pyramid of numbers
Represents the number or organisms at each trophic level. The bars are drawn with lengths
proportional to the numbers present at each level. The area of each block is proportional to
the number of organisms; often the numbers are so large that some blocks are deeper than
others. Usually, the number of organisms at the lower level exceeds those at the higher levels.
Limitations:
o No account taken of size. Eg. 1 tree is equated to 1 aphid and each parasite has the
same number as its larger host.
o Number of individuals can be too great to represent on same scale with others. One
tree may have millions of greenflies living off it.
o Does not account for juveniles that may have different dietary and energy
requirements from adults.
o Most times do not include microorganisms, which are an important part of energy
flow.
o Only organisms present at a particular time are shown, seasonal differences not
apparent.
o Suggests that consumers feed only on the trophic levels directly below them.
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Pyramid of biomass
Biomass is the total mass of animals and/or plants in a particular place over a period of time.
This type of pyramid shows the decrease of biomass with each successive trophic level (from
producers to top carnivores). This type of pyramid takes into account the different sizes of
organisms in ecosystems. This requires taking samples of organisms at each trophic level and
weighing them. Dry mass is often used since plants have varying quantities of water
depending on environmental conditions. This is done by drying the plant matter and
reweighing to constant mass. Finding the dry mass of animals is easier, since the water
content of animal tissues does not fluctuate as much as that of plants. Water represents about
70% of animal tissues. The advantages of pyramids of biomass are that the potential food
available at each trophic level to consumers is indicated.
Hence to summarize, Biomass would account for the total mass of a population or trophic
level occupying a certain area of the environment. Biomass is thus measured in g m-2. A
single poui tree would have greater biomass than the entire ant population within it.
Limitations:
o Presence of varying amount of water can make it unreliable. Dry mass can overcome
this problem but involves the death of the organism.
o Only organisms present at a particular time are shown, seasonal differences not
apparent.
o Two organisms of same biomass can store different amounts of energy eg 1 gram of
fat stores 2x the amount of energy as 1 gram of carbohydrate.
o Suggests that consumers feed only on the trophic levels directly below them.
o Much of the material is not always edible to organisms in the next trophic level.
o Depends on sampling and estimating so may not be very accurate.
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Pyramid of Energy
Producers capture and convert light energy from the sun to chemical energy. This flows
within a food chain from producer to top carnivore. Data is collected in a given area for a set
period of time (kJm-2yr-1). This energy flow is determined by finding out what consumers
feed on and estimating the quantity and the energy content of what they consume. The energy
content of organisms or parts of organisms, e.g., leaves, is found by burning the material in
oxygen in a calorimeter.
The base shows energy utilization at the producer level while the apex shows that of top
carnivores. Best represents the energy flow through a food web. The advantages of pyramids
of energy are that the size and edibility of organisms or parts of organisms do not have an
effect on the size of the blocks. This is the best way to represent the functioning of an
ecosystem as a pyramid. They show that the energy transferred from one trophic level to the
next decreases with position in the food chain. This explains why few food chains have more
than four trophic levels. There simply is not enough energy to support another trophic level of
predators that feed on other predators. There will,
however, be enough energy to support the external
and internal parasites of these large predators.
In short summary, A PYRAMID OF ENERGY
always has the typical pyramidal shape, like the
pyramid of biomass. This is because it represents
the flow of available energy from one trophic level
to another.
Recall that a large amount of energy is required to
carry out metabolic processes in living organisms
and only a 10% average may be stored in the cells,
so at tertiary and quaternary trophic levels, the
amount of energy becomes exponentially lower.
Limitations:
o Data collection is difficult and complex to collect.
o Suggests that consumers feed only on the trophic levels directly below them.
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3.3: Describe how nitrogen is cycles within an ecosystem
While the flow of energy may be linear, the flow of matter is cyclical. There is a finite
amount of nitrogen available in the biosphere. Without recycling, life would grind to a halt.
Nitrogen is necessary to manufacture proteins, nucleic acids and other nitrogen containing
compounds like ATP and NAD.
The nitrogen cycle demonstrates how nitrogen from the air travels to land, is utilized by soil
species, and finally is released back in the atmosphere. Nitrogen gas forms 78% of the
atmosphere by volume, but it has low chemical reactivity. Nitrogen can be recycled at a
sufficient rate in the atmosphere to allow plants to grow.
Below shows 3 variations of the Nitrogen Cycle (Learn either one depending on your
preference) (ALL CONSIST OF THE SAME INFO)
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The nitrogen cycle has 5 main stages:
1. Nitrogen fixation
2. Assimilation
3. Ammonification
4. Nitrification
5. Denitrification
Much of the nitrogen cycle is dominated by reactions involving enzyme-catalysed
conversions in microbes, plants and animals. Many of the reverse reactions can be catalysed
by microorganisms.
The air contains 78% nitrogen (N2). There are three (3) ways that nitrogen can enter the soil
(Nitrogen Fixation):
1. Due to the action of lightning, some nitrogen gas in the atmosphere combines with
oxygen to generate nitrogen oxides. N2 (g) + O2 (g) → 2NO (g)
This NO formed can be further oxidized: 2NO (g) + O2 (g) → 2 NO2(g)
They are dissolved in rain and are washed into the soil where they form nitrates
2NO (g) + H2O (l) → HNO2 (aq) + HNO3 (aq)
2. By nitrogen fixing bacteria: These bacteria are found in the soil or in root nodules
(swellings in roots). To create nitrates, they take nitrogen gas that is found in the soil's
air pockets and combine it with other materials. (Fixation by microbes)
o Free-living nitrogen fixers include bacteria that reduces gaseous nitrogen to
ammonia which they use to make amino acids. They release nitrogen rich
compounds when they die and decay.
o Mutualistic nitrogen fixers eg Rhizobium which lives in the nodules (root
swellings) of leguminous plants. Rhizobium converts nitrogen gas into
ammonium ions using H+ ions and ATP. This reaction in catalysed by
nitrogenase under anaerobic conditions. The plant produces a pigment known
as leghaemoglobin to absorb any oxygen in root nodule. Plant uses the NH4 +
ions to combine with carbohydrates to form amino acids and the bacteria
receive energy and a place to live. This is an example of a mutualistic
relationships)
3. By adding synthetic nitrogen fertilizers, ammonia is created when nitrogen and
hydrogen mix. Ammonium fertilizers are created by combining ammonia with other
ions. Farmers can incorporate these into the soil. We refer to this as industrial fixation
(Industrial process- Haber process where nitrogen and hydrogen are combined under
high pressure and temperature to form ammonia. Used to make nitrogen containing
fertilisers.).
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Assimilation
Plants with mutualistic nitrogen fixers assimilate nitrogen in the form of ammonium
ions however all of them absorb nitrates from the soil. Nitrates (NO3 -) are reduced to
nitrites (NO2-) and then ammonium ions (NH4+ ) for incorporation into amino acids
and protein. Animals assimilate nitrogen from protein in their diet.
Ammonification
Production of ammonia (NH3) from organic nitrogen containing compounds like urea,
proteins, nucleic acids and vitamins. Decomposers (fungi and bacteria) feed on these
materials and release ammonia which form ammonium compounds in the soil
Nitrification
Nitrifying bacteria eg Nitrosomonas and Nitrobacter conduct the oxidation reactions
below in order to convert ammonia to nitrates in well aerated soil (Ploughing and
good drainage ensure this). This is done in two stages:
Stage 1
Stage 2
Denitrification
Anaerobic denitrifying bacteria reduce soil nitrates to gaseous nitrogen. Populations
of these bacteria increase in waterlogged soil. (Hence, does the reverse of nitrogen
fixation, turning nitrates back into nitrogen gas and returns it to the atmosphere, thus
restarting the cycle.)
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3.4: Explain how energy flow and nutrient cycling are important to ecosystems to remain
self-sustaining units
Ecosystems are self-contained units as biotic and abiotic factors interact efficiently. Within
an ecosystem, energy is an infinite resource. It enters the ecosystem at the producer level and
is passed up the food chain in one direction by primary and higher consumers. The amount of
energy at each level decreases for reasons outlined above but this flow of energy through the
ecosystem is necessary for the sustenance of life at the various levels. Energy is continually
available to the ecosystem through producers.
Unlike energy, nutrients are not an infinite resource and must be recycled for life to continue.
Many organisms and processes play a role in recycling the nutrients within the ecosystem.
That way, sufficient amounts of it will be available for use by organisms within the
ecosystem when necessary. Different organisms present within the ecosystem convert the
nutrient containing compounds into forms that are accessible by others in the ecosystem.
Let’s break it up a little more on How to distinguish between an ENERGY FLOW and a
NUTRIENT CYCLE?
Nutrients move within the ecosystem in biogeochemical cycles. A chemical element moves
through the biotic and the abiotic components of an ecosystem. These include: carbon,
hydrogen, oxygen, nitrogen and others, such as sulphur and phosphorus. These elements can
be fixed into organisms, such as carbon being fixed into green plants during photosynthesis,
or nitrogen into legume root nodules by Rhizobium.
All of these cycles are driven by ENERGY FLOW. Energy flowing through the ecosystem
originates from the Sun, which is captured by chlorophyll to make food. This food is then
consumed by heterotrophs. Both autotrophs and heterotrophs eventually die and decompose.
Decomposer bacteria and fungi allow nutrients from the cells of these organisms to return to
an INORGANIC NUTRIENT POOL in the soil and atmosphere,
ready to be taken up by plants once more.
Energy flow is referred to as a „flow‟ as none of the energy is
cycled (unlike nutrients). Energy does not return to its source (the
Sun). During each step where biotic factors (producers,
consumers and decomposers) are involved, HEAT is always
transferred out to the atmosphere due to respiration and excretion.
A note on decomposers
•
•
•
It should also be noted that the removal of dead material can
be done by numerous organisms, but decomposers are the only ones that break down
dead organic matter into inorganic matter.
Detritus feeders (or detritivores) are larger organisms, such as earthworms and maggots,
digest and metabolize dead material.
Even larger are carrion feeders (or scavengers), which eat large quantities of dead
organic matter. These include vultures and hyenas.
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4. ECOLOGICAL SYSTEMS, BIODIVERSITY AND CONSERVATIONS
4.1: Discuss how ecosystems function as dynamic systems
Ecosystems are described as dynamic due to the various interactions between biotic and
abiotic factors that occur. Biotic factors include different types of interactions classified
below. Abiotic factors include temperature, light intensity, O2 concentration, CO2
concentration, water supply, pH, availability of inorganic compounds, soil factors,
atmospheric humidity, wind speed and wave action. You are required to be able to discuss the
above in terms of a named ecosystem. Pick an ecosystem and outline examples of the above.
Examples provided are generally from a coral reef ecosystem.
Interactions between biotic factors fall into the main categories below:
▪
Competition- Two organisms require a resource that is in limited supply. [Where multiple
organisms occupy similar niches and must vie for limited resources.]
o Interspecific- competition between organisms of different species.
o Intraspecific- competition between organisms of the same species.
▪
Predation- One organism (predator) kills and eat another (prey). [Where one organism
hunts and eats another. This helps control several populations in the food web.]
▪
Symbiotic Relationships:
o Mutualism- Two organisms (of different species) living in close interaction that
benefit each other (e.g., pea plants and Rhizobium)
o Commensalism- Two organisms associate where one benefits and the other is not
affected (neither benefits nor is harmed). unaffected (e.g., remora fish and shark)
o Parasitism- One organism (the parasite) lives in or on another organism (the host)
and causes it harm. (e.g., ticks and dogs)
o Altruism, where organisms cooperate for a common goal (e.g., ant colonies)
Competition
Competition limits growth and reproductive success. Recall that niche has to do with an
organism’s role within its community. In order to accomplish this, they usually have a
particular set of requirements (habitat, food source, environment). When more than one
organism share the same needs they will compete for the same resources. The weaker would
usually starve or be unable to reproduce. This results in only one organism occupying a
particular niche within an ecosystem. This is known as competitive exclusion. Eg. after storm
damage, coral species compete to recolonise the exposed areas and will compete for food
(invertebrate organisms) and light. Some even adapt to have tentacles with increased
nematocysts (specialised cell containing venomous thread) long enough to sting other corals.
Resource partitioning can occur where organisms feed on the same prey but avoid direct
competition with each other. They find a way to coexist. They can use the resource at
different times or places. An example of this is bumblebees in Colorado. While all species
feed on nectar from flowers, species have adapted different length proboscis (tubular, flexible
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and elongated sucking mouthpart) in order to feed on flowers with different length corollas
Competition can drive the evolution of differences that allow for resource partitioning.
Predation
Both predator and prey evolve to develop adaptations that either increase their efficiency of
finding and capturing prey or their ability to avoid being predated (defensive mechanisms).
Eg. the barracuda (Sphyraena barracuda) in coral ecosystems have developed into fast
swimmers with the ability to rapidly accelerate to swiftly attack prey. The fish they feed on
however have adapted by hiding in crevices when they (predators) are visible or schooling
with fish that better protected. Grazing is also a form of predation. Algae that grow on rock
are fed on by parrotfish and butterflyfish. If left uninhibited, algae would take up much of the
space where coral larvae would settle to restore the ecosystem.
Mutualism
The most common mutualistic relationship in the coral reef ecosystem is the one between
coral polyps and zooxanthellae. Zooxanthellae are single-celled photosynthetic algae that live
within the polyps and produce carbohydrates while receiving protection and support (CO2
and nitrogenous waste) from the coral polyp
Commensalism
This classification is somewhat difficult as new information may result in establishing a
benefit or harm to the 2nd organism. Despite this, the most common example of
commensalism in a coral reef ecosystem is that of the remora (aka suckerfish or shark
suckers) that attach themselves to the skin of larger marine organisms such as sharks without
damaging tissue. They travel with their host and collect food the organism unknowingly
distributes.
Parasitism
An example of this would be isopods (sealice) on the skin of fish. They feed on blood and
skin and reduce the vigour of the fish.
Interactions between abiotic factors include:
Wave action- This leads to constant mixing of water that brings oxygen for respiring
organisms and food eg plankton to stationary organisms. Intense wave action can be
destructive and damaging to coral reef systems eg during a hurricane or storm.
Temperature- High temperatures, while it may not be the sole cause, is associated with
extensive coral bleaching. Coral bleaching is when corals expel their mutual partners
zooxanthellae. A rise in temperature 1°C above maximum summer temperature can cause
this.
Oxygen concentration- The normal range for water surrounding a coral reef is 3- 9 cm3dm3. O2 concentration is proportional to water turbulence as it incorporates oxygen from air into
seawater at surface. Higher temperatures reduce the solubility of O2 in water.
Light intensity- If the sediment level is low, increased light intensity would result in
photosynthesis by zooxanthellae resulting in the production of O2 at a greater rate than it is
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incorporated at the surface. During low light intensity, the respiring organisms would cause
the O2 levels to drop significantly, which may affect some of the high movement organisms.
Carbon dioxide- This is usually present in high concentration either as dissolved CO2,
hydrogen carbonate (HCO3 -) and carbonic acid (H2CO3). An increase in atmospheric CO2
has led to an increase in dissolved hydrogen carbonates and carbonic acid. This leads to
acidification as it results in a reduction in pH.
pH- Measurement of acidity or alkalinity of soil or water; impacts habitat.
Soil characteristics- Also known as edaphic factors. Soil aeration and soil pH affects
subterranean life; particle size affects drainage; contains inorganic ions such as nitrates;
soilpH affects type of terrestrial life and vegetation.
Water characteristics- Availability of water supply affects flora and fauna for sustenance
and some for habitat; turbidity (muddiness) of water affects visibility; salinity and pH affects
type of aquatic life.
Humidity- High humidity decreases rates of evaporation and transpiration.
Wind speed- High wind speed increases rates of evaporation and transpiration.
Topography- The land‟s physical features, which impacts layout of habitats, and allows
animals and vegetation to reside at multiple altitudes.
For the CAPE Unit 2 syllabus, you are required to describe a model ecosystem. In this
manual, that ecosystem will be the Aripo Scientific Reserve (Taken from Sperwin
Zinger/kringer) [you can research your own model ecosystem and use that as well]
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Mesocosms (Activity specified in syllabus objective) are enclosed environments that allow a
small part of a natural environment to be observed under controlled conditions.
A terrarium is a small transparent container (e.g. glass or plastic) in which selected plants (or
animals) are kept and observed
Making a Self-Sustaining Terrarium
A terrarium can be created using a glass or plastic bottle with a lid, according to the following steps:
1. Building a verdant foundation
▪ Add a bottom layer of pebbles, gravel or sand – this layer exists for drainage (smaller vessels
require thinner rock layers)
▪ Add a second thin layer of activated charcoal – this will prevent mold and help to aerate the
soil
▪ Spread a thin cover of sphagnum moss (or use
an organic coffee filter) to create a barrier
between the lower layers and soil
▪ The final layer is the pre-moistened growing
medium (i.e. potting mix)
▪
▪
2. Selecting the right plants
Ideally, choose plants that are both slow growing and thrive
in a bit of humidity (e.g. most ferns, club moss, etc.)
Inspect the plant thoroughly for any signs of disease or
insects before introducing to the terrarium
3. Maintaining appropriate conditions
▪ Ensure the terrarium is placed in a location
that provides a continuous source of light
▪ Locate the terrarium in a place that does not
experience fluctuating temperature conditions
(i.e., avoid direct sunlight)
▪ Do not initially over-water the plants – once
the right humidity is established, a terrarium
can go months without watering
▪ Occasional pruning may be required –
however, as level of soil nutrients decrease,
plant growth should slow down
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4.2: Explain the concept of biodiversity
The number of different species on earth have been estimated as high as 100 million and as
conservatively as low as 6 million. Biological diversity (biodiversity) is the variability among
living organisms from all sources (aquatic, terrestrial and marine), the ecological complexes
and diversity within and between species and ecosystems.
How does one define BIODIVERSITY?
Biodiversity is a difficult factor to quantify, but we can think of it as being an amalgamation
of three (3) factors:
▪
▪
▪
Species Diversity
Genetic Diversity
Ecosystem Diversity
NB: each factor has 2 POV; both fairly possesses the same info just stated differently.
Species Diversity
The number of species in a defined area (quadrat, habitat, ecosystem, geographical region) is
its species diversity. Species diversity is highest in the tropics and decrease as you move
further away from the equator but there are regions all over the world that are hotspots for
diversity. Factors that affect species diversity in trees are temperature, solar radiation and rate
of water loss from leaves. High humidity, high solar radiation and low rates of water loss
from leaves are associated with high species diversity in that area. The factors that lead to
high mammalian species diversity is not as well understood but it is believed that it may be a
product of plant species diversity.
In other words, it refers to the variety of different species found within a biome. For example,
it can refer to the members of communities in a pond, such as different species of algae,
weeds, mosses, plankton, snails, small fishes, frogs and so on. Tropical regions tend to have a
high species diversity due to the high rainfall, humidity and light intensity, which all result in
high tree density. A limitation of species diversity, however, only accounts for presence of
species, not abundance.
Genetic Diversity
Within a species, diversity that is heritable is known as genetic diversity. High levels of
genetic diversity within a species is associated with its ability to evolve, adapt to changing
environments and survive. Loss in population size inadvertently results in a loss of genetic
diversity.
In other words, it refers to the variation of genetic information within the populations. Great
population numbers usually indicate high genetic diversity. Recall that having selective
pressures, isolation mechanisms and high rates of outbreeding increase the size of the gene
pool and number of favourable alleles (less deleterious alleles). As a result, a species is more
likely to resist pathogens and negative environmental consequences, raising chances of
survival. Recall Galapagos finches and peppered moths.
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Ecosystem Diversity
The number of ecosystems in a particular area is also known as ecosystem diversity. An
increase in the ecosystem diversity within an area is associated with an increase in species
diversity however it cannot fully account for it.
In other words, it refers to the variations in ecosystems in a defined geographical area. For
example, the Aripo Reserve consists of multiple ecosystems, including the open savannah, a
palm marsh and a marsh forest. It is also held within a watershed that sits between the Aripo
and Quare Rivers. Having all of these different biomes adjacent to each other encourages
intermingling of species and a “choice‟ of abiotic factors that encourage survival.
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4.3: Discuss the importance of the maintenance of biodiversity
Before we discuss the importance for maintaining biodiversity, we should highlight some of
the threats to it. Increasing human population results in a demand for resources that results in
destructive practices.
▪
Habitat loss- destruction of forests for timber, industrial and agricultural developments
(mining and farming).
▪
Competition from humans- further clearing of land for housing. Habitat reduction leads
to increase in competition among wildlife for food, shelter and breeding sites. Humans
introduce new species to ecosystems that out-compete local ones.
▪
Hunting, poaching and fishing- reduction in populations for sport as well as for skins
(crocodile, fox), ivory tusks (elephants), oil (whales) and horns (rhinoceros) and food
(wide variety)
▪
Climate change- The rise in emission of greenhouse gases leads to global warming.
o Leads to changes in weather patterns that change habitats.
o Rising sea levels- problematic for coastal ecosystems.
o Increased temperature in tropics associated with coral bleaching. Loss of energy
source for coral polyps.
▪
Pollution- further habitat loss or reduction in populations of species.
o Waste disposal
o Oil spills
o Overuse of pesticides
Why is it important to MAINTAIN BIODIVERSITY?
Natural ecosystems provide biodiversity so when these are destroyed, or their resources
exploited (examples above) their benefits are less pronounced. Natural ecosystems provide
clean water, climate regulation and food production. A balance between the human need for
resources and the protection of the environment is sustainable development. It allows for the
demands of today to be met without compromising the ability of future generations to meet
their needs
It is important to maintain biodiversity for a number of reasons; intrinsic (ethical or existence
values), direct (known economic use) and indirect (unknown economic use). These include:
❖ Intrinsic reasons for maintaining biodiversity:
▪
▪
▪
People hold the view that:
Humans as custodians for the earth should value and protect it and the other organisms on
earth
Other organisms have equal right to exist on earth as humans so. Changes caused by
humans should be mitigated by us to ensure the survival of other organisms.
Humans have not inherited the natural world from ancestors but are simply renting it from
our descendants.
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▪
Ecological stability (intrinsic) Discussed on previous page. Maintaining a high species
diversity will promote greater chances of ecological recovery after negative impacts.
▪
Protecting endemic species (intrinsic) Certain species can only be found in single
locations (endemic), such as the pawi and El Tucuche golden tree frog in Trinidad. If
these or their habitats are not protected, they will go extinct.
▪
Aesthetic (intrinsic) Nature itself is a source of relaxation and beauty for visitors. Many
people take joy in knowing that various species simply exist in their natural habitats.
▪
Flood prevention(indirect) Removal of trees and vegetation leaves soils exposed and
waterlogged after periods of rainfall. This can lead to floods and soil erosion, further
decimating habitats and depriving man of natural resources.
▪
Bequest value (intrinsic) When a generation places importance on preserving biodiversity
so that future generations may be able to experience it.
❖ Direct value to humans:
▪
Many of the drugs that we use originate from our study of organisms. Antibiotics are
isolated from fungi and bacteria; anti-cancer drugs have been isolated from plants such as
the Madagascan periwinkle, Catharantus roseus, and the Pacific yew tree, Taxus
brevifolia. There is currently much interest in cataloguing plants used in Chinese
medicines to see if they can provide drugs that can be mass produced. Herbal remedies,
once widespread in the Caribbean, may also be developed along similar lines.
▪
Although much of the food for humans and our domesticated animals comes from
agriculture, we continue to harvest animals and plants from the wild. Fish stocks in the
Caribbean have been heavily fished since the 17th century and many species globally are
near extinction; as a result, we now fish lower down the food chain. Timber is extracted
from forests with loss of biodiversity.
▪
Many people appreciate the aesthetic appeal of species diversity. There are many amateur
ornithologists (person who studies birds) and botanists who enjoy wildlife. The natural
world continues to provide much inspiration for artists, photographers, poets, writers and
other creative people.
▪
Wildlife is a source of income for many countries as ecotourism has increased in
popularity. Countries such as Belize, Dominica and Costa Rica have developed facilities
for tourists to visit their National Parks
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▪
Our crop plants do not have much genetic diversity. The wild relatives of maize grow in
the states of Oaxaca and Puebla in Mexico; they can provide the genetic resources we
might need to widen the genetic diversity of cultivated maize if it is affected by
widespread disease or other catastrophes. Many of these wild relatives are threatened by
climate change, habitat destruction and the spread of GM crops.
▪
Organisms are the source of many useful products. The heat-stable enzyme, Taq
polymerase, was discovered in a thermophilic bacterium, Thermus aquaticus, from a hot
spring in Yellowstone Park. This enzyme is mass produced by genetically modified
bacteria for use in the polymerase chain reaction (PCR), routinely used by forensic and
other scientists to increase quantities of DNA. Other bacteria are used to extract metals,
such as copper, from low grade ores.
▪
Tourism (direct) Coral reefs, safaris and nature trails tend to attract tourists from which
countries earn revenue. Money can be made from nature tours.
▪
Raw materials (direct) By having good preservation and restorative practices (such as
reafforestation), raw materials such as timber can be easily obtained without great
disturbances to habitat.
❖ Indirect value- ecosystems provide services for us:
▪ Forests and peat bogs absorb carbon dioxide and may help to reduce the effect of
increases in carbon dioxide in the atmosphere.
▪
Organic waste material added to waters is broken down.
▪
Plants transpire, which contributes to the water cycle to provide us with drinking water.
▪
Soil fertility is maintained by nutrient cycling, e.g., decomposers and nitrifying bacteria.
▪
Reefs and mangroves protect coasts from erosion.
▪
Water is filtered through soils and rock before it enters the supply
▪
Scientific value and research (indirect) Researchers tend to observe ecosystems and
organisms as models for medicine and technology. Velcro was modelled after burrs
sticking to clothing; Trinidad guppies and Anolis lizards are frequently observed as
evolution models; and certain antibiotics have been extracted from tropical fungi; genes
from daffodils were spliced into rice plants to make Vitamin A-rich Golden Rice.
High biodiversity would ensure the stability of these ecosystems and their ability to continue
to provide the services we depend on
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4.4: Discuss how species diversity is related to the stability of an ecosystem
An ecosystem is considered to be stable if it is able to return to a steady state after a
disturbance. It is generally known that the more complex the food webs within an ecosystem
are, the more stable it is. Increased food web complexity is as a direct result of increased
species diversity
Hence, Ecosystem stability refers to the ecosystem’s resilience and ability to return to a
normal state after being negatively impacted. Think of it as an ecosystem overcoming
„selective pressures‟. A good example would be a grassland being able to regrow most of its
vegetation after a period of drought.
It is said that HIGH SPECIES DIVERSITY increases ecosystem stability, as less species are
prone to migrating from or becoming extinct in that ecosystem after a disturbance, such as a
disease or catastrophe. More members of populations would be able to survive, especially if
there is also HIGH GENETIC DIVERSITY among the individuals. As a result, perturbations
in the food web should be minimal over time and chances are greater for a return to
equilibrium. If a single species dies out or migrates, this could affect the entire food web and
feeding relationships among many organisms in that ecosystem, making it unstable.
Ecosystem 1 has 5 species and
Ecosystem 2 has 10 species. If an
environmental change affected on of
the species in the ecosystem, the
impact of that change will likely affect
Ecosystem 1 more severely than
Ecosystem 2.
Apply the situation that if a particular species was removes from the diagrams below
how would it be affected in terms of its stability.
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4.5: Explain how in situ and ex situ conservation methods are used to maintain biodiversity.
Conservation can be a determined effort to maintain high biodiversity. Steps are taken to
protect species, habitats and ecosystems from damage and encourage their survival.
Conservation tends to focus on individual or groups of species eg. Leatherback turtles or on
ecosystems eg tropical rain forest.
Thereby which, Conservation is the discipline of maintaining diversity by protecting species
and their habitats, as well as ecosystems and biomes.
There are two main types of conservation:
•
In situ conservation- organisms are kept in their natural habitat
•
Ex situ conservation- building up the species population in another environment. This
occurs at a site remote to where the organism lives.
In situ conservation
This is the ideal way to conserve a species. Methods for in situ conservation are extremely
diverse. They include:
•
Protection of habitats- It is the hope that if habitats are preserved then the biodiversity
within it would also be preserved. To achieve this, reserves and/or protected areas are set
up. Legislation is passed to ensure large areas of land are designated to be relatively
undisturbed eg. Morne Diablotin National Park in Dominca. Human activities outlined
above that lead to loss of biodiversity are prohibited in these areas.
Habitats are protected from:
o
o
o
o
o
•
Erosion
Poaching
Sea Acidification
Deforestation
Hunting
(Morne Diablotin Naitonal Park
Dominca)
Specific management regimes that favour endangered species eg The Pacuare Nature
Reserve in Costa Rica has the most important beach for nesting for the leatherback
turtle. This area is protected from poachers during breeding season.
o Protection from introduced species (removal)- New species introduced to an
ecosystem can outcompete local species and eliminate them. The absence of natural
predators mean that populations of these new species usually go unchecked.
In situ conservation does not just involve putting a line around a particular area of natural
interest and preventing development, logging, poaching, fishing and hunting. It also involves
enforcing measures in areas that are not designated as special areas, such as parks or reserves
of one sort or another. Examples are:
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•
•
•
•
•
Reclaiming ecosystems that have been damaged by human activities and in natural
catastrophes, such as volcanic eruption, hurricanes and flooding.
Creating new habitats, for example by allowing vegetation to ‘take Over’ land
abandoned by people; digging ponds; deliberately sinking ships to provide new surfaces
for corals to colonise.
Setting up exclusion zones to prevent fishing at certain times of the year, particularly
during breeding seasons.
Preventing pollution or placing limits on levels on pollution to reduce the damage to
ecosystems
Issuing permits to companies so that timber and other products may be removed from
important ecosystems without causing long-term damage.
In summary of In-situ
In situ conservation means conservation which takes place on-site. The major aim of this
type of conservation is to preserve natural habitats of the organisms and maintain their
number. This type of conservation includes designation, managing and supervise the target
species. Examples include:
o National parks (e.g., Yosemite and Sequioa)
o Wildlife reserves and sanctuaries (e.g., Aripo)
Ex situ conservation
This becomes necessary when conservation in the organism’s natural habitat is untenable or
the organism is so endangered in this environment that it must be removed.
•
Seed banks- Seeds from various plants are collected and stored under ideal conditions to
prevent damage (mold etc). The Mellinium Seed Bank in the UK is the largest and most
diverse wild plant species genetic resource in the world. The usual method is that seeds
are dried at 15°C until the reach a sufficient moisture content (15% relative humidity),
they are then cooled to -20°C and stored at this temperature. Not all seeds are amenable
to this type of conservation so alternative methods would need to be employed for these
•
Botanic gardens- Botanic gardens are where endangered plant species are grown for their
preservation. They don’t only provide aesthetic benefit but also conduct research in
reproduction of how the species can be grown and propagated. They also conduct
research to be able to introduce species to new habitat if the original was damaged or
destroyed. They eventually reintroduce species to habitats where they have declined in
population. The final role of a botanic garden would be public education of the roles of
the conserved plants in ecosystems and their likely economic value
•
Zoos- While zoos are a source of entertainment for its human visitors, this is not its only
function. They are commissioned to protect endangered species, conduct breeding
programmes of amenable species and biological research to learn more about habitat,
breeding habits and genetic diversity. They also breed with the aim of eventually
reintroducing species into the wild when populations continue to decline. Finally, while
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entertaining visitors, they also educate the public about wildlife as well as the need for
conservation
•
Sperm/Embryo (Gene) banks- In an attempt to replicate the success observed in seed
banks, sperm/embryo (gene) banks have been set up for the conservation of animals. The
goal of this is to preserve genetic material for the future. However, the feasibility of
regenerating an extinct organism from stored DNA is currently very low. Sperm storage
conservation requires corresponding egg storage and the possibility of in vitro
fertilisation. Note that egg storage is more difficult as it takes longer to freeze due to its
size and experience more damage during the freezing process. Eggs are also fertilised
(embryos) in vitro and then frozen. When the sperm is collected, it is washed to remove
liquid component and stored in a buffer that increases viability. This is then stored in
straws (narrow tubes with preserving liquid) that usually hold 1 cm3. This is then stored
in liquid nitrogen (-196°C).
In summary of Ex-situ
Ex situ conservation means conservation which takes place off-site. In this method of
conservation, sampling, shifting, storage and preservation of target species is carried out
outside the natural habitat of the organisms. Examples include:
o
o
o
o
o
Zoos
Botanic Gardens
Seed banks and pollen storage
In vitro storage for sperm & embryos
Captive breeding programmes
THAT’S THE END OF MODULE 1 OF BIOLOGY UNIT 2 :)
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MODULE 2
1. THE UPTAKE AND TRANSPORT OF WATER AND MINERALS
1.1: Explain the uptake of ions by active transport in roots; emphasis on the role of the
endodermis.
Plant cells require a readily available supply of CO2, O2, organic nutrients and inorganic
nutrients. However, as plants are comparatively less active that animals, they manage with
much slower transport systems. CO2 and O2 are not transported in any particular system,
these travel to and from the environment by diffusion alone. Plants have separate transport
systems for transporting organic nutrients eg glucose and inorganic nutrients and water.
What is TRANSPIRATION?
Transpiration is simply defined as the movement of water through a plant and evaporation
through its above-ground parts, such as the stomata of leaves.
Plants uptake inorganic ions such as nitrates and magnesium (for growth and chlorophyll
production) along with water molecules through hairs in the root through channels as ions
cannot simply diffuse across the cell membrane. Root hairs are specialised exchange surfaces
in plants which are extensions of the epidermal cell. They have large surface area, thin (single
celled) and permeable (no waxy cuticle). The route they take is solution in soil→ Root hair→
across root→ xylem→ rest of plant. The mechanism by which the ions enter the root hair
depends on the concentration gradient. While water is taken up through osmosis, inorganic
ions are taken up into the cytoplasm from the soil through active transport or facilitated
diffusion.
RE: If you recall from Unit 1, facilitated diffusion is a passive method of transport,
meaning that it requires no ATP. Molecules move from regions of higher to lower
concentration across channel proteins. Active transport moves molecules from regions of
lower to higher concentration. This requires ATP to allow the carrier proteins to work
to transport the ions across. This usually happens through the endodermis of the root,
as this layer contains many carrier proteins.
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Hence, If the ion concentration is higher in the soil compared
to the root hair, then it will enter by facilitated diffusion ie. no
energy is needed. If, however, the concentration within the
soil is lower than in the root (often the case), active transport
would be required as the ion would have to be moved against
its concentration gradient. This requires energy and carrier
proteins. The root cells respire aerobically to produce the ATP
necessary for uptake of ions by active transport. Therefore, in
waterlogged soil, uptake of ions would be very poor.
Once inside the root cell, ions would dissolve in water and
travel through the cytoplasm of cells from epidermis to cortex
to endodermis before entering the xylem. The endodermis acts
as a checkpoint for ions that access the xylem as it has to cross its cell membrane before
entering the xylem. Ions are actively pumped through carrier proteins that span the
endodermal membrane and into the xylem.
Nb: Root hairs increase the surface area of the roots, increasing the rates of both these
processes.
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1.2: Describe the entry of water into plant roots in terms of water potential;
Water enters the plant root through the root
hair by osmosis. The soil solution that
surrounds soils particles are very dilute or
have a high-water potential. The cytoplasm
of the root hair cell has a high concentration
of ions and nutrients and there has a low
water potential. Water therefore moves
passively from an area of high-water
potential to an area of low water potential ie
down the water potential gradient.
Water can also enter the root by travelling
through the cell walls of root hair cells
instead of entering the cell. It then moves
through the cell walls of other tissue to the
centre of the root.
Once water enters the cell it can follow 1 of 2 pathways through the cortex to the centre of
the root. The absorbed water is making its way to the xylem, which has the lowest water
potential within the root. Water will passively make its way there.
The 1st pathway is the apoplast pathway where water is drawn into endodermal cells. This
creates a flow of water due to the cohesive nature of water molecules. This tension draws
water along the cell walls of the cortical cells (cell in the cortex). This is also known as the
non-living pathway as water does not cross the cell membrane.
The 2nd pathway is the movement of water through the cytoplasm of the cells through
plasmodesmata (direct connections between adjacent cells) based on a difference in water
potential. This is the symplast pathway. The dominant pathway used by plants is species
specific and also depends on environmental conditions. The apoplast pathway in general
tends to be the most common route. Water can move between the pathways through
specialised protein channels called aquaporins that span cell surface membranes. Cells can
increase and decrease the number of aquaporins in their cell membranes as a form of control
of water movement across root.
NOTE: An easy
way to remember
this is water can
either move
“a”cross cell
walls (apoplast)
or “s”traight
through
cytoplasm
(symplast).
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When water reaches the stele it meets a barrier (Casparian strip) as the endodermis is
surrounded by a thick, waterproof, waxy substance called suberin and prevents the flow of
water. At this point, water must enter the cytoplasm of these endodermal cells in order to
make it to the xylem. This serves as a checkpoint for water and inorganic nutrients entering
the xylem. Ions are actively pumped into the xylem across endodermal membrane effectively
lowering the water potential, this causes the increased movement of water into the xylem.
Water leaving the endodermis to enter the xylem does so through the apoplastic pathway.
Extra on the two (2) pathways;
Another thing to note is the way active transport affects rate of osmosis in the endodermis.
Recall that the endodermis is loaded with transport proteins for inorganic ions. As ions are
actively transported from the endodermis to the xylem (4 to 5 in the diagram), it reduces the
water potential in the xylem.
This steepens the water potential gradient and facilitates faster movement of water molecules
into the xylem from the endodermis.
This contributes to a “force” that pushes the water into and along the xylem called ROOT
PRESSURE.
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1.3: Relate the structure of the xylem vessels to their function;
Now we will learn about a plant structure call the Xylem
Vessel.
What is the Xylem...?
Xylem vessels consist of elements that were once alive i.e.,
contain dead, empty cells that are lignified, long narrow and
have no end walls. They provide the route for water to go
from the roots of plants all the way to the top of the plant or
in other words are primarily used for the transport of water
and dissolved inorganic ions from the roots to the leaves.
The Xylem Vessels however, they are made up of a rigid, dead
polymer known as lignin, which is used as structural support.
This lignin can have a number of arrangements, including annular
(ring-like) and reticulated (web-like). To better understand what
Lignin is, it’s a strong waterproof substance that fortifies the
vessel elements as well as keep water inside them. The elements
are arranged end to end to form continuous tubes through which
water would flow in an unbroken column. Due to the fortification
of the xylem vessels by lignin, they also serve a structural role in
providing support to the plant.
Xylem vessels usually run adjacent to each other. The xylem
also has pits in its walls that allow flow of water to and from
adjacent cells. The tubes themselves are devoid of cell material,
allowing uninterrupted flow.
FUNCTION
Transport
•
water
through
•
plant.
•
•
Prevents
collapse of
tubes/resist
tension
Low
resistance to
flow
Allow lateral
movement of
water
FEATURES
Vessel elements arranged end to end
in columns to forms tubes
Cellulose walls are hydrophilic and
therefore aid in adhesion
Narrow to support columns of water
Lignified walls prevent water from
escaping
•
•
Thick cellulose walls
Fortified with lignin
•
•
No cell contents (Membranes,
nucleus, cytoplasm)
No end walls separating vessel
elements
•
Pits in cell wall
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1.4: Explain the ascent of water in plants;
Xylem vessels provide the route for water to go from the roots of plants all the way to the top
of the plant. These vessels don’t have an inherent pump of any kind but the flow of water is
maintained by the pull resulting from the evaporation of water vapour from the surfaces of
the spongy mesophyll cells into the air spaces. It then diffuses out the air spaces into the
atmosphere through the open stomata. This loss of water is transpiration. Plants can control
the rate of water loss by closing the stomata in low humidity atmospheric conditions.
The humidity (amount of water vapour in the air) of the atmosphere is usually lower than that
of the sub-stomatal space so water will continually diffuse out of the leaf provided the stomata
remain open. The loss of water from the spongy
mesophyll cells are replaced by water from the
xylem vessels. This reduces the hydrostatic
pressure at the top of xylem vessels which creates
the pull or suction at the top. Water therefore flows
up the xylem vessel as the hydrostatic pressure at
the bottom is higher. The cohesive nature
(attraction to other water molecules) of water
molecules and adhesive forces (attraction of water
molecules to the walls of the xylem vessel) keeps
the column of water moving up the xylem vessel
continuous. The combined forces of cohesion and
adhesion gives the column of water the tendency
to crawl up the xylem vessel. This is known as
capillarity. This reduces water potential at the base
of the xylem vessels which causes water to flow in
from the root. The more water is lost from the top,
the more water needs to be absorbed by the roots.
The continuous movement of water from root, up
through the xylem, into the leaves and out into the
atmosphere is known as the transpiration stream.
The flow of water in plants is unidirectional and the
main driving force is the difference in water
potential between the soil and the air.
Root pressure can also contribute to the upward
movement of water in the xylem. As mentioned
before, active transport of ions through the
epidermis lowers the water potential inside the
xylem vessels in the root. Water flows in and
increases the hydrostatic pressure at the bottom.
This forces water to move upwards to regions
where the hydrostatic pressure is lower. Root
pressure compensates when atmospheric humidity
is high, therefore the rate of water loss and the pull
of the transpiration stream would be lower.
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1.5: Discuss the impact of environmental factors on the rate of transpiration.
Stomata are tiny pores in the epidermis
(usually lower) of a leaf that allows diffusion
of water vapour (transpiration) and other
gases.
They are surrounded by guard cells and their
shape and function are influenced by the
turgidity of these guard cells. If the guard cells
are turgid (due to water moving in due to a
high K+ ion concentration), they swell in a
curved way, which allows passage of water.
If the guard cells are not filled, they become
flaccid and no diffusion of water occurs.
9Some stomata are organized in large stomatal
chambers (or sunken stomata). These are
typically covered in hair to trap still air and
moisture. These are usually found in
xerophytic plants (plants that retain large
amounts of water).
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MEASUREMENT OF TRANSPIRATION RATES
The set-up in the diagram is called a potometer, for
measuring and comparing rate of transpiration. The
starting position of the air bubble is marked. The air
bubble moves towards the cut shoot as water is taken up.
After a fixed amount of time, the final position of the
bubble is marked, and a distance is determined. This
distance will be short, for example, in a cold
environment with no air movement. It will be longer in
a warmer environment with high air movement.
•
•
•
Capillary tube: Here, a bubble travels a distance due to water absorption by the plant.
We can measure water uptake through regular gradations on the tube.
Reservoir: It is like a funnel with a tap. We can reset the bubble by turning on the tap.
Some potometers also use a syringe in place of a reservoir.
End tube: It holds the shoot. The stem end must be in touch with the water. Additionally,
we need to fix the cork Bauer on the end tube to avoid air bubbles.
How does a potometer measure transpiration?
Calculation: The transpiration rate is equal to the distance that an air bubble moved within the
capillary tube at a given time. The transpiration rate is measured in ml/min or cm/min.
Precautions
•
•
•
•
•
Plant shoot must be fresh and healthy.
The whole apparatus must be airtight.
The cut stem must be fixed to the end tube underwater.
Leaves of the desired shoot must be dry before cutting.
There should not be any air bubbles in the apparatus
Advantages
•
•
It measures the transpiration rate by estimating water uptake by the plant.
It helps to study the effect of variables like light, humidity, temperature and wind speed
on the transpiration rate.
Limitations
▪
▪
▪
▪
It isn’t easy to set up, as an air bubble may alter the results.
The potometer does not give accurate results. Because not all the water that the plant takes is
used for transpiration. Plants may take water for photosynthesis or to maintain cell turgidity as
well.
The cut shoot does not remain active for a long time.
The air temperature outside may change the position of the air bubble within the capillary tube.
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2. TRANSPORT IN THE PHLOEM
2.1: Relate the structure of sieve tubes and companion cells to their function;
Previously, we discussed the transport system for water and mineral ions in plants. Organic
substances produced by the plant also needs to be transported. The movement of these soluble
organic substances (assimilates) is known as translocation and occur within the phloem vessels
within plants. Assimilates are transported in sieve elements within phloem tissue. Phloem
tissue is made up of a variety of cell types including sieve elements and companion cells.
RE: In Unit 1, the xylem and phloem were
observed, discussed and drawn. The images to
the right are a reminder of the placement of these
tissues in dicotyledonous roots and stems.
What is the PHLOEM?
The xylem is usually paired with another vessel called the PHLOEM. The phloem assists with
the process of TRANSLOCATION, which is the transport of soluble organic substances such
as sucrose (As mentioned above). These are assimilated into cells for use. This transport occurs
from photosynthetic organs (e.g. leaves) called sources to non-photosynthetic organs (e.g.
roots) called sinks.
For translocation to occur, sieve elements and companion cells have to work closely. Sieve
elements join end to end vertically to form sieve tubes. Unlike xylem vessels, the sieve
elements making up the sieve tubes are living cells
The phloem consists of numerous sieve tube elements. These are elongated cells that only have
a few organelles, not even a nucleus or ribosomes, and very few mitochondria. This is why
they are joined onto companion cells. [Sieve elements contain: • A cellulose cell wall • Plasma
membrane • Cytoplasm (very little) with endoplasmic reticulum and mitochondria • No
nucleus • No ribosomes]
Essential to normal functioning of the sieve tube element is the Companion cells. At least one
of these is associated with each sieve element. These cells possess all the attributes of a normal
plant cell however they are very metabolically active to support the sieve element cell by which
they have a large concentration of ribosomes and mitochondria to supply ATP for “loading”
and “unloading” assimilates into and out of cells through their plasmodesmata. Another
difference is that they do not contain large vacuoles, instead they remain very small. To provide
direct support, plasmodesmata (strands of cytoplasm) are direct pathways between the
cytoplasm of both cells.
Most notable about sieve elements are their endplates. Where two sieve tube elements
meet, their end walls form a sieve plate. A sieve plate is a perforated disc with many sieve
pores (Both end walls contain holes called a sieve pore and the sieve plate is described as
perforated). Sieve plates facilitate mass flow through the phloem, and the pores may also
reduce resistance by increasing the pressure through them (in other words These reduce
resistance to flow of substances flowing through the tubes.)
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2.2: Explain how phloem loading in leaves occurs against a concentration gradient;
Unlike the xylem, the phloem is bidirectional, meaning that flow can over either up or down
the stem. This is determined by the location of sources and sinks.
The liquid conducted by the sieve tube is called phloem sap. Like the xylem vessel, phloem
sap moves through the tubes by mass flow. A major difference between the two is the energy
requirement. Mass flow within the xylem vessel is a passive process while in sieve tubes,
energy from the plant is required for flow to occur.
▪
A SOURCE is any photosynthetic organ capable of producing
sugars in excess, and able to transport it. Sucrose is unloaded
from sources. An example is a mature leaf.
▪
A SINK is a non-photosynthetic organ that does not produce
sugars but instead needs them to meet their own requirements.
Sucrose is loaded into sinks. Examples include roots, tubers,
nectaries, developing fruits and immature leaves.
At the source; (point from which sucrose needs to be
transported from) sucrose is loaded into the sieve element.
This reduces the water potential in the sap inside it. Water
therefore follows down water potential gradient.
At a lower point in the sieve tube, sucrose will be unloaded
where it is needed (sink). As the tissues needing sucrose will
have a lower concentration of it, this transfer will happen by facilitated diffusion and water will
flow across by osmosis due to the resulting change in water potential.
The movement of water into sieve elements at the source and the movement of water out of
them at the sink creates the pressure difference to establish mass flow. Unlike mass flow within
xylem vessels that is unidirectional, source to sink flow can happen in any direction (as
mentioned above). The sink can be higher in the plant than the source. Flow within any single
phloem tube however, is unidirectional
It is important to note that the reasons why sugars are transported as sucrose is that sucrose is
not as reactive as glucose and is more mobile than starch.
Now we will learn about specifically how loading and unloading occurs…
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How does LOADING AND UNLOADING occur in the PHLOEM?
It is important to first understand that translocation occurs due to hydrostatic pressure
differences in the phloem. This occurs due to a combination of osmosis and active transport.
Loading:
Sucrose is made in the mesophyll layer within the
leaf and moves out of the cell by either the apoplast
or symplast pathway. It is then loaded into
companion cells (by active transport).
Companion cells have proton (H+) pumps that pump
ions out of the cell to maintain the concentration
gradient of it being high outside the cell and low
inside. Another pump in the membrane (using ATP)
moves sucrose into the cell by co-transport down the
H+ concentration gradient but against the sucrose
concentration gradient. The sucrose then enters the
sieve element through the plasmodesmata.
As the assimilates move into the phloem, the water
potential decreases at that point. This facilitates
osmosis of water from the xylem. As a result, the
pressure from the incoming water pushes the
assimilates down the phloem as mass flow.
Unloading:
For movement out of the phloem tissue (When the
sucrose is unloaded from the phloem into sinks (e.g.,
roots), facilitated diffusion occurs as the
concentration of sucrose in these cells would be
much lower than within the phloem tissue. Once in
the tissue, sucrose is converted to another molecule
thereby maintaining the concentration gradient.
E.g., Sucrase (Invertase) would breakdown sucrose
into glucose and fructose. While passive facilitated
diffusion does occur, active uptake can also occur.
This causes the water potential to increase and so,
water flows back into the xylem, where it flows up
to the leaves again.
A video attached below to better understand:
https://www.youtube.com/watch?v=DnH67AYtkFw&ab_channel=Scienceo
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2.3: Discuss the mass (pressure) flow hypothesis as a possible mechanism of translocation.
What EVIDENCE is there for mass flow in the phloem?
Evidence that supports mass flow revolves around the concentration of H+ ions in the phloem
sap and surrounding companion cells:
1. During mass flow, there is a great positive charge outside the companion cell and
negative charge inside it. This is due to the large concentration of positively charged H+
ions outside the cell, creating an electrical gradient.
2. The pH of phloem sap is slightly alkaline before the influx of acidic H+ ions from the
companion cell.
3. The rate of flow is 10,000 times faster in sieve tubes than would be expected if
assimilates were moving by diffusion.
4. Assuming the sieve pores are open and unobstructed, pressure differences at source and
sink coincide with actual rates of flow
The main argument against the mass flow hypothesis is that it does not account for
bidirectional flow of sucrose, such as up the stem. For example, the flow of sucrose from
mature leaves to immature leaves near the top of a plant. Another issue is that amino acids
and sucrose flow at different rates in the phloem, something not possible with mass flow.
Evidence for sucrose-hydrogen co-transporter: (a re-wording of no.1 and 2 above)
1. Phloem sap is alkaline (pH:8) which makes sense if H+ ions are consistently pumped out
of the companion cells.
2. As the concentration of H+ ions are higher on the outside of the companion cell plasma
membrane, an electrical potential difference exists (more negative inside and positive
outside).
A video attached below to recap the topic…
https://www.youtube.com/watch?v=MxwI63rQubU
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3. THE CIRCULATORY SYSTEM OF MAMMALS
3.1: Describe the structure of the heart, arteries, veins, capillaries, erythrocytes and
leucocytes, relating their structures to their functions.
Previously, we talked about plants and how their main mode of transport is via translocation
and mas flow in the xylem and phloem.
Mammals however, they are more active organisms compared to plants which most of the
time don’t move. This means that mammals require much more energy as they are more
mobile.
Mammals require a more extensive transport system because:
•
•
•
•
They are more active than plants and therefore respire more to keep up with energy
demands
Low surface area: volume ratio as bodies are not branching like plants
O2 and CO2 cannot simply be gained and excreted by diffusion from all cells to the
environment
Most cells a long way from the gaseous exchange surface
As such an extensive system that is in constant motion is needed by mammals to keep up
with demand. While transpiration pull or differences in turgor pressure was sufficient for
movement with the transport systems in plants, the mammalian transport system requires a
pump known as the heart.
What are the different parts of the MAMMALIAN HEART?
The circulatory system is comprised of the heart, which acts as a pump; blood vessels, which
act as a connected pipe network; and blood, which acts the transport medium. The heart is
essentially a muscular bag filled with blood that pumps blood around the body. This is a
special type of muscle known as cardiac muscle. These contracts and relaxes throughout life
to circulate blood.
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Segment / Blood Vessel
•
•
•
Aorta
•
•
•
•
Pulmonary Artery
•
•
Pulmonary Vein
•
Superior Vena Cava
Inferior Vena Cava
Coronary Arteries
(Sinus)
•
•
•
•
•
Septum
Atrium
•
•
•
Ventricle
•
•
Atrio-Ventricular
Valves
Function / Description
Leaves the Heart
Largest Artery
Has branch to the head and the main to the rest of the
body
Contains Valves to prevent the backflow of blood
Carried oxygenated blood away from the heart and to
the lungs
Leaves heart
Takes deoxygenated blood away from the heart and to
lungs.
Branches soon after leaving heart for left and right lung
Contains valve to prevent backflow of blood into the
heart
Brings oxygenated blood (re-oxygenated blood) from
lungs to the heart
Brings deoxygenated blood to heart from head
Brings deoxygenated blood to heart from rest of body
Supplies heart muscle with blood
Branches from aorta
wall of muscle that separates the left and right side of
the heart. Keeps oxygenated and deoxygenated blood
from mixing. Each half has an atrium and ventricle.
upper chamber that receives blood from veins.
The right atrium has a small patch of muscle
called the SAN (sino-atrial node), which initiates the
cardiac cycle.
lower chamber that receives blood from atria and then
squeezes it out of the heart to lungs or rest of body.
The Left Ventricle is the Muscle-dense region of heart
responsible for pumping blood to aorta.
separates the atria from the ventricles. The
mitral/bicuspid valve separates the left atrium and
ventricle while the tricuspid valve separates the right
atrium and ventricle.
Little Note - Use the acronyms:
LORD (Left Oxygenated, Right Deoxygenated)
T”R”icuspid (Right),
MitraL (Left)
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Notable about the mammalian circulatory system is that it is considered a double circulatory
system.
What this means is that the blood enters and exits the heart twice per cycle:
•
•
When the heart pumps to and receives blood from the lungs. (Pulmonary circulation)
When the heart pumps to and receives blood from the body. (Systemic circulation)
Blood always flows in a unidirectional manner through the chambers of the heart (the upper
atria and lower ventricles).
To facilitate this, valves are present. They prevent backflow.
There are two types: atrioventricular (tricuspid and bicuspid/mitral) and semi-lunar
(pulmonary and aortic).
These synchronize to allow blood to flow in one direction.
Brief recap:
https://www.youtube.com/watch?v=GMBSU2GK3E&ab_channel=NationalGeographic
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What are the types of BLOOD VESSELS in the circulatory system?
In a nutshell…There are three main blood vessels in the circulatory system: arteries, veins
and capillaries. Blood vessels transporting blood away from the heart are known as arteries
whereas those transporting blood to the heart are known as veins. Capillaries are the smallest
of the blood vessels and join arteries to veins.
❖ Arteries :
Blood squeezed out of the heart by the ventricles does so under extremely high pressure. The
force it exerts on the walls of the vessels is known as blood pressure. The blood in arteries
travel in surges as it is squeezed from the heart. This is felt as the pulse. In order to withstand
these surges, the artery wall must be thick and elastic so that it can expand and recoil. The
further away from the heart and the closer to the tissue the blood needs the service, the arteries
break into smaller vessels known as arterioles.
They are thick-walled vessels with small lumens. They always transport blood away from the
heart to body cells. They have a thick tunica media, consisting of elastic fibres, and thick tunica
externa, consisting of collagen. As a result, they are able to withstand high pressures (as
mentions above). The main artery is the aorta. Coronary arteries supply the heart muscles with
oxygen.
❖ Capillaries:
Arterioles further branch into vessels that are one cell thick known as capillaries. They take
blood as close to cells as possible. They form a network called capillary beds. The pressure of
blood at this point is extremely low compared to arteries. They are so narrow that only one (1)
red blood cell can pass at a time. This optimises exchange of gases at the cell level (rapid
diffusion). There are tiny gaps between the cells of the endothelium that allows easy exchange
with blood plasma and surrounding cells.
❖ Veins:
Capillaries then join up to form venules (small veins) that continue joining to form small veins
then large veins. Veins return blood to the heart. Blood in veins is at a much lower pressure
than arteries therefore there are notable structural differences. The walls of veins are much
thinner and possess semilunar valves to keep blood flowing in one direction
In other words, they are thinner-walled vessels with large lumens that will collapse if blood
were to stop flowing through them. They always transport blood towards the heart from the
body cells. The main veins are the superior and inferior vena cava.
The Diagrams in the next pages shows each structure and annotation…
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What are the types of BLOOD CELLS in the body?
Blood is comprised of numerous cells, which makes it a tissue. These cells are transported via
a yellow liquid known as plasma, consisting of proteins, and dissolved nutrients and
nitrogenous waste products in water. Any cell that does not receive blood will eventually
undergo necrosis (death).
The cells include red blood cells (erythrocytes), white blood cells (leucocytes) and platelets
(thrombocytes). In Module 3, the topic of Immunology delves more into leucocyte actions.
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3.2: Explain the cardiac cycle and its initiation.
What is the Cardiac Cycle…?
The cardiac cycle refers to the sequence of events that comprises one heartbeat OR The
sequence of events that takes place for the heart to beat once.
This is a continuous process that happens throughout life and one cycle can be described
from anywhere in the cycle.
As we know, the heart has two “thumps” per beat, the second one “louder” than the other.
These two events or “thumps” are referred to as:
•
Systole – Contraction of atria or ventricles, causing atrioventricular (AV) blood flow,
or blood flow out of the heart (into the arteries). Think “S” in systole as “stress” or
“squeezing” blood out.
•
Diastole – Relaxation of atria and ventricles, allowing blood to flow into the heart to
refill the chambers. Think “D” in diastole as the heart “dilating” or “de-stressing”.
Stages of the Cardiac Cycle:
❖ Atrial Systole –
Both atria contract and force blood through the
atrioventricular valves into the ventricles. Backflow of blood
into the vena cavae and pulmonary veins is prevented by
semilunar.valves.
❖ Ventricular Systole –
After a minor delay, both ventricles contract, increasing
ventricular pressure and forcing blood out of the heart into the
aorta and pulmonary artery. The force is great enough to push
open the semilunar valves in these vessels. The pressure
difference between the ventricles and atria keeps the atrioventricular.valves.shut.
❖ Ventricular Diastole –
Both atrial and ventricular walls are relaxed. Blood does not
flow back into the heart due to presence of aortic and pulmonary
valves. It is at this point that blood flows into the atria from the
veins supplying the heart. Some blood flows into the ventricle
as well but the atria will soon contract to start the cycle again.
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3.3: Discuss the internal factors that control heart action;
Did you know that the cardiac muscle in the heart is MYOGENIC…?
What does that mean…well this means that it is capable of contracting rhythmically on its
own. Cardiac cells joined together will contract together. The heart has a built-in system that
coordinates the contracting of cardiac muscle.
The cardiac cycle is initiated by a group
of cells in the right atrium known as the
sino-atrial node (SAN). It is commonly
referred to as the pacemaker. Its job is
to set the pace and rhythm for the other
cardiac cells (it’s a myogenic muscle,
which means it doesn’t need an impulse
to “initiate”) . When they contract, they
initiate a wave of electrical activity
(electrical impulse/action potential) that
spreads throughout the heart
The wave initially spreads to the atria
which causes them to simultaneously
contract. This impulse does not pass
directly from atria to ventricles as there
is a band of fibres between them that
prevents conduction.
Instead, the impulse must travel down
the atrio-ventricular node (AVN). It is
then passed on to the Bundle of His/AV
bundle that then splits into two smaller
bundles of Purkinje (Purkyne) fibres that
run down to the base of the septum
before dividing to run up the walls of the
ventricles. This ensures the impulse
starts from the base of the ventricles
which would cause it to push blood up
and out of the heart. However, it is
important to note that the wave of
excitation sent experiences a “refractory
period” or “delay” (about 0.3s) so that
the atria and ventricles don’t contract
simultaneously.
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Although the shape of the graph above is quite complex, there are only a few things we have
to focus on.
First of all, observe the periods of systole and diastole shown. You‟ll see that the pressure has
a steep increase during ventricular systole, mostly due to the density of the cardiac muscle in
the left ventricle. Recall that this pressure has to be high enough to pump blood through to the
aorta to the arteries and body cells. This is why aortic pressure increases at this point as well.
Also keep in mind that these valves (semi-lunar and AV) are open and closed due to changes
in pressure. Note the pressure values 120/80 mm Hg. This is the typical systolic and diastolic
pressure respectively.
Here is a little calculation…If the entire cycle above had been completed in 0.85s, how many
heartbeats would there be per minute?
Just divide 60s by 0.85s and you’ll get approximately 70, which is the number of beats per
minute for the average adult heart.
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Which FACTORS influence CARDIAC OUTPUT?
Cardiac output is the volume of blood pumped out of the heart per minute. Think of it as a
combination of heart rate (HR), which is the number of cycles per minute, and stroke
volume (SV), which is the amount of blood pumped per cycle.
❖ O2 and CO2 concentrations –
Physical activity stimulates increased oxygenated blood flow. The oxygen deficiency in
cells result in the release of nitric oxide. Nitric oxide dilates (widens) arterioles,
allowing increased blood flow and cardiac output.
High carbon dioxide concentrations can increase rate of heart beat, as well. These
concentrations are detected by chemoreceptors in arteries.
While cardiac muscle is myogenic, the nervous system can have effects on heart rate through
the release of certain compounds. The release of these compounds is coordinated by the
cardiovascular centre in the medulla of the brain.
❖ Parasympathetic control/Parasympathetic nerves –
During exercise, carotid (brain) artery walls may swell, stimulating baroreceptors
(“stretch” receptors) to send signals along the vagus nerve to the brain. This lowers
cardiac output to avoid overexertion.
In simpler words… This is brought about by the vagus nerve (as mentioned above).
Acetylcholine, when released next to the SAN leads to the slowing down of the heart rate.
❖ Sympathetic control/ Sympathetic nerves –
Conversely, during exercise, sympathetic nerves will stimulate SAN and AVN to
increase heart rate.
To give a better perspective… The sympathetic nerve releases noradrenaline.
Noradrenaline has the opposite effect of acetylcholine and speeds up the heart rate.
Adrenaline, released by the adrenal glands during the fight or flight response, has a
similar effect.
❖ Adrenaline –
Works the same as sympathetic nerves, except the hormone stimulates adrenoreceptors
(hormonal receptors) to achieve the stimulatory effect on SAN and AVN.
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3.4: Discuss factors affecting blood pressure;
We would’ve learned by now that blood pressure is influenced by cardiac output (which is
influenced by nervous and hormonal activity), as well as blood vessel structure.
NB: Pulse- rhythmical throbbing of arteries as blood flows through it. This coincides with the
heart rate or rate of ventricular systole.
Blood pressure is the force of blood exerted on the walls of the vessels.
This is measured using a sphygmomanometer. Two (2) measurements are taken:
Systolic pressure- maximum pressure achieved by the contraction of the left ventricle.
Diastolic pressure- minimum pressure as a result of ventricular relaxation.
Both values are important however the diastolic pressure reveals greater knowledge of the
health of the circulatory system.
Consistently elevated diastolic pressures increases risk of heart conditions/attack/stroke. As
we age, the walls of our vessels naturally harden to a small extent. When this is exacerbated
(atherosclerosis), it causes high blood pressure. The ability of the vessels to expand and recoil
is severely reduced. This is also caused by the build-up of cholesterol deposits on the walls of
these vessels known as plaques.
Exercise or excitement can cause systolic pressures to go up. Stimulation of the SAN by the
sympathetic nerve or the hormone adrenaline leads to the heart to beat stronger. This
increases the stroke volume (the amount of blood pumped out of the heart). This means blood
moves around the circulatory system faster. This increases aerobic respiration and ATP
production for contraction.
Here is a table simplifying the points above…
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3.5: Explain the role of haemoglobin in oxygen and carbon dioxide transport;
Haemoglobin (Hb) is a protein found in red blood cells and has the key function as the
oxygen transporter in the RBC in blood. It has a quaternary structure consisting of two alphachains and two-beta chains. These four sub-units each have prosthetic haem groups, each
with an iron molecule.
Each of these iron molecules can bind an oxygen
molecule, meaning that up to four oxygen molecules
can be bound by one haemoglobin (tetramer)
molecule. When these oxygens are bound, it is now
referred to as oxyhaemoglobin (HbO2).
It binds oxygen when present in high concentrations
(eg lungs) and releases (dissociates) it when oxygen is
present in low concentrations (eg respiring tissues).
Like oxygen, haemoglobin can also bind CO2 and
transport it back to the lungs. While this is not the main
transport mechanism for carbon dioxide, it is one of the ways it is transported (accounts for
1/10th or 10% of Carbon Dioxide in the Blood). When haemoglobin combines with CO2 it
forms carbaminohaemoglobin. This reaction is reversed in the lungs, freeing up haemoglobin
to bind with O2.
However, Oxygen is faster picked up than carbon dioxide, so it is said to have a higher
affinity for haemoglobin.
Carbon monoxide from cigarette smoke and car exhaust has an extremely high affinity for
haemoglobin, so much that it binds for dangerously prolonged periods of time (forming
carboxyhaemoglobin) and prevents oxygen from binding. This most likely will result in
asphyxiation and death.
Also notable about haemoglobin molecules is that they exhibit a characteristic called positive
cooperativity. This means that it may take a certain amount of oxygen concentration to bind
one oxygen molecule, but as soon as that happens, there is a greater chance to bind the 2nd
molecule, an even greater one for the 3rd and the greatest for the 4th. So, haemoglobin takes
the shortest time to bind the final oxygen molecule when it already has the other three bound
to it.
This is because haemoglobin experiences conformational changes (also known as an
allosteric effect) with each successive binding of oxygen. The quaternary structure of the
protein subtly changes to accommodate each new molecule. Think of the haemoglobin
molecule as one of those blooming tea balls or compressed tissue towels that exponentially
opens up more and more as it absorbs water. More of this will be understood in the next
objective.
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3.6: Describe oxygen dissociation curves for adult haemoglobin;
In order to obtain oxygen dissociation curves, experiments were run to observe the behaviour
of haemoglobin under varying concentrations/partial pressures of O2. The amount of oxygen
that binds to the haemoglobin at different partial pressures is noted.
The maximum amount of O2 a sample of haemoglobin could bind is assigned a value of
100% and is described as 100% saturated. At lower partial pressures, less oxygen would bind
and the haemoglobin would be described as being less saturated. A graph of % saturation at
varying partial pressures is known as an
oxygen dissociation curve.
From the graph we can observe that the more
oxygen available (greater partial pressure),
the higher the % saturation.
Oxygen saturation increases as partial
pressure increases. It is most saturated in the
lungs (close to 100%), so this ensures many
oxyhaemoglobin molecules are formed. At
lower partial pressures, it is more difficult for
oxygen to bind. So as oxygen is unloaded unto
tissues for respiration, the saturation
decreases.
Why the S shaped curve?
This is due to corporative binding (as
explained above) in haemoglobin. When the
first O2 molecule is bound, haemoglobin
undergoes an allosteric change which makes it
easier for the 2nd to bind. The initial dip in the
curve corresponds to the period where the
haemoglobin is binding its first oxygen
molecule. After this, it is easier for subsequent
O2 molecules to bind and the curve will be
steep again.
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3.7: Explain the Significance of the effect of Carbon Dioxide on oxygen dissociation curves
(Bohr Effect).
Haemoglobin binds O2 in high concentration environments and releases it in low
concentration environments. In addition to this, CO2 plays a role in this as well. High
concentrations of CO2 cause a series of steps in the RBC that causes haemoglobin to release
some of its oxygen. This causes the haemoglobin to give up even more oxygen at respiring
tissues that it would normally do as there is a high concentration of CO2 in these tissues.
Carbon dioxide lowers the affinity of haemoglobin for oxygen. The observed change in
oxygen affinity or shift in the curve is known as the Bohr effect.
In simpler terms, The Bohr effect shows that haemoglobin’s affinity for oxygen is affected in
certain conditions, meaning that it is less likely to bind with it.
The curve “shifts” to the right if there are increased CO2 levels (from respiring tissues). This
shows a decrease in oxygen affinity. This makes sense, as in this case, we’d want oxygen to
dissociate from haemoglobin to replenish these tissues.
The curve “shifts” to the left if CO2 levels are low (as in the lungs), allowing more O2 to be
taken up.
pH is also a factor due to CO2 converting into carbonic acid and releasing H+ ions.
Temperature affects haemoglobin as high temperatures can affect its structure and bonds,
hence reducing affinity.
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4. HOMEOSTASIS AND HORMONAL ACTION
4.1: Discuss the concept of homeostasis.
What is Homeostasis…?
Homeostasis- the controlling of internal conditions in order to maintain a stable internal
Environment…or…is defined as the regulation of the body’s internal environment in
response to stimuli. This response is called feedback.
In biology, internal environment has a specific meaning, and it refers to the tissue fluid
immediately surrounding every cell. Factors such as concentration of glucose, temperature
and the amount of water present, water-salt levels and blood pH can significantly affect the
ability of a cell to function optimally. If these factors were to reach extremes, they would
have severe effects on metabolic functions. For example, in high temperatures, enzymes can
denature, and in low temperatures, not enough kinetic energy is available to initiate chemical
reactions.
To coordinate this control, different parts of the body need to be in communication with each
other. This is mediated through hormonal or nervous channels which both involve cell
signalling. Cell signalling is the passing of information from one cell to the next. Hormones
(or plant growth regulators in plants) are chemical substances that transfer information from
one part of the body to the other. They are released in one part of the organism and has its effect
on another part of the organism. Hormones tend to act slowly and have longer term effects
when compared to the nervous system that usually mediates rapid, short-term changes.
As mentioned above the response to a stimulus is known as “feedback”. Feedback can occur
in two (2) ways:
•
Negative feedback, which attempts to reverse the change to a set point to achieve
equilibrium
(e.g. when blood glucose levels are too high, insulin is released to convert glucose to
glycogen).
•
Positive feedback, which reinforces the change that has happened and allows the process
to continue.
(e.g. during childbirth, uterus contractions occur due to continued release of the hormone,
oxytocin. Action potentials in nerves are propagated through continuous reactions.)
Key terms:
o Set point- the ideal value for a particular factor. Eg. 37°C body temperature/ blood
glucose level of 80-120 mg per 100cm3 of blood.
o Receptor (Detector) - detects or monitors the factor to be controlled.
o Regulator- compares level of factor detected with set point.
o Effector- causes an action to return level of factor to normal.
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Feedback mechanisms
This cycle is an example of negative feedback. The corrective mechanisms work in the opposite
direction to the initial change to restore normalcy. There can be positive and negative feedback
mechanisms. In positive feedback systems, the mechanisms activated causes the condition to
further deviate in the same direction from the initial value.
The set point for body temperature is 37.5 oC. Temperature is monitored by cells called
receptors (or detectors) typically on the skin. These transport electrical signals to a regulator,
which in this case, is the hypothalamus.
The regulator compares this detected value to the set point, and sends out a signal if they are
too far apart. If they are, a signal is sent to effectors, which try to bring the value back to the
set point.
In this case, if too high, sweat glands may be activated to cool the body down. If too low,
skeletal muscles will contract continuously to produce heat (shivering). Changes in blood
vessel diameters may also occur (vasodilation or vasoconstriction).
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What is Homeostatic Equilibrium…?
Homeostatic equilibrium- level of a factor is not generally maintained at a fixed value,
instead it hovers around the set point value. Feedback mechanisms are corrective by eliciting
a series of small changes constantly to maintain level within a narrow range. This is a
continuous process.
Hence, this is why the point of the negative feedback system is to achieve homeostatic
equilibrium. It is important to keep in mind that hormones act a lot more slowly than
electrical impulses from the nervous system. So, for factors such as blood glucose level, there
is a delay between detection, regulation and action from the effector.
As a result, there is a never a fixed return to set value. Instead, it hovers around a range as
many factors are being regulated simultaneously. This is referred to as a dynamic mechanism.
However, if a regulator or control centre is damaged, there won’t be a return to a set point,
possibly leading to disease of death.
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4.2: Outline the general principles of hormonal action in animals;
The hormonal action response in animals is mainly effected through the endocrine system.
This system is made up of glands (ductless glands) which secrete hormones. These hormones
travel in the plasma of blood all over the body however they only have effect on specific cells
or tissues (targets) that have specific receptors.
What is a gland…?
Gland- a group of specialised cells that secrete at least one useful substance. Endocrine
glands secrete directly into the blood in the capillaries within the gland (eg islets of
Langerhans) as opposed to exocrine glands which secrete substances into ducts which carries
them to a particular part of the body (salivary gland).
To further assess this, Glands are tissues or organs that secrete a substance. There are two (2)
types:
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Hormones
Hormones are defined as secretions of ductless glands that are directly released into the
bloodstream.
There are many different types of hormones. Some are proteins/polypeptides while others are
steroids. They are usually present in small amounts ie their rate of secretion is low however
this is enough for their effects to be felt. They usually have a short life in the body ie they are
either broken down by enzymes/cells or excreted in urine. Insulin lasts for about 10-15
minutes.
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Target cells are identified based on receptors found
on or in these cells. Protein hormones are detected
by receptors found on the cell surface membrane
while steroid hormone receptors are found within
cells.
Protein hormones therefore have no need to enter
cells as they bind to the receptor on the outside
which elicits a response within the cell. Steroids,
being lipid soluble, easily cross the cell membrane
and bind to receptors within the cytoplasm.
To put this in other words…Hormones, they can
act on cells in the vicinity or on distant target cells
that have receptors specific to the hormone (as
mentioned above in another way). Hormones
influence the metabolic activities of cells and act
as chemical messengers.
This system is known as the endocrine system
and though it is slower-acting than the nervous
system, some hormones bring about more longterm effects.
To better understand the categories of hormones (ie. Above when talking about steroid
hormones etc...) here are the two main ones:
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4.3: Explain how insulin and glucagon regulate blood glucose concentration;
As previously mentioned, the maintenance of blood glucose levels within a specific range is
key to optimal functioning of the body. Normal levels are between 80-120 mg per 100 cm3 of
blood. This is maintained by a negative feedback system.
Hypoglycaemia- low levels of blood glucose
Hyperglycaemia- high levels of blood glucose
Both extremes are dangerous.
•
•
Hypoglycaemia is particularly dangerous for cell types that solely use glucose for
respiration eg. brain cells.
Hyperglycaemia results in alteration of the water potential of blood (re: increased solute
means lower water potential). This results in net movement of water out of cells and into
blood by osmosis
When persistent elevated levels of glucose exist, this results in diabetes. Blood glucose levels
are adjusted by two key hormones, insulin and glucagon, which are both secreted by the islets
of Langerhans in the pancreas. Specifically, the alpha cells within the islets of Langerhans
produce glucagon while the beta cells produce insulin.
NB; Glucose is transported around the body in blood plasma and when there is excess, this is
stored as glycogen (what do we know about this?) in muscle and liver cells.
What are the actions of INSULIN & GLUCAGON?
As mentioned above Insulin and glucagon are two hormones secreted by the pancreas by a
group of cells called the islets of Langerhans. These can be sub-divided into α-cells and βcells. β-cells secrete insulin in response rise in blood glucose level. α cells secrete glucagon
when blood glucose drops. Both cells act as receptors.
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Insulin is required to transport glucose from the bloodstream into cell’s cytoplasm. Glucose is
one of the raw materials for aerobic respiration and production of ATP.
Glucose, however, is a large molecule and cannot diffuse through the phospholipid bilayer. It
relies on transport proteins that will only “open” if insulin binds to one of its receptors.
Muscle cells have a particular transport protein called GLUT4. However, these are held in the
cytoplasm along vesicles. What insulin does is signal for these to come to the surface. As
they fuse with the plasma membrane, glucose can enter via facilitated diffusion.
In liver cells, it is a little different. No GLUT4 protein is necessary. Liver cells have insulin
receptors on their plasma membranes, and two particular enzymes, glucokinase and glycogen
synthase. Glucokinase phosphorylates glucose and moves it into the cell. Glycogen synthase,
as you can guess, converts glucose into glycogen.
Glucagon is mainly required to increase blood glucose levels. It can do this by breaking down
stored glycogen (usually in the liver), or by converting other compounds such as lipids and
amino acids into glucose (a process called gluconeogenesis). You may have heard of the
latter occurring during starvation and muscle loss.
The action of glucagon varies from insulin. The action of glucagon requires a first messenger
and second messenger (outlined on previous page). The first messenger is the glucagon and
the second is cAMP.
Observe the diagram. Step by step, this is
happening:
1) Glucagon in the blood binds to a proteincoupled receptor on the liver cell‟s plasma
membrane.
2) The protein is hydrolysed and “breaks off” a
fragment, called a G-protein, that acts as a
molecular switch. This fragment completes a
molecule of an enzyme called cyclase.
3) Cyclase converts ATP into cyclic AMP
(cAMP).
4) cAMP then helps break glycosidic bonds in
glycogen
to
form
glucose.
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A note on G-proteins and cAMP:
G-proteins are complexes that act as signal transducers, broken off from larger proteins.
Think of the process as the „parent protein‟ sending the „child protein‟ to relay instructions
to an enzyme or another factor. cAMP‟s function can be likened to a piece of mRNA, but
messaging instructions for reactions than for making proteins.
Lets look at this process in a diagrammatic form now…
Effects of insulin
•
•
•
Increased permeability of glucose in cell membranes of liver, muscle and adipose cells.
Glucose can only cross the cell membrane through transporter proteins. The transporter
proteins in muscle cells (GLUT4) are usually kept in the cytoplasm. When insulin is
detected, these are moved to the cell surface thereby increasing transport of glucose into
these muscle cells. This is not the case in liver or braincells as they have different glucose
transporters that are always on cell surface membrane.
Increased rate of glycogen production from glucose (glycogenesis) in liver cells. When
insulin binds to cell surface receptor, glucokinase enzymes are activated and these
phosphorylates glucose. This traps glucose in the cell as it can no longer pass through
transporters.
Activation of phosphofructokinase and glycogen synthase which catalyses the formation of
α1-4 glycosidic bonds to produce glycogen.
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Effects of glucagon
•
•
Increased rate of glycogen breakdown (glycogenolysis). Glucagon binding stimulates
activation of enzymes catalysing this breakdown. Leads to glucose being transported out
of cell by facilitated diffusion.
Increased gluconeogenesis- production of new glucose molecules form amino acids or
lipids.
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4.4: Discuss the commercial use made of ethylene in supplying market-ready fruit.
Plants also produce chemical substances that has effect in other places in the plant. Plant growth
regulators (PGRs) are analogous to hormones in animals. Some examples are gibberellin,
abscisic acid and ethylene (ethene).
When a fruit ripens, it means that its internal components have fully developed. These include
seeds, which are sometimes eaten by animals and dispersed via their faeces, where they grow
into new plants. This process is advantageous to those species of plants as it reduces
competition, introduces them to new habitats and encourages adaptation.
When a fruit ripens, the following has occurred:
•
•
Increase in edibility – The fruit attains characteristics for easy consumption, including the
breakdown of cell walls to soften its texture, the increase in sweetness (due to complex
sugars hydrolysing into simpler ones, such as sucrose) and the production of aromatic
compounds, that instill scent and flavour.
Change in colour – Fruits become brighter in colour (e.g. bananas turn yellow, cherries turn
bright red) due to the conversion of the fruit‟s green chloroplasts to coloured chromoplasts.
This makes the fruit more attractive to animals (including humans at the marketplace) and
more likely to be consumed.
Fruit ripening is caused by a plant hormone (or growth regulator) called ETHYLENE.
Other growth regulators include auxins (for
phototropic responses) and gibberellins (for
seed germination).
When fully mature fruit develop all features
necessary to make it attractive to animals, this
process is known as ripening. A unique feature
of ethylene is that it’s a gas. This gives it the
ease of spreading from one fruit to another
through the air. It’s small lipid soluble structure
means it can move from cell to cell with ease as well. All plant tissues that have been studied
produces ethylene at some point in development. Climacteric fruits are those that produce a
sudden burst of ethylene gas as they begin to ripen. This is usually accompanied by a sudden
rise in respiration. Examples of climacteric fruits are tomatoes, bananas, avocado, melon,
mango apple and citrus fruits.
In other words…Ethylene is a GAS, meaning that it can undergo simple diffusion through the
air and influence ripening on adjacent fruits.
Ripe bananas can thus be placed in a container or in a warm room with other fruits to
accelerate the ripening process and quicker produce market-ready fruits. This results in
increased profits from grocers and farmers.
Fruits that produce large amounts of ethylene are called climacteric fruits, including:
tomatoes, bananas, avocadoes, mangoes, apples and pears.
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Effects of ethylene
Ethylene causes its effects by directly affecting regulatory genes. These genes control whether
certain genes are expressed or not resulting in the following changes.
•
Colour change
Unripe fruit is green in colour due to chlorophyll in chloroplast. In the ripening process
chloroplasts are converted to chromoplasts that contain other pigments beside chlorophyll. It
is broken down to various carotenoid compounds that change the colour of fruit to yellow,
orange or red. Unripe tomatoes are green. At the start of ripening they stop synthesising
chlorophyll and start producing the red pigment, lycopene. This is also rich in antioxidants
which increases the plants nutritional value.
•
Softening of texture
Fruits soften as they ripen. This is due to breakdown of the middle layer of the cell wall made
up mostly of pectin. This makes it easier for cells to separate from one another. Increased
hydration of the pectin also makes the fruit juicier.
•
Production of new aromatic compounds
Characteristic scent and flavour associated with each fruit. Each fruit produces its own
combination of aromatic compounds that leads to this. These tend to build up as the fruit ripens.
•
Increase in sweetness
In the ripening process, starch is broken down into sugars (glucose/fructose/sucrose). These
sugars dissolve in the water inside cells, adding to the juice.
Ethylene production in controlled by a positive feedback mechanism. Ethylene is synthesised
from the AA methionine by enzymes. Ethylene increases the activity of the enzymes further
encouraging the production of more ethylene
• Commercial use
Ethylene is easily manufactured and is manipulated by the fruit marketing industry to maximise
the supply of fruits in optimal condition. Fruits picked while still green are easier to pick and
transport without damage. When they arrive at their destination country, they can be treated
with ethylene gas to achieve the ideal stage of ripeness for sale in supermarkets etc. This
maximises profits for businessmen and also allows the availability of fruits in destinations
further away.
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How does ETHYLENE affect RESPIRATION?
Many vendors prefer pick bananas while they‟re unripe as
they‟re tougher (cellulose is still intact) and easier to
transport in this state. Also, even one ripe banana in the
bunch can prematurely ripen the others, giving the vendor
little control over sales strategy.
In addition to ethylene being a gaseous compound (and
thus being able to diffuse quickly over a large area), it also
activates enzymes within the fruit that act as catalysts to
produce more ethylene. Therefore, once the process
begins, ripening occurs at a rapid rate. This uses a
considerably amount of energy, as a number of reactions
are occurring in the fruit to hydrolyse cell walls and sugars
to make them soft and sweet. Ethylene also has a low
melting point, allowing it to remain a gas (and not
condense) even at low temperatures.
Rate of respiration increases as ethylene production is increased. This can be proven by
observing carbon dioxide volumes released from the fruit. The graph below shows the
relationship:
The graph shows that as ethylene production increases (from Day 2 to 3), there is a steep
increase in the evolution of carbon dioxide from fruit tissues due to increased rate of respiration.
Both ethylene and CO2 concentrations reach a peak around Day 4. This is when the fruit has
completely ripened.
After this point, CO2 levels drop due to a reduction in metabolic activity after the ripening
process has ceased. At the same time, ethylene concentration has „plateaued‟, meaning that it
is still being released and can influence the ripening of other fruits around it. However, the
quality of a fruit declines after this point, which will eventually result in cell death.
Certain factors also influence this process, including humidity, temperature and oxygen
concentration.
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5. THE KIDNEY, EXCRETION AND OSMOREGULATION
5.1: Explain the need to remove nitrogenous and other excretory products from the body;
As a result of the metabolic reactions occurring within the body, unwanted products are
produced. Two of the main excretory products produced are carbon dioxide and urea. Every
cell in the body produces CO2 when they respire. This is brought to the lungs in the blood
stream and excreted in the air we breathe out after diffusing into the alveoli. Alternatively, urea
is only produced by the liver due to the deamination of excess amino acids and excreted by the
kidney in urine.
In other words, if waste products from metabolic reactions are allowed to accumulate in tissues,
they will become toxic. These waste products include carbon dioxide, excess water and urea.
The removal of these products from the body is called excretion (also recall that egestion is the
removal of non-metabolic waste, such as faeces).
Urea Formation
While the excess fats and carbohydrates that we eat can be stored but excess proteins are not
stored. Any excess is broken down in the liver by a process called deamination. In this process
the amino group is removed and forms ammonia. The rest of it forms a keto acid which can be
respired to release energy or converted to fat and stored.
Urea is the main waste product formed during the process of deamination, which is the removal
of the amino (NH2) group when an amino acid is broken down. The other parts of the amino
acid (the carboxyl group, the R group and the hydrogen) go on to form ketone bodies, which
are then used in gluconeogenesis. You may be familiar with this if you’ve ever read about
extremely low-carb “keto diets”.
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As seen in the diagrams above, the amino group is extracted to form the very toxic ammonia.
In the liver cells, in a process called the ornithine cycle (Urea formation is as a result of the
energy dependent ornithine cycle), Ammonia, with the help of ATP, combines with carbon
dioxide to eventually form urea (Ammonia is very soluble and toxic and cannot be allowed to
remain in the body. For safe transport, it is combined with CO2 in the liver to form urea
[CO(NH2)2]. In this less soluble, less dangerous form, it is transported to the kidney for
excretion via the blood.). Urea therefore, has a lower toxicity and though less soluble, can be
easily transported in the blood plasma.
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5.2: Describe the gross structure of the kidney and the detailed structure of the nephron
and associated blood vessels;
▪ Kidneys- are Bean-shaped Organs that
filter blood in which it filters waste
materials out of the blood and pass them out
of the body as urine.
▪ Ureter- long tube that runs from the
kidneys to the bladder that facilitates the
transfer of urine.
▪ Bladder- the organ in which uine is
stored until it is emptied from the body
through the urethra.
▪ Urethra- tube that carries urine from the
bladder to the outside of the body.
The Kidney
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These are the main components of the kidney:
▪
Renal artery – Carries blood from the aorta to the kidneys (branches off from the aorta
and brings blood to the kidney.)
▪
Renal vein – Carries blood from the kidney back to the heart (vena cava) (Takes blood
away from the kidney and returns it to vena cava.)
▪
Cortex – Outer part of the kidney, surrounded by a fatty tissue capsule. Contains the
glomerulus and convoluted tubules of the nephron. the outer part of the kidney where
nephrons start.)
▪
Medulla – Inner part of the kidney, containing collecting ducts and loops of Henle.
(inner/middle layer of the kidney in which loops of Henle and collecting ducts are found.)
▪
Ureter – Transports urine to the bladder.
▪
Renal pelvis – Acts as a funnel for collecting urine flowing into the ureter. (Innermost part
of the kidney where nephrons merge into the ureter.)
▪
Capsule- thin membranous sheath that covers and supports the outside of each kidney
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The NEPHRON
Nephrons are kidney sub-units consisting of capsules, tubules and ducts and are the structural
and functional unit of excretion. They are responsible for these processes:
▪
Ultrafiltration – A build-up of capillary pressure forces small molecules in the
capsules of the nephron into the tubules. These small molecules include water,
glucose, sodium chloride and urea. Together, they form a filtrate.
▪
Selective reabsorption – Certain nutrients (e.g. glucose) are removed from the
filtrate and transported back into the bloodstream, leaving only the components of
urine in the filtrate (e.g. urea and water) to be excreted.
▪
Osmoregulation – With the help of the hormone, ADH, permeability of collecting
ducts is affected dependent on body water levels and temperature. Water can be
conserved in the blood this way.
There are two (2) types of Nephrons:
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NOTE: Though typically not depicted in the diagrams for simplicity, kidney nephrons are
entwined with peritubular capillaries. These facilitate rapid transfer of materials away
from the nephron filtrate (reabsorption) and into it (secretion).
The diagrams above show the basic layout and functions segments of a renal nephron. It
includes:
▪
Afferent arteriole- small artery that branched off from the renal artery that brings blood
to nephron (specifically the glomerulus).
▪
Efferent arteriole- small artery taking blood away from the glomerulus
▪
Glomerulus – A cluster of blood vessels that filters blood to the Bowman’s capsule (Ball
of capillaries with blood under high pressure within the Bowman’s capsule.).
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▪
Bowman’s (or glomerular) capsule – A cup-like sac that accepts the filtrate from
glomerulus (cup-shaped structure at the start of the nephron into which ultrafiltration
occurs).
▪
Proximal convoluted tubule (PCT) – Site of selective reabsorption (region of the
nephron between the Bowman’s capsule and the loop of Henle.).
▪
Loop of Henle – Regulates the fluid and ion composition of the filtrate (the section of the
nephron that dips down into the medulla and then back into the cortex of the kidney).
▪
Peritubular capillaries- network of capillaries running alongside the nephron to
facilitate further excretion and reabsorption.
▪
Distal convoluted tubule (DCT) – Connects the loop to the collecting duct (region of the
nephron between the loop of Henle and the collecting tubule.).
▪
Collecting tubule- Collects urine from distal convoluted tubule and transports it to the
collecting ducts
▪
Collecting duct – Responds to ADH by increasing wall permeability, allowing water to
be reabsorbed. Transports urine to the renal pelvis and ureter (the final part of the nephron
that joins the ureter.).
HISTOLOGY OF KIDNEY TISSUE
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5.3: Explain the function of the kidney in terms of excretion and osmoregulation;
How does the kidney help with EXCRETION?
Now that we’ve seen the basic layout of a kidney nephron,
we’re now going to delve into the complex processes that
occur in each segment.
In the Glomerulus and Bowman’s Capsule
Firstly, you’ll notice on the diagram two arterioles: the
afferent and efferent. The afferent (or “arriving”) vessel
brings blood into the glomerulus. The efferent (or “exiting”)
vessel carries the blood away.
Within the Bowman’s capsule, the glomerulus has blood under high pressure. This causes
blood plasma (and dissolved substances) to be forced into the Bowman’s capsule. This process
is known as ultrafiltration. Only small substances can be filtered and what ends up inside the
urinary space within the Bowman’s capsule is called the glomerular filtrate.
The reason for the high pressure within the glomerulus is the difference in diameter between
the afferent and efferent arterioles Due to the efferent arteriole being narrower, the amount of
blood entering the glomerulus is greater than the mount leaving it for a given time period, this
therefore ensures that a high pressure is always maintained within the glomerulus to facilitate
ultrafiltration (in other words the smaller lumen of the efferent arteriole causes a build-up in
hydrostatic pressure in the glomerulus. Smaller diameter increases ultrafiltration.). As a result
of this pressure, water and small solutes from the glomerulus are forced through pores in the
capillary endothelium, and through the Bowman capsule aka the basement membrane which
acts as the filter. No cells or large proteins can pass through this filter.
Reabsorption in the Proximal Convoluted Tubule
The objective now is to transfer „useful‟ materials back into the bloodstream while at the same
time, keeping waste molecules in the PCT, so that it can eventually form urine.
The glomerular filtrate contains many useful substances (inorganic ions, glucose, amino acids)
that the body needs. These therefore need to be reabsorbed before urine in excreted. As the
filtrate flows along the nephron, these are selectively reabsorbed. Most reabsorption occurs in
the proximal convoluted tubules.
The cells of the nephron have tight junctions therefore substances being reabsorbed must pass
through the plasma membranes of these cells. (In other words, PCT epithelial cells export
certain ions and water back into the capillaries through active transport and diffusion. This
happens through numerous villi and very thin membranes in the PCT epithelial cells, so they
are lined with numerous mitochondria).
The tricky part is the export of glucose. This involves the use of a sodium-potassium pump
(This allows two K+ ions to enter the cell, while at the same time allowing three Na+ ions to
transfer out.).
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Sodium/potassium pumps ensure that the
concentration of Na+ within the cytoplasm of
these cells remain low. It ensures a concentration
gradient exists.
The concentration of Na+ within the tubule
would be higher than the tubule cell. The Na+
would then diffuse down its concentration
gradient through transporter proteins. There are
various types of transporters that can carry other
compounds while transporting Na+ (cotransport). (As this occurs, glucose can be carried with these Na+ ions against the concentration
gradient in a symport process. Think of it as Na+ opening a door for glucose to go along with
it).The image below is an example of the different kinds. E.g. The passive movement of sodium
down its concentration gradient provides enough energy for to move glucose against its
concentration gradient. Glucose, amino acids, vitamins, sodium and chloride ions are absorbed
here.
The transference of solutes results in variations of water potential. The water potential in the
tubule increases as it becomes less concentrated while the water potential in the tubule cell and
capillaries decrease due to addition of solute.
Water therefore moves by osmosis from within the tubule outward. This is why 65% of water
is reabsorbed in the proximal convoluted tubule. Counter-intuitively, 50% of urea in the filtrate
is also reabsorbed. Kidneys remove urea from the blood but not completely. Urea is a small
molecule and would therefore easily pass-through membranes. Any filtrate that hasn’t been
reabsorbed now flows to the Loop of Henle.
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The Loop of Henle
We only need enough water to dissolve urea in the urine. After the PCT, the objective now is
continued water reabsorption into the bloodstream. When it comes to producing very
concentrated urine, the length of the loop of Henle becomes important. Not all nephrons are
the same. Most are cortical nephrons and are what we’ve been discussing before. However,
there is a subset called juxtamedullary nephrons with longer loops of Henle than run further
down into the medulla.
This allows the nephrons to pump large amounts of Na+ and Cl- into the tissue fluid of the
medulla (lowering the water potential). This causes water to leave the nephron (at specified
points) and be reabsorbed by the capillaries and returned to the body. This is important when
water must be conserved.
The Loop of Henle has a descending and ascending limb. The descending limb of the loop of
Henle is permeable to water while the ascending limb is not. The ascending limb pumps out
the Na+ and Cl- by active transport and diffusion which causes more water the flow out from
the descending limb (sodium and chloride ions are actively transported into the cells and
capillaries (called vasa recta) surrounding the descending limb). This causes the fluid leaving
the loop of Henle from the ascending limb to be very concentrated or in other words, as these
ions arrive at the capillaries and cells, they reduce their water potential. This is the countercurrent system that exists in the loop of Henle.
Due to the reduced water potential in the surrounding cells, osmosis now occurs, allowing
water to flow from the descending limb to these cells and then into the capillaries, thus
conserving water needed for metabolic reactions and cooling.
At the base of the loop, the solute concentration is very high inside and out of the tube. This is
also facilitated by the fact that the walls of descending limb are permeable. The ascending
limb’s walls are impermeable, so no water is lost here.
Hence, the longer the loop, the more the concentration of solutes can be built up in the medulla
and therefore the more water is reabsorbed.
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Distal Convoluted Tubule and Collecting Duct
As the concentrated filtrate flows through the distal convoluted tubule, Na+ is actively
pumped out while K+ are pumped in. The collecting duct must also pass through the medulla
on its way to the pelvis and would therefore also pass through the same low water potential
environment the loop of Henle is in allowing for further reabsorption.
Osmoregulation
The collecting duct is located at the end of the nephron, just before urine is sent to the renal
pelvis and ureter.
As we discussed in homeostasis before, the internal environment must be maintained at a
constant level for optimal metabolic reactions within the body. One key factor that must be
maintained is the water content of the body. The regulation of the water content of the body is
known as osmoregulation.
This involves the kidneys, pituitary gland and the hypothalamus and is regulated by a
negative feedback mechanism.
Within the hypothalamus in the brain, there are osmoreceptors that detect the water potential
of the blood. Their cell bodies synthesize a hormone called anti-diuretic hormone (ADH)
which is a small nonapeptide. These are transferred to the posterior pituitary gland through a
neuron where they are released when needed.
If water potential is low (lacking water) ADH is released from the ends of the axons into the
blood. ADH alters the permeability of the walls of the collecting ducts and therefore
influences the amount of water reabsorbed (ADH interacts with the plasma membranes of the
collecting duct walls). ADH makes the walls of the collecting duct more permeable therefore
more water is reabsorbed. The cells of the walls of the collecting ducts are the target cells for
ADH. When ADH binds to receptors on the cells of the collecting duct walls. This causes
groups of proteins called aquaporins within the cytoplasm to move to the plasma membrane
and insert themselves (aquaporins move from the cytoplasm to line the duct’s walls). They
form channels through which water molecules can pass through. Less water is excreted in
urine and therefore conserved (increasing permeability to water and facilitating transport of
water out of the duct).
If water potential in blood is high, only a little ADH is released and the changes observed
above happens on a much smaller scale in that no aquaporins will be present on the walls, so
water is kept in the ducts and eventually excreted with the urine. This urine will be in larger
volumes and quite diluted (or „clear‟ in colour).
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EXTRA NOTE: A person may produce unusually large amounts of diluted urine. This
condition is called diabetes insipidus. Extremely small amounts of ADH is produced, leading
to prolonged periods of dehydration and impermeability of the collecting duct walls. This
could also result from a tumour in the hypothalamus or posterior pituitary gland.
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5.4: Discuss the Clinical significance of the presence of glucose and protein in the urine.
As a urine sample is a much less invasive sample than a blood sample, it is easily accessible.
An individual’s urine can give an idea of someone’s health by conducting simple tests. The
presence of substances such as glucose and protein in urine can serve as early indicators of
adverse health conditions.
All glucose in the glomerular filtrate should be reabsorbed in the proximal convoluted tubule.
As such, there should be none in urine. However, in persons with elevated blood glucose
(diabetics), all the glucose in the filtrate cannot be reabsorbed and persist in urine.
As previously mentioned, the basement membrane acts as a filter through which the
glomerular filtrate passes. Proteins are generally too big to pass through and remain within
capillaries. Persisted presence of protein in urine can indicate a few conditions:
1. Kidney problems eg disease affecting glomeruli or kidney infection
2. High blood pressure (which can also indicate risk of heart disease).
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6. NERVOUS CO-ORDINATION
6.1: Describe the structure of motor and sensory neurons;
The brain, spinal cord and nerves make up the human nervous system.
This can be subdivided into the central and peripheral
nervous system where the brain and spinal cord makes up the
central nervous system (CNS) and the nerves make up
the peripheral nervous system (PNS). Specialised
cells known as neurons are responsible for
functioning of the nervous system. Neurons pass
information between the CNS and the rest of the
body via the PNS. This information is sent as
nervous impulses which are action potentials.
An action potential is a fleeting reversal of the resting
potential, which sweeps along an axon. There are two
main types of neurons: motor neurons and sensory
neurons. Motor neurons take impulses from the CNS
to effectors (muscle/gland) while sensory neurons
deliver impulses from receptors to CNS. There are another class of neurons
known as intermediate neurons found within the CNS. These carry impulses from
and to numerous other neurons.
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This particular topic is quite complex and introduces many new concepts. For ease, let’s
familiarize or re-familiarize ourselves with some terms:
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What is the difference between SENSORY and MOTOR NEURONES?
MOTOR NEURON
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A MOTOR NEURONE. Starting from the top, you will see branch-like structures. The largest
branch is called a dendron, which separate into dendrites. These allow connection to other
neurones for reception and propagation of impulses. A cell body (or soma) is present at the
end, containing organelles such as mitochondria to provide ATP to transmit impulses.
These impulses travel along the long segments called axons until they get to axon terminals.
At the end of these terminals are synapses, which are gaps that separate neurones but must still
allow transmission of impulses.
Notable about the axon is the myelin sheath. The myelin sheath allows rapid conduction of
impulses and also acts as an insulator. Each ‘segment’ of myelin is called a Schwann cell, and
between each two Schwann cells is a small segment of axon called a Node of Ranvier.
Cell body- larger part of the neuron containing cytoplasm and nucleus. The cell body
remains in the spinal cord.
Dendrite- short processes that project from the cell body of the motor neuron that conduct
impulses towards the cell body
Axon- Longer process that takes impulses away from the cell body.
Cytoplasm- Contains many of the usual organelles found in cells such as ribosomes, ER,
Golgi body and mitochondria.
Schwann cell- special cells that wrap themselves around the length of axons of neurons.
Myelin sheath- coating made up of Schwann cells wrapped around axon in concentric
circles. Therefore, made up mainly of lipids and proteins. This increases the speed and
efficiency in conduction of nervous impulses along the axon.
Node of Ranvier- spaces on the axon between Schwann cells that are not covered. These
occur every 1-3mm.
Axon terminal- axon forms branches that end in synaptic bob/buttons
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SENSORY NEURON
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A SENSORY NEURONE. It is similar in structure to a motor neurone, but its cell body is
located along the middle of the axon instead of at the end of it.
These can be found on sense organs, such as the skin and retina to detect stimuli and pass them
to the central nervous system (CNS) to be interpreted. If the stimulus is extreme (e.g. touching
a hot stove), the impulse is passed to the dorsal root ganglia in the spine and directly to a motor
neurone. This produces an involuntary action that moves the body away from danger. This
action is called a reflex.
Neurones are bundled into dense tubular tissues called nerves. A large stimulus may stimulate
multiple nerves.
Annotations are mentioned above
INTERNEURON (INTERMEDIATE NEURON)
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Reflex arc
The different types of neurons work together to in the body to form a reflex arc. This is the
pathway that an impulse takes from receptor to effector without conscious thought.
Nerves
Nerves are actually bundles of axons (several thousand) surrounded by the perineurium
which is a protective coating. They can be made up entirely of one type of neuron or mixed.
Think of wire in mesh (image to the right)
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6.2: Explain the role of nerve cell membranes in establishing and maintaining the resting
potential;
Nerve impulses are electrical signals but is not the flow of electricity that we may have
learned about before ie. it is not a flow of electrons.
They are quick and temporary changes in the distribution of electrical charge across plasma
membranes due to the movement of charged ions. These are mainly due to changes in
distribution of sodium and potassium ions. These are facilitated by sodium-potassium pumps.
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The plasma membrane of the neuron normally has a difference in charge across it. There
tends to be a more positive charge outside and a more negative charge inside. The difference
in charges across the membrane is known as the resting potential. In most neurons it is
-70mV on the inside compared with the outside.
In other words, how can we define resting potential…?
First, it is important to understand the concept of a membrane potential (or membrane
voltage). This occurs when there is a difference in charge in the exterior and interior of a cell.
For example, if the interior is negative and the exterior is positive. This produces an electrical
gradient that allows charges to flow. If chemicals or ion concentrations are involved as well,
it is called an electrochemical gradient.
There are two main positive ions involved: Na+ and K+. The neurone is sometimes referred
to as a ‘salt- covered banana’ (recall that bananas contain K), meaning that, when at rest (not
firing impulses), it has more Na+ ions on the outside than there are K+ ions on the inside.
This “uneven” distribution occurs due to proteins called sodium-potassium pumps as
mentioned above.
The sodium-potassium pumps work constantly to ensure this difference (3 positive charged
ions move out while 2 move in). These ions can leak back across the membrane at other
points and this is more common with potassium ions than sodium ions further maintaining the
net positive charge on the outside and negative charge on the inside.
Let’s break it down in more simpler terms …
This pump, once interacted with ATP (active transport), can “push” Na+ ions out of the cell
in return for “pulling” K+ ions into the cell cytoplasm.
However, the trade is not equal. For every 3 Na+ pumped out, only 2 K+ are pumped in.
Keep in mind that this is what happens in a neurone at rest. What this uneven trade does is
ensure that there is a greater amount of positive charges outside than inside. The inside
becomes negative.
What also helps the above are channels on the membrane that are more permeable to K+ over
Na+, and will quicker “leak” K + ions out of the cytoplasm.
And likewise, to the statement above, this “difference in charge” generates a small voltage of
approximately -70 mV (in humans). This is the resting potential of the neurone. It remains at
that voltage, and at rest, until a stimulus (e.g., pain or heat) is detected.
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6.3: Describe the conduction of an action potential along the nerve cell membrane;
Action potential
An action potential is an event that coincides with the transmission of an electrical impulse.
That is, when you actually experience a sensation or must contract or relax a muscle in
response to a stimulus. Action potentials thus occur when the nerves are not at rest; they are
experiencing action!
We’d just established that when impulses are not firing, the neurone is at rest. And a neurone
at rest has a negative membrane potential of -70mV (due to the interior of the cell being
negative). For an action potential to occur, we need the interior of the cell to be positive. But
how? We need an influx of Na+ ions from those sodium-potassium pumps!
Due to the difference in charge across the membrane, it is described as being polarised. Re: an
action potential is a fleeting reversal of the resting potential, which sweeps along an axon. The
reversal in charge is known as depolarisation. The reversal in charge is due to the presence of
other transmembrane proteins that are voltage-gated channels (open at particular voltage and
close at particular voltage). These facilitate the rapid passage of sodium and potassium ions.
These will move down their gradients once the channels are open.
A double gradient exists as the cations would move to the negatively charged region (inside
the cell)- electrical gradient. There is a difference in concentration of the ions as well- chemical
gradient. Therefore, the double gradient is known as an electrochemical gradient.
Stimulus at the receptor (end of sensory neuron) causes sodium ion channels to open, causing
the interior of the neuron to become less negative. This change in voltage would cause other
voltage gated sodium channels to flood open causing a rapid influx of sodium ions into the
neuron that it becomes temporarily positive inside (depolarised) (In other words Na+ ions to
diffuse rapidly into the cytoplasm from the outside, down the electrochemical gradient. The
aim is to “even” out the +ve and –ve charges in and out of the cell) to give a membrane potential
of 0 mV. But this doesn’t happen as expected. Instead, more Na+ rushes in than expected
(sometimes called “overshooting”),
These sodium channels then close so no more sodium ions come in. These “extra” Na+ ions
inside the cell cause the interior to become positively charged, and the exterior to become
negative (the opposite of „rest‟). The previously negative rest voltage of -70 mV is now a
positive voltage of about 30 mV.
This change in polarisation then causes the voltage gated potassium channels to open to remove
positive ions from within the neuron. This causes the interior to become increasingly negative
again (repolarisation). This can cause an overshoot as well and the neuron can become
temporarily more negative than the resting potential (You’d expect the membrane potential to
return to -70 mV, but instead it goes a bit more negative than that value (maybe -80 mV). This
is called HYPERPOLARIZATION.) The voltage-gated potassium channels close. The
overshoot is rectified by the sodium-potassium pumps to restore the membrane potential to the
normal resting potential (This allows some time for those leak channels and sodium-potassium
pumps to bring everything back to rest potential. The time it takes to return to rest is called the
refractory period). And during this time, another action potential cannot take place.
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NB: All stimuli don’t result in an action potential. In order for one to be generated, the
potential must reach between -50 to -60 mV (-55mV on average) based on the neuron. This is
known as the threshold potential.
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Transmission of Action Potential
An action potential in one part of a neuronal membrane will trigger an action potential in the
region adjacent to it. Theoretically this can happen in both directions however the period of
repolarisation, the concentration of sodium and potassium ions are not back to normal as yet
and therefore incapable of generating another action potential. This is known as the refractory
period and ensures the action potential wave is unidirectional along the axon.
Let’s break it down simpler…
The electrical impulse is transmitted along the axon like an energy-carrying “wave” along the
surface of the ocean. The “wave” itself consists of a series of depolarizations. One
depolarized region impacts the successive region, and that becomes depolarized. This
continues until the impulse reaches its destination.
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Some axons are myelinated. There is a difference in how an action potential travel along a
myelinated axon vs unmyelinated axon. As sodium and potassium ions cannot flow through
the myelin sheath, this happens in ‘jumps’ between the nodes of Ranvier. The local circuits
are set up between the nodes with are 1-3mm apart. This type of conduction is called
saltatory conduction (The word “saltatory” means “proceeding by leaps” as opposed to
gradual or continuous movement.) and speed up transmission X50.
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In a myelinated axon, the action potentials are conducted in a high velocity transmission as
the spread of depolarization occurs in “leaps” across these nodes and not the myelin sheaths.
In an unmyelinated axon, the velocity is much lower, as the action potential must be
propagated from cell to cell along the axon in a continuous progression.
FREQUENCY OF ACTION POTENTIALS
Unlike waves and forces, an action potential does not have a magnitude or amplitude. You
can think of an action potential as a basic constituent of a sensation or impulse.
If there are a small number of action potentials generated in a few neurones, it is most likely
as a result of a weak stimulus, like a soft touch. If there are a large number of action
potentials generated in many neurones, it is most likely a stronger stimulus, like a hard slap or
a burn.
Strong stimuli may also generate a high frequency of action potentials, which means that
there are many occurring per second Anaesthetics such as Lidocaine, used by dentists,
interfere with sodium channels to the point where, even with a strong stimulus, no
depolarization occurs and thus no action potential is generated.
In simple terms, Action potentials are always the same size. Either it occurs or not. However,
to relay intensity of the stimulus, the frequency of action potentials changes. Higher the
frequency, the stronger the stimulus. It is also likely like a stronger stimulus will excite more
neurons in an area
The brain can therefore interpret the frequency and number of neurons with simultaneous
potentials to infer location and strength of stimulus.
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6.4: Explain Synaptic transmission;and,
What is a SYNAPSE?
A fact that makes nervous transmission more complex is the involvement of synapses.
Synapses are sites that lie between two adjacent neurones (A junction between 2 neurons.),
which don’t touch but have an extremely small gap that is 20 – 50 nm wide. That gap is called
a synaptic cleft and the two neurones surrounding that cleft are called the presynaptic neurone
(connected to an axon) and postsynaptic neurone (connected to a dendrite).
= before the synapse
= Neuro Transmitters
= After synapse
End of Neuron
In the pre-synaptic neuron, there are many mitochondria as well as synaptic vesicles. The
mitochondria produce ATP so that the synaptic vesicles (Contain neurotransmitter) can be
refilled as necessary. Inside of each synaptic vesicle, there are numerous neurotransmitter
molecules (One of the main neurotransmitters is called acetylcholine (or ACh)). The synaptic
cleft is the tiny space between the pre and postsynaptic neurons. The postsynaptic neuron
contained numerous receptors for neurotransmitter molecules. The neurotransmitter molecules
are not inherently excitatory or inhibitory. The effects that occur at the synapse are determined
by the properties of the receptor sites on the postsynaptic neuron. The shape of the
neurotransmitter molecule is complementary to the shape of the receptor. Post-synaptic neuron
will have in its membrane, Na+ and K+ pumps, gated Na+ channel proteins, gated and nongated K+ channel proteins and chloride ion channels.
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How does an ACTION POTENTIAL “CROSS” A SYNAPSE?
Action potentials must be able to propagate across a synapse in order to get from a presynaptic
neurone to a postsynaptic neurone. Acetylcholine (ACh) is the neurotransmitter that acts as the
“bridge” to get allow this action potential to “cross”. Molecules of ACh are held in vesicles.
On the presynaptic bulb, there are calcium and sodium channels.
Transmission of an impulse across synapse:
•
•
•
•
•
When an impulse arrives at the synaptic knob of a presynaptic neuron, the presynaptic
membrane becomes depolarized and Ca2+ channels open up.
The entry of Ca2+ into the presynaptic neuron occurs. This causes synaptic vesicles to move
towards the presynaptic membrane, fuse with it, and release neurotransmitter molecules
into the synaptic cleft (exocytosis).
The neurotransmitter molecules rapidly diffuse across the cleft and fit into the receptors
located on the post-synaptic neuron. These are called ligand-gated channels and when
bound to ACh, they alter their shape to allow an influx of Na+ ions into the postsynaptic
cytoplasm. This, of course, depolarizes the postsynaptic membrane and sets off another
action potential, thus continuing the propagation as if it had “crossed a bridge”.
The neurotransmitter molecules trigger certain effects in the postsynaptic neuron.
o If this is an excitatory synapse, Na+ channels will open, followed by K+
channels. This leads to depolarization and development of an excitatory postsynaptic action potential. This will then be transmitted along the post-synaptic
neuron
o If the post-synaptic neuron is inhibitory, Cl- channels open moving ions into
the neuron. K+ move out of the neuron. The overall negative charge leads to
hyperpolarization and no action potential will take place.
The neurotransmitter molecule (acetylcholine) has to be removed from the receptors so that
there will not be a permanent effect. Acetylcholinesterase (enzyme that breaks down
acetylcholine) catalyses the breakdown into acetate and choline. These then move back to
the pre-synaptic neuron where they will eventually reform acetylcholine (using energy from
mitochondria) which will be enclosed in synaptic vesicles.
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6.4: Outline the role of synapses.
•
•
•
•
Transmission in one direction
o Synaptic vesicles containing neurotransmitters are located in the synaptic knob of the
presynaptic neuron. It is important that they fuse with the pre-synaptic membrane.
o The receptors for neurotransmitter are located on the postsynaptic neuron only and
therefore an impulse will move from pre to post and never in reverse.
Synapses also allow for a wider range of functions within the nervous system. Synapses
are usually compounded so that multiple neurons converge at a synapse. This allows for
multiple pathways to be possible. In some cases, in order for an action potential to be
generated in a post-synaptic neuron, action potentials from multiple presynaptic neurons
would need to arrive simultaneously. This is known as summation.
Memory and learning o Frequent impulses lead to the formation of new synapses between
neurons involved in passing information along particular pathways.
Other chemicals can affect synapses as well.
o Nicotine has a similar shape to acetylcholine and will bind to post-synaptic receptors.
It is not rapidly broken down therefore a large dose can be fatal.
o Botulinum toxin (botox) is produced by an anaerobic bacterium that acts on the
presynaptic membrane preventing the release of acetylcholine. Large doses can be fatal.
This has been manipulated and used for medicinal and cosmetic purposes.
o Organophosphorus insecticides and other nerve gases work by preventing the activity
of acetylcholinesterase. As such, action potentials are continually generated at
postsynaptic membranes.
THAT’S THE END OF MODULE 2 OF BIOLOGY UNIT 2 :)
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MODULE 3
1. HEALTH AND DISEASE
1.1: Discuss the meaning of the term ‘health’;
According to WHO (World Health Organisation):
health is ‘a state of complete physical, mental and social well-being and not merely the
absence of disease or infirmity.
Disease is any deviation from that. Anything that disrupts the normal functioning of the
body (or is the impairment of the functioning of the body and mind).
Physical Health- this refers to the normal functioning of the systems of the body (skeletal,
circulatory etc). We tend to immediately think of major diseases like cancer and diabetes
but this also refers to sleep, exercise, nutrition, weight management etc. Symptoms can
usually be observed by a health care professional.
Mental health- this refers to how individuals think, feel or cope with daily routines and
demands (stress, depression, bi-polar disorder etc). Persons with compromised mental
health may not have any physical symptoms but display behavioural problems that affect
how the person interacts in society.
Social Health- this refers to the way people interact with other people within our
environment (public, family, peers etc.). It’s the compromise we make between social
interaction and the need for solitude
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1.2: Explain the categories of disease or illness;and,
There are numerous diseases that affect individuals in the world. Some of them are infectious
(or communicable), which means that they can spread from one individual to another. Some of
them are non- communicable, such as lifestyle and hereditary diseases, meaning that they
cannot be spread from one individual to another.
Abnormal functioning of the three main aspects of health discussed above result in disease.
This can be sub-divided into many categories; however, they are not mutually exclusive ie a
particular disease can fall into many categories simultaneously.
There are two (2) Tables below…both contain merely the same info…so its what you are
comfortable with… :)
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NOTE: It is important to realize that diseases are not restricted to a single category.
For e.g.
o Cholera can be classed as physical, social and infectious.
o Diabetes (Type II) can be classed as physical, social, chronic and self-inflicted.
So, pay careful attention when trying to classify them.
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1.3: Analyse data involving incidence and mortality rates of disease.
How does one ASSESS RISK OF A DISEASE?
Occurrence of disease varies in different parts of the world due to many factors. Studying
rates of incidence and mortality, especially in relation to these factors can reveal insights into
causality of disease and methods of prevention and cure. Epidemiology is the study of pattern
of distribution of disease, and of the factors that influence frequency (factors such as sex, age
and geographical distribution, certain sets of data)
These mainly focus on:
o Incidence-the number of new cases of a disease that arise in a population over a given
time period, typically a year.
o Prevalence- the number of people in the population with the disease. (Existing Cases)
o Mortality- the number of people who die from a disease in a year.
This is easy to note per country but comparison between countries become more informative
when scaled to the size of the total population. It is therefore expressed as the number of
affected persons per 100,000.
Look at this 2021 Covid-19 Statistics;
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The Following below in the next page is for knowledge and understanding not to necessarily
be crammed off but more to familiarize yourself with and to be able to answer any questions
on these.
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Diseases to know
Common diseases you should be familiar with are AIDS, diabetes and cancer. Most
questions are based around these
AIDS
AIDS stands for Acquired Immune Deficiency Syndrome which is caused by the human
immunodeficiency virus (HIV).
Viruses are not cells and are not considered to be living. It’s a ball of protein and lipid
surrounding a core containing RNA which is the genetic material for viruses. It comes prepackaged with reverse transcriptase which makes a DNA copy of the RNA within the virus.
The host/infected cell then executes the instructions of the DNA made. These instructions use
the resources of the host cell to make more copies of the virus. Viruses cannot replicate or
survive outside of a host. They target cells of the immune system to do this. T-lymphocytes
that possess CD4 receptors are particularly susceptible.
RE:
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More on this diagram above in the rest of Mod 3…HOW HIV WORKS?
Transmission
HIV is spread person to person through exchange of bodily fluids. It cannot survive outside
the human body except in blood.
Common transmission routes:
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Notes:
• Unprotected sex- main form of transmission in the Caribbean. Particularly common in
relation to sex workers and clients.
• Regions of high level of poverty and unemployment are associated with higher rates of
HIV infection.
• Stigma against HIV/AIDS- this results in persons avoiding testing/ treatment or not
declaring status in key situations. This increases risk of transmission.
Notes:
Education campaigns have increased general knowledge of transmission routes helped to
reduce stigma. Persons are also better able to determine risk factors.
Timeline
After initial infection, within 2-4 weeks the virus replicates but no symptoms are seen. This is
the incubation period (the number of days between when you're infected with something and
when you might see symptoms). Flu-like symptoms appear which are usually overlooked. At
this stage, antibodies the immune system produces to attempt to combat the virus can be
detected. Virus then becomes more active, replicating at a higher rate, destroying T-lymphocyte
cells in the process. This stage, a person is considered to have AIDS. This is officially
diagnosed when a person is HIV+ and has a CD4+ cell count of 200 microL of blood. Can
range from 2-20 years in progression.
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Globally, tuberculosis is the main cause of death for persons with AIDS.
Treatment
Many classes of drugs have been developed to treat HIV infection. Image above show main
targets of these drugs. Most treatment regimens would incorporate a combination of these.
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AFFECTED AREAS
Sub-Saharan Africa,10 with more than two-thirds of all people living with HIV globally, is
the hardest hit region in the world, followed by Asia and the Pacific (see Table 1). The
Caribbean as well as Eastern Europe and Central Asia are also heavily affected.
•
•
•
•
•
•
•
Eastern and Southern Africa. An estimated 20.7 million people are living with HIV in
Eastern and Southern Africa, more than half (54%) of all people living with HIV. Twothirds of children living with HIV (67%) are found in this region. Despite the significant
impact, new infections in the region have declined by 38% since 2010. Almost all of the
region’s nations have generalized HIV epidemics – that is, their national HIV prevalence
is greater than 1%. South Africa has the highest number of people living with HIV in the
world (7.5 million). Eswatini (formerly known as Swaziland) has the highest prevalence
in the world (27%).
Western and Central Africa. An estimated 4.9 million people are living with HIV in
Western and Central Africa. New HIV infections among adults declined by 25% between
2010 and 2019. Women and girls account for 58% of the estimated 240,000 new HIV
infections in the region. Another issue facing the region is coverage of antiretroviral
therapy for pregnant women, which has been declining in recent years (from 62% in 2016
to 58% in 2019).
Asia and the Pacific. An estimated 5.8 million people are living with HIV in Asia and the
Pacific. The region’s annual number of new HIV infections declined by 12% since 2010.
However, trends vary from country to country, and the decline in the region may obscure
increases in some countries. The region is also home to the two most populous nations in
the world – China and India – and even relatively low prevalence translates into large
numbers of people.
Western and Central Europe and North America. An estimated 2.2 million people are
living with HIV in this region. High coverage of ART plays a key role in the reduction of
AIDS-related deaths in the region; since 2010, the number of AIDS-related deaths
decreased by 40%. 4 in 5 people living with HIV (81%) are on treatment, and 2 in 3
people living with HIV (67%) are virally suppressed.
Latin America. An estimated 2.1 million people are living with HIV in Latin America.
Between 2010 and 2019, new HIV infections increased by 21% while the number of
AIDS-related deaths fell by 8% in the region overall. In 2019, 40% of new HIV infections
in Latin America occurred in Brazil, which has the greatest number of people living with
the disease (920,000) in the region.
Eastern Europe and Central Asia. An estimated 1.7 million people are living with HIV in
this region, including 170,000 newly infected in 2019. New HIV infections in the region
increased by 72% and AIDS-related deaths increased by 24% between 2010 and 2019.
Most of the new infections (99%) in the region are among key populations and their
sexual partners, including 48% of infections occurring among people who inject drugs.
The Caribbean. An estimated 330,000 people are living with HIV in the Caribbean. The
number of people living with HIV on treatment more than doubled since 2010 (from
68,000 in 2010 to approximately 210,000 in 2019). However, the percentage of people
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•
living with HIV who have suppressed viral loads in the region (50%) is below the global
average (59%).
Middle East and North Africa. An estimated 240,000 people are living with HIV in the
Middle East and North Africa. New infections increased by 25% from 2010 to 2019,
while AIDS-related deaths remained stable. Treatment coverage among people living
with HIV in this region is 38%, the lowest of any region.
Based on this data, it can be seen why AIDS is considered both an epidemic and a pandemic.
o Epidemic- widespread outbreak of an infectious disease with many people being
infected at the same time.
o Pandemic- a disease that has spread worldwide. Differences in lifestyles, treatment
availability and education about the disease will contribute to variance in incidence and
mortality rates between countries.
Diabetes Mellitus (DM)
More commonly referred to as Diabetes or colloquially as ‘sugar’. It is a metabolic disorder
where blood glucose levels are not adequately maintained within healthy levels without
external assistance. Large fluctuations in blood glucose levels over time leads to significant
damage to internal organs. This is why early diagnosis and proper management is key in
controlling this disease. The two main types of diabetes are:
10%
90%
o Type 1 DM aka insulin dependent DM. This is due to the inability of the pancreas to
produce enough insulin. This is normally diagnosed early in life.
o Type 2 DM aka non-insulin dependent DM and is generally diagnosed in the later
stages of life. The body does produce insulin however there is a significant level on
insensitivity to this insulin. This accounts for the majority of diabetes cases.
T2DM is better understood than T1DM. The risk factors for T1DM is generally less
understood. It is believed to be partially genetic (complex). The body’s immune system
attacks their β cells, compromising their ability to produce insulin. Why this happens is not
well understood. The risk factors for T2DM are better understood. These include:
❖ High body weight (BMI > 27)- while BMI>30 is categorised as obese, persons with
BMI>27 should be careful as risk increases.
❖ Age > 45- more common in older persons but the age of diagnosis has been decreasing
in recent years.
❖ Persons
with
‘apple
shaped
figures’concentration of fat in the midsection. More bulk
means that target cells don’t respond as readily to
insulin. Fat tissue interferes with the body’s ability
to use insulin
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❖ Poor diet- diet high in fat and refined sugar without enough fibre increases risk
❖ Sedentary lifestyle- lack of physical exercise
❖ Asian/Africa descent- these ethnicities show a higher prevalence when compared with
others.
❖ High blood pressure or coronary heart disease (from high cholesterol)
❖ Prenatal malnutrition- Studies show mothers who had poor nutrition during gestation
have children with a higher prevalence of diabetes. This is likely because it predisposes
them to being obese.
❖ Family history of DM [Genes (stronger evidence than T1DM)]- persons with relatives
with T2DM have a higher risk of developing it. Genes, coupled with lack of exercise,
poor diet and obesity are important.
Many of these factors can be mitigated by lifestyle changes.
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In the Caribbean 95% of diabetic cases are T2DM while this figure is closer to 90% for the
rest of the world. Genetics seems to be a likely contributor as the Asian and African diaspora
make up significant proportions of the population in these countries and these ethnicities are
associated with a higher risk for developing diabetes than others. This, coupled with lifestyle
contributes to increased prevalence in the region.
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2. IMMUNOLOGY
2.1: Define the term, “Immune Response”;
The topic of immunology is quite complex, so it is beneficial to familiarize and refamiliarize
with some terms before reading about the topic.
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There are many ways to define the term “Immune Response” but here are two (2) ways you
can (either or can be used):
-
Immune response is the way in which white blood cells respond when pathogens are
introduced to the body.
-
The IMMUNE RESPONSE is defined as the reaction of white blood cells to the
presence of a substance not recognized as a constituent of the body.
Such a substance that is not a recognized constituent of the body is referred to as a “foreign‟
substance or “non-self” substance. These non-self-substances are usually contained structures
called ANTIGENS, which the immune system can detect. Think of an antigen as something
that triggers a burglar alarm.
Firstly, they have to be able to recognise foreign (non-self) cells and differentiate it from self.
This job is done by leucocytes.
The term immunity refers to the ability of the body to resist damage from foreign organisms
eg. bacteria and viruses. This can be broken down into:
Specific- humoral immunity in which the B- cells produce antibodies. This also includes
cell mediated immunity in which T- cells are directly involved in defending the body.
Non-specific- the phagocytic response of which there are 3 types:
-
Neutrophils
Monocytes
Macrophages
These often work in response to pathogens. Pathogens are microorganisms that cause disease.
They generally comprise of bacteria, viruses, fungi and protozoa. Well adapted pathogens do
not kill their host immediately, they either do not kill them at all or kill them slowly.
Even though immune responses are complex interactions between these phagocytes and
lymphocytes, they are categorized as HUMORAL (involving B-cells) or CELL-MEDIATED
(involving T-cells).
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2.2 & 2.3: Distinguish between humoral and cell-mediated immune responses; explain the
role of memory cells in long-term immunity;
Specific immunity involves humoral immunity and cell mediated
immunity. These are conducted by lymphocytes which are small
white blood cells. There are two types known as B-lymphocytes
and T-lymphocytes however they look identical. They only differ
in their functions.
B-lymphocytes are developed in the bone marrow while Tlymphocytes need to mature in the thymus gland during
childhood.
Lymphocytes function by responding to antigens. These are molecules found on the surface
of invading foreign cells and differ from any molecules produced by the body. Each
lymphocyte responds to one kind of antigen therefore there are a large number of (~1M)
different kinds of lymphocytes in the blood. As they mature, lymphocytes produce small
quantities of particular glycoproteins called antibodies. Just as each lymphocytes respond to a
different antigen, they produce a unique antibody as well. The antibodies are stored in the
plasma membranes and serve as receptors that are able to bind antigens when present in the
blood.
B-Lymphocyte (humoral) response
B-lymphocytes can be introduced to antigens by either meeting it in the blood or through
antigen-presenting cells (APCs) such as a macrophage. B-lymphocyte binding to antigen is
called clonal selection. In response the B-lymphocyte will divide rapidly by mitosis producing
clones of the stimulated cell.
This is known as clonal proliferation/expansion. A subset of these cells differentiates into
plasma cells with increased protein-making machinery (more ER, ribosomes and Golgi
apparatus) in order to rapidly produce more of the specific antibody. A plasma cell can produce
2000 antibody molecules per second. These cells have a short lifespan of only a few weeks.
This is released from the cell by
exocytosis into the blood and
distributed to the rest of the body.
They bind to the antigens of invading
bacteria which results in their
destruction. The remaining clones of
the
stimulated
B-lymphocyte
become memory cells. Unlike
plasma cells, these have a long
lifespan and remain in circulation
long after the invading bacteria are
destroyed. These allow for a more
rapid response the next time the same
antigen enters the body again.
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T-lymphocyte (cell mediated) response
Like B-lymphocytes, T- lymphocytes are also activated when antigens bind to glycoproteins
in their cell membrane. This occurs when a macrophage presents it or when molecules are on
the surface of a body cell that has been invaded by a virus.
There are several types of T-lymphocytes such as T-helper cells and T-killer cells. A T-helper
cell with the complementary receptor binds to the antigen that it has found. It then divides to
form a clone of itself. The cloned T-helper cell then begin to secrete chemicals called
cytokines. These chemicals stimulate other cells to fight against the invaders. For example,
they may stimulate macrophages to carry out phagocytosis or they may stimulate Blymphocytes specific to this antigen to divide rapidly and become plasma cells. They also
help to stimulate appropriate T-killer cells.
T-killer cells Actually destroy the cell to which they have become bound. A body cell
displaying virus particles will be destroyed by T-killer cells. This is the only way of
destroying the viruses (it can't be done without destroying the cell in which they are
multiplying). The T-killer cells destroy the infected cell by secreting chemicals such as
hydrogen peroxide. The T-killer cells are our main defense against viral diseases.
Like B-lymphocytes, some of the clones also remain in the blood as memory cells. Likewise,
they allow for rapid response the next time the same antigen presents
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2.4: Compare the origin and maturation of B- and T- Lymphocytes;
Origin Stem cells in the bone marrow divide by mitosis to form potential B- and T- cells.
This means both types originate there.
Maturation
Beyond this, they go through different maturation processes which involves the
rearrangement of the genes that code for cell surface receptors. This is responsible for the
large variation observed in these cells.
B-lymphocytes
B-cells have receptors that correspond to the antibodies they secrete, as such, each would
have different shaped receptors (which makes them specific). B-cells mature in the bone
marrow.
T- lymphocytes
T-cell receptors are also specific and are structurally different to B-cell receptors. T-cells are
produced early in life in the bone marrow and goes to the thymus gland for maturation. Only
2% of T-cells maturing in the thymus gland pass all the required steps to be released
A key step in the maturation process for both types is the elimination of cells that recognise
self-antigens. This minimises the chance of the immune response targeting body cells
resulting in autoimmune diseases. Both cell types also develop additional surface receptors
called CD (cluster of differentiation) proteins that separate the cells into different classes.
Without these, lymphocytes are destroyed.
(Major histocompatibility complex (MHC), group of genes that code for proteins found on
the surfaces of cells that help the immune system recognize foreign substances.)
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HIV and CD4 receptor
HIV infects a few different cell types including helper T-cells as they have CD4 receptors on
their surface. The gp120 glycoprotein on the surface of the HIV binds to the CD4 protein to
gain entry to the cell.
So let’s compare the B- and T-lymphocytes once again:
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2.5: Describe the mode of action of phagocytes;
Phagocytes (neutrophils and macrophages) are
an important part of the immune response.
During an active infection, the number of
neutrophils increase rapidly. They are activated
by a series of events. When there is a break in the
skin/lining of the airway that allows pathogens
to enter, it triggers mast cells (located in all
tissues near blood vessels) to release a local
hormone histamine from their granules (makes
CAPILLARIES dilate and more permeable to
allow easy flow of blood (and white blood cells)
to the inflamed location and even through the
capillaries to infected tissues.). Histamine does
not travel in the blood as its target cells are right
in the localised area. This encourages a range of
non-specific responses known as inflammation
which results in in neutrophils in the blood being
attracted to the site of infection and tissue
phagocytes being activated. Inflammation leads
to:
-
Leaky capillaries
Neutrophils and monocytes (macrophages in blood) moving from blood into tissues
Complement proteins* and antibodies leave the blood
Area swells with plasma fluid and becomes hot and red
Activated macrophages become more aggressive at engulfing bacteria.
*Complement proteins and antibodies combine with bacteria and attach to receptors on mast
cells. They are so named as they increase activity of phagocytes and antibodies. There are
about 25 different ones that are always present in the blood. They are usually precursors for
several enzymes ie when part of the molecule is removed they are activated.
This sets off a cascade process as activated complement proteins activate other complement
proteins. The cascade process can be initiated in two ways:
When an antibody binds to antigen, the complement protein binds to antibody and is
activated due to the resulting change in shape.
A complement protein binds to pathogen resulting in a change in shape and activation.
Both ways lead to a significant increase in proteins that assist in destroying invading
microorganisms.
This is done in various ways:
Opsonisation- complement proteins bind to bacteria and coat them with a protein called
opsonin. Phagocytic cells have receptors that bind to opsonin stimulating them to engulf and
destroy the bacterium.
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Attracting macrophages and other cells to site of infection. When complement proteins
drift from local site of infection into tissue fluid and then blood, its presence draws
phagocytes and other WBCs. This is an example of chemotaxis (movement of cells in the
direction of a chemical stimulus).
Destroying foreign cells- they destroy the cells that activated it cascade process by making
holes in their plasma membrane.
Phagocytes engulf pathogens by endocytosis (phagocytosis). After engulfing bacteria,
neutrophils are eventually destroyed. With such a short lifespan, they need to be replaced
constantly from the bone marrow. Macrophages however can survive after engulfing foreign
matter as they break it down to component molecules and incorporate some of them on their
cell membrane. This is why they are known as antigen-presenting cells (APCs). They help to
expose other cells of the immune system to these foreign molecules, essentially teaching them
what to look for so they can mount a response when they encounter the foreign matter in other
places in the body.
Phagocytosis occurs in a series of steps:
1. Phagocyte moves towards microorganism.
2. Microorganisms bind to plasma membrane
of phagocyte (aided by complement proteins
and cytokines). Cytokines increase the
efficiency of phagocytes that have engulfed
bacteria.
3. Plasma membrane moves around bound
microorganism and re-joins forming a
phagosome (phagocytic vacuole).
4. Lysosomes (containing digestive enzymes)
in the cell join with phagosome.
5. The microorganism is killed and digested.
6. Component molecules not absorbed by the
cell are egested by exocytosis
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2.6: Relate the molecular structure of a typical antibody molecule to its function;
Antibodies aka immunoglobulins (Ig) are
plasma proteins consisting of four
polypeptide chains therefore having a
quaternary structure. There are different
kinds of immunoglobulins that bind to
corresponding antigens due to the variable
region (differing amino acid sequences
would give different shapes when folded).
Within this region in the epitope: the point
where the antibody attaches to the antigen.
The effect of an antibody-antigen bond varies
depending on the type of immunoglobulin
and what the antigen is eg. if the antigen is a
toxin, the antibody may directly neutralise it.
The polypeptide chains are joined together
by disulphide bridges that give the molecule
some flexibility to bind with antigens at
slightly varying distances. The constant
region for antibodies of the same class are the
same. These bind to receptors on the surfaces
of phagocytes
Z
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What are the PRIMARY AND SECONDARY IMMUNE RESPONSES?
Inevitably, high antibody concentration results in a much more rapid immune response, but it
does not come all at once. An initial exposure to an antigen, A, will yield a moderate conc. of
short-term plasma cells until the infection is cured. This is called PRIMARY RESPONSE and
occurs after a first vaccine dose or natural exposure.
The primary response will also allow formation of long-term memory B-cells, so upon a second
exposure to A, whether naturally or via a second (or booster) vaccine dose, these can be
activated and differentiated into a greater conc. of plasma cells. This is the SECONDARY
RESPONSE and allows much more rapid proliferation of antibodies, so antibody concentration
steeply increases. Of course, since antibodies are specific to antigens, an exposure to a new
antigen, B, will initiate a whole new primary response.
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2.7: State what is meant by a monoclonal antibody;
Monoclonal antibodies are those produced from one clone of B-cells. All of the cells that
belong to that clone produce identical antibodies. These antibodies are useful in the diagnosis
and treatment of various conditions. Normally, during a humoral response, many clones of Bcells are produced. As a result, a mixture of antibodies is produced. The production of
monoclonal antibodies means that diagnosis and treatment can be more specifically targeted.
What is a MONOCLONAL ANTIBODY? How is it formed?
The advent of monoclonal antibodies has been a hot
topic in immunology, especially in the fight against the
COVID-19 virus.
A monoclonal antibody is an antibody made by cloning
a unique B-lymphocyte.
The purpose was to provide large amounts of one type
of antibody for treatment and research. What’s the
difficulty? We must understand two things:
1. Cloned B- plasma cells do not secrete antibodies.
2. Antibody-secreting B- plasma cells do not divide.
Scientists discovered, however, that fusing a B- plasma
cell with a CANCER cell (which are known for their
ability to divide and proliferate) can form a B- plasma
cell that CAN divide! This fused cell is called a
HYBRIDOMA.
These hybridoma can then naturally proliferate in
fermenters and produce an enormous amount of
monoclonal antibodies.
Scientists had used mice to stimulate production of the
initial B- plasma cells by injecting them with the
counterpart antigen.
Monoclonal antibodies are used in a cancer treatment
drug called MabThera to treat non-Hodgkin lymphoma
and kill mutated cancer cells. They are also used in
pregnancy tests, AIDS diagnosis, tissue typing, and
tumour detection.
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How do MabThera work?
MabThera is the brand name for a target cancer drug called Rituximab. It is a treatment for a
few types of lymphomas and leukaemias.
It is a monoclonal antibody that targets a protein called CD20 on the surface of malignant Bcells, which contribute to the cancerous diseases. The killer T cells of the immune system then
pick out the marked cells and destroy them.
It is important to destroy as many of these malignant B- cells quickly, as they quickly replenish.
This quick targeted production makes monoclonal antibodies an efficient method of cancer
treatment.
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2.8: Describe the use of monoclonal antibodies
in diagnosis and treatment;
Pregnancy tests
The urine of a pregnant woman contains human
chorionic gonadotropin (HCG) hormone.
The strip is dipped in into a urine sample that
possibly contains HCG. Urine will move up the
test strip where there are mobile (free) antiHCG antibodies that have been complexed with
dyes. If HCG is present, it will bind with the
anti-HCG antibodies and will move into the test
site of the strip. In the mobile phase would also
have anti-HCG antibodies that have not bonded
to HCG. At the test site there are immobilised
(fixed) anti-HCG antibodies. All of those
mobile anti-HCG antibodies that have bound to
HCG will be trapped in the test site on the
immobilised anti-HCG antibodies. A colour will
appear in the window as the mobile anti-HCG
antibodies have the dye complexed with it. This
will indicate if the person is pregnant.
The mobile anti-HCG antibodies that did not bind
with HCG will continue to move into the control site where a colour
would also appear. If a person is pregnant, they will see two lines; one
in the test window and the other in the control window. If the person
is not pregnant, then all of the mobile anti-HCG antibodies that are
complexed with dyes will move to the control site where a colour will
appear, showing that the test has worked. No colour would appear in
the test window. This test is reliable and accurate.
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How can each reaction be described?
Reaction A is in the control window, due to the presence of anti-mouse antibodies and
activated dye. Note that no hCG is bound to the enzyme-dye antibody. This will produce a
blue line, positive or not.
Reaction B is in the reaction zone, where urine is picked up. hCG was found in the urine,
which is why it is bound to the monoclonal antibodies here. The dye is yet to be activated.
Reaction C is in the result window, showing the enzyme-activated dye and antibodies bound
to hCG. This will produce a blue line due to a positive result.
PREGNANCY TEST RECAP VIDEO
Blood Clot Locating
Monoclonal antibodies can be used to determine where particular types of cells are present in
the body. It can be used to locate where blood clots have formed. To produce these, a mouse
is injected with human fibrin (key protein in clot formation) which acts as an antigen in the
mouse causing it mount an immune response with B-lymphocytes producing antibodies for it.
This especially happens in the spleen. After about a month, the spleen cells producing the
anti-fibrin antibodies can be extracted and mixed with cancer cells to produce hybridomas
(cells that divide continuously to produce clones of cells that make monoclonal antibodies).
These are then cultured in a fermenter and radioactively labelled (chemical that produces
gamma radiation). These can be injected into a patient’s blood and a gamma camera used to
observe where the labelled antibodies congregate in the body.
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Cancer Treatment
Cancer Treatment Monoclonal antibodies can be used to recognise and bind with antigens
that are found on the surface of cancer cells. Eg. MabThera is used to eradicate CD20 cells in
lymphoma (cancer of the lymph glands) patients. Cancerous B-cells continuously divide
producing large numbers of B-cells that form tumours in the lymph nodes. MabThera is often
sold as Rituximab. As with all treatments, there are certain side effects of monoclonal
antibodies. Some are fever, allergic reactions, chills, headaches, nausea, vomiting etc.
Rituximab works by labelling B-cells (the only cells with CD20) so that the immune system
can attack them. Note that both cancerous and non-cancerous B-cells are destroyed however
new non-cancerous B-cells are produced by the body. This treatment is also effective in other
diseases such as autoimmune diseases like rheumatoid arthritis (RA).
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2.9: Distinguish between active and passive immunity, natural and artificial immunity; and,
What are the VARIOUS TYPES OF IMMUNITY?
We’ve already understood how primary and secondary responses to infection take place, seeing
that immune responses happen due to exposure of non-self substances or antigens that are
attached to pathogens or toxins.
This immunity occurs due to the production of antibodies from B-cells. This can be passive (if
antibodies are introduced from an external source, e.g. monoclonal antibodies) or active, if the
body is allowed to produce its own antibodies and memory cells (such as with a multi-dose
vaccine).
Active Immunity
Natural
This occurs when someone is infected by a particular pathogen by natural means eg breathing
in moisture droplets containing viruses expelled by a person coughing. A primary immune
response takes place in which memory cells are produced and T- and B-cells are activated. It
takes a while for a primary response to develop resulting in persons exhibiting signs and
symptoms of the pathogen. Generally, once the response has occurred the person would
become immune to the pathogen. If they are subsequently infected, their immune system will
mount an immediate rapid response and the effects of the pathogen will not be felt. E.g.
Chickenpox exposure allows for lifelong immunity.
Alternative Explanation:
If one contracts COVID-19 due to contact, they undergo a primary response and their B-cells
develop antibodies and memory cells. Therefore, naturally acquired active immunity is
obtained from the primary response to pathogen exposure.
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Artificial
This is achieved by administering a vaccine containing live, attenuated organisms or dead
organisms (antigen is introduced) so that the person’s immune system will be stimulated to
produce memory cells as well as activated B- and T- cells. The person does not show signs of
the disease as the organisms introduced will not be able to reproduce and invade cells. It is their
antigens that stimulate an active immune response. E.g. measles/polio vaccines.
Alternative Explanation:
Also called vaccination. severely reduces the chance of contracting COVID-19. A weakened
form of the pathogen, an antigen or instructions to build the antigen (mRNA) is introduced to
the bloodstream to stimulate a primary response and long- term immunity. Therefore,
artificially acquired active immunity is obtained from the primary response due to intentional
exposure to the antigen/pathogen.
Passive Immunity
Natural
In this case, ready-made antibodies that have been manufactured by a person during
pregnancy can pass across the placenta to the foetus giving it immunity to a particular
disease. This type of immunity is temporary since no memory cells are produced. Another
example of natural passive immunity is the movement of antibodies to baby during
breastfeeding. The antibodies are present in large amounts in colostrum which is the first
secretion from the breast after birth. The antibodies pass through the walls of the digestive
system of the baby into the bloodstream.
Alternative Explanation:
Occurs when a foetus prenatally obtains antibodies through its mother’s placenta while still in
the uterus. Postnatally, the baby obtains it from breast milk. Therefore, natural passive
immunity is obtained from mother to offspring transfer of antibodies.
Artificial
In this type of immunity, a person in injected with ready-made antibodies produced by
another animal or antitoxins. Eg. antibodies against diphtheria or tetanus can be injected into
a person in the case of an emergency. This will give temporary immunity as no memory cells
are produced and the B- and T- cells are not activated. This immunity will only last as long as
the antibodies/anti-toxins persist. The body recognises these substances as foreign and will
therefore work to actively clear it from the body.
Alternative Explanation:
If one has contracted COVID-19, vaccination is not an option as that is a preventative
measure. A common treatment is the use of external monoclonal antibodies introduced to the
patient as a serum. These can quickly reduce pathogen number but does not provide longterm immunity as no memory cells are developed. Therefore, artificial passive immunity is
the short-term immunization obtained from the injection of antibodies.
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2.10: Explain the role of vaccination in providing immunity.
Vaccines are excellent at preventing persons from acquiring infectious diseases. The larger
the proportion of the population that is vaccinated, the lower the chance that anyone (even
unvaccinated) will acquire the disease. This is known as herd immunity and 80-85% of the
population is usually needed to be vaccinated in order to accomplish this.
Successes:
-
-
Eradication of the pathogen responsible for the disease. Eg smallpox
Elimination of the disease (even if pathogen is not eradicated). Eg. measles has been
eradicated in 4 WHO regions however the possibility of reintroduction persists.
Control of mortality, morbidity and complications. Individuals protected from
untimely death when they receive vaccines. Eg. DPT protects infants against
diptheria, pertussis and tetanus. Persons who receive Hep B and Rubella are prevented
from suffering throughout the greater part of their lives.
Diseases are less severe in persons who have been previously vaccinated who are
exposed to a pathogen. Their symptoms are usually mild.
Protection against certain forms of cancer in the long term. HPV vaccines reduce
chances of developing cervical cancer.
Less persons suffering from infectious diseases lowers burden/expense on health care
systems.
Extends life expectancy. Older persons receiving the flu vaccine have a 20% less
chance of suffering from heart attacks and strokes than those who have not.
Challenges:
-
Some vaccines are expensive so poorer countries are unable to purchase the vaccines.
Reaching all communities in a particular country may be difficult (lack of roads,
electricity or telephones).
Vaccines have specific storage requirements. Some have to be kept at a certain
temperature therefore lack of proper storage can render them ineffective.
In some countries, conflict and civil war affect the delivery and distribution of
vaccines.
Allergic reactions to various components of the vaccine. They may suffer from a lifethreatening reaction after the vaccine has been given.
The way vaccines are handled- proper hygiene and disposal of needles
Some viruses mutate rapidly eg. influenza virus. Each year a new vaccine has to be
produced to address the prevalent viral strains.
Some vaccines have to be administered in multiple doses. The recipients may not
always be compliant/diligent in returning for subsequent shots and remain vulnerable.
“Anti-vaxxers”. Persons who firmly believe vaccines make them sick or result in
severe complications such as autism. As a result, they dissuade themselves and others
from being vaccinated. This actively works against vaccination campaigns and
increases the spread of infectious diseases.
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Alternative Explanation of this Objective;
What are the ARGUMENTS FOR AND AGAINST VACCINATION?
We’ve just learnt that vaccines are considered ARTIFICIALLY ACQUIRED ACTIVE
IMMUNITY, which means that it stimulates the production of antibodies due to intentional
introduction of a pathogen (or its components). Vaccines are used for COMMUNICABLE
(infectious) diseases such as measles, HPV, rubella and malaria. They have numerous modes
of action, including:
o Live attenuated vaccines – containing weakened forms of pathogens.
o Inactivated vaccines – containing pathogens that cannot reproduce but can still be
detected.
o Subunit vaccines – containing a detectable component (e.g. viral spike protein) of the
pathogen.
o mRNA vaccines – containing the mRNA blueprint of a pathogen or its component, so
it can be synthesized or “rebuilt” in the body for detection.
Vaccines have been successful at near-eradicating diseases such as polio and smallpox.
However, measles, a contagious disease once thought near-eradication had seen a resurgence
in the U.S. in 2019 due to a decrease in vaccination rates. Vaccination rates must be around
80% to achieve what is called herd immunity, to reduce the reproductive rate and spread of
the pathogen. When people have doubts about taking the vaccine, this is called vaccine
hesitancy.
Below are a few reasons and responses for vaccine hesitancy:
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3. SOCIAL AND PREVENTATIVE MEDICINE
3.1: Discuss the causative relationship among diet, obesity and diabetes;
Your diet is the sum of food you consume. What and how much you eat will determine if you
remain in good health. It is therefore imperative to consume a balanced diet which comprises
all of the nutrients required by the body in the correct proportions and supplies the right amount
of energy.
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What is OBESITY?
We’ve learnt that consumption of foods that contain carbohydrates and energy-dense lipids are
used to form ATP. However, when consumed in excess, a large portion of those molecules get
converted for storage and become deposited in ADIPOSE cells, found below the dermis and
around tissues, such as in the liver and coronary arteries. This highly increases the chances of
developing Type II diabetes, CVD‟s D(cardiovascular diseases), kidney failure and fatty liver
disease.
When more than what is required is consumed in the diet, a person can become overweight
which increases their risk for lifestyle diseases such as diabetes. A metric used to gauge if a
person is a healthy weight for their height is the use of BMI (body mass index). This is
calculated using the formula:
If the result from this calculation is 30 or over, an individual is considered obese. Note that
this measurement does not take into account factors such as muscle mass and can falsely
claim obesity in people like bodybuilders.
Obesity results from consistently consuming more food than what is required/used by the body.
This, coupled with lack of exercise results in the body storing the surplus energy as fat in
adipose tissue under the skin and around the organs. Studies have proven that fat in the
abdominal area aka visceral fat is a significant risk factor for T2DM. Studies have shown that
90% of T2DM cases are due to obesity. With the prevalence of obesity (notable childhood
obesity) increasing, it is expected that the prevalence rate of lifestyle diseases will also increase.
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Figure based on data from the USA
showing increase in childhood
obesity
by age group form 1971-2006.
Recall that a BALANCED DIET is defined as one that contains all the different nutrients
required by the body in the appropriate proportions to supply energy. Any nutrient deficiency
may lead to a disease such as scurvy (lack of Vitamin C) or night blindness (lack of Vitamin
A).
Diabetes Mellitus (DM)
More commonly referred to as Diabetes or colloquially as ‘sugar’. It is a metabolic disorder
where blood glucose levels are not adequately maintained within healthy levels without
external assistance. Large fluctuations (hyperglycaemic (TOO HIGH) to hypoglycaemic (TOO
LOW)) in blood glucose levels over time leads to significant damage to internal organs. This
is why early diagnosis and proper management is key in controlling this disease since there is
no cure. The two main types of diabetes are:
-
-
Type 1 DM aka insulin dependent DM. This is due to the inability of the pancreas to
produce enough insulin. This is normally diagnosed early in life.
Type 2 DM aka non-insulin dependent DM and is generally diagnosed in the later stages
of life. The body does produce insulin however there is a significant level on
insensitivity to this insulin. This accounts for the majority of diabetes cases.
T2DM is better understood than T1DM. The risk factors for T1DM is generally less
understood. It is believed to be partially genetic (complex). The body’s immune system attacks
their β cells, compromising their ability to produce insulin. Why this happens is not well
understood. The risk factors for T2DM are better understood. These include:
•High body weight (BMI > 27)
• Age > 45
• Persons with ‘apple shaped figures’- concentration of fat in the midsection
• Poor diet
• Sedentary lifestyle- lack of physical exercise
• Asian/Africa descent
• High blood pressure or coronary heart disease
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• Family history of DM
• Genes (stronger evidence than T1DM)
Many of these factors can be mitigated by lifestyle changes. Many persons are only diagnosed
with DM after complications arise. It means they would have had the condition for some time
before seeking help. Studies in the Caribbean indicate that 50% of people who have diabetes
do not know.
Hyperglycaemic symptoms include:
Dry mouth
Blurred vision
Extreme thirst
Frequent urination
Headache
Weakness
Proper management is key to keeping blood glucose levels within an acceptable range. This
would involve checking levels regularly using simple handheld sensors.
Also, urine can be checked for the presence of glucose as well managed persons should have
minimal glucose in urine. Dietary and lifestyle changes would also aid a patient in controlling
their condition.
What is the link between DIET, OBESITY and DIABETES TYPE I AND TYPE II?
Recall that the pancreas is a major organ
within the endocrine system. It secretes
two hormones that regulate blood glucose
level, INSULIN and GLUCAGON.
Insulin binds to insulin receptors on cell
plasma membranes. These allow glucose
molecules to enter the cytoplasm of the cell
to begin glycolysis and enter the
mitochondria to produce ATP. It also helps
convert glucose to its storage form,
GLYCOGEN, by this means.
Diabetes, whether be Type I or II, restricts
this movement of glucose from the blood
capillaries into the cell cytoplasm,
resulting in fatigue and dehydration and, in
worse cases, tissue necrosis and
amputation.
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Type I diabetes – the pancreas of the people who suffer from this type usually produce little
to no insulin. This form of diabetes is genetic and usually diagnosed in childhood or in early
adulthood and the people who have the condition usually need to use insulin all their life.
Type II diabetes – in this type of diabetes, the patient’s pancreas produces insulin, but the
insulin receptors on cells do not respond, usually due to impairment caused by fatty
accumulation and sedentary lifestyles. This is called INSULIN RESISTANCE. The people
suffering from this type of diabetes usually receive oral medication (e.g. metformin) to help
with the processing of the insulin.
Long-term regular exercise can be done to stimulate the cells‟ insulin receptors, negating
insulin resistance effects.
Naturally, when a person consumes a sugar, that sugar is digested and absorbed into the
bloodstream from the small intestine, thus causing an increase in blood glucose level. Blood
glucose level decreases when the glucose enters the cytoplasm of the body cells to be used for
ATP. Recall that this is called ASSIMILATION.
In diabetics, assimilation is delayed. It is therefore recommended that the consumption of
carbohydrates (especially refined) is limited to avoid a continuous build- up of glucose in the
bloodstream.
After an 8-hour „fast‟, diabetics usually have a higher blood glucose level than non-diabetics.
Typically, the normal fasting range is given as 70 – 130 mg/dl blood glucose. Above that range,
the individual is considered prediabetic or diabetic.
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3.2: Describe the effects of fats on the cardiovascular system;
A healthy amount of fat in the diet is good. When consumed, it is digested into fatty acids and
glycerol in the small intestine and absorbed. They are reformed into fat as chylomicrons and
transported to the liver. Cholesterol is also and transported in this way. When these need to be
transported from the liver, it is carried in the form of lipoproteins (small balls of lipids,
cholesterol and protein). The more protein in the lipoprotein, the denser it is. This is why we
have several types of lipoproteins:
Type of lipoprotein
Very low-density
lipoproteins
Low density lipoproteins
Abbreviation
VLDLs
LDLs
High density lipoproteins
HDLs
Function
Transport fat for storage in
adipose tissue
Transport cholesterol from
liver to tissues
Remove cholesterol from
tissues and return to liver for
excretion in bile
High ratios of LDLs:HDLs is associated with cardiovascular disease. This is because LDLs
deposit the cholesterol, they carry in the damaged walls of arteries which contribute
significantly to plaque formation discussed below. HDLs tend to have the opposite and
somewhat protective effect against CHD.
However, as with all nutrients, if too much fat is consumed, the body can’t use all of it.
Particularly important is consuming high levels of cholesterol and saturated fats (high amounts
of LDLs). It ends up being stored and deposited in places that can be significantly detrimental
to health. This is especially true when it comes to the arteries of the heart.
In persons with coronary heart disease (CHD), atherosclerosis (hardening of the arteries)
occurs. As a result of this reduced flexibility of the arteries, a build of fat can occur. This
reduces the size of the lumen (space where blood can pass).
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Reduction in the diameter of the lumen by 50% means that the oxygen demands of the region
supplied by that coronary artery can no longer be met during exercise. Persons with this initially
experience angina or pain in the left chest, shoulder or arm while exercising.
Blood clots can also form on or around these plaques called a coronary thrombosis. Collagen
that may be exposed in the arterial wall will bind platelets in blood. In turn, the platelets secrete
a chemical that initiates the clotting process. This further narrows the arteries and can even be
dislodge and block smaller vessels. If the muscles supplied by these smaller vessels die, the
heart can no longer beat effectively and the person will suffer a myocardial infarction. If the
heart stops beating all together it is known as a cardiac arrest or heart attack.
Alternative,
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NOTE: You would’ve noticed that people frequently get heart attacks during great periods of
physical or mental exertion (exercise or stress). This is because these generate high-pressure
blood flow, which will lead to rupturing of the coronary thrombosis, most likely leading to
the clot “clogging” the coronary arteries.
Detailed Stages of Atherosclerosis
Beginning in childhood, a cascade of events slowly and quietly leads to the development of
atherosclerosis. Children develop fatty streaks along the walls of their large arteries largely
from diets high in fat. These streaks are sites where lipoprotein particles are protected from
direct contact with the blood. The lipoproteins become oxidized into destructive molecules
and the resulting oxidants injure nearby cells.
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The initial steps of atherosclerosis. It includes adhesion of blood leukocytes to the activated
endothelial monolayer, directed migration of the bound leukocytes into the intima, maturation
of monocytes (the most numerous of the leukocytes recruited) into macrophages, and their
uptake of lipid, yielding foam cells.
Lesion progression. It involves the migration of SMCs from the media to the intima, the
proliferation of resident intimal SMCs and media-derived SMCs, and the heightened synthesis
of extracellular matrix macromolecules such as collagen, elastin and proteoglycans. Plaque
macrophages and SMCs can die in advancing lesions, some by apoptosis. Extracellular lipid
derived from dead and dying cells can accumulate in the central region of a plaque, often
denoted the lipid or necrotic core. Advancing plaques also contain cholesterol crystals and
micro vessels.
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Thrombosis. It is the ultimate complication of atherosclerosis, often complicates a physical
disruption of the atherosclerotic plaque. A fracture of the plaque’s fibrous cap, which has
enabled blood coagulation components to come into contact with tissue factors in the plaque’s
interior, triggering the thrombus that extends into the vessel lumen, where it can impede blood
flow.
Blood Pressure
As previously discussed, blood pressure is the pressure exerted on the walls of the blood vessels
through which it flows. When a pressure reading is taken, the top number is the systolic
pressure and the number below is the diastolic pressure. The diastolic pressure gives the best
idea of the health of the circulatory system and persons with persistently high diastolic
pressures are hypertensive. Persons with hypertension have a markedly increased risk of
myocardial infarction/stroke. It is also associated with atherosclerosis therefore with obesity
and diet. High salt consumption and smoking also increases risk of hypertension.
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Stroke
Similarly, to blockages in heart
blood
vessels
leading
to
myocardial infarction and heart
attack, blockages to blood vessels
in the brain can lead to stroke.
Stroke is acute damage to the brain
caused by problems with the blood
vessels supplying it. 4 out of 5
strokes result from clots due to
atherosclerosis while the rest is
due to brain bleeds.
Brain cells have a high metabolic rate, as such, they require constant supply off oxygen and
glucose (sole energy source). Short periods without these would lead to cell death.
Due to the overlap in causation with CHD, stroke and CHD share common risk factors such
as hypertension. The effects of a stroke can vary as it depends on the region of the brain
affected. For instance, right
cerebrum injury would lead to
symptoms displayed on the
left side of the body. That
region of the brain is also
responsible for spatial
awareness so patient would
have difficulty judging
distance so walking and
coordination would be off.
In Summary,
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3.3: Discuss the consequences of exercise on the body and the benefits of maintaining a
physically fit body;
Exercise can be defined as activity requiring physical effort, carried out to sustain health and
fitness.
The correlation between exercise and health has been well documented. Some benefits include
reduced incidence of lifestyle diseases such as coronary heart disease and T2DM. It also
encourages an overall sense of wellbeing as it affects processes in the brain making people feel
happier, positive and more energetic.
For the most efficient exercise, muscles need to be well supplied with an energy source eg
glucose and oxygen. This is needed for respiration to occur so that ATP can fuel muscle
contraction. Muscles can continue to contract in an anaerobic environment but only for a
limited time as it results in a build-up of lactic acid that would eventually cause the muscle to
stop working. The more fit an individual, the better their heart and lungs are at supplying tissues
with oxygen.
Short Term Effects
Circulatory System
•
•
•
•
•
Increased heart rate due stimulus from the sympathetic nervous system.
Secretion of adrenaline hormone which also increases heart rate
Nitric oxide secretion causes dilation of arterioles (vasodilation) by relaxing the muscles in
the walls of the vessels which result in increased return of blood to the heart which
stimulates increased cardiac output. The stroke volume (amount of blood pumped out of
the heart by ventricles) increases.
Diversion of blood to muscles by changes in dilation of arterioles. Areas where oxygen and
glucose needs are less urgent constrict their arterioles so that the supplies rushes to area of
demand. Regular blood supply to muscles at rest is 20%, however this can increase up to
80% during strenuous exercise.
Dilation of arterioles supplying skin capillaries, increasing heat loss from the skin via
radiation.
Gaseous Exchange System
•
Breathing (ventilation) rate increases to increase the rate at which oxygen diffuses into the
blood and carbon dioxide out of it.
• Tidal volume increases
• Increased rate and extent of diaphragm and intercostal muscle contraction (harder and
faster). Increased respiration rate means increased carbon dioxide production. This
increases the acidity of the blood which is detected by chemoreceptors. To compensate, the
brain sends stimulus to affect diaphragm and intercostal muscles increase depth of breath.
Air is therefore moved faster maintaining a steep concentration gradient between alveoli
and capillaries.
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Investigating the immediate effect of exercise on the body
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Long Term Effects
Consistent exercise over a long period of time can cause improvements to the circulatory and
gaseous exchange systems as well as muscles. The more exercise is done, the more drastic
the changes observed. Muscles:
•
•
•
•
•
Increased number of capillaries in the muscle thereby increasing the ratio of capillaries to
muscle fibres. This increased blood supply increases the ability of the circulatory system
to meet the oxygen demand for the muscle during exercise.
Increased amount of myoglobin. Myoglobin is the respiratory pigment in muscle that stores
oxygen. More of this means more oxygen stored within the muscle.
Increased number and size of mitochondria in muscle cells which increases the number of
respiratory enzymes present. Since the Kreb’s cycle and oxidative phosphorylation occurs
in the mitochondria, more mitochondria mean these processes can occur at a faster rate
within muscle.
Increased glycogen stores. These can be rapidly broken down to glucose for use in
respiration.
Increase in muscle mass. Specifically, an increase in slow-twitch muscle fibres. This is the
type of muscle fibre that can be used during aerobic respiration.
VO2 max and the circulatory system
The heart rate usually increases as the level/rate of exercise increases in order to match
increased oxygen consumption. There comes a point where this plateau. Either the muscles
cannot use the available oxygen at any further increased rate or oxygen cannot be supplied at
a faster rate. Both instances result in muscles switching over to anaerobic respiration. The
maximum rate at which oxygen is used before the muscles make the switch is called VO2
max. More fit individuals have an increased VO2 max and this is due to the following
changes.
•
•
•
•
Increased RBC count. Increases the oxygen carrying capacity of the blood.
The left ventricle becomes thicker as well as other areas of the muscular heart wall. This
increases the force with which the heart can pump blood out of the heart.
Increased stroke volume. More blood is pumped out of the heart with each beat.
Increased cardiac efficiency. This means the heart does more work per unit of oxygen that
it uses
Given these changes, the more fit an individual the lower their resting heart rate ie less beats
are necessary to move the same amount of blood around the body due to higher stroke
volume. These persons also experience a reduced recovery period. This is the time taken for
the heart rate to return to normal after exercise. This is usually used as a fitness indicator
Gaseous Exchange System
Increased fitness means that the rate at which oxygen is brought to the body and CO2 is
removed is increased. This is due to greater breathing rate and depth of breath that is possible.
This increases with regular aerobic training.
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3.4 & 3.5: Describe the mechanisms of infection for viral diseases and their causative
agents; Explain the modes of transmission of HIV and Dengue Virus.
A short recap on PATHOGENS and VECTORS
We previously learnt that pathogens are disease-causing microorganisms that can be
transmitted from one organism to organism through vectors. For example, the protozoan
pathogen Plasmodium falciparum, which causes malaria, can be picked up by Anopheles
mosquitoes from infected humans spread the disease to uninfected humans.
In this objective, the focus will be on two
viral diseases: dengue fever and AIDS. It
is notable that viruses cannot be killed by
antibiotics, like bacteria.
Instead, antiviral drugs, artificial passive
immunity (e.g. monoclonal antibodies)
and immune responses are relied upon to
fight viruses.
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RECALL: In previous objectives we discussed HIV/AIDS...(Refer to those info)
Human Immunodeficiency Virus (HIV) is caused by a retrovirus that contains 2 RNA
molecules, reverse transcriptase enzyme, integrase enzyme and a protease enzyme. The
virus has glycoproteins on its surface. The glycoprotein GP120 can fit into CD4 receptors
which are found on the surface of helper T cells. During its lifecycle, the following events
occur:
1. The virus approaches the helper T cell.
2. GP120 fits into the CD4 receptor on the surface of the T-lymphocyte.
3. These triggers infolding of the cell surface membrane, allowing the virus to enter.
4. The viral RNA as well as the enzymes are released into the cytoplasm of the host.
5. Reverse transcriptase enzyme is used to synthesize a double stranded DNA copy of
the viral RNA.
6. The viral DNA copy enters the nucleus of the cell and integrase enzyme is used to
insert DNA into the host cell DNA.
7. After some time, the viral DNA becomes active and now viral RNA is produced. This
leaves the nucleus and enters the cytoplasm.
8. Protease enzymes are used to breakdown proteins in helper T cells so that amino acids
can then be used to make viral proteins.
9. New viruses are assembled and enclosed in membrane. They move to the surface of
the cell and exocytosis takes place.
10. New viruses go on to infect other cells while the original host cell dies.
Dengue Fever - Dengue fever aka “break bone” fever is a viral mosquito-borne disease that
usually occurs in tropical areas of the world. It is caused by flaviviruses. These are RNA
viruses of which there are 4 strains: Den 1, Den 2, Den 3, Den 4. Its signs and symptoms
include a high fever, muscle and joint pain, severe headache, nausea and skin rashes. In more
severe versions of dengue, called dengue haemorrhagic fever, blood vessel linings become
damaged and the blood clotting process is interrupted. As a result, internal bleeding occurs.
The virus is spread by (vector) the bite of an infected Aedes Aegypti mosquito (Female).
These characteristics make it an ideal vector:
•
•
•
•
•
•
It usually bites around sunrise & sunset. It will bite at night under
artificial light.
It prefers human blood
It can pass the virus into its eggs, which is laid in clean water that
has no other species.
The eggs can resist drying out for up to one year.
The AA mosquito is found in tropical and semi-tropical regions
such as Africa, Asia, Caribbean, Central and South America and Mexico.
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Transmission Cycle
1. The female mosquito becomes infected with the virus when she feeds on blood of a person
who is experiencing symptoms and showing signs of an illness.
2. There is an incubation period in the mosquito about 8-10 days during which the virus moves
from the stomach to the salivary gland.
3. The virus is transmitted when an infected mosquito bites a person and injects saliva into
that wound.
4. There is an incubation period in the human host of about 3-14 days. This is the period of
time between infection and the onset of signs and symptoms.
5. Following the incubation period, the person will suddenly start to experience fever,
headache, pain in the body and joints, backache and nausea. Certain signs such as vomiting,
decreased platelet count, drop in blood pressure and haemorrhaging may indicate that a
person has dengue fever.
6. Near to the end of the disease, red blotches can appear in their feet and hands.
Life Cycle of the Virus
When the virus is introduced into the body through the skin, it usually enters specialised
immune cells that are located in the skin and replicate within these cells. The virus attaches to
the surface of the host cell and enters via endocytosis. Viral RNA is released and moves to
ribosomes in the host cell. Viral proteins are synthesized and new viruses are assembled on the
rough ER. The immature viruses are transported through the Golgi body and new viruses are
released from the cell at the cell surface membrane. These viruses go onto affect other immune
cells eg. macrophages and monocytes.
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NOTE: Think of the virus transforming a cell into a “photocopying” or „cloning‟ machine
to make copies of itself, with the RNA being the “rogue instructions” being fed into it.
Dengue Treatments
•
Painkillers (that do not include aspirin)
•
Rest
•
Rehydration
•
Platelets may be transfused if platelet count falls below an acceptable level. Controlling
the Vector
The vector can be controlled by the following:
•
Covering all water that is stored
•
Draining and thoroughly cleaning any containers with eggs
•
Using chemicals to spray and kill the adult mosquito
•
Use of insects repellents.
•
Infect the mosquito with bacteria that will reduce lifespan eg. Wolbachia
•
Use genetically altered male mosquitoes that will mate with females and pass on a gene
that reduces the growth of wings in female offspring. The females would be unable to fly
but the males would remain unaffected, reducing the mosquito proliferation.
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3.6: Discuss reasons for distribution of Acquired immune Deficiency Syndrome (AIDS),
Diabetes and Cancer;
RECALL: Aids and Diabetes were covered in Prior Objectives
Cancer
Cancer is not a single disease, but a group of diseases that affect various parts of the body. It
results when the normal control mechanisms in the cell controlling division breaks down.
These mechanisms are usually controlled by multiple genes and becomes defective when they
are altered. It begins when this occurs in a single cell that rapidly and uncontrollably divides
and grows to form a tumour. Not all tumours are cancerous however, they are described as
being malignant (cancerous) or benign (non-cancerous). Benign tumours usually stay in a
singular location and does not invade surrounding tissue. Malignant tumours spread from
where they began by invading surrounding tissue and other areas around the body. When
cells break away and cause secondary tumours in other areas in the body, this is known as
metastasis.
There are many different types of cancers and the prognosis differs with each type. Factors
such as when the cancer is diagnosed and location affect this. Treatments are consistently
improving as cancer research is a big and usually well-funded area of research.
Minor Alternative summary...
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Causes
There are several substances capable of causing cancer, called carcinogens. Some of these are
found in:
-
Cigarette smoke chemicals (e.g. nitric oxide)
-
Ionizing radiation (e.g. X-rays)
-
Food additives and certain artificial sweeteners (e.g. saccharin)
-
Viral RNA (e.g. human papilloma virus, or HPV, which causes cervical cancer)
• Genetic factors- cells contain regulatory genes called protooncogenes that can mutate to
form oncogenes that allow uncontrollable cell division. They also contain repressor genes
that usually prevent cell division. Mutation of these also lead to uncontrollable cell
division. It usually takes mutations in multiple genes before a cancer is initiated. Certain
alleles of these genes are more likely to mutate than others. This is why some persons
have a higher predisposition than others. These alleles are likely passed on within families
and may be responsible for certain cancers occurring in multiple family members. Mutant
alleles are also inherited in a dominant fashion. Alleles of BRCA1 and BRCA2 account
for 5-10% of breast cancers.
•
Environmental factors- these can increase the risk of mutations happening and are called
carcinogens. Examples of these are:
o ionising radiation (X-rays and cosmic rays)- These can break bonds in DNA and
cause base sequence changes. Cells are most vulnerable during late interphase and
mitosis. We are always exposed to some radiation and this is known as background
radiation. Exposure increased by taking X-rays, radon gas or nuclear fallout which
can sometimes penetrate deep within the body and affect many organs.
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o Ultraviolet (UV) light- electromagnetic radiation not visible to the eye. It affects
cells in early interphase. It has less energy than ionising radiation and therefore
cannot penetrate skin but is associated with skin cancers. Darker skin pigmentation
(melanin) is protective as it absorbs more UV light and protects cells underneath.
o Chemicals – these react directly with DNA and alter their structure. Mustard gas
used in WW1 resulted in increased cancers of the nose, bronchus and larynx.
Tobacco smoke causes multiple carcinogens such as nitrosamines and oxides of
nitrogen. These form free radicals (oxidises other compounds such as DNA).
o Viruses-certain viruses have been linked with developing cancer. Eg human
papilloma viruses (HPV) with cervical cancer. Prolonged infection with Hep B and C
viruses can lead to liver cancer. HIV infection increases risk of blood cancers and the
rare Kaposi’s sarcoma. This is due to a compromised immune system.
o Food additives- there is evidence that some food additives in processed foods can
increase risk of cancer. Nitrites and nitrosamines in red meat and processed meat
increase risk of gastric cancer. These are usually used as preservatives or colouring.
Symptoms Awareness of symptoms can decrease mortality as early diagnosis increases the
chances of successful treatment. Some symptoms of more common cancers are:
• Breast cancer- painless lump in breast
• Cervical cancer
o Abnormal vaginal bleeding
o Vaginal discharge with unpleasant odour
o Discomfort/pain during sex
• Lung cancer
o Persistent cough
o Coughing up blood o Chest/shoulder pains
• Testicular cancer- unusual painless lumps on the testes.
Screening campaigns (cervical smears and mammograms) and educational programmes aid in
early detection.
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• Higher rates of cervical cancer in Caribbean may be associated with higher rates of
unprotected sex.
• Lower rates of lung cancer may be associated with lower rates of cigarette smoking.
Points listed above are lifestyle related. Increased awareness will allow persons to make safer
choices to minimise risk.
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3.7 & 3.8: Assess the impact of communicable and non-communicable diseases regionally;
and, Discuss the roles of social, economic and biological factors in the prevention and
control of viral infections.
RECALL: Aids and Diabetes were covered in Prior Objectives
Dengue (communicable)
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Social
• Proper sanitation and disposal of containers that collect water should be practiced.
• Efficient water supply system will ensure the population does not need to store water thus
eliminating the need for storage containers.
• Educating the public of the lifecycle of the vector its habitats appearance and how it spreads
diseases.
• Education about measures to protect oneself from being bitten by the mosquito as well as
signs and symptoms of dengue.
• Community centers and hospitals as well as schools should develop programs and these
programs should be accessible to all.
Economic
• Funding should be allocated to health care and developing programs educate community
about the vector under disease
• Funding must be spent on research develop effective cheap vaccines against dengue
• Funding should be allocated to regional corporations to improve drainage and sanitation in
their regions.
Biological Factors
• Knowledge of the life cycle of the vector as well as the transmission cycle.
• Patients who have dengue should be kept under mosquito nets while they are in the hospital
and at home.
• Use biological control methods eg bacteria to shorten the lifespan of the adult mosquito.
• Release genetically engineered male mosquitoes into the community, so that there will be
fewer females to pass on the virus,
• Inoculate members of the population with a vaccine. There is currently a vaccine that is
available. It is, however, not 100% effective.
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4. SUBSTANCE ABUSE
4.1: Discuss the meaning of the term, “drug abuse”;
A drug is any substance that alters the body’s physiology (how it works) or A drug is defined
as an externally administered substance that alters the body’s physiology.
They influence the chemical reactions in the body. They do so by mimicking the activity of
transmitter substances.
These can be:
o Medicinal/therapeutic drugs such as antibiotics or painkillers used to treat specific
conditions or
o Psychoactive drugs such as cocaine, heroin and marijuana (ganja) which interact with
the central and/or peripheral nervous systems.
Its internally produced counterpart may be something akin to a hormone. They are used for a
number of purposes, such as treating illness or therapeutic purposes (e.g. penicillin, quinine,
tetracycline, diazepam), as painkillers (e.g. morphine, ibuprofen, naproxen) or for recreation
(e.g. nicotine, alcohol, cannabis).
These drugs are further classified as:
o Stimulants- this increases mental and/or physical functions. Eg nicotine, caffeine,
amphetamines and cocaine. Users experience greater wakefulness and alertness. Some
claim that nicotine and caffeine help with concentration.
o Hallucinogens- these cause changes in mental state and the way users perceive their
environments. Eg. ganja and LSD induce changes in consciousness that users compare
to having dreams or going into trances.
o Depressants- these have inhibited the central/peripheral nervous systems. They reduce
feelings of anxiety, induce sleep and even relieve pain. They can lower blood pressure,
heart rate and breathing rate. Egs. Alcohol, opiates (heroin, morphine, codeine) and
barbituates.
These can be obtained both legally (sanctioned by the government for use) and illegally but
once they are not used in the manner in which prescribed, they are abused. A drug is abused
when it is used in a manner that causes harm either to the individual or others. These lead to
both physical and mental health issues. Legal drugs such as alcohol and nicotine can be abused
and cause more damage than some illegal drugs.
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To Alternatively summarise…
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4.2: Distinguish between psychological and physical dependence;
When drugs are used repeatedly over a period of time, the body can adjust to its use. Users
therefore end up having to use more of the drug to experience the same effects. This is known
as tolerance to the drug. This happens as a result of the body being able to metabolise the drug
faster or increasing the number of synapse receptors that the drug targets so more drug is needed
to occupy them. As a result, users come to rely on the drug and feel like they cannot
function/survive without it. They are drug dependent. This dependence can be classified as:
•
Physical dependence- this results from changes in physiology and structure of neurones
in the brain. Without the drug the user will experience withdrawal symptoms such as
irritability, anxiety, sleeplessness, vomiting, diarrhoea, abdominal pain etc.
• Psychological dependence- lack of drug does not elicit withdrawal symptoms as
described above. There is a constant craving for the drug. To the user, it is as essential
as the other requires needed for life. It is debated that psychological dependence is more
difficult to break that physical dependence.
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4.3: Describe the short-term and long-term consequences of alcohol consumption on the
nervous system and the liver;
What is ALCOHOL? What are its EFFECTS on the human body?
Alcohol (more specifically ethanol) is both fat and water soluble. is a recreational drug, which
means that it is taken in social situations and has mild effects on the body if taken sparingly.
When it is drunk on an empty stomach, more of it is absorbed than if there is food in the
stomach. It enters the blood stream quickly as it requires no digestion. When ingested, 80% of
it will be absorbed by the walls of the small intestine and enter the bloodstream. It is then
distributed to all tissues including the brain.
It is good to note, however, alcohol is also a depressant, which means that it reduces nervous
activity and slows bodily functions. Alcohol changes the structure of receptors of certain brain
neurones, which affect neurotransmitter action potentials.
If consumed in excess, it can heavily impair nervous transmission and lead to dehydration of
the brain cells. Alcohol is broken down in hepatocytes by an enzyme called ethanol
dehydrogenase, which converts ethanol to ethanoate, which can enter the Krebs cycle to
produce ATP. This occurs in the liver. In the long-term, it can lead to scarring of liver tissue,
called liver cirrhosis. Since the liver is used to detoxify the body, having it severely impaired
will be fatal.
Men have an enzyme called ethanol dehydrogenase that women either don’t have or have in
small amounts. It acts to lower the amount of alcohol so less enters the bloodstream. As a result,
women will absorb a greater proportion of alcohol ingested into their bloodstream and their
alcohol level will remain higher longer. Furthermore, women have a higher proportion of body
fat than muscle while the opposite is true in men. Muscle is well vascularized so alcohol can
leave the blood and enter muscle, thereby lowering blood alcohol level. This is another reason
why women’s blood alcohol level will remain higher longer.
Alcohol metabolism will also differ between a child and an adult as a child will have a lower
blood volume. This means that if the same amount of alcohol is consumed, the child’s alcohol
concentration will remain higher longer
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Short-term effects
Alcohol dissolves very easily in the fatty acid tails of the phospholipid tails that make up cell
surface membranes. This can cause a change to channel proteins. In the brain, it can distort
neurone membrane receptors that bind the GABA (gamma aminobutyric acid)
neurotransmitter. GABA acts to inhibit the formation of action potentials. Alcohol causes an
increase in the effect and duration of GABA. Glutamate, the most common neurotransmitter in
the brain is also affected as alcohol blocks the receptors that it binds to. Glutamate is necessary
for interaction between neurones in the brain. The result of affecting these two
neurotransmitters is that alcohol reduces the activity of the brain. This is why it is considered
to be a depressant. These effects are particularly evident in the cortex of the cerebrum and the
cerebellum. The cerebrum is responsible for clear and logical thinking and decision making
while the cerebellum is responsible for co-ordination. In large amounts, alcohol can lead to
drowsiness and unconsciousness that can be as severe as a coma. If nervous stimulation for the
muscles controlling breathing is blocked, the individual can die.
As mentioned above… Ethanol metabolism- Ethanol is broken down by hepatocytes (liver
cells). Ethanol is converted to ethanal by ethanol dehydrogenase. This is then converted to
ethanoate by aldehyde dehydrogenase. Ethanoate can then be used as a substrate in the Kreb’s
cycle in mitochondria to produce ATP. Note than in each step, reduced NAD is produced.
Long term effects
When consumed in large amounts, alcohol damages the liver. Oxidised NAD usually functions
to oxidise fatty acids in the liver. If most of this is used up in detoxifying ethanol, this leads to
accumulation of these FAs in the liver. There is a strong correlation between increased alcohol
consumption and fat deposits in the liver. Increased fat storage in hepatocytes reduce their
ability conduct other necessary functions. This is known as fatty liver. In addition to fatty liver,
the liver can become inflamed due to excessive alcohol consumption and this is known as
hepatitis.
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As the hepatocytes become damaged, they are replaced by fibrous tissue. This process is known
as cirrhosis. This results in reduced blood supply through the liver which severely affects many
of the detoxification functions of the liver. Eg. damaged hepatocytes means less conversion of
ammonia to urea leading the increased ammonia concentration in the blood. This negatively
impacts the CNS which can lead to coma and death.
Long-term alcohol consumption can also lead to:
o High blood pressure which increases incidence of heart attacks and stroke.
o Damage to the lining of the stomach.
o Increase water loss in urine and therefore dehydration as it inhibits the release of ADH.
o Demyelination- loss of myelin sheaths from neurones. Severe impact on brain function as
the speed of neurone transmission is reduced.
o Increased risk of developing cancers of the mouth, oesophagus, liver, breast and bowel.
o Risk of dependency.
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4.4: discuss the social consequences of excessive alcohol use, and;
How persons respond to certain amounts of alcohol can differ from person to person. Abuse of
alcohol can have far reaching consequences, some of which are discussed below. In general, it
is a good idea for persons to keep track of the amount of alcohol they are consuming. This is
generally measured in units. 1 unit of alcohol is usually metabolised in one hour.
Unit of alcohol= 8g of alcohol
Excess alcohol consumption is considered being over the recommended DAL (daily alcohol
limit), which is considered to be no more than 2 – 3 for a woman and no more than 3 – 4 for a
man, depending on body mass. One unit of alcohol can be calculated by using the following
formula:
ABV refers to Alcohol by Volume, which is a measure of alcoholic strength, as a percentage.
So for e.g. a Heineken contains 330ml of beer. Working with an ABV of 5%, one bottle of
Heineken would have 1.65 units of alcohol. A 200ml glass of Puncheon (75% ABV) would
have 15 units of alcohol, well over the DAL (and even for the week!).
Breathalyzer tests are able to test blood alcohol concentration, as the amount
of alcohol in the breath is directly related to the concentration of alcohol in
the blood.
The liver is said to “break down” 1 unit of alcohol every hour that passes,
using the enzyme ethanol dehydrogenase.
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Drinking and driving
Initially, alcohol consumption affects the cerebrum (logical thought and decision making),
then the cerebellum (coordination) and then the medulla oblongata (passes messages between
brain and spinal cord, essential of respiratory and cardiovascular systems). Driving under the
influence of alcohol is ill advised as it is a depressant by nature, it increases reaction time and
adversely affects judgement (judging distances as well as risk taking). A drunk driver will be
less likely to respond to danger appropriately and rapidly. This can result in loss of life for the
driver and other unsuspecting drivers on the road.
Due to this, countries have laws that limit the alcohol concentration in blood while driving.
This is generally accepted as 0.08% or 80mg of alcohol per 100 ml of blood. In Jamaica this
is 0.35% while in Barbados and Cuba it is 0%. This is enforced by law enforcement by
administering Breathalyzer tests. There is a direct correlation between the amount of alcohol
in breath and the amount of alcohol in the blood. As a loose guide, 1 unit of alcohol will raise
the blood alcohol concentration by 15 mg per 100 ml (re: size and gender of person will alter
this).
Violence
Alcohol affects some persons by making them act more aggressively and/or violently. They
may/may not be aware of this effect and may not recall actions taken while under the
influence of alcohol. This happens publicly at times but can also affect domestic situations.
Family members can suffer physical and mental abuse due to a frequently drunk relative.
This leads to the breakdown of many families due the resulting abuse.
Crime
Police records show that alcohol is often a factor in petty crime. Criminals often drink before
committing crime. This coincides as we know alcohol impairs judgement and weakens
inhibitions. People therefore, make decisions they would not have ordinarily made if sober.
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4.5: Describe the effects of the components of cigarette smoke on the respiratory and
cardiovascular systems.
Cigarettes are made from the dried tobacco leaves of the plant Nicotiana tabacam.
cigarette smoking has been vastly proven to contribute to one of the most deadly conditions,
COPD (Chronic Obstructive Pulmonary Disorder), where alveoli become enlarged due to
elastin breakdown; mucus- secreting goblet cells proliferate; and ciliated cells become
destroyed.
As a result, bacterial and viral infections (such as pneumonia and bronchitis) become more
common; there is reduced oxygen supply to cells and increased risk of CHD and stroke
occurs.
Cigarette smoke contains many harmful chemicals such as:
o Tar- a black oily liquid containing many aromatic compounds and is breathed in as
tiny droplets that settle and coat the bronchi. It is known to cause cancer.
o Nicotine- exists naturally in the plant to act as an insecticide but has a very addictive
nature in humans. This is the principal reason why cigarettes are smoked. It affects the
brain and other parts of the nervous and cardiovascular system.
o Carbon monoxide (CO)- a highly toxic gas produced by the incomplete combustion of
compounds within tobacco leaves. It is dangerous because it reduces the oxygencarrying capacity of the blood.
o Particulates- tiny particles that irritate the lungs
o Carcinogens- eg. benzopyrene
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This is why smoking and even second-hand smoke (passive smoking) can cause severe health
issues. Persons who live/work with smokers develop the same medical conditions. Children
are particularly at risk for slow lung development and asthma.
NOTE: Even being in an environment of smokers and inhaling the components poses a
threat. This is commonly called second-hand smoke or PASSIVE SMOKING.
Let’s go more in-depth with the table above with its relative effects…
Respiratory effects
Tar is an irritant that results in inflammation of the epithelial cells of the respiratory tract. In
response, the goblet cells and mucous glands in the lining proliferate and overcompensate by
producing excess mucous that collects in the bronchi. This increased number of extra cells is
called hyperplasia. The tar also prevents the cilia from beating so this excess mucous cannot
be easily cleared. This results in the characteristic “smoker’s cough” as they attempt to
forcefully clear the build-up in their bronchi. This accumulated mucous is the perfect
breeding ground for pathogens to grow as it is moist and warm. This increases their risk of
airborne infections significantly
Cardiovascular effects
Smokers have an increased risk of hypertension, coronary heart disease and stroke. While
blockages in coronary arteries lead to heart disease, blockages in arteries in other areas within
the body like the brain can lead to stroke. Smokers have a 20X increased risk of stroke than
non-smokers.
CO permanently binds to haemoglobin to form carboxyhaemoglobin. This can reduce the
oxygen-carrying capacity of blood by up to 10%. This affects the fitness of smokers as less
energy is available when exercising. In order to compensate, the body increases the number
of RBCs. This occurs as low oxygen concentration causes the kidneys to secrete a hormone
called erythropoietin which stimulates production of RBCs by stem cells in the bone marrow.
Smokers therefore tend to have a higher red blood cell count. This is associated with
symptoms such as dizziness, weakness, headache and joint pain as increases the viscosity of
blood (Thickens). This blood is harder to pump and platelets are stimulated to secrete factors
that promote clotting (20 X risk of blood clots). Nicotine damages the nervous system and is
therefore a neurotoxin. It’s small size means it is able to permeate into tissues easily
including brain tissue. In the brain in stimulates the release of dopamine, a transmitter
substance in the “reward centre” of the brain. This gives users a sense of pleasure and make
smoking enjoyable.
Nicotine also stimulates the release of the adrenaline hormone from adrenal glands. This can
lead to increased blood pressure, heart and breathing rate. It also acts as a vasoconstrictor
(constricts the blood vessels). It stimulates the sympathetic neurones in the walls of the
smooth muscles of the walls of arteries and arterioles to contract. This narrows the lumen and
increases resistance to blood flow. This increases blood pressure and risk of clot formation. In
the long-term it can lead to peripheral vascular disease which can progress to gangrene and
amputation of limbs.
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Lung Diseases
Chronic Obstructive Pulmonary Disease (COPD)-This is the collective term used for
conditions that affect the bronchi and lungs. This results in most cases from smoking and
asthma. Respiration becomes increasing difficult as the conditions result in the airways
becoming progressively obstructed. While this occurs as part of the aging process, it is
particularly pronounced in smokers.
Chronic Bronchitis - Bronchitis is the inflammation of the bronchi and other air passages.
It usually presents with a productive cough ie it brings up sputum. As the lining of the bronchi
deteriorates, the cilia is lost and is replaced by scar tissue. This further exacerbates the
accumulation of mucous and increases the need to cough. Coughing is then accompanied by
wheezing and breathlessness throughout the day. In the late stages of the diseases, it will
become difficult for persons to walk short distances without becoming breathless and coughing.
Swelling of feet, heart failure and the lips and skin appear blue. Chronic bronchitis then leads
to emphysema. These persons are severely prone to infection.
Emphysema -This disease results in structural changes to the lungs. Alveoli gradually lose
their elasticity and break down forming larger air spaces. This reduces the surface area
available for gaseous exchange. Breathing rate therefore has to increase to compensate. Blood
vessels in the lung become damage and lead to damage to the right ventricle of the heart. As
the condition progresses, lung tissue deteriorate and the blood vessels bringing deoxygenated
blood become narrower and are destroyed. The right side of the heart therefore has to work
harder to pump blood to the lungs. This causes the right ventricle to increase in size and
pressure increases in the veins returning blood to the heart. This results in tissue fluid build-up
in tissues, especially legs and ankles. Emphysema eventually results in heart failure. Smoking
irritates macrophages in the alveoli which releases chemicals that attract neutrophils. These
neutrophils release proteases eg elastase, which are capable of digesting lung tissue. Oxidants
and free radicals in smoke damage the enzyme inhibitor responsible for protecting alveoli from
proteases.
Cancers -Almost all cases of lung cancer are related to smoking. In addition to promoting
lung cancer, smoking is also a contributory factor to other cancers, such as cancer of the mouth.
The carcinogens and co-carcinogens in tobacco smoke interact with DNA in bronchial
epithelial cells, causing mutations. Cells become cancerous if the genes that control the cell
cycle and mitosis mutate. Some of these gene’s code for inhibitory proteins. Once lost, cells
continue to divide unchecked. If a mutated cell survives and evades destruction by
lymphocytes, then it can grow into a mass of cells, or tumour, within the bronchial epithelium.
Blood vessels and lymph vessels grow into the tumour, supplying it with oxygen and nutrients
so that the cells can continue to divide. Although this is uncontrolled growth, it is not fast. It
may take 20–30 years for a tumour to be large enough to cause problems and be detected. As
the tumour, or bronchial carcinoma, grows within the lung tissue it will obstruct airways and
blood vessels. Symptoms in a smoker, such as coughing up blood, will suggest lung cancer as
the diagnosis. If the cancer is still a primary tumour (see the flow chart), then it may be removed
by surgery and/or treated by chemotherapy and radiotherapy. If metastasis has occurred, there
will be secondary tumours in other parts of the body and it will be more difficult to treat
successfully.
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THAT’S THE END OF MODULE 3 OF BIOLOGY UNIT 2 :)
BEST OF LUCK IN EXAMS
DINELL MOTILAL CAPE BIOLOGY UNIT 2 SUMAMRY NOTES
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