1
CAPE BIOLOGY
UNIT TWO MANUAL
(by Sperwin Zinger)
MODULE ONE – BIOENERGETICS AND CONSERVATION
THIS MODULE CONTAINS FOUR TOPICS:
1. PHOTOSYNTHESIS AND ATP SYNTHESIS
2. CELLULAR RESPIRATION AND ATP SYNTHESIS
3. ENERGY FLOW AND NUTRIENT CYCLING
4. ECOLOGICAL SYSTEMS, BIODIVERSITY AND CONSERVATIONS
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TOPIC 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
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.
ATP functions as the intracellular energy currency in
all organisms. The name stands for adenosine
triphosphate. 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.
First, a few basics about photosynthesis
Firstly, recall that photosynthetic organisms contain CHLOROPLASTS (such as plants) or the lightcapturing pigment, CHLOROPHYLL, in membranes (such as phytoplankton). The word and chemical
equations for photosynthesis in green plants can be written as:
Photosynthesis involves a set of light-dependent and light-independent reactions. A basic outline of these
reactions is depicted below.
During the light-dependent stage, light energy is used to break the bonds of water molecules (a process
called PHOTOLYSIS). OXYGEN diffuses out as a bi-product. The HYDROGEN molecules combine
with CARBON DIOXIDE molecules, which are reduced to form GLUCOSE.
REMEMBER:
The light-dependent
stage occurs in the
THYLAKOIDS inside
the chloroplast.
The light-independent
stage occurs in the
„background material‟ of
the chloroplast, called the
STROMA.
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THE DICOTYLEDONOUS LEAF (internal structure)
Segment
Description
Function
Upper epidermis
Thin layer of transparent cells,
usually coated with a watertight,
waxy cuticle.
Waxy cuticle limits water loss through the top
of leaf; protects against insects and microbes;
transparent to allow sunlight in.
Lower epidermis
Thin layer of cells interspersed
with GUARD CELLS, which
form stomata.
Guard cells‟ unevenly thickened cell walls
absorb water via osmosis and „curve‟ to open
the stomata. This allows DIFFUSION and
TRANSPIRATION to occur.
Spongy mesophyll
Loosely and irregularly packed
layer of cells with numerous air
spaces.
Facilitates diffusion of materials and gaseous
exchange between the palisade mesophyll and
stomata.
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.
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.
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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.
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
a 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.
1.2: Explain the process of photophosphorylation with respect to photosynthetic electron transport
PHOTOPHOSPHORYLATION? PHOTOSYSTEMS? What is that?
Let‟s break the word down: Photo (use of light),
phosphorylation (adding a phosphate to a
compound).
The concept is, thus, simple:
Photophosphorylation is a biochemical
process that uses light to attach a phosphate
group to an organic compound.
ADP has two phosphates (diphosphate), while ATP has three (triphosphate). So photophosphorylation
refers to the production of ATP from ADP (by adding a phosphate) using light energy. This energy
enables an ELECTRON to move through a series of ELECTRON CARRIERS to form an
ELECTRON TRANSPORT CHAIN in the chloroplast‟s thylakoids.
Think of that electron as a ball in a pinball machine, zipping around, gradually losing energy. The initial
energy to move this „ball‟ around comes from light particles (photons) being caught by an antenna
complex in a PHOTOSYSTEM, which is a chlorophyll-protein complex in the chloroplast. There are
two such systems, named PSI and PSII.
In some circumstances, PSI generates ATP. It may also generate NADPH (or reduced NADP). NADPH
is an electron donor and reducing agent necessary for photosynthesis. It is easy to confuse it with NAD,
the coenzyme needed for respiration. Think of the “P” in NADP as a link to the word „Photosynthesis‟. A
very important cofactor to make NAD and NADP is Vitamin B3.
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CYCLIC AND NON-CYCLIC PHOTOPHOSPHORYLATION (Light-Dependent)
Think of these as a series of steps in a metabolic pathway. The main goal is produce ATP from ADP, in
light-dependent reactions. Both involve excited ELECTRONS that break loose from the chlorophyll a
molecule when light hits them, which then pass through an ELECTRON TRANSPORT CHAIN (ETC).
Let‟s define each one and then note the differences:

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 „returns‟ to the PSI chlorophyll, and the cycle restarts. This usually
occurs in isolated chloroplasts and photosynthetic bacteria.

Non-cyclic Photophosphorylation can be defined as the synthesis of ATP during the light
reaction stage of photosynthesis in which an electron donor is required and oxygen is produced as
a by-product. The excited electron passes from PSII to PSI. It then replaces any electron lost in
PSI. Instead of PSI producing ATP here, the electrons reduce NADP to NADPH. This process
may be the one more familiar to us, since this usually occurs in green plants.
Factor
Cyclic
Non-cyclic
Is ATP produced?
Yes
Yes
Photosystems involved?
PSI only
PSI and PSII
Is reduced NADP made?
No
Yes
PSI replacement electrons found
where?
From the electron that it
emitted itself
From the electron emitted in PSII
PSII replacement electrons found
where?
PSII is not involved in cyclic.
From the photolysis of water.
Predominates when?
Anaerobic conditions
Aerobic conditions
Evolution of oxygen?
No
Yes
KEEP IN MIND: Recall that ‘photolysis’ is the splitting of a water molecule to produce oxygen and
hydrogen. H+ ions are released, which reduce NAPD. Electrons are emitted, which return to PSI.
PROTON GRADIENT IN NON-CYCLIC PHOTOPHOSPHORYLATION
1. Water is split into H+ ions, O62 and
electrons, which are released as they
become “excited” by light.
2. 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.
Think of the electron as a ball in a pinball machine, bouncing off proteins
and allowing reactions to occur, such as moving H+ ions or reducing NADP.
These H+ are like the „final ingredient‟ for ATP in the ATP synthase „oven‟.
3. 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.
4. Finally, H+ ions and electrons
reduce NADP to form NADPH.
1.3: Outline the essential stages of the Calvin cycle and light independent fixation of carbon dioxide;
CALVIN CYCLE (Light-Independent)
What were two products of photophosphorylation? Remember the goal was to produce ATP and noncyclic produces NADPH. And this all required light to excite electrons and occurred in the
THYLAKOIDS.
In the light-independent stage, the goal is to produce GLUCOSE and other carbohydrates. This occurs in
the STROMA of the chloroplast, because in the stroma is a special enzyme called ribulose biphosphate
carboxylase (referred to as RUBISCO from now on). Rubisco catalyses a reaction to combine carbon
dioxide with a molecule called RuBP. This occurs in the CALVIN CYCLE, shown below.
As you recall, glucose is a 6C sugar (hexose). RuBP is a 5C sugar (pentose), so it needs a carbon from
CO2 to become a hexose. This doesn‟t occur all at once, and must first build some 3C sugars (triose).
The entire purpose here is to create GLUCOSE (or fructose,
sucrose, etc.) These sugars are made from the triose phosphate (or
G3P), after the reduction of phosphoglyceric acid. G3P is a key
phop
molecule
here, as it also helps re-initiate the cycle.
CARBON FIXATION (Carboxylation)
A CO2 molecule combines with the 5C
RuBP, thanks to rubisco. This creates a 6C
intermediate (not glucose), which then
break down into two 3C acids
(phosphoglyceric acid).
REDUCTION
ATP and NADPH are used to convert the
3C acids into G3P (triose phosphate).
NADPH donates electrons to do this. G3P
goes on to make GLUCOSE or even amino
acids, if nitrogen is added.
REGENERATION
ATP is used to allow unused G3P molecules
to be recycled back into RuBP to restart
cycle.
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So far, let‟s recap some key compounds we encountered.
Compound
Function
NADPH
Reduced NADP. A reducing agent for reactions, such as to form G3P.
G3P
(or triose
phosphate)
The first sugar made in photosynthesis, and helps to form sucrose and other
carbs. These also help reform RuBP molecules to restart Calvin cycle. Formed
after reduction of the compound, phosphoglyceric acid (or PGA)
RuBP
A 5C sugar in the chloroplast that will eventually take in CO2 to become a 6C
and eventually lead to the formation of glucose.
Rubisco
The enzyme in plants that helps combine RuBP with CO2 (carboxylation).
H+ ions
Protons. Released during photolysis and helps to form ATP and NADPH.
1.4 & 1.5:Discuss the concept of limiting factors in photosynthesis; and discuss how knowledge of these
can be applied to the improvement of plant productivity.
What are LIMITING FACTORS OF PHOTOSYNTHESIS?
You‟ll recall that photosynthesis requires the presence of the following:




Energy in the form of sunlight
Raw materials (carbon dioxide and water)
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. For example, a green plant in
a warm room supplied with carbon dioxide and water will photosynthesise at a high rate during the day
outdoors; however, in a room with dim sunlight, the process will be very limited and occur at a slower
rate. Thus, these are known as LIMITING FACTORS of photosynthesis.
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Table representing limiting factors of photosynthesis:
Limiting Factor
Graph
Explanation
Light intensity
In the light-dependent stage, light provides
energy to excite ELECTRONS in chlorophyll
reaction centres 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
concentration
Carbon dioxide is required in the chloroplasts to
donate carbon atoms to RuBP to produce
hexose sugars that eventually turn into glucose.
Remember this is facilitated through the
enzyme, RUBISCO.
If CO2 concentration is limited, this Calvin
Cycle process is slowed down, and rate of
photosynthesis decreases. Same as light
intensity, it reaches saturation at a certain
concentration and plateaus.
Temperature
In Unit 1, we learned that enzymes are globular
proteins that usually have tertiary structures.
Their bonds can be broken if too much heat or
kinetic energy is applied, causing the enzyme‟s
structure to change, leading to
DENATURATION.
This can happen to rubisco, causing it to
„malfunction‟ and instead waste RuBP by
combining it with OXYGEN (photorespiration)
severely decreasing photosynthetic rates.



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.
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TOPIC 2: CELLULAR RESPIRATION AND ATP SYNTHESIS
2.1: Explain the sequence of steps in glycolysis.
What is GLYCOLYSIS?
Glycolysis translates to „breaking apart of glucose‟. As glucose is broken down by enzymes in the
CYTOSOL of cells, energy is released. This energy is used to make ATP, the currency of life necessary
for metabolic processes. This breakdown of glucose occurs over a sequence of steps.
Keep in mind this is a simplified depiction. Pay attention to the sections labelled 1 – 3.
LABEL 1
.

Glucose is first phosphorylated to form glucose-6phosphate by adding a phosphate. This uses 1 ATP.

Glucose-6-P is isomerized to form Fructose-6-P.

Fructose-6-P is phosphorylated to produce Fructose
Biphosphate. This uses 1 ATP.
LABEL 2

Fructose biphosphate is unstable and eventually
undergoes LYSIS to become two 3C sugar molecules,
one of them being G3P and the other being an isomer,
DHAP, which rearranges to also become G3P.
LABEL 3

Now we have two G3P molecules. These will
eventually become a compound known as
PYRUVATE.

To do this, they must be oxidized with the help of a
DEHYDROGENASE (hydrogen-removing) enzyme.
Dehydrogenase functions if an enzyme helper
(coenzyme) called NAD is present.

NAD „receives‟ the hydrogen that the enzyme removes
(imagine it like a catcher‟s mitt for H). It then reduces
to form NADH.

Both G3P‟s are oxidized to form two 3-carbon
molecules of pyruvate.
In the end, ADP molecules are converted to ATP. Some
energy from the initial glucose molecule is transferred to
these ATP molecules, a process called SUBSTRATELEVEL PHOSPHORYLATION

Finally, 2 ADP are phosphorylated to form 2 ATP.
This happens twice, so 2 NADH‟s and 4 ATP are
made in the end here. Only 2 net ATP are gained as
the first phase with glucose (Label 1) uses 2 ATP.
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2.2: Describe the structure of a mitochondrion, relating its structure to its function
The MITOCHONDRION – everyone‟s favourite „powerhouse‟ of the cell
Recall that the goal of glycolysis was to break glucose down into a compound known as PYRUVATE.
Pyruvate is responsible for RESPIRATION after it moves into the mitochondria.
If OXYGEN is sufficient in the cytosol, it converts into Acetyl CoA and enters the Krebs cycle
(discussed later) and AEROBIC respiration can occur. In the absence of oxygen, ANAEROBIC
respiration occurs as pyruvate is broken down into ETHANOL or LACTATE.
Observe the diagram and annotations of a mitochondrion cross-section below:
Into the
mitochondria:
 NADH
 ADP + Pi
 Pyruvate
 Oxygen
Out of the
mitochondria
 NAD
 ATP
 CO2
 H2O
For such a tiny organelle, there‟s a great
amount of complex reactions occurring in
the mitochondria.
Much of the action occurs in the MATRIX,
the fluid-filled space. ATP is made here due
to the energy from the flow of hydrogen
ions.
The INNER MEMBRANE contains an
enzyme called ATP synthase, that helps
make ATP. It also contains carriers for
electron transport chains that carry electron
energy used to produce ATP.
The CRISTAE are inward folds of this
membrane. The more cristae present, the
more active the mitochondrion due to
increased amounts of ATP synthase.
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2.3 – 2.5: State the fate of pyruvate in the cytosol when oxygen is available; explain the significance of
the Krebs cycle in ATP production; and oxidative phosphorylation w.r.t. the electron transport chain
Before we continue, there are going to be some new compounds and terms we‟re going to have to get
acquainted (or re-acquainted) with:
Compound / Term
Description
Pyruvate
Product of glycolysis. Two are produced. Eventually converted to acetyl CoA.
NAD
A coenzyme. After accepting a hydrogen, it becomes NADH.
Coenzyme A (CoA)
Helps convert pyruvate to acetyl CoA. Also helps produce citrate.
Acetyl CoA
A 2C compound that acts as the „fuel‟ to keep the Krebs cycle going.
Link reaction
Process that forms carbon dioxide as pyruvate is converted to Acetyl CoA. Also
called oxidative decarboxylation.
Krebs cycle
A series of reactions that generate ATP through the oxidation of acetate.
Oxidative
phosphorylation
Process where ATP is formed. Occurs as a result of the transfer of electrons from
NADH or FADH2 to O2.
Electron transport
chain (ETC)
A cluster of proteins in the inner mitochondrial membrane that shuttle electrons
and drives the creation of ATP and water during respiration.
FAD
Like NAD, but accepts two hydrogens to reduce to FADH2.
KEEP IN MIND: You can think of NAD and FAD as ‘uncharged batteries’ that become charged after having
accepted hydrogens to become reduced. NADH and FADH2 can then be reoxidized to make ATP molecules.
Remember that this series of reactions represents
the stages of AEROBIC respiration, where the
inputs are glucose and oxygen and the products
are carbon dioxide, water and ATP.
Glycolysis converts 6C glucose into 3C pyruvate.
The link reaction turns 3C pyruvate into 2C
acetyl coA, needed for the Krebs cycle. A carbon
leaves via creation of CO2.
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.
The ETC also drives ATP production but also
helps create water.
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What is THE LINK REACTION?
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). Observe the diagram below.
So, what is happening?



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!
What is the infamous KREBS CYCLE?
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 called FAD. FAD works like NAD. It accept
hydrogens to reduce to FADH2, which can go on to form
1.5 ATP when reoxidized. (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.
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So, to put the link reaction and the Krebs cycle step-by-step, so far:







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.
What is OXIDATIVE PHOSPHORYLATION and the ELECTRON TRANSPORT CHAIN?
Oxidative phosphorylation can be defined simply: 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, a series of electron carriers and proteins.
In the ETC, electrons are shuttled from one
molecule to another. This releases energy. This
energy is used to form an electrochemical
gradient (more on this later) 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.
Remember all those NADH‟s? They once were NAD‟s that caught a hydrogen and became reduced.
When NADH oxidizes and releases this hydrogen (imagine the catcher‟s „tossing‟ out the H+ ion), it turns
back into NAD. This NAD can then be returned to the Krebs cycle to be reused.
The hydrogen atom splits into two components: a H+ ion (known as a
„proton‟) and an electron (or e-).
It is the electrons‟ journey that we‟ll observe. The electron is passed from carrier to carrier until it
reaches the end of the chain, where there would be a molecule of OXYGEN. Now, remember that as each
carrier loses the electron, it is oxidized and the subsequent carrier that gains the electron is reduced. The
very act of this occurring is what releases energy needed to make ATP.
When the electron reaches the OXYGEN at the end of the ETC, it combines with H+ ions to produce a
WATER (H2O) molecule.
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Now let‟s look at a bigger picture of what is happening and let‟s focus on labels 1 – 3:
SIDENOTE: 34 molecules
of ATP are made in
glycolysis, link reaction
and Krebs cycle.
However, 2 ATP were
used up during glycolysis.
This means a net total of
32 ATP is made from one
glucose molecule during
aerobic respiration.
Label
What happens?
1
This is what was described on the previous page. 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 intermembrane space of the mitochondrion.
These have a POSITIVE charge, of course, and create an ELECTROCHEMICAL GRADIENT
between the matrix and intermembrane space, with the greater positive charge being in the
intermembrane 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 helps convert ADP into ATP.
Let‟s sum this up:
1.
2.
3.
4.
Electrons from split hydrogen atoms contain energy and are shuttled along carriers in the ETC.
Oxygen is the final receptor of the electron. The oxygen, the electron and H+ ions make water.
This electron energy helps pump H+ ions through the inner membrane.
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 allows the enzyme
to make ATP.
7. This process CANNOT occur without oxygen, as it is the final destination of the electron.
15
So how many ATP are produced from one molecule of glucose?
Let‟s break it down! During oxidative phosphorylation, each NADH yields 2.5 ATP and each FADH2
yields 1.5 ATP.
Glycolysis
-
Produces two pyruvate molecules.
Produces two 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
Process
Products formed
Total ATP
Glycolysis
2 ATP from substrate
phosphorylation
2 NADH (5 ATP)
7
Link reaction
2 NADH (5 ATP)
5
Krebs cycle
6 NADH (15 ATP)
2 FADH2 (3 ATP)
2 ATP at substrate level
phosphorylation
20
Totals
4 ATP from substrate-level, 10
NADH, 2 FADH2
32
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2.6: Compare the fate of pyruvate in the absence of oxygen in animals and yeast.
What happens during ANAEROBIC RESPIRATION and 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.
Anaerobic respiration in humans
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.
In yeast,
pyruvate
is decarboxylated,
releasing
NOTE:
In yeast,
pyruvate
is decarboxylated,
releasing
CO
,
to
form
ethanal
before
forming
ethanol.
2
CO2, to form ethanal before forming ethanol.
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).
In YEAST, the above process is similar but two different
products are yielded: ETHANOL and CO2. Ethanol is a
major constituent of commercial alcohol, such as beer,
rum and wine. In bread making, the CO2 is released from
yeast causing dough to „rise‟.
Lactobacillus bacteria can produce lactate to produce
yoghurt and also help preserve grass feed for livestock.
Also, the lactate that is produced builds up in the blood
plasma of skeletal muscle cells, such as biceps and
quadriceps. This can lead to painful CRAMPS. The
lactate can also be taken in by the LIVER cells
(hepatocytes) as they produce more pyruvate.
When oxygen is supplied once again, the pyruvate can
once again enter the link reaction and Krebs cycle. And
that extra build-up of lactate in the liver can be
„dissipated‟ by the oxygen, called an OXYGEN DEBT.
So let‟s outline some differences between aerobic and anaerobic respiration:
Aerobic
Anaerobic
Processes involved
Glycolysis, link reaction, Krebs
cycle, oxidative phosphorylation
Glycolysis, fermentation.
Decarboxylation of pyruvate to ethanal.
Net ATP gained per glucose
32
2
Max ATP gained per glucose
34
4
Products formed
Carbon dioxide and water
Yeast – Ethanol and Carbon dioxide
Bacteria and humans - Lactate
17
TOPIC 3: ENERGY FLOW AND NUTRIENT CYCLING
3.1: Discuss the efficiency of energy transfer between trophic levels;
First of all, let‟s get re-familiarized with a few ecological terms:
Term
What happens?
Habitat
A place where an organism lives.
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.
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?
On the food chain shown, the grass is the
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.
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).
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.
18
Above, we observe the interlinking of multiple food chains. This is called a food web. 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. Observing such a food
web, let‟s browse through a few scenarios:
1. A pathogen infects all of the aquatic vegetation (SAV).
It is likely that all of the herbivorous ducks would die from starvation or migrate to another
ecosystem that contains SAV (or other food from their diet).
2. Overfishing results in the removal of most of the large piscivorous fish.
Since the large fish are the only source of food for the osprey, it would likely die or migrate.
It is also likely that sea duck population would decrease as the bald eagle would lose a
source of food. The small planktivorous fish population may increase initially, causing
wading bird and gull population to also increase, and other „ripple effects‟ in the food chain.
3. An insecticide is dumped into the bay and assimilated into benthic invertebrates.
Certain insecticides or pollutants can increase in concentration as they taken up into
organisms with greater mass (biomagnification). The sea ducks and the bald eagle would
become poisoned and potentially die, causing ripple effects in multiple other populations,
such as bivalves, tundra swans, osprey and large piscivorous fish.
19
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.
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.
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. This 6 units is known as the NPP or
NET PRIMARY PRODUCTIVITY.
20
3.2: Discuss the concept of biological pyramids.
Pyramids of Numbers, Biomass and Energy
Pyramids in the topic of ecology are ways to visually conceptualize information, similar to a bar graph or
line graph. They usually sort information based on data collected from ecosystems with regards to
population numbers and feeding relationships and sorts this data along trophic levels. Therein lies several
limitations:
1. Population numbers are never static. They are dynamic or always changing, so collecting a true
number of organisms is quite difficult, no matter the collection method (e.g. quadrats, transects,
sweep nets, etc.). Organisms will have to be observed for a very long time in their habitats.
2. Organisms can occupy more than one trophic level simultaneously.
3. Feeding relationships may be affected by season or time of year.
Nevertheless, pyramids are suitable for representing data on a large-scale basis. Let‟s see how this is done
based on the table below, with regard to a PYRAMID OF NUMBERS, which simply represents the
number of organisms that fall within each trophic level:
Organism
Feeding
Number
Bald eagle
Cichlid
Tiger Barb
Phytoplankton
Seaweed
Grass carp
Zooplankton
Top Carnivore
Carnivore
Carnivore
Producer
Producer
Herbivore
Herbivore
3
80
40
8000
4000
200
2800
Trophic
level total
3
120
12000
3000
Bear in mind that a pyramid of numbers may not have the
typical „pyramid‟ shape, such as in a food chain that includes
large producers such as trees or parasites within the
organisms. This is because the pyramid does not take into
the individual mass or size of each organism, only the
counted number.
A PYRAMID OF 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.
21
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.
A final summary of GPP, NPP and ENERGY LOSS
Let‟s recap once more the definitions of GPP and NPP.
Term
Definition
Gross Primary Productivity
(GPP)
The total quantity of useful chemical energy (in plant tissues) converted
from energy from sunlight.
Net Primary Productivity
(NPP)
The quantity of useful chemical energy converted from energy from
sunlight AFTER RESPIRATION HAS TAKEN PLACE, thus: NPP
= GPP – R.
Various ecosystems will differ in NPP due to the area and type of vegetation and tree cover. For example,
a desert will have a very low NPP due to the scarcity of green plants, while a tropical rainforest will
have a very high NPP as it has a great amount of leaf cover to capture sunlight.
Let‟s calculate the values for A,
B and C in the chart shown:
A: 20 810 − 11 977 = 8833
B: 1478 − 383 = 1095
C: 383 − 67 = 316
The GPP would be 20810 units,
as that is how much the producers
make from the sunlight.
The NPP would be the GPP
minus the respiration loss
(11977), which would be 8833
units.
22
3.3: Describe how nitrogen is cycled within an ecosystem.
Observe the diagram and table below with relation to THE NITROGEN CYCLE:
Component
Notes
N2 (atmosphere)
Nitrogen gas occupies 78% of the atmosphere. It has a triple covalent bond,
making it unreactive in this state in both plants and animals.
Nitrogen-fixing
bacteria
These „fix‟ N2 and convert the gas into a more reactive form, such as a nitrate or
ammonium, using hydrogen and ATP in anaerobic conditions. The most common
of this bacteria is RHIZOBIUM, which live in legume root nodules (e.g. peas).
Lightning
Nitrogen fixation can also occur in the atmosphere when lightning provides
energy to combine nitrogen and oxygen to form nitrogen oxides. This can also be
done synthetically by using the HABER PROCESS.
Nitrifying bacteria
Ammonium tends to be formed during decomposition (and decayed, fallen
leaves) and as urea in animal urine. Nitrifying bacteria can convert this
ammonium to a nitrite and then into a useable nitrate. Examples of this bacteria
include Nitrosomonas and Nitrobacter.
Nitrate (NO3-)
Considered the type of nitrogen that a plant would absorb and assimilate into its
cells to form larger molecules such as amino acids and nucleic acids.
Denitrifying
bacteria
Does the reverse of nitrogen fixation, turning nitrates back into nitrogen gas and
returns it to the atmosphere, thus restarting the cycle.
23
3.4: Explain how energy flow and nutrient cycling are important to ecosystems.
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.
24
TOPIC 4: ECOLOGICAL SYSTEMS, BIODIVERSITY & CONSERVATIONS
4.1: Discuss how ecosystems function as dynamic systems.
BIOTIC AND ABIOTIC FACTORS
Ecosystems are complex networks that consist of interactions between biotic and abiotic factors:
Biotic factor
Note
Predation
Where one organism hunts and eats another. This helps control several populations in
the food web.
Competition
Where multiple organisms occupy similar niches and must vie for limited resources.
Symbiotic
relationships
A relationship where at least one organism benefits. These include:
 Parasitism, where one benefits from harming the other (e.g. ticks and dogs)
 Commensalism, where one benefits while the other is unaffected (e.g.
remora fish and shark)
 Mutualism, where both benefit (e.g. pea plants and Rhizobium)
 Altruism, where organisms cooperate for a common goal (e.g. ant colonies)
Abiotic (non-living) factors include:
Abiotic factor
Note
Light intensity
Impacts the rate of photosynthesis and animal habits.
Temperature
Impacts the rate of evaporation and water supply; type of vegetation; and the
metabolism of organisms;
Gas concentrations
O2 impacts rate of respiration and CO2 impacts rate of photosynthesis; on a
larger scale, CO2 affects climate change and acidification of water biomes.
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; soil
pH 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.
Wave action
Helps with movement of nutrients and gases; continuous wave action can
result in erosion or damage, e.g. to shorelines or coral reefs.
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.
25
EXAMPLE OF AN ECOSYSTEM – The Aripo Savannah Scientific Reserve in Trinidad
Left: Marshy area in Aripo Savannah; Middle: Student (J. Awong) in open savannah
Right: (Top) A parasitic Cassytha vine. (Bottom) A carnivorous sundew plant (Drosera capillaris)
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.
The Aripo Reserve is situated has contains numerous biomes, including an open savannah and a marsh
forest. In the savannah, the topography is very flat with small depressions caused by the burrowing of
earthworms and termites. Since it is situated in a tropical climate, there is a high annual rainfall
average of 2500mm, a stable medium-high temperature of 20 – 25oC, and a high humidity more than
50%. Since the open savannah has a constant high wind speed, it promotes rapid evaporation and
transpiration in the plants. Grass growth is sparse in areas of acidic pH caused by domestic runoff.
Since the soil mostly consists of low-drainage clay and has an impermeable clay layer at the surface, the
land becomes easily flooded during the rainy season. The small depressions act as irrigation channels,
which lead to soil becoming very dry, leading to water supply shortages to plants. Plants, as a result, have
adapted to have XEROPHYTIC characteristics, such as reduced leaves and succulent tissues to retain
water. Some of their roots have bulbs that store water. They also have stilted roots to keep them anchored
during flooding.
In terms of biotic factors, the Aripo Reserve contains over 250 species of plants, including many grasses,
shrubs, mosses, orchids and tall woody trees. These plants exhibit numerous facets of symbiosis.
Parasitic orange love vines (Cassytha) lack chlorophyll and thus must sap nutrients from other plants,
harming them. Commensalistic epiphytes grow atop the woody trees to obtain sunlight. A common
example of mutualism would be the nitrogen-fixing Rhizobium bacteria that live in the nodules of
leguminous plants. Carnivory is observed in sundew plants, which trap and digest insects.
Fauna in the Aripo Reserve include grass mice, agouti, opossum, numerous birds, insects and reptiles,
such as iguanas, frogs and lizards. These exhibit typical feeding relationships.
Human interference in the Reserve include squatting, quarrying, agricultural and industrial runoff,
poachers setting fires, and illegal removal of timber from Galba trees and cocorite palms.
26
4.2 – 4.4: Explain the concept of biodiversity & discuss the importance of the maintenance of
biodiversity; and how species diversity is related to ecosystem stability
How does one define BIODIVERSITY?
Biodiversity is a difficult factor to quantify, but we can think of it as being an amalgamation of three
factors:
1. Species diversity
2. Genetic diversity
3. Ecosystem diversity
Species diversity 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 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.
Ecosystem diversity 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.
What impacts SPECIES DIVERSITY and ECOSYSTEM STABILITY?
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.
27
Why is it important to MAINTAIN BIODIVERSITY?
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:
Reason
Notes
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.
Tourism
Coral reefs, safaris and nature trails tend to attract tourists from which countries
earn revenue.. Money can be made from nature tours.
(direct)
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.
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.
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.
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.
28
4.5: Explain how in situ and ex situ conservation methods are used to maintain biodiversity.
What is CONSERVATION?
Conservation is the discipline of maintaining
diversity by protecting species and their
habitats, as well as ecosystems and biomes. There
are two types:
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:


National parks (e.g. Yosemite and
Sequioa)
Wildlife reserves and sanctuaries (e.g.
Aripo)
In situ conservation
Ex situ conservation
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:





Zoos
Botanic Gardens
Seed banks and pollen storage
In vitro storage for sperm & embryos
Captive breeding programmes
Here is a rundown of comparisons for both types of conservation:
In situ
Ex situ
Involves natural habitats, so it is cheaper and
allows for the process of adaptation and evolution.
Usually used when natural habitats have been
destroyed, or species has been in rapid decline.
Usually does not have any issues with breeding or
reproduction, though inbreeding may be possible
with plants.
Since organisms are in man-controlled
environments, abiotic factors such as light intensity
and temperature may affect courtship behaviours if
not regulated, e.g. for seasonal organisms.
No technology utilized for medical aid, organism
health or to maximize reproductive success.
Organisms can have long lifespans due to access to
medical aid and security.
Requires large areas of space.
Requires smaller areas, though this may affect
organism behaviour.
29
MODULE TWO – BIOSYSTEMS MAINTENANCE
THIS MODULE CONTAINS SIX TOPICS:
1. THE UPTAKE AND TRANSPORT OF WATER AND MINERALS
2. TRANSPORT IN THE PHLOEM
3. THE CIRCULATORY SYSTEM OF MAMMALS
4. HOMEOSTASIS AND HORMONAL ACTION
5. THE KIDNEY, EXCRETION AND OSMOREGULATION
6. NERVOUS COORDINATION
30
TOPIC 1: THE UPTAKE AND TRANSPORT OF WATER AND MINERALS
1.1 & 1.2: Explain the uptake of ions by active transport in roots & describe the entry of water into plant
roots in terms of water potential.
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.
Inorganic ions such as nitrates and magnesium (for growth and chlorophyll production) are also taken up
by the roots along with water molecules. While water is taken up through osmosis, inorganic ions are
taken up into the cytoplasm from the soil through active transport or facilitated diffusion.
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.
Water moves into the root hairs from the soil
via osmosis. The water then moves from cell to
cell along the permeable cell walls (the
apoplast pathway) or through the cytoplasm
(the symplast pathway). More on that later.
The water (and dissolved ions) is then moved to
the centre of the root, where xylem vessels are
stacked end to end, going up the stem.
From there, water is transported up the stem to
the leaves. Along the way, it is absorbed by
cells that need it. Excess water then leaves the
stomata as vapour.
All of this occurs because there is a gradually
decreasing water potential gradient from the
roots to the atmosphere, facilitating osmosis and
water flow up the plant.
However, there are numerous abiotic factors
that affect this process, such as humidity.
Root hairs increase the surface area of the roots, increasing the
rates of both these processes.
31
What are the APOPLAST and SYMPLAST pathways?
NOTE: An easy way to
remember this is water
can either move “a”cross
cell walls (apoplast) or
“s”traight through
cytoplasm (symplast).
Water diffuses from cell to cell down a water potential gradient until it gets to the xylem vessels at the
centre of the root. This can occur along two pathways, shown in the diagram and in the table below:
Pathway
Movement of water
Extra notes
Symplast
Water enters the root cells by crossing the
plasma membrane and moving from cell
to cell across gaps in the cell walls, called
plasmodesmata.
Water can continue until it reaches the
xylem once it keeps diffusing down the
water potential gradient.
Apoplast
Water does not enter the cytoplasm of the
root cells. It stays in the freely permeable
cell walls, where it flows from cell to cell.
Water cannot continue to the xylem, due to
waterproof blockages in the endodermis
called Casparian strips. From the
endodermis, the water molecules switch to
the symplast pathway to get to xylem.
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.
32
1.3 & 1.4: Relate the structure of xylem vessels to their function & explain the ascent of water in plants.
Transverse Section of Xylem Vessels
What is the XYLEM?
Xylem vessels consist of elements that were once
alive. They are primarily used for the transport of
water and dissolved inorganic ions from the roots to
the leaves.
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).
Because they usually come in close bundles, this
also helps with structural support. 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.
How is ASCENT OF WATER through xylem facilitated?
Xylem vessels allows upward unidirectional movement of water in
bulk, known as mass flow, similar to a drinking straw. To facilitate
this kind of mass flow, the following factors must assist:
Longitudinal Section of Xylem Vessels

Water is cohesive, meaning that the molecules easily bind
with each other due to its dipole nature. Water is also
adhesive, which means that it sticks easily to the xylem walls.
This allows a process called CAPILLARITY.

As water molecules move into the leaf and leaves the stomata
as water vapour, there is a tiny „pull‟ that occurs as each
molecule exits, pulling the transpiration stream higher and
higher up the stem. This is known as TRANSPIRATIONAL
PULL.

The xylem vessels are very narrow and unsegmented
(continuous) facilitating capillarity and „transpirational pull‟.

As mentioned on the previous page, ROOT PRESSURE
builds up in the endodermis as inorganic ions are actively
transported into the xylem. This lowers the water potential in
the xylem, allowing more water to enter via osmosis.

If there is low humidity (low amounts of atmospheric water
vapour) and high wind speed, water molecules will diffuse
out of the stomata at a fast rate, allowing the transpirational
stream to flow faster.
33
1.5: Discuss the impact of environmental factors on the rate of transpiration.
How do STOMATA function?
Stomata are tiny pores in the epidermis (usually lower) of a
leaf that allow 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.
Some 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).
Which FACTORS influence RATE OF TRANSPIRATION?
Factor
Notes
Temperature
More kinetic energy in the water molecules would lead to a faster flow of the
transpirational stream, especially as rates of evaporation increase.
Light intensity
Some plants close stomata at night (as they cannot photosynthesize at night), so water
molecules cannot escape during that time.
Humidity
High humidity reduces transpirational rates, as it reduces the water potential gradient
between the atmosphere and leaf. Low humidity increases transpiration.
Air movements
If there is moderate to high humidity, wind can allow pockets of air saturated with water
vapour to move away from the stomata, steepening the water potential gradient.
Plant anatomy
Size and number of leaves; presence of hair on stomata; thickness of a waxy cuticle
contribute to rate of transpiration.
MEASUREMENT OF TRANSPIRATION RATES
The set-up on the left 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.
34
TOPIC 2: TRANSPORT IN THE PHLOEM
2.1: Relate the structure of sieve tubes and companion cells to their function
What is the PHLOEM?
In Unit 1, the xylem and phloem were observed,
discussed and drawn. The images above are a reminder
of the placement of these tissues in dicotyledonous roots
and stems.
We learnt about the xylem in the last topic and its
ability to help with transpiration, which is the
movement of water and dissolved inorganic ions. 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. 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.
The phloem consists of numerous sieve tube elements.
These are elongated cells only have a few organelles,
not even a nucleus or ribosomes, and very few
mitochondria. This is why they are joined onto
companion cells.
Companion cells have a large concentration of
mitochondria to supply ATP for „loading‟ and
„unloading‟ assimilates into and out of cells through
their plasmodesmata.
Where two sieve tube elements meet, a sieve plate is formed. A sieve plate is a perforated disc with many sieve
pores. Sieve plates facilitate mass flow through the phloem, and the pores may also reduce resistance by increasing
the pressure through them.
35
Observe the micrographs of the phloem, & the table of comparisons between the xylem and
phloem.
Characteristic
Xylem
Phloem
Function
Transport of water and inorganic
ions. Lignified walls are used for
stem support.
Transport of assimilates, such as sucrose
and amino acids.
Living or non-living?
Non-living elements containing
cellulose and lignin.
Both sieve elements and companion cells
are alive. However, the latter is more
metabolically active.
Segmented?
Not segmented. Continuous.
Segmented. Separated by sieve plates.
Passive or active?
Passive transport. No ATP.
Active transport. Loading uses ATP.
Direction of flow
Unidirectional. Water flows from
roots to leaves (transpiration).
Bidirectional. Assimilates flow from source
to sink, either up or down stem.
2.2: Explain how phloem loading in the leaves occurs against a concentration gradient
What is a SOURCE and a SINK?
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.


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.
Sugars are transported in the form of sucrose as it is not as reactive as
glucose and is more mobile than starch. It is transported by mass flow, like
water in the xylem.
36
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.
Sucrose and ions are loaded onto the phloem from
sources (e.g. leaves). This is usually done by active
transport. H+ ions are pumped, using ATP, out of
the companion cells, which creates a large
concentration outside of the cell.
As the H+ ions move back into the companion cell
via a transport protein, they move into the sieve tube
with sucrose. Think of this process as turning on a
H+ ion „faucet‟ that pushes sucrose along with it.
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.
When the sucrose is unloaded from the phloem into
sinks (e.g. roots), the water potential increases and
so, water flows back into the xylem, where it flows
up to the leaves again.
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.
As said, think of the H+ ions turning on a tap or
faucet (the sucrose H+ co-transporter) that
allows sucrose to flow from outside companion
cells to phloem sieve tubes.
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.
37
TOPIC 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
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.
Only complex multicellular organisms require circulatory systems due to their high activity and metabolic
levels, requiring a constant supply of oxygen and nutrients to cells and tissues for respiration. These types
of organisms are said to exhibit a low surface area to volume ratio, unlike protozoans and insects.
The structure of the human heart can be seen below, as well as descriptions of some main segments:
NOTE: The right atrium has a small patch of muscle
called the SAN (sino-atrial node), which initiates the
cardiac cycle. More on that later.
Segment
Function
Vena cava
Carries deoxygenated from the body
cells into the heart.
Aorta
Carries oxygenated blood away from
the heart to the body cells.
Pulmonary
artery
Carries deoxygenated blood away from
the heart and to the lungs.
Pulmonary
vein
Carries re-oxygenated blood to the heart
back from the lungs.
Valves
Open and close to prevent backflow of
blood.
Septum
Separates the left and right halves.
Left ventricle
Muscle-dense region of heart
responsible for pumping blood to aorta.
Use the acronyms:
LORD (Left Oxygenated, Right Deoxygenated)
T”R”icuspid (Right), MitraL (Left)
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.
38
What are the types of BLOOD VESSELS in the circulatory system?
There are three main blood vessels in the circulatory system: arteries, veins and capillaries. Arteries and
veins have muscular layers around them all prefixed tunica, with the tunica externa (outer), tunica media
(middle) and tunica intima (inner, smooth endothelial tissue).

Arteries 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. The main
artery is the aorta. Coronary arteries supply the heart muscles with oxygen.

Veins 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.

Capillaries are very narrow blood vessels that surround tissues and organs. They have a single
layer of endothelial cells that facilitate rapid diffusion. Red blood cells flow through these in
single file.
Characteristic
Arteries
Veins
Direction of flow
Away from heart.
From cells to heart.
Wall thickness
Thicker (tunica media thicker than
tunica externa)
Thinner (tunica externa thicker than
tunica media)
Lumen diameter
Smaller (about 0.7mm)
Larger (larger than 1mm)
Blood pressure
Higher. Has a pulse.
Lower. No pulse.
Semi-lunar valves?
No valves.
Valves present.
Oxygenated or deoxygenated?
Oxygenated (except pulmonary)
Deoxygenated (except pulmonary)
Another note on CAPILLARIES
While arteries and veins have elastic tissue and smooth
muscles in their walls (the tunica layers), capillaries only
have a single layer of endothelial cells. Most substances
can diffuse though these cells but sometimes use exoand endocytosis to package them in vesicles.
They only have a diameter of about 0.8µm, a little wider
than an erythrocyte (red blood cell). They connect
arterioles and venules in the capillary bed.
Diagram showing longitudinal section of capillary
39
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.
The following are examples and images of these cells in the blood:
Cell / Component
Erythrocyte
(red blood cell)
Lymphocyte
Neutrophils
Monocytes and
Macrophages
Platelet
(thrombocyte)
Microscope Image
Function
Adaptations or Characteristics
Has haemoglobin, 
which binds to
oxygen and

carbon dioxide for
transport to and
from cells.

Has a biconcave shape, which allows
rapid diffusion of gases.
No major organelles (e.g. ER,
mitochondria, nucleus), so more room
for haemoglobin.
Small in size (about 7µm) to fit through
capillaries.
Either makes
antibodies (B-),
sends signals (Thelpers) or kills
infected cells
(cytotoxic Tkillers)

Has receptors on surfaces to bind
antigens or toxins.
Large round nuclei to store genetic data
about antigens and instructions.
Mature in either bone marrow (B-cells)
or thymus (T-cells). All are produced in
bone marrow.
Engulfs
pathogens and
digests them.
Able to „present‟
antigens to
lymphocytes.


Monocyte is a
precursor to a
macrophage.
Comprises a small
amount of white
blood cells.



Helps form blood
clots to slow and
stop bleeding as a
response to
injury.






Large, multi-lobed nuclei. Granulated.
Able to extend itself to create a
pseudopodium („false foot‟) to move.
Able to evaginate pathogens and
package them in vesicles.
Large, irregular nucleus.
Very slightly granulated.
Macrophages act similarly to
neutrophils but are more involved in
phagocytosis.
They can „present‟ antigens as well.
Small fragments that have broken off
from bone marrow cells.
Activates enzymes and clotting factors
that eventually convert soluble
fibrinogen in the plasma to insoluble
fibrin, to eventually form a scab.
40
3.2 - 3: Explain the cardiac cycle & its initiation & discuss the internal factors that control heart action.
What are the processes involved in the CARDIAC CYCLE?
The cardiac cycle refers to the sequence of events that comprises one heartbeat.
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‟.
This can be further broken down into these events, as shown on the table. Imagine the cycle starts when
the upper chambers (atria) of the heart are already filled with blood:
Event
Description
Atrial systole


The atria contract.
The vein valves close, preventing
backflow into the veins. This carries
blood from the atria to the ventricles.
Ventricular systole

The ventricles contract, pushing the
blood into the aorta and pulmonary
artery.
The AV valves close, preventing
backflow of blood into the atria.

Ventricular diastole 

Both atria and ventricles relax, allowing
blood to flow into the heart from the
veins.
Semi-lunar valves shut to prevent the
blood from flowing „out‟.
INITIATION OF THE CARDIAC CYCLE
The SAN (or pacemaker) of the heart, located in the right
atrium, is the site of initiation of the cardiac cycle. The
SAN‟s muscle contracts and produces an electrical
impulse, which propagates through the atria muscles,
causing them to contract.
This impulse then „activates‟ another node, called the
AVN (atrioventricular node), which „relays‟ that impulse
to the ventricles, causing them to contract. The process
then repeats. Further detail on next page.
Diagram
NOTE:
It is important to
remember that
all of the cardiac
muscle cells
must contract in
unison during
the cardiac
cycle. A
coordination
centre called the
pacemaker or
SAN (sino-atrial
node) or
pacemaker helps
this happen.
This is the sequence of events for one cardiac
41 cycle:
1. The SAN is a myogenic muscle, which means it
doesn‟t need an impulse to „initiate‟. sends out a
wave of excitation across the nerves in the atria.
2. This causes the atria to contract.
3. The AVN picks up the signal and sends another
wave of excitation to go to the ventricles.
However, this wave experiences a „refractory
period‟ or „delay‟ (about 0.3s) so that the atria
and ventricles don‟t contract simultaneously.
4. Electrically excitable cells called Purkyne (or
Purkinje) fibres conduct the signal from the
AVN. They move into branches in the septum
called Bundles of His.
5. The ventricles contract upon reception of signal.
GRAPHICAL REPRESENTATION OF THE CARDIAC CYCLE
NOTE:
If the entire cycle on
the left 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.
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.
42
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.
Here are the factors that influence cardiac output:
Factor
Description
O2 and CO2
concentrations
Physical activity stimulates increased oxygenated blood flow. The oxygen deficiency in
cells results 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.
Parasympathetic During exercise, carotid (brain) artery walls may swell, stimulating baroreceptors
(„stretch‟ receptors) to send signals along the vagus nerve to the brain. This lowers
nerves
cardiac output to avoid overexertion.
Sympathetic
nerves
Conversely, during exercise, sympathetic nerves will stimulate SAN and AVN to
increase heart rate.
Adrenaline
Works the same as sympathetic nerves, except the hormone stimulates adrenoreceptors
(hormonal receptors) to achieve the stimulatory effect on SAN and AVN.
3.4: Discuss factors affecting blood pressure.
What FACTORS influence 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.
Vessels with small lumens such as arteries have high pressures. If that lumen becomes smaller, such as
due to the build-up of plaques (caused by „bad cholesterol‟), pressure becomes even higher. If diastolic
pressure becomes persistently high, this condition is known as HYPERTENSION.
Factor
Explanation
Exercise
Explained above. Stimulation of nitric oxide allows increased blood flow.
Cigarette smoking Tobacco contains nicotine, which constricts vessels and makes lumens smaller. They
also contain nitric oxides.
Adrenaline
Explained above. Released during stress or excitement, which raises blood pressure.
Atherosclerosis
The accumulation of LDL‟s (low density lipoproteins) in arterial lumens reduces the
area of the passageway for blood flow. Discussed further in Module 3.
43
3.5 – 3.7: Explain the role of haemoglobin in O2 and CO2 transport; describe oxygen dissociation curves
for adult haemoglobin; and explain the significance of the effect of O2 on oxygen dissociation curves
What is the role of HAEMOGLOBIN?
Haemoglobin (Hb) is a protein found in red
blood cells. It has a quaternary structure
consisting of two alpha-chains 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
molecule. When these oxygens are bound, it is
now referred to as oxyhaemoglobin (HbO2).
When oxygen is picked up in the lungs and
transported to body cells, the oxygen is then
„released‟ from the haemoglobin. It is said to
have dissociated from it.
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.
Carbon dioxide can also bind to haemoglobin,
forming carbaminohaemoglobin. This only
happens to 1/10th of CO2 in the blood.
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.
44
OXYGEN DISSOCIATION CURVES
Previously, we said that haemoglobin has a relatively high affinity for oxygen, meaning that oxygen
molecules will readily bind the haem groups when placed together. However, this only occurs when the
oxygen concentration is high enough. The main place where this binding occurs is in the alveoli. Since air
is a mixture of various gases, this value of just oxygen concentration is referred to as a partial pressure.
When partial pressures are high (such as in the alveoli), there is a greater percentage saturation of the
haemoglobin (more O2 bound to haemoglobin). When partial pressures are low (such as in respiring
muscle tissue), there is a lower percentage saturation of the haemoglobin.
Keep in mind that oxygen levels in haemoglobin are lower around body tissues because oxygen
dissociates from it to be taken up and used for aerobic respiration. There is also a certain amount of
oxygen that is never taken up into the haemoglobin. This is known as dead space.
On the graph to the left, you can see that curve
makes a sigmoidal shape, with the graph being
steeper at the beginning. This is because O2
saturation increases due to conformational changes
in the haemoglobin protein.
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.
Think of it being similar to phloem loading and
unloading, with the lungs being the source and
respiring tissues being the sink.
What is the BOHR EFFECT?
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 is 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.
45
HISTOLOGY OF ARTERIAL TISSUE
TS of carotid artery
When drawing, remember to show:





Cells or nuclei on innermost layer or endothelium
Layer of elastic fibres beneath endothelium (thick wavy lines)
Tunica media beneath elastic membrane
Middle layer (tunica media) with dense fibres and smooth muscle
Outer layer (tunica externa) with loose fibres and collagen tissue.
46
TOPIC 4: HOMEOSTASIS & HORMONAL ACTION
4.1: Discuss the concept of homeostasis.
What is HOMEOSTASIS?
Homeostasis is defined as the regulation of the body‟s internal environment in response to stimuli.
This response is called feedback. Feedback can occur in two 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.)
There are many factors that are controlled in homeostatic processes, including body temperature, watersalt levels and blood pH. 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.
Therefore, these factors usually have an optimal value, called a set point. For example, 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).
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.
47
4.2: Outline the general principles of hormonal action in animals.
What is the ENDOCRINE SYSTEM? What occurs during a HORMONAL ACTION?
Glands are tissues or organs that secrete a substance. There are two types:
Type of gland
Characteristics
Examples
Endocrine
Secretes substances on the
„inside‟. Ductless gland.
Adrenal glands, pituitary gland, ovaries, testes.
Exocrine
Secretes substances on the
„outside‟. Has ducts.
Salivary glands, sweat glands, mammary glands,
lacrimal (tear) glands.
Hormones are defined as secretions of ductless glands that are
directly released into the bloodstream.
They can act on cells in the vicinity or on distant target cells that
have receptors specific to the hormone. 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 long-term effects.
Hormones tend to come in two main categories:
Type of
hormone
Characteristics
Examples
Steroid
Can diffuse through phospholipid bilayer. Lipid-soluble.
Oestrogen, progesterone,
testosterone, cortisol
Nonsteroid
Cannot diffuse through phospholipid bilayer. Lipidinsoluble. Typically made of polypeptides or amino acids.
GH, ADH, adrenaline,
oxytocin, insulin, glucagon
FIRST AND SECOND MESSENGERS
Non-steroid hormones that we‟ll encounter, such as
adrenaline and glucagon, cannot diffuse through plasma
membranes. Instead, they bind to receptor proteins on
the plasma membranes.
This usually stimulates the activation of an enzyme
(sometimes by hydrolysing a protein and changing its
shape) This enzyme converts ATP to a compound
known as cyclic adenosine monophosphate (or just
cAMP).
cAMP is a second messenger, meaning that it will now
„relay‟ instructions to the target cell from the first
messenger, which was the hormone. In the case of
glucagon, this means to convert glycogen to glucose.
48
EXAMPLES OF HORMONES & GLANDS IN THE BODY
Observe the diagram below, which displays a layout of a few glands and their secreted hormones. Note
that some of these hormones are for supplementary knowledge:
Hormone
ADH
Adrenaline
Calcitonin
Cortisol
Dopamine
Erythropoeitin
FSH
Gastrin
GH
Glucagon
GnRH
Insulin
LH
Melatonin
Oestrogen
Oxytocin
Progesterone
Prolactin
Thrombopoietin
Thyroxine
Basic description of function
Assists with conservation of water, and water reabsorption in kidneys.
Increases heart rate and breathing rate in periods of stress or excitement.
Regulates levels of calcium and phosphate in blood, protects against bone loss.
Increases blood glucose level, and assists in tissue repair in times of stress.
A neurotransmitter that assists in cognitive function and reward.
Plays a key role in erythrocyte production, especially in low-oxygen environments.
Stimulates growth of eggs in ovary. Helps in regulation of menstrual cycle.
Stimulation of acid and mucosal secretions in stomach walls.
Acts on body tissues to stimulate growth.
Promotes breakdown of glycogen into glucose.
Stimulates the release of the hormones, FSH and LH.
Promotes conversion of glucose into glycogen.
Triggers the release of the egg from the ovary.
Controls the body‟s sleep-wake cycle.
Maturation of endometrium and egg cells.
Promotes contraction of uterine contractions during labour. Used for human bonding.
Maintenance of endometrium.
Colostrum production and development of mammary glands.
Promotes formation of thrombocytes (platelets) for blood clotting.
Regulates metabolic activity such as digestion, energy levels and keratinous growth.
49
4.3: Explain how insulin and glucagon regulate blood glucose concentration
What are the actions of INSULIN & GLUCAGON?
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 β-cells. β-cells secrete insulin in response rise in
blood glucose level. α cells secrete glucagon when blood glucose drops. Both cells act as receptors.
Insulin is required to transport glucose from the
bloodstream into cells‟ 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 above. Step by step, this is happening:
1) Glucagon in the blood binds to a protein-coupled receptor on the
liver cell‟s plasma membrane.
2) The protein is hydrolysed and „breaks off‟ a fragment, called a Gprotein, 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.
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.
50
4.4: Discuss the commercial use made of ethylene in supplying market-ready fruit..
What happens during RIPENING? What is ETHYLENE?
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).
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.
51
How does ETHYLENE affects 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.
52
TOPIC 5: THE KIDNEY, EXCRETION & OSMOREGULATION
5.1 & 5.2: Explain the need to remove nitrogenous and other excretory products from the body; &
describe the gross structure of the kidney and detailed structure of the nephron and blood vessels
Why is EXCRETION necessary? What is UREA?
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 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‟.
As seen in the diagram above, the amino group is extracted to form the very toxic ammonia. In the liver
cells, in a process called the ornithine cycle, ammonia, with the help of ATP, combines with carbon
dioxide to eventually form urea. Urea has a lower toxicity and though less soluble, can be easily
transported in the blood plasma.
The GROSS STRUCTURE of the KIDNEY
These are the main components of the kidney:
-
Renal artery – Carries blood from the aorta to
the kidneys
-
Renal vein – Carries blood from the kidney back
to the heart (vena cava)
-
Cortex – Outer part of the kidney, surrounded by
a fatty tissue capsule. Contains the glomerulus
and convoluted tubules of the nephron.
-
Medulla – Inner part of the kidney, containing
collecting ducts and loops of Henle.
-
Ureter – Transports urine to the bladder.
-
Renal pelvis – Acts as a funnel for collecting
urine flowing into the ureter.
53
What are NEPHRONS?
Nephrons are kidney sub-units consisting of capsules, tubules and ducts. 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 are
affected dependent on body water levels and temperature. Water can be conserved in the blood
this way.
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 diagram above shows the basic layout and functions segments of a renal nephron. It includes:

Glomerulus – A cluster of blood vessels that filters blood to the Bowman‟s capsule.

Bowman‟s (or glomerular) capsule – A cup-like sac that accepts the filtrate from glomerulus.

Proximal convoluted tubule (PCT) – Site of selective reabsorption.

Loop of Henle – Regulates the fluid and ion composition of the filtrate.

Distal convoluted tubule (DCT) – Connects the loop to the collecting duct.

Collecting duct – Responds to ADH by increasing wall permeability, allowing water to be
reabsorbed. Transports urine to the renal pelvis and ureter.
54
5.3 & 5.4: Explain the function of the kidney in terms of excretion and osmoregulation; & discuss the
clinical significance of the presence of glucose and protein in the urine.
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. Usually, the efferent arteriole would be much
lower in concentrations of urea, glucose, water and amino
acids, as these form the nephron filtrate due to
ULTRAFILTRATION.
Since the efferent arteriole lumen is smaller than the
afferent‟s, this builds up hydrostatic pressure in the
glomerulus. Smaller diameter increases ultrafiltration.
In the Proximal Convoluted Tubule (PCT)
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‟s
basement membrane, which acts as a „filter‟.
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.
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
(more on this later). This allows two K+ ions to
enter the cell, while at the same time allowing
three Na+ ions to transfer out.
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.
More than half of the water exits the PCT during this selective
reabsorption. Surprisingly, dissolved urea can also diffuse out
of the PCT, as well. Any filtrate that hasn‟t been reabsorbed
now flows to the Loop of Henle.
In the Loop of Henle
55
We only need enough water to dissolve urea
in the urine. After the PCT, the objective
now is continued water reabsorption into the
bloodstream.
The Loop of Henle has a descending and
ascending limb. In the ascending limb,
sodium and chloride ions are actively
transported into the cells and capillaries
(called vasa recta) surrounding the
descending limb.
When these ions arrive at the capillaries and
cells, they reduce their water potential.
The “counter-current” type of flow 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 is permeable. The ascending limb‟s walls are
impermeable, so no water is lost here.
In the Collecting Duct
The collecting duct is located at the end of
the nephron, just before urine is sent to the
renal pelvis and ureter.
The contents of the filtrate here are what
constitute urine: primarily water, urea and
any dissolved salts. Everything else should
have been reabsorbed.
Anti-diuretic hormone (or ADH) is a
hormone secreted by the posterior pituitary
gland. If the water potential of the blood is
low (dehydration) or the environment is
warm, ADH secretion is stimulated. If it is
high or the environment is cool, ADH
secretion is suppressed.
The role of ADH is to aid in water reabsorption into the bloodstream and osmoregulation. ADH interacts with the
plasma membranes of the collecting duct walls. If ADH is present in high amounts, water-transporting proteins called
aquaporins move from the cytoplasm to line the duct‟s walls (similar to insulin‟s effect on GLUT4), increasing
permeability to water and facilitating transport of water out of the duct. This water will possibly be used to form sweat.
If ADH is in low amounts, 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).
56
Here‟s a recap of what we know about ADH:
In low water potentials (or hot temperatures)
In high water potentials (or low temperatures)
ADH secretion stimulated.
ADH secretion suppressed.
Collecting duct walls increase permeability.
Collecting duct walls remain impermeable to water.
Aquaporins bind to surface membrane.
No aquaporins on surface membrane.
Water flows out of collecting duct.
Water remains in collecting duct.
Small volume of concentrated urine.
Large volume of dilute urine.
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.
PRESENCE OF PROTEINS & GLUCOSE IN URINE
Recall that urine is only supposed to comprise water, salts and urea. If any other solutes are present in a
urine sample, then this is an indication of an issue or disease of the kidneys or cardiovascular system.
These include:
Component Present
Reason
Disease Implied
Proteins
Proteins are too large to pass through the
basement membrane of the Bowman‟s
capsule. With very high pressure or
membrane damage, they can be present.
Kidney failure, hypertension
Glucose
Capillary blood glucose concentration may be
too high, limiting the diffusion of blood
glucose from the PCT.
Diabetes mellitus
57
HISTOLOGY OF KIDNEY TISSUE
Though kidney tissue may be almost indiscernible in a light microscope due to high density and proximity of the
nephrons, here are a few things to help with labels:

Bowman‟s capsules are large and globular, looking almost brain-like.

DCT‟s usually have less cytoplasm in their cells than PCT‟s and so appear to be more nuclear-dense. In better
resolutions, a slight „brush border‟ (villi) may be observed in PCT‟s.

Loops of Henle are typically tiny circles adjacent to each other.

The thin segment of the Loop allows for diffusion of water and sodium ions and hence has to be thin to facilitate
this.

The thick segment of the Loop allows active transport so there are more transport proteins. It is also impermeable
to water, so it has to be thicker.
58
TOPIC 6: NERVOUS COORDINATION
This particular topic is quite complex and introduces many new concepts. For ease, let‟s familiarize or refamiliarize ourselves with some terms:
Term
Definition
Neurone
The fundamental cell of the nervous system. They are able to receive sensory
input (sensory neurones), enact responses from muscles or glands (motor
neurones) or connect the two (relay neurones).
Nerve
A tissue consisting of a group of neurones.
Dorsal root ganglia
A group of cell bodies that transmits sensory input to roots of spinal nerves.
Dendron
A branch-like extension of a neurone that propagates impulses received from
other neurones. Smaller branches are called dendrites.
Axon
Long part of the neurone along which impulses are conducted.
Myelin
A protein wrapped around axons that acts as an insulator and also helps
speed up transmission of impulses by saltatory conduction.
Schwann cell
Cells that „wrap‟ around axons to produce a myelin sheath.
Node of Ranvier
A gap in the myelin sheath, between adjacent Schwann cells.
Stimulus
A detectable change that produces a response in an organism.
Sodium-potassium
pump
A protein located in many cells that creates an electrochemical gradient by
„exporting‟ 3 sodium ions for every 2 potassium ions „imported‟. This means
the inside of a cell is negative and outside is positive.
Resting potential
The state of a neuron relative to its surroundings when not stimulated or
involved in passage of an impulse. Its electrical potential is usually -70mV.
Action potential
The change in electrical potential that results in the passage of an impulse
along a neurone, e.g. to experience touch or move a muscle.
Threshold potential
The critical electrical potential where a stimulus occurs, but an action
potential has failed to generate, e.g. a very gentle touch.
Depolarization
The shift in electrical charge of a neurone to initiate or propagate an
electrical impulse.
Refractory period
A period when the electrical potential has a more negative value than resting
potential, causing a delay in the subsequent action potential. Occurs during
the phase of hyperpolarization.
Synapse
The junction between two neurones by which impulses may only pass with
the aid of a chemical neurotransmitter.
Acetylcholine (ACh)
A neurotransmitter used at neuro-muscular junctions (motor neurones).
Synapses that contain them are referred to as cholinergic.
Acetylcholinesterase
(AChE)
An enzyme that rapidly breaks down acetylcholine to stop transmission of an
impulse at a synapse.
59
6.1: Describe the structure of motor and sensory neurons
What is the difference between SENSORY and MOTOR NEURONES?
We‟ve established that the nervous system uses electrical impulses as very rapid messengers of sensory
input from receptor cells, and carrying instructions to muscles or glands (effectors). This information is
usually relayed to the spinal cord (via tissues adjacent to vertebrae called dorsal root ganglia) and the
brain.
The diagram to the left illustrates 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.
More on these later.
The diagram to the right illustrates 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.
60
6.2 & 6.3: Explain the role of nerve cell membranes in establishing and maintaining the resting potential;
describe the conduction of an action potential along the nerve cell membrane
What is 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 ‘saltcovered 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.
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.
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.
So to sum up resting potentials:







Neurones are still „active‟ even at rest, trying to establish and maintain a „rest potential‟ of -70mV.
The rest potential is attained by the „polarization‟ or difference in charge between the interior and exterior of
the cell.
The interior is negative and exterior is positive.
The exterior is positive because there are much more Na+ ions there. A smaller number of K+ ions are inside.
Hence, „salt-covered banana‟. There are also Cl- ions inside.
This difference happens because sodium-potassium pumps allow 3 Na+ ions to leave for every 2 K+ that enter.
Leaky channels permeable to K+ on the cell membrane also allow K+ ions to exit. So even more +ve charges
on outside.
This electrochemical gradient maintains the resting potential.
61
What is an 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!
Remember how there were „leaky‟ channels permeable to only K+? Some channels permeable to only Na+
are able to open with the right stimuli. For example, mechanically-gated channels in the skin open to
allow Na+ to enter the cell in response to touch.
So let‟s say that you get pinched. This pinch opens a Na+
channel in those local neurones that allow 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, a process called
DEPOLARIZATION.
But this doesn‟t happen as expected. Instead, more Na+
rushes in than expected (sometimes called
„overshooting‟), like an overbooked flight or a crowded
store on Black Friday. Of course, the Na+ channels will be
closed by now.
Along the membrane are channels that open in response to
this rise in voltage. These are known as voltage-gated
channels and are permeable to K+ ions. These are like
„guards‟ trying to disperse a crowd. As these channels
open, K+ ions quickly shuffle out, trying to reduce the
voltage of the cell back to the negative „rest potential‟.
This is called REPOLARIZATION.
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 K+
channels are closed by now. 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.
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.
62
So to sum up an action potential:
1.
2.
3.
4.
5.
6.
The axon membrane starts at its resting potential of -70 mV. All voltage-gated channels closed.
The stimulus triggers voltage-gated Na+ channels to open. Na+ diffuse into the axon.
More Na+ channels open, causing even more Na+ to diffuse in. (Depolarization)
The membrane potential reaches about +30 mV, and voltage-gated Na+ channels close.
Voltage-gated K+ channels now open, causing K+ to diffuse out of the axon. (Repolarization)
K+ keeps diffusing out until the membrane potential is slightly more negative (about -80 mV) than resting
potential (Hyperpolarization). K+ channels close.
7. Sodium-potassium pumps use ATP to return membrane potential to -70 mV (rest). During this time
(refractory period), another action potential cannot take place.
IMPULSE TRANSMISSION
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.
GRAPHING AN ACTION POTENTIAL
The graph below shows all of the different phases of an action potential, along with some annotations of voltagegated channels and the movement of ions during each phase. Observe the graph and match it with the summary at the
top of this page. Keep in mind that the axon cytoplasm at rest is negative (due to the excess of Na+ ions being pumped
out of it). The depolarization phase „overshoots‟ (which is why it goes above 0 mV) and the repolarization phase
„undershoots‟ (which is why it goes below resting potential).
NOTE: Not all changes
produce an action potential!
If the stimulus is very small
(for e.g. a sound below 20
Hz), it may not activate
enough Na+ channels to
cause depolarization. Thus,
no action potential develops.
It is said that the threshold
for an action potential is
between -50mV to -55 mV.
Only around then will
voltage-gated Na+ channels
be activated. This is called
the all-or-nothing law.
63
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 more strong 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.
SALTATORY CONDUCTION
The word “saltatory” means
“proceeding by leaps” as
opposed to gradual or
continuous movement.
So saltatory conduction
describes the way an electrical
impulse skips across nodes of
Ranvier down the full length of
an axon. This continues until
the impulse reaches its
destination.
Recall that a node of Ranvier is the gap between two myelin sheaths. Also recall that myelin is an
insulator, which means that Na+ and K+ ions cannot be pumped through these. This means that action
potentials cannot be generated in a myelinated segment of the axon! But they can be generated in a node
of Ranvier. Thus:

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.
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6.4 & 6.5: Explain synaptic transmission & outline the role of synapses
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, 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).
Although action potentials can undergo saltatory
conduction, they cannot „leap‟ across a synaptic cleft.
Instead, the action potential is propagated from the preto the postsynaptic neurone with the help of a secreted
chemical called a neurotransmitter, typically held in
vesicles. One of the main neurotransmitters is called
acetylcholine (or ACh), and synapses that secrete ACh
are called cholinergic synapses.
A synapse located between a motor neurone and muscle
fibre is called a neuromuscular junction. A signal from
such a synapse would cause muscle fibres to contract.
Another neurotransmitter is GABA, which is in the brain
cells. Depressants such as alcohol inhibit the production
of GABA, producing the notable symptoms of slurred
speech, delayed reaction time, reduction in motor skills,
and dehydration due to suppressed ADH secretion.
What are some FUNCTIONS OF SYNAPSES?
Function
Explanation
Neural summation
Summation is defined as the cumulative effect of several electrical impulses at a
synapse. For example, when driving a car, many decisions must be made such as
braking, turning, accelerating. Summation ensures that many different sectors of the
brain are „firing‟ to decide which moves to make.
Learning process
The brain „records‟ data from receiving multiple signals from the various sense
organs. Synapses allows these „memories‟ to coordinate and form new ideas. The
more learning that occurs, the more these signals can „interact‟.
Directed transmission
Synapses direct impulses to travel to specific neurone pathways. This is important
when doing precise actions.
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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. Let‟s outline what happens, correlated with the diagram on the right:
1. The action potential arrives from the
axon.
2. Upon arrival of the action potential,
channels open to allow Na+ and Ca2+ ions
to enter the bulb‟s cytoplasm. The calcium
ions stimulate movement of the vesicles
towards the cleft and release their contents
via exocytosis. Rapid diffusion of ACh
occurs across the cleft.
3. On the postsynaptic membrane, there are
receptors that are activated when an ACh
molecule binds with it. 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‟.
4. An enzyme called Acetylcholinesterase
(AChE) breaks down ACh into acetate
and choline. This is done to „reset‟ the
entire process and ensure that synapses
don‟t keep „firing‟ constantly (this can
possibly be seen with people who suffer
from Parkinson‟s disease).
5. The choline is returned to the
presynaptic bulb, where it re-forms ACh
after using ATP to combine with acetyl
CoA.
A NOTE ON NICOTINE AND PESTICIDES
Nicotine, like ACh, from cigarettes can bind to postsynaptic
membrane receptors but, unlike ACh, cannot be broken down
by AChE. As a result, the synapse keeps generating a high
frequency of action potentials. This is why nicotine is
considered a STIMULANT.
Some insecticides and nerve gases contain malathion, which
inhibit AChE by irreversibly deactivating it. Because ACh
cannot break down, there is a rapid build-up and action
potentials occur continuously, eventually leading to organ
failure and death.
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MODULE THREE – APPLICATIONS OF BIOLOGY
THIS MODULE CONTAINS FOUR TOPICS:
1. HEALTH AND DISEASE
2. IMMUNOLOGY
3. SOCIAL AND PREVENTATIVE MEDICINE
4. SUBSTANCE ABUSE
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TOPIC 1: HEALTH AND DISEASE
1.1 & 1.2: Discuss the meaning of the term „health‟; and explain the categories of disease and illness
Before delving into this module, it is important to understand how the terms HEALTH and DISEASE
are defined. The World Health Organization (WHO) defines each as:


Health is a state of complete physical, mental and social well-being.
Disease is the impairment of the functioning of the body and mind.
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 noncommunicable, such as lifestyle and hereditary diseases, meaning that they cannot be spread from one
individual to another.
Categories of disease (and examples) include:
Category
Description
Examples
Physical
Occurs as a result of a physiological malfunction in the
body, usually impairment of an organ or system.
Diabetes, coronary heart disease,
asthma, osteoarthritis
Mental
Occurs due to an impairment of the mind or
deterioration of the tissues and matter within.
Alzheimer‟s disease, clinical
depression, schizophrenia
Chronic
A disease that is long-term, even lasting for a lifetime.
Chronic bronchitis, diabetes
Infectious
Caused by the introduction of pathogens (viruses,
bacteria, fungi, protozoans) to the body.
Dengue fever, malaria, cholera,
tuberculosis (TB)
Social
Caused by the individual living or working within an
environment prone to contamination by pollutants (e.g.
cigarette smoke) and pathogens, or not having access
to a balanced diet.
Tuberculosis, cholera, scurvy,
rickets, night blindness
Degenerative
Caused by the gradual loss of function of tissues and
organs.
Alzheimer‟s disease, multiple
sclerosis, osteoarthritis
Hereditary
Caused by inheriting alleles that translate to
malfunctioning proteins.
Sickle cell anaemia, haemophilia,
cystic fibrosis (CF)
Self-inflicted
Also referred to as lifestyle diseases. These occur due
to the intake of excess nutrition or drugs.
Liver cirrhosis, lung cancer,
coronary heart disease
Deficiency
Occurs due to the lack of a particular nutrient in the
diet.
Night blindness, scurvy, cholera,
rickets, kwashiorkor.
NOTE: It is important to realize that diseases are not restricted to a single category. For e.g.


Cholera can be classed as physical, social and infectious.
Diabetes (Type II) can be classed as physical, social, chronic and self-inflicted.
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1.3: Analyse data involving incidence and mortality rates of disease.
How does one ASSESS RISK OF A DISEASE?
In order to study diseases and
assess their immediate
importance and risk, as well as
observe them with respect to
various epidemiological
factors such as sex, age and
geographical distribution,
certain sets of data must be
assessed and compared:
Factor
Definition
Incidence
The number of new cases of a disease in a given time period.
Prevalence
The number of people with a disease in the population at a current time.
Mortality rate
The number of people die from a particular disease (usually per year)
‟
Using the above graph as an example of data collection, we can observe that:

The number of HIV cases (per 100,000) generally increased from 1982 to 2003, with small dips and
fluctuations along the time period. One such dip would have been around 2001. After 2007, there was a
sharp decline in cases, most likely due to increased awareness and antiviral technology.

The number of AIDS cases was always less than HIV cases due to a dormancy period before AIDS
develops, or that some cases may die before AIDS develops.

AIDS deaths (mortality rate) are lower than AIDS cases, especially after 2001, possibly due to earlier
detection and antibiotic treatment of opportunistic infections.
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TOPIC 2: IMMUNOLOGY
The topic of immunology is quite complex, so it is beneficial to familiarize and refamiliarize with some
terms before reading about the topic.
Term
Definition
Pathogen
A disease-causing microorganism (bacteria, virus, fungi, protozoan).
Vector
An organism that transmits a pathogen from one organism to another (e.g. mosquito)
Antigen
A foreign substance which induces a specific immune response in the body.
Antibodies
An immunoglobulin. A blood glycoprotein that counteracts an antigen, destroying it.
Phagocyte
A white blood cell capable of absorbing and engulfing pathogens. These include
monocytes, macrophages and neutrophils.
Lymphocyte
A white blood cell that originates in the bone marrow and either matures in the bone
marrow (B-lymphocytes) or the thymus gland (T-lymphocytes).
Humoral response An immune response mediated by antibodies produced by B-lymphocytes.
Cell-mediated
response
An immune response not mediated by antibodies, but instead by phagocytes and Tlymphocytes.
Memory cell
A lymphocyte capable of responding to antigens long after its production.
Histamine
A compound released during inflammatory or allergic responses.
Mast cell
A cell that has granules containing histamines and heparin (a blood thinner).
APC
Antigen-presenting cell. An immune cell (usually a phagocyte) that processes and
presents antigens to lymphocytes to initiate an immune response.
Clonal
proliferation
Mitosis and multiplication of lymphocytes after recognition of an antigen, in order to
counter it.
Complements
Proteins synthesized in the liver that enhance immune responses & phagocytosis.
Passive immunity
Short-term immunity that results from the introduction of antibodies from another
source.
Active immunity
Long-term immunity that results from the production of antibodies from an immune
response (sometimes acquired artificially from a vaccine)
Monoclonal
antibodies
Antibodies produced from a cloned white blood cell fused with a cancer cell. Usually
used for pregnancy tests, AIDS diagnosis, detect tumours, and cancer treatment.
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2.1 - 2.4: Define the term, “immune response”; and distinguish between humoral and cell-mediated
responses; the role of memory cells; the origin and maturation of B- and T- lymphocytes
What are the various TYPES OF IMMUNE RESPONSES?
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 is referred to as a „foreign‟ substance or
„non-self‟ substance. These non-self substances are usually contain structures called ANTIGENS, which
the immune system can detect. Think of an antigen as something that triggers a burglar alarm.
The two main types of white blood cells involved are
PHAGOCYTES and LYMPHOCYTES.
Phagocytes patrol the bloodstream (and can even leave) in search
of non-self substances. When they encounter non-self substances,
they engulf them. They may also engulf their antigens and
„present‟ these antigens to other immune cells such as T-helpers
(more on this later). They are usually short-lived.
Lymphocytes originate in the bone marrow. B-cells mature in
the bone marrow while T-cells mature in the thymus gland.
-
B-lymphocytes multiply and secrete antibodies, which
counter non-self substances.
T-lymphocytes can be „helper‟ cells, which stimulate Bcells and phagocytes. Or „killer‟ cells, which destroy the
cells infected by the pathogen.
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).
T killer cells are our primary
defense against viruses. They
usually secrete hydrogen peroxide
into cells to destroy them with the
viruses within. The chemical that
the T helper cells secrete to
stimulate other cells are called
cytokines.
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So let‟s compare the B- and T-lymphocytes once again:
Factor
B-lymphocytes
T-lymphocytes
Originate where?
Bone marrow
Bone marrow
Mature where?
Bone marrow
Thymus gland
Which response?
Humoral (rapid response))
Cell-mediated (delayed response)
Secretory products
Antibodies
Cytokines from T helper cells
Differentiate into?
Antibody-secreting plasma cells and
memory cells
T killer cells, T helper cells,
memory cells (and more)
Let‟s look at both immune responses a bit more in-depth:
The B-cells experience a specific binding
response, which means that the antigen must be in
contact with the receptor on the B-cell surface
membrane (similar to an enzyme‟s lock and key
mechanism).
T-cells utilize an APC (or antigen presenting cell),
which will have the antigen attached to it (as in Bcells or dendritic white blood cells) , or engulfed
within it (such as phagocytes). T-helpers and Tkillers will then bind to these antigens.
Both B- and T-cells experience clonal proliferation,
which means one clone is first selected and then
divided multiple times to produce a large number
of cells.
Both B- and T-cells produce MEMORY CELLS,
which provide long-term immunity and can
provide rapid responses to antigens long after their
production. As a result, the pathogens can be killed
more efficiently during future infections.
While B-cells produce antibodies to kill pathogens,
T killer cells must destroy the entire infected cell,
causing them to undergo lysis.
Think of T killer cells as close quarter combatants,
B-cells as snipers, T helper cells as messengers,
and APC‟s as spies/recon. Memory cells are
veterans who have already seen war.
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2.5: Describe the mode of action for phagocytes.
What do PHAGOCYTES do?
Phagocytes are large white blood cells that have a
MULTI-LOBED nucleus and operate by ingesting
pathogens and non-self substances into their
cytoplasm. They patrol the bloodstream and
surrounding tissues (such as lung alveoli) using
extensions of its plasma membrane called
PSEUDOPODIA (Latin for „false foot‟).
They ingest the pathogens via the process of
ENDOCYTOSIS by extending and evaginating
(wrapping) the pseudopodia around them. After the
pathogen is ingested into a „sac‟ called a
PHAGOSOME, organelles called LYSOSOMES
secrete enzymes to digest the material. Digested
products can then exit the cell via EXOCYTOSIS.
However, sometimes the phagocyte will lyse and
release chemicals called CYTOKINES to attract
new white blood cells to fight the pathogens.
NOTE: Recall that phagocytes can work as APC‟s
to assist T-lymphocytes when they ingest the
pathogen and its antigen.
What is the INFLAMMATORY RESPONSE?
Cytokines are able to interact with blood proteins
known as COMPLEMENTS. These complements help
activate enzymes in a complex series of enzyme
reactions called the cascade process that lead to
swelling, fever and redness (inflammation).
Cells known as MAST CELLS release a chemical
known as HISTAMINE, which 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. This is why an
inflamed area looks red. Dead, lysed white blood cells
may remain in the area, forming PUS.
Mast cells and histamines are unfortunately also
responsible for allergies and autoimmune diseases (e.g.
multiple sclerosis), where the immune system is
misdirected to attack the body‟s own cells.
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2.6: Relate the molecular structure of a typical antibody molecule to its function.
How does an ANTIBODY work?
Antibodies (or immunoglobulins) are blood
glycoproteins secreted by B-LYMPHOCYTES during
the HUMORAL RESPONSE of the immune system.
They consist of light chains and heavy polypeptide
chains connected to each other by DISULPHIDE bonds.
Each antibody is specific to the antigen that attaches to
it, similar to enzymes and substrates. There is one region
that is common for all antibodies simply called the
CONSTANT REGION. This does not change, no
matter the type of antibody. What distinguishes each
antibody is the VARIABLE REGION, which contains
a specific antigen-binding receptor for its antigen
counterpart. Think of variable regions as analogous to R
groups in amino acids.
Each antigen-binding receptor is also called a
PARATOPE. These bind to regions on the antigen
called EPITOPES. This may either neutralize the
antigen or call phagocytes to action to destroy it.
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 & 8: State what is meant by a monoclonal antibody; & describe their use in diagnosis and treatment.
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.
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 B-cells, 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 Bcells quickly, as they quickly replenish. This quick
targeted production makes monoclonal antibodies an
efficient method of cancer treatment.
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How do PREGNANCY TESTS work?
Most pregnancy tests use a dip stick that comes into
contact with the pregnant woman‟s urine. If you recall, a
woman produces a hormone known as hCG to maintain
progesterone production during gestation.
I – Here is the reaction zone coated with mobile mouse
monoclonal antibodies that can specifically bind to hCG.
These have an enzyme that activates a coloured DYE
(usually blue) attached to them, so if hCG is present, the
antibodies can carry the dye. If not, no dye is activated
and the urine and antibodies „wash‟ through.
II – This is the result window. This contains fixed hCG
antibodies. If hCG is present, the antibodies will bind to
the dye in I and produce a blue line to indicate a positive
result for pregnancy. If no hCG, no dye activates and
this window is blank.
III - A control window is present that reacts with the
urine to ensure the dip stick is functional. This happens
with a positive or negative result. This window contains
anti-mouse antibodies and dye, so these will activate
when binding to the mouse antibodies in I.
NOTE: Keep in mind that the control region with
the anti-mouse antibodies are NOT specific to hCG,
unlike the regions in I and II. Also keep in mind
that monoclonal antibodies are made in mice.
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.
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2.9 & 2.10: Distinguish between active and passive immunity, natural and artificial immunity; and
explain the role of vaccination in providing immunity.
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).
Using COVID-19 as an example, let‟s break down four types of immunity:
Type
Definition / Note
Naturally
acquired active
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.
Natural passive
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.
Artificially
acquired active
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 longterm immunity.
Therefore, artificially acquired active immunity is obtained from the primary
response due to intentional exposure to the antigen/pathogen.
Artificial passive
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 long-term 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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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:




Live attenuated vaccines – containing weakened forms of pathogens.
Inactivated vaccines – containing pathogens that cannot reproduce but can still be detected.
Subunit vaccines – containing a detectable component (e.g. viral spike protein) of the pathogen.
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:
Reason
Response
Viruses mutate
often.
Viruses replicate rapidly, which increases chances of mutation, leading to variants.
The antibodies produced by vaccines thus cannot detect mutant antigens fast enough.
However, some vaccines (especially subunit and mRNA) tend to focus on antigens
that have the lowest risk of mutation.
Vaccines cause
allergic
reactions.
Severe allergic reactions (or anaphylaxis) to vaccines are rare. Physicians should
always be consulted before getting a vaccine. Antihistamines can be used to mitigate
allergic reactions in some cases.
Fortunately, there may be more than one brand or make of vaccine for critical
diseases, some not containing allergic components.
The immunocompromised
are at risk of
getting ill with
the vaccine.
Very young children or older people with severe co-morbidities often have concerns
about taking vaccines due to concerns about not being able to withstand the primary
immune response. This is a legitimate concern and once again, physicians should
advise those individuals of risk on a case by case basis.
Spread of
misinformation
This is a sensitive topic. Most vaccines comply by religious rules (such as being
halal). There had once been a popular claim that vaccines cause autism, which turned
out to be a hoax. Education and awareness campaigns should be prominent enough to
penetrate vaccine-hesitant populations without making the decision to get vaccinated
unsavoury. As said, this is a sensitive and complex topic.
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TOPIC 3: SOCIAL AND PREVENTATIVE MEDICINE
3.1: Discuss the causative relationship among diet, obesity and diabetes.
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
(cardiovascular diseases), kidney failure and fatty liver disease.
.
A measurement called BMI (Body Mass Index) is sometimes used to
define obesity. The calculation is done by using the formula to the left. 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.
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).
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.

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.
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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 buildup 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.
3.2: Describe the effects of fats on the cardiovascular system.
What causes ATHEROSCLEROSIS and CORONARY HEART DISEASE (CHD)?
Recall that arteries are high-pressure blood vessels with thick muscular walls and small lumens. They
transport blood away from the heart and towards body cells. This blood contains oxygen used for aerobic
respiration.
ATHEROSCLEROSIS can lead to these arteries becoming blocked
due to accumulated deposits of LDL‟s (low-density lipoproteins that
are high in fat content, commonly known as „bad cholesterol‟) and
chemicals from TOBACCO smoke. These form a PLAQUE that
adheres to the arterial walls, reducing the lumen size and limiting blood
flow. This also increases blood pressure.
High pressure blood flow can make the plaque break, causing blood to
enter and form a clot called a CORONARY THROMBOSIS. This
further reduces lumen size and reducing blood flow to body cells.
Worse yet, this blood clot can fracture and enter a coronary artery that
supplies blood to the heart muscles, thus cutting off their oxygen
supply. This is called a MYOCARDIAL INFARCTION and is what
leads to a heart attack.
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.
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What are HYPERTENSION and STROKE?
Hypertension and stroke are generally associated with atherosclerosis. Recall that atherosclerosis causes
arterial lumen size to decreases.
This decrease in size means that less area is available for blood to
flow to body cells unless the heart can apply more force or beats
per minute. A decrease in area and an increase in force equates
elevated blood pressure levels or HYPERTENSION This is
usually considered to be above 140/90 mm Hg (the numbers
respectively representing systolic and diastolic pressure).
A STROKE is caused by acute damage to the brain. Almost
similar to a myocardial infarction, a ruptured coronary thrombosis
can become lodged in a blood vessel connected to the brain, thus
depriving it of oxygen and glucose. The person can die if this
carries on for long enough. If they survive, it is likely their
memory and motor skills are affected, including paralysis.
3.3: Discuss the consequences of exercise on the body & the benefits of maintaining a physically fit body.
Exercise can be defined as activity requiring physical effort, carried out to sustain health and fitness.
Exercise has numerous long-term and short-term physical benefits, but also mental as it is known to
release chemicals called endorphins from the brain, which improve mood and well-being.
A major long-term effect to observe is the increase in VO2 max. This is the maximum rate of oxygen use
during aerobic respiration before switching over to anaerobic respiration. In other words, muscles and
other body cells can use oxygen quickly to allow pyruvate to turn into ATP. A high VO2 max means that
the individual can exercise at a faster rate without switching to anaerobic respiration to produce lactate.
Long-term consequences of exercise:
Aspect
Long-term effect
Cardiac efficiency
Increase in red blood cell count and oxygen-carrying capacity.
Increase in heart muscle size and stroke volume (vol. of blood per heartbeat)
Increase in VO2 max to increase efficiency of oxygen usage by muscles.
Muscles
Increase in number and size of mitochondria
Increase in cross-sectional area of muscles, as well as glycogen storage.
Increase in number of capillaries in the muscle, improving oxygen supply
Increase in myoglobin pigment, leading to increased O2 storage in muscle
Reducing risk of
NCD‟s
Maintaining a healthy body mass reduces risk of chronic NCD‟s such as Type II
diabetes, coronary heart disease, hypertension, stroke and kidney failure.
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There are also numerous short-term effects of exercise, which are usually physiological changes and
adaptations that occur to supply muscles with more oxygenated blood and increase removal of CO2.
Short-term consequences of exercise:
Aspect
Short-term effect
Gaseous
exchange
Increase in breathing rate and tidal volume (amt of air circulating in lungs)
Increases diaphragm and intercostal muscle contractions; caused by increase in acidity
detected by chemoreceptors
Circulation
Increase in heart rate due to adrenaline secretion and nerve impulse activity in pacemaker.
Secretion of nitric oxide from blood vessels due to low oxygen levels, which dilates
arterioles and increases blood flow to the heart (cardiac output) and to the muscles.
Dilation of arterioles lead to heat loss through the skin (leading to „flushed‟ appearance).
3.4 & 3.5: Describe the mechanisms of infection & modes of transmission for viral diseases and their
causative agents
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.
Here are a few examples of types of pathogens and their infectious diseases:
Pathogen Type
Example diseases
Bacterium
Cholera , Tuberculosis, Typhoid, Tetanus, Leptospirosis, Syphilis
Virus
Dengue fever, AIDS, Herpes, Cervical Cancer, Influenza
Fungus
Ringworm, Candidiasis (yeast infections), Athlete‟s foot (T. crucris infection)
Protozoa / Protoctist
Malaria, Chagas disease, African Sleeping Sickness
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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What is DENGUE FEVER?
Dengue fever is a viral mosquito-borne disease that usually occurs in tropical areas of the world. 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 vector for the dengue virus is the female
Aedes aegypti mosquito, which injects its
proboscis (mouthparts) into the skin and draws
blood from a vessel. Its saliva enables this to
happen without clotting. If the bitten person has
the dengue virus in their skin cells, the mosquito
will draw it in as well and become a vector.
If the mosquito then bites an uninfected person,
the virus will enter their skin cells. After an
incubation period of 4 - 10 days, signs and
symptoms start to appear.
How do VIRUSES ENTER CELLS AND SPREAD in the body?
Observe the diagram to the right:
1. Attachment – Viral spike proteins bind with
receptors on cell surface membrane to allow entry.
2. Entry – Virus enters cell via endocytosis, where
it is taken into by a vesicle. The capsid breaks
down, releasing RNA.
3. Replication and Gene Expression – The RNA
uses the enzyme, reverse transcriptase, to make
multiple DNA copies of itself.
4. Assembly - Synthesis of new viral proteins is
done in the rough ER and ribosomes (translation)
5. Release – New viruses are packaged into
vesicles by the Golgi body and fuse with the cell‟s
plasma membrane to produce its phospholipid
coat. The virus then exits via exocytosis.
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.
HIV is worse because that host cell is usually a T helper cell called a CD4 cell. The cells are eventually destroyed,
compromising the immune system to pathogens and opportunistic infections. More on this later.
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What is AIDS?
AIDS is the most advanced stage of HIV
infection. It is a disease of the immune system,
where the HIV (Human Immunodeficiency
Virus) invades helper T lymphocytes called
CD4 cells. Recall that helper T cells help signal
to phagocytes and other lymphocytes to rally
together to attack an infection. Not having these
leaves a lot of these other white blood cells „in
the dark‟. The T-cells‟ nucleic genetic code is
rewritten to produce even more HIV copies, just
as seen on the previous page.
When the helper T cell count falls below 200
cells per mm3 of blood, the patient is now said to
have AIDS (Acquired Immune Deficiency
Syndrome). The AIDS patient‟s immune system
now is highly compromised and produces
serious complications if the patient contracts
another viral infection, known as an
opportunistic infection, such as influenza.
Symptoms of HIV/AIDS include: persistent
fever, severe weight loss (wasting), recurrent
pneumonia, lesions, persistent diarrhoea.
HIV can be transmitted from person to
person by means of bodily fluid exchange,
such as:




Unprotected sexual intercourse –
due to exposure to semen, vaginal
fluids and blood (if vaginal or anal
linings are damaged)
Through the placenta – from
mother to foetus if antiretroviral
therapy isn‟t employed. Can also
occur during childbirth.
Breast milk – from HIV-infected
mothers, though the level of risk is
unknown
Blood transfusions – due to transfer
of contaminated blood during
surgeries or while sharing
hypodermic needles.
HIV can be detected by doing blood tests. However, it has an incubation period of about 3 months, which
means that a person could have contracted HIV two months ago and still test HIV-negative. There is
currently no vaccine for HIV/AIDS.
However, antiviral drugs such as AZT (azidothymidine) can be used to preserve T-cell count and prolong
life. These drugs are expensive, unfortunately, and not affordable to the common citizen.
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3.6: Discuss reasons for the regional distribution of AIDS, diabetes and cancer.
What affects regional distribution of AIDS and DIABETES?
With respect to total HIV/AIDS population in the Caribbean, the top three countries are Haiti (1.9%),
Jamaica (1.7%), and Trinidad and Tobago (1.5%). In sub-Saharan Africa, prevalence is 5.0% while in
East Asia, it is only 0.1%.
The factors that affect this distribution include the following:
Factor
Notes
Culture or lifestyle
Due to stigma and unwillingness to admit HIV status or get tested, many people
with multiple partners unknowingly transmit the virus. Some cultures encourage
more liberal views on sexual freedom, while others discourage use of
contraception (condoms). All of this encourages spread.
Long incubation
period
Since HIV may not be detected by blood tests until 3 months into incubation, an
HIV-positive person can unknowingly spread it.
Ease of travel
Wherever there is a large number of tourists, especially those partaking in „sex
tourism‟ with locals, the virus can quickly spread to local populations.
Availability of
drugs and condoms
Drugs that help mitigate the effects of HIV (e.g. AZT) are expensive and hard to
obtain. In some countries, condoms are not commonly available
Poverty
Poverty and high unemployment rates may encourage sex work, which facilitates
spread if done irresponsibly. Some countries may not be able to avoid
antiretroviral therapy for patients and pregnant mothers.
Lack of education
Citizens of some countries simply do not understand how the virus is transmitted
or may have false beliefs in „curing‟ it (e.g. intercourse with virgins). Some may
even believe that heterosexuals cannot contract HIV.
And these are factors which influence prevalence of Type II diabetes:
Factor
Notes
Diet
In some countries, „fast food‟ is the most economic and convenient option. Some
cultures also prioritize foods that are high in refined carbohydrates and LDL‟s
(e.g. „doubles‟ in Trinidad). Overconsumption of these foods leads to obesity,
which greatly increases risk of diabetes.
Sedentary lifestyle
Countries or areas with long hours of office work and no time for outdoor
recreation raises risk of obesity and diabetes.
Prenatal
malnutrition
An ongoing study has linked malnourished mothers to children who are more
likely to develop Type II diabetes later on in life.
Ethnicity and
genetics
People of African and Asian descent are observed to more commonly develop
Type II diabetes.
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What affects regional distribution of CANCER?
Cancer is a general term given to a group of
diseases where cells in a certain organ or tissue
uncontrollably divide. These form lumps called
tumours, which can then break away and form
tumours in other parts of the body, a process
called metastasis. Bear in mind that tumours can
be benign, which means that they are harmless.
Age influences cancer risk, as the cancer cell is
usually formed due to a random mutation.
Certain repressor genes help prevent these
mutations, but those can also mutate and lose
function if enough time passes.
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)
Going with this, we can also deduce what affects regional distribution of cancer cases:
Factor
Notes
Environmental
hazards
Chemicals from factories or buildings such as asbestos and vinyl chloride can
affect employees or tenants over time. Also, places that allow exposure to secondhand smoking.
Outdoor environments subjected to frequent UV radiation (from the Sun) without
high SPF sunscreen can increase risk of melanoma (skin cancer). Indoor ones
subjected to ionizing radiation (e.g. nuclear power plants, labs or clinics) should
also take the proper precautions to avoid exposure.
Food additives
Regions that use food additives that contain benzoates may be at risk of cancers.
Viruses
HPV, which causes cervical cancer, can be transmitted via sexual intercourse. In
areas where people usually have multiple partners and condom use is rare, this
type of cancer can quickly spread to women.
Genetic factors
Alleles that express risk of developing certain cancers can be higher in
concentration in certain countries. For example, the Caribbean has a relatively
high amount of alleles that result in mutations leading to breast cancer.
Failure to seek
treatment on time
Since mortality rates are affected by how quickly cancer is detected and treated, it
is important for a patient to observe their symptoms and visit a physician for
screening (e.g. mammograms for breast cancer) or biopsies (tissue samples).
Unfortunately, in many developing nations, this is very difficult for the common
citizen and they may not seek treatment until it has metastasized.
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3.7: Assess the impact of communicable and non-communicable diseases regionally.
What are some IMPACTS OF DISEASES ON SOCIETY?
Factors are listed and explained below:
Factor
Explanation
Economy
If a disease becomes uncommonly prevalent, it puts a strain on State-funded
medical care. Charities and volunteers may have to step in to reduce the financial
impact. Money has to also be diverted to awareness campaigns for the disease,
as well as the purchase of PPE (personal protective equipment).
Patients won‟t be able to work while ill, so there will be reduced labour force and
overall drop in productivity.
In cases where nationwide quarantines and lockdowns are necessary for
communicable diseases, this can result in businesses closing down.
Trade relations
Due to decrease in productivity, there will be reduced income from exports of
locally manufactured goods.
Tourism sectors may suffer due to stigma of contagious diseases.
Food availability
If the agricultural sector is affected by reduction in labour force, there will be
food shortages and increase in food prices as a result.
Household income
There will be high costs for privatized healthcare and medical bills, in addition
to reduced income from unemployment if a breadwinner has fallen ill or become
debilitated by their disease (e.g. a stroke)
Quality of life
The emotional toll of illness and death reduces the quality of life for either
individuals or families. In the case of lockdowns, being quarantined for lengthy
periods has a psychological toll.
Positive change and
awareness
When a disease, especially one that is self-inflicted, becomes prevalent in a
society, many individuals make a positive change in their lifestyles to avoid
developing that disease.
This includes changing their diets to include less LDL‟s and carbohydrates,
quitting smoking, exercising more often or, in the case of infectious diseases,
washing their hands more often.
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3.8: Discuss roles of social, economic & biological factors in the prevention & control of viral infections.
What are the roles of factors involved in PREVENTION & CONTROL OF VIRAL INFECTIONS?
Factor
Explanation
Quarantine and selfquarantine
Previously explained. Quarantines can limit the spread of a viral infection,
especially if caused by droplet infection, but can also have a severe effect on
businesses and household earnings.
(social & economic)
Those aware of their symptoms should practice staying away from the
workplace and others.
Resting at home is the best option when no vaccine or drug can be prescribed,
such as with dengue fever.
PPE
(biological)
Safe sex
(social)
Sanitation
(economic)
Pest control
(economic)
The use of PPE, such as masks, help limit the spread of viruses via droplet
infection. Note that they do not prevent the wearer from contracting it, as
viruses are very small and can sometimes pass through the material of the
mask.
By being faithful to one‟s partner, limiting partners or ensuring condoms are
worn during sexual intercourse, viral STI‟s can be prevented, such as HIV and
herpes.
Workplaces and public buildings should be sanitized with disinfectants on a
regular basis. Keeping refuse from piling up also reduces chance of vector
breeding.
Some viruses are spread via insect and animal vectors, such as dengue virus
and yellow fever virus. By clearing out stagnant water sources, mosquitoes
have no breeding grounds for their eggs.
Insecticides could be sprayed in areas where mosquito-borne viruses are
common.
Vaccination
(biological)
Regular screening
(biological)
Awareness campaigns
(economic)
Antiviral drugs
(biological)
Individuals who are vaccinated against a virus are much less likely to contract
that virus as they have already developed antibodies to produce a rapid
immune response against it. This limits spread of that viral infection in
populations.
The spread of viruses, such as HIV, can be limited if sexually active people get
their blood screened after each new sexual partner.
Campaigns to disseminate information to the public is always helpful in
educating about limiting spread and infection.
Antiviral drugs and monoclonal antibodies can be used to treat some viral
infections, if available.
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TOPIC 4: SUBSTANCE ABUSE
4.1 & 4.2: Discuss the meaning of term “drug abuse”; psychological and physical dependence
What is a DRUG, and DRUG ABUSE?
A drug is defined as an externally administered substance that alters the body‟s physiology.
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).
Drugs can be legal or illegal and may fall into four main categories:




Stimulants, which increase nervous activity (e.g. nicotine, cocaine, caffeine)
Depressants, which reduce function and nervous activity (e.g. alcohol, codeine)
Hallucinogens, which cause perceptual anomalies (e.g. cannabis, LSD, PCP)
Analgesics or Opioids, which act as pain relievers (e.g. heroin, morphine, fentanyl)
Drug abuse occurs when the use of the drug
leads to physiological or psychological harm
to the user, their family or society at large. This
can happen with illegal drugs, such as cocaine,
which would lead to drug dependency,
withdrawal symptoms and possibly, overdose.
The progressive decrease in response to a drug is
called tolerance. This can also happen with
legal drugs such as antibiotics, antidepressants,
such as the brands Prozac and Xanax, where the
drug may be used for therapeutic reasons but
have addictive mood-changing properties. A
good example of this is the depressant, codeine,
which is an ingredient in the mood-altering
drink, Lean.
What are the types of DRUG DEPENDENCY?
Observe the cases below:
1) Sandra is 40 years old and uses heroin in two to four injections, four to twelve hours apart. When
she goes for longer than twelve hours without heroin, she feels sick and becomes anxious.
2) Wayne is 16 years old and smokes cannabis with his friends. He often goes without cannabis for
days at a time, with no ill effects. However, after a week has passed, he feels a strong urge to
smoke, especially when he feels depressed or bored.
Sandra shows PHYSICAL dependence on the drug due to strong cravings and withdrawal symptoms, such
as nausea and restlessness if the drug is abrupt reduced or stopped for short periods. Symptoms worsen as
frequency of drug abuse increases and tolerance of the drug builds up.
Wayne shows PSYCHOLOGICAL dependence on the drug due to lack of strong withdrawal symptoms
and cravings, ability to go prolonged periods without the drug. Use of the drug usually due to influence of
societal factors and occurs when mentally unstimulated by other aspects of life.
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4.3 & 4.4: Describe the short- & long-term consequences of alcohol consumption on the nervous system
& liver, as well as social consequences of alcohol use.
What is ALCOHOL? What are its EFFECTS on the human body?
Alcohol (ethanol) is a recreational drug, which means that it is taken in social situations and has mild
effects on the body if taken sparingly. 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.
Below is a summary of the effects of alcohol on the human body:
Effect
Notes
Fatty liver hepatitis
(short-term)
Alcohol is used as an energy source by liver cells, allowing fat to accumulate
around the liver. A common condition, but it is a precursor to liver cirrhosis.
Liver cirrhosis
(long-term)
Liver cells become replaced with scar tissue, which impacts the liver‟s ability to
produce bile salts, detoxify the blood and store glycogen.
Impaired nervous
transmission
Since neurotransmitter activity slows down, reaction time increases and
perception becomes distorted (e.g. blurry vision, reduced motor skills) due to the
cerebrum and cerebellum being affected.
Cancers
Alcoholics have an increased risk of oral and throat cancers.
Dehydration of
brain cells
Since the pituitary gland is affected, ADH release is suppressed. This means that
less water is reabsorbed into the blood from the kidneys, leading to dehydration
and „hangovers‟. Demyelination (loss of myelin sheath) of neurones also occur in
the long-term, severely affecting brain activity.
Increased risk of
heart attack and
stroke
Even though alcohol is a depressant, it actually increases blood pressure. This is
because it allows calcium ions to bind to blood vessels, causing them to constrict.
This increases the chances of a coronary thrombosis rupture and ensuing heart
attack or stroke.
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What are the SOCIAL CONSEQUENCES of ALCOHOL ABUSE?
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.
Here are a few social consequences of exceeding DAL regularly:
Effect
Notes
Car accidents
Due to decreased reaction time, impaired motor skills and judgment, car accidents
occur much more frequently with alcoholics at the wheel. This is why a
„designated driver‟ is recommended to accompany a group.
Violence
Alcohol leads to a loss of inhibition, which can escalate altercations both in
public, especially if both parties are drunk. This can also occur domestically.
Intra-family issues
and family
breakdown
If a family member is an alcoholic, they may exhibit very aggressive behaviour
with other family members due to loss of inhibition and poor judgment. If the
alcoholic is a breadwinner, they may be at risk of unemployment, throwing the
family into financial turmoil.
Neglect of children by parents may also occur if they are frequently drunk.
Petty crime
Due to reduced inhibition, committing petty crimes such as theft, harassment
(sexual or otherwise) or vandalism may occur.
Poor sexual
intercourse
decisions
Though it is deemed immoral (and in a number of countries, illegal) to have sex
with an individual who is drunk, reduced inhibition can lead to an individual
having unprotected sex with someone undesirable, risking transfer of STI‟s and
pregnancy.
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4.5: Describe the effects of components of cigarette smoke on the respiratory & cardiovascular systems
How is CIGARETTE SMOKING dangerous to your health?
A familiar topic, 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; mucussecreting 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.
Here‟s a rundown of how the four cigarette smoke components (tar, CO, nicotine and particulates) lead
to one‟s health becoming compromised:
Component
Notes
Tar and
particulates
These mostly contain carbon and lead to irritation in the airways. This irritation
leads to white blood cells secreting an enzyme that breaks down the elastin of the
alveoli. This creates large air spaces in the alveoli, separating the alveolar
membranes from the capillaries, reducing surface area and capacity for gaseous
exchange. This condition is known as EMPHYSEMA.
The particulates can also result in excess mucus being produced due to
proliferation of goblet cells in the trachea and bronchi. This is called
HYPERPLASIA. Mucus is also a breeding ground for bacteria.
Finally, ciliated cells become destroyed. These cells are known for catching
bacteria-laden particles of dust and residue. Since these are gone, diseases like
bronchitis become more common.
Carbon monoxide
(CO)
Haemoglobin has a very high affinity for CO, which means that it will quicker
take up CO than oxygen, leading to severely reduced oxygen uptake and reduced
delivery to the heart and body cells.
Due to the oxygen shortage, a hormone called erythropoietin is secreted, which
increases red blood cell count. This may lead to an increase in blood viscosity
(„thicker‟ blood), increasing chance of ruptured blood clots and CHD.
Nicotine
Nicotine is very addictive. It also helps to constrict blood vessels, reducing lumen
size of vessels and leading to increased risk of blood clot formation and CHD.
Carcinogens
These also contribute to risk of cancers, especially lung cancer.
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.
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The Effect of NICOTINE on HEALTH
Previously, we‟d established the following facts about nicotine that can affect health:
1. Nicotine is a stimulant. It closely resembles acetylcholine and tends to bind to ACh receptors in
synapses. However, since acetylcholinesterase cannot break down nicotine, it stays bound for
prolonged periods of time, causing the synapse to be overly excitatory. This can potentially
increase heart rate (tachycardia) and blood pressure to the point of causing a stroke or a
thrombosis.
2. Nicotine constricts blood vessels. In arteries, where atherosclerotic plaques have builta up, this
greatly increases the possibility of a ruptured blood clot. This is because the reduced lumen size
increases blood pressure and makes it less flexible. This ruptured clot can result in a heart attack
or stroke.
3. The effect of nicotine on pregnant women‟s foetuses can cause much pre-natal harm. Nicotine
causes constriction in the placental blood vessels, thus reducing exchange of nutrients and gases.
It also delays excretion of waste from the foetus. All of this can lead to the foetus being
undernourished or even miscarriage.
4. Nicotine may also constrict blood vessels and deprive oxygen flow to the extremities, such as
the arms and legs. This leads to a reduced rate of respiration and prolonged fatigue. In worst case
scenarios, especially if coupled with nerve damage from diabetes, it may lead to cell death and
amputation.
5. Nicotine is highly addictive. People who regularly consume nicotine usually exhibit physical
dependency on it. When suddenly stopped, it can produce a myriad of withdrawal symptoms,
which may include anxiety, depression, cravings and irritability.
6. The nicotine from tobacco relaxes the valve between the oesophagus and stomach (lower
oesophageal sphincter). This can allow stomach acid and juices, the chemicals that break down
food in the stomach, to back up (reflux) into the oesophagus, which causes heartburn, peptic
ulcers and nausea.
7. Nicotine changes chemical processes in the cells to increase insulin resistance. Glucose cannot
bind to cell receptors to activate GLUT4 proteins to transport them through the membrane. This is
a precursor of type II diabetes and results in a number of issues, including dehydration, nerve
damage, cell death and coma.
-