Characteristics of living organisms
There are seven characteristics of living things;
1.
2.
3.
4.
5.
6.
7.
Nutrition
Excretion
Respiration
Reproduction
Growth
Sensitivity
Movement
1. Nutrition
✓ obtaining organic substances and mineral ions from which organisms gain their
energy and raw materials for growth and tissue repair.
✓ Food is the source of energy and raw materials for growth and tissue repair in living
organisms
✓ Green plants make their own food using photosynthesis , such organisms are called
autotrophs
✓ Animals that eat other animals and plants are called heterotrophs
2. Excretion
✓ The removal of toxic materials and the waste products of metabolism from
organisms
✓ The waste products are formed during metabolism in cells of living organisms
✓ Metabolism refers to all chemical reactions taking place in cells for survival of
organism eg respiration
✓ Example of a waste product is carbon dioxide
3. Respiration
✓ The release of energy from food substances in all living cells
✓ The energy is released when living organisms break down food , usually in the
presence of oxygen
✓ This energy is used in other life processes of the organism, otherwise the organism
would die
4. Sensitivity
✓ The ability to sense and respond to changes in the surroundings
✓ The surrounding changes could be temperature , light or sound ( external changes )
or Ph (internal change)
✓ Animals respond more quicker than plants
1
5. Reproduction
✓ Producing offspring, preventing extinction of the species
6. Growth
✓ An increase in body size, mass and complexity of an organism
✓ This may include the growth of new parts
7. Movement
✓ A change in position of the whole body or any part of the organism
✓ Eg contraction of a muscle to cause movement a particular body part or swimming
Classification of living organisms
✓ Living things are put into groups based on their similarities i.e the organisms are
sorted into classes according to features they have in common
✓ Classification makes identification of living things easier
✓ This classification system is called taxonomy ( there are seven levels of taxonomy)
The seven levels of taxonomy
1.
2.
3.
4.
5.
6.
7.
Kingdom
Phylum
Class
Order
Family
Genus
Species
Binomial system of classification
The system of naming organisms using two latin names, genus and species
✓
✓
✓
✓
✓
✓
✓
Every species has two names that the species is grouped into.
The first name begins with a capital letter and it is the genus name
The second name always begins with a small letter and it is the species name
Both the genus and species must be written in italics or underlined
The genus name can be abbreviated e,g H. sapiens for Homo sapiens
can also be written as Homo spp (spp >> species)
species are a group of organisms that are capable of interbreeding and produce
viable offspring
2
✓ The binomial system of naming organisms is important to avoid confusion. Different
organisms could have the same name from different languages one of the
organisms could be dangerous/ poisonous.
There are five kingdoms into which all organisms belong to.
The kingdoms of organisms
There are five kingdoms;
1.
2.
3.
4.
5.
Animalia
Plantae
Fungi
Prokaryotae( bacteria)
Protoctista (algae)
Kingdom animalia
(Phylum chordata)
Animals are classified into vertebrates and invertebrates.
Classification of vertebrates
Vertebrates are animals that have an internal skeleton (or endoskeleton) made up of bones
which include vertebral column (back bone)
There are five different classes of vertebrates;
1.
2.
3.
4.
5.
Mammals (mammalia)
Amphibians ( amphibia)
Reptiles (reptilia)
Birds (aves)
Fishes (pisces)
The following tables shows characteristics of vertebrates
Vertebrate
class
mammals
Birds
Body
coverin
g
Fur or
hair
movement
Reproduction
Examples
Walk using
four limbs
Cow,dog, humans,
lion, bat
Feather
s (scales
on legs)
Fly with
two wings
and walk
with 2 legs
1. Give birth to live
young ones
2. breastfeed young
ones with milk from
mammary glands
Internal fertilization,
lay hard shelled eggs
3
Chickens ,
Ostrich,Swallow,Dov
e
Reptile
Scaly
skin
Amphibian
s
Moist
skin
Fish
Scales
Walk with
4 limbs
(except
snakes)
Jump with
4 limbs
Fins for
swimming,
streamline
d body
Internal fertilization,
lay leathery eggs on
land
Snakes , Lizards,
Tortoise,
Crocodile
External fertilization,
lay jelly like eggs in
water
Frogs , Newts ,
Toads, Tadpoles
externalFertilization,la
y jelly covered eggs
Trout, catfish,
sardines, pilchard
Invertebrates >>>> arthropods , annelids , nematodes, and molluscs
Phylum arthropoda (arthropods)
Arthro- jointed
-poda
legs
All athropods are invertebrates. They all have the following special features:
1. Jointed legs
2. Segmented body
3. Exoskeleton
There are four classes of arthropods
1.
2.
3.
4.
Insect (insects)
Arachnida (arachnids)
Crustacea ( crustaceans )
Myriapoda (myriapods)
Insects
insects have the following characteristics;
➢
➢
➢
➢
➢
➢
Have a pair of compound eyes
3 pairs of legs
Wings may be present
Body consist of a head, thorax, abdomen (3parts)
One pair of antennae
Examples are butterfly, bee, beetle, ant, locust
Arachnids
➢ Body is divided into two parts: cephalothorax (fused head and thorax) and abdomen
4
➢ Four pairs of legs
➢ Examples are spider, tick, scorpion
Crustaceans
➢
➢
➢
➢
Body is divided into 2 parts : cephalothorax and abdomen
More than four pairs of legs
Two pairs of antennae
Examples are cramps , prawns, shrimps, woodlouse
Myriapods
➢
➢
➢
➢
Body consists of a head and a long segmented trunk
One or two pairs of legs per segment
A single pair of antennae
Examples are millipede and centipede
Classification of other invertebrates
Annelids (phylum Annelida)
➢
➢
➢
➢
➢
➢
Body is made up of ring –like segments
Body is cylindrical and long
Has obvious head region
Have chaetae(bristles ) for movement
Have a saddle or clitellum for reproduction
Examples are earthworm, leech
Nematodes (phylum nematode)
➢
➢
➢
➢
The body is pointed at both ends, no obvious head region
Body is cylindrical, thin and long
No body segments
Examples include Ascaris, Caenorhabditis elegans
Molluscs ( phylum Mollusca)
➢
➢
➢
➢
➢
Soft unsegmented body
Muscular foot
Most have shells
Have tentacles with eyes
Examples include snails, slugs , octopuses
5
Kingdom plantae (plants)
➢ Plants are multicellular
➢ There are two types of plants;
1. Flowering plants (Angiosperms)
2. Non-flowering plants conifers , ferns, mosses
Classification of flowering plants
➢ Flowering plants have two groups;
1. Monocotyledons (monocots)
2. Dicotyledons ( dicots)
Differences between monocots and dicots
Monocots
One cotyledon
Parallel veins
Narrow leaves
Fibrous roots system
Flower parts in threes
Examples; maize, grass, sorghum, wheat,
sugarcane etc
Dicots
Two cotyledons
Network veins
Broad leaves
Tap roots system
Flower parts in fours or fives
Examples; beans, avocadoes, mangoes,
peach, etc
Classification of prokaryotes (Bacteria)
➢
➢
➢
➢
➢
➢
➢
They belong to a kingdom known as Prokaryotae
Bacteria are unicellular organisms
They can only be seen under a microscope, 1000 times smaller than a plant cell.
Have a cell wall made up of material called Murein
have no nucleus but have DNA in the form of a single thread
some have one or more flagella, for locomotion
examples include ; Vibrio, Salmonera, Treponema pallidum etc
kingdom fungi
Key features
➢ are multicellular and composed of hyphae (thread like structures) which form a
network called mycelium
➢ cells have nuclei and have cell walls made of cellulose or chitin
➢ do not produce chlorophyll and do not photosynthesise , but some grow in the soil
➢ they feed saprotrophically / saprophytically on dead organic materials like faeces,
human food , dead plants and animals.
➢ Fungi have feeding hyphae/ mycelium that secrete enzymes to digest food.
6
➢ Examples include bread mould , puffballs, toadstool, mushroom
Structural differences between fungi and bacteria
Bacteria
Have no nucleus
Have no hyphae
Some have flagella
Unicellular
Have cell walls made of neither chitin nor
cellulose
Fungi
Have one or more nuclei
Have hyphae or mycelium
Have no flagella
Multicellular
Have cell walls made of chitin
7
ORGANIZATION AND MAITENANCE OF THE ORGANISM
The cell structure
The cell is the smallest unit from which organisms are made. It is;
✓ The basic unit of life
✓ Building block of life
Properties of a cell
✓ They are microscopic
✓ They come in different shapes and types
Types of cells
1. Animal cell
2. Plant cell
Animal cell
See fig.2.5 page 23
Plant cell
See fig.2.8 page 25
Similarities between plant and animal cells;
1.
2.
3.
4.
They both have cell membrane
They both have a cell nucleus
They both have the mitochondrion
They both have the cytoplasm
Differences between animal and plant cells
Plant cell
Has a chloroplast
Has a cell wall
Has a large vacuole
Regular shape
Has a starch grain
Has cellulose
Animal cell
Has no chloroplast
Has no cell wall
Has a small or no vacuole
Has irregular shape
Has a glucagon grain
Has no cellulose
8
Organelles
✓
✓
✓
✓
✓
✓
Nucleus- contain individual hereditary information
Vacuole- contain cell sap which help to keep the cell /turgid
Mitochondrion – where respiration occurs to release energy
Chloroplast – trap sunlight energy in the process of photosynthesis
Cytoplasm – jelly like part of the cell where reactions occur
Cell wall – supports And protect the cell from bursting
Development
Development is an increase in complexity through differentiation of cells.
Tissue is a group of cells of similar structure that work together to perform a special
function.
The following table shows examples of plant and animal specialised cells;
Plant specialised cells
Root hair cells
Palisade mesophyll cells
Xylem cell
Animal specialised cells
Ciliated cell
Goblet cell
Muscle cell
Red blood cell
Levels of organisation
The cell structure can be modified or change as there is an increase in complexity of an
organism through the differentiation of cell.
Cells are modified into tissues; In all tissues the cells have a particular characteristics which
help the cell to carry out their function.
✓ Root hair cell.
Found underneath the tip of the roots that are growing into the soil
Adaptation;
Have hair like structures or finger like projections which give them a large surface
area.
Function;
Absorb water and mineral salts from the soil.
Anchors the plant in the soil
Section through the root hair cell
See fig.2.14 page 29
9
✓ Xylem vessels/ tissues
Adaptation;
The cells making up xylem vessels are long and thin, arranged end to end to form
vessels that are hollow and tubular.
The walls of the xylem cell are made out of lignin (tough protein)/ the cells have
lignified walls.
The end walls have disappeared completely (eg umhlanga)
Function;
Transport water and mineral salts from one part of a plant to another.
Xylem vessels also provide mechanical to the plant.
Longitudinal section of the plant stems showing the xylem tissue
See fig.2.15 page 29
✓ Palisade cell
Found in the palisade mesophyll layer in of the plant leaves.
Adaptations;
Contain many chloroplasts which increase the surface area for absorption of sunlight
energy.
Function;
For photosynthesis.
Diagram of palisade cell
See fig.2.16 page 29
✓ Muscle cell/ tissue
Adaptation;
Made of elastic protein strands / fibres.
Muscle cells merge together to form fibres that can contract
Function;
Contract and relax to cause movements in the body.
Diagram of muscle tissue
See fig. 2.19 page 30
✓ Red blood cell
Adaptation;
Red blood cells are very small.
They have no nucleus but have a cytoplasm containing a red pigment called
haemoglobin.
10
Function;
Transport oxygen around the body- their small sizes makes it easier for the rbc to
squeeze through very thin capillaries, taking oxygen close to almost every cell in the
body.
Haemoglobin helps to bind to oxygen molecules to form oxyhaemoglobin.
Side view of the red blood cell
See fig.2.17 page 29
✓ Ciliated cells.
Found in tubes like trachea and oviduct in females
Adaptation;
Have tiny hairs called cilia which can move back and forward.
Function;
Move dust away from lungs.
In trachea they help to sweep mucus with bacteria with trapped bacteria and dust up
the throat from the lungs.
In oviduct ciliated cells helps to move the egg away from the ovary towards the
uterus.
Diagram of a ciliated cell
See fig. 2.18
page 30
✓ Goblet cell
Adaptation;
Function;
See fig. 2.20
page 30
Organ – several tissues grouped together to make a structure with a special function eg
kidney, leaf, skin, liver and heart.
Organ system – a group of organs with closely related functions eg the eye works with other
organs to form the nervous system.
Organism – individual plant or animal. All organ systems must be working to keep the
organism alive.
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MOVEMENT IN AND OUT OF CELLS
There are processes by which substances enter and leave cells.
1. Diffusion
2. Osmosis
3. Active uptake
Diffusion
This is the movement of particles from a region of their higher concentration to a region of
their lower concentration, down a concentration gradient.
Factors affecting the rate of diffusion.
1. Distance - the shorter the distance moved by diffusing particle, the faster the rate of
diffusion (the shorter the distance the better). Diffusion of substances across walls of
the alveoli and capillaries would fast because the walls are thin.
2. Concentration gradient - the bigger the concentration difference of the particles
between the two regions the faster the rate of diffusion. The big duifference can be
maintained by removing the substance as it passes across the diffusion surface. Eg
oxygenated blood being carried away from the surface of the alveoli.
3. The size of the molecules – the smaller the size of the diffusing particles the faster
the rate of diffusion.
4. Surface area - the larger the surface area where the particles must cross the faster
the rate of diffusion. Eg there are millions of alveoli in lungs giving a large surface
area for the diffusion of oxygen. There are millions of villi in the lining of the small
intestines giving a larger surface area for the diffusion of the products of digestion
into the blood stream.
5. Temperature – molecules have more kinetic energy at higher temperature. The
higher the temperature the faster the rate of diffusion.
Importance of the process of diffusion in living organisms
✓ Living organisms obtain many of their requirements by diffusion. They take in oxygen
through the process of diffusion.
✓ Organisms also get rid of waste products using the process of diffusion. Eg animals
get rid of carbondioxide in the lungs through diffusiuon.
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Osmosis
In osmosis, water molecules diffuse through a partially permeable membrane. The cell wall
is said to be fully permeable because it does not prevent the movement of substances
across it.
Definition; osmosis is the net movement of water molecules from a region of their higher
concentration ( higher water potential ) to the region of their lower concentration (lower
water potential ), through a partially permeable membrane.
✓ Water diffuses from a dilute solution ( with higher water potential ) into a
concentrated solution.
✓ The concentrated solution will become diluted because of the extra water molecules
coming into it.
✓ Osmosis is a special form of diffusion, it always involves the movement of water
molecules across a semi-permeable membrane.
Osmotic water potential
✓ This is the potential of the water to move. This is the best term to use in osmosis
instead of concentration.
✓ A dilute solution, where there is a lot of water molecule, has a high water potential.
✓ A concentrated solution, where there is less water, has a low water potential.
✓ A water potential gradient is created between the two solutions, water molecules
diffuse down a water potential gradient from high water potential to a lower water
potential region.
Osmosis and animal cells
Animal cell in pure water
✓ Water diffuses into the cell through a partially permeable membrane.
✓ The solution in the cytoplasm is more concentrated.
✓ As more water enters the cell, it swells up and burst.
Animal cell in concentrated solution
✓ if the solution outside the cell is more concentrated than the cytoplasm, water
molecules will diffuse out of the cell through the cell membrane.
✓ The cell shrinks and become flaccid.
13
Osmosis and plant cells
In pure water
✓
✓
✓
✓
✓
A plant cell takes up water by osmosis through the partially permeable membrane.
As the water moves into the vacuole and cytoplasm, the cell swells.
The plant cell has a very strong /tough cell wall around it, so it will not burst.
A plant cell in this state is said to be turgid.
Turgidity of a plant cells help the plant that has no wood to stand upright and leaves
kept firm.
Plant cell in a concentrated solution
✓
✓
✓
✓
A plant cell that is put in a concentrated solution loses water by osmosis.
The cytoplasm shrinks and stops pushing outwards in the cell wall.
The cell becomes floppy and it is said to be flaccid.
The cell loses its firmness and begins to wilt.
In a very concentrated solution
✓ A lot of water will move out of the cell through the process of osmosis across the
cell membrane.
✓ The cytoplasm and vacuole shrink further into the centre of the cell, the cell wall
gets left behind
✓ The cell membrane tears away from the cell wall. A cell like this is said to be
plasmolysed.
NB: sugar and salts donot move by osmosis. The cell membrane is selective.
The importance of osmosis on living things
1. Plants rely on osmosis to obtain water through their roots. They use the water to
obtain /maintain the turgidity of the cell and as transport medium to carry mineral
salts, sucrose and amino acids around the plant.
2. Our body cells obtain water through osmosis
3. Fish living in salty water lose water by osmosis, they have very efficient kidney to
reduce water in urine.
Osmolarity
✓ Osmolarity is the total concentration of all solutes in the solution.
✓ Low osmolarity solution has few solute particles (dilute solution) – low
concentration.
14
✓ High osmolarity solution has more solute particles per litre of the solution
(concentrated solution) – highly concentrated.
✓ Water always move from lower osmolarity (dilute ) to higher osmolarity
(concentrated )
Hypotonic, isotonic, hypertonic
➢ These terms are used to compare osmolarity of the cell to the osmolarity of the
extracellular ( outside cell ) fluid around the cell
➢ When we use these terms we consider only solutes that cannot cross the membrane.
➢ If the extracellular solution has a lower osmolarity (dilute), then the fluid outside the
cell is said to be hypotonic- hypo means less than ( to the cell) and the net
movement of water will be into the cell from the surrounding of the cell.
➢ In the reverse case, if the extracellular fluid has a higher osmolarity than the cell’s
cytoplasm then the fluid is said to be hypertonic. Hyper- means greater than (to the
cell) and water will move out of the cell to the region of higher solute concentration.
➢ In an isotonic solution (iso- means the same) the extracellular fluid has the same
osmolarity as the cell and there will be no net movement of water into or out of the
cell.
➢ If an animal cell I placed in a hypertonic solution, water moves out of the cell
through a semi permeable membrane and the cell will shrink. There is higher water
potential in the cell than in the hypertonic solution.
➢ In an isotonic environment, the relative concentration of solute and water are
equal on both sides of the membrane. There is no net movement of water so there is
no change in the size of the cell.
➢ When an animal cell is placed in a hypotonic solution environment, water will move
from the hypotonic solution to the cell across a semi-permeable membrane. There is
higher water potential in the n the hypotonic solution than in the cell, the cell will
swell and burst.
➢ The hypotonic extracellular solution is ideal for plant cells. The cell membrane can
only expand to the limit of the rigid cell wall so the cell will not burst or lyse. In fact
the cytoplasm in plants is generally a bit hypertonic to the external cellular
environments and water will enter the cell until its internal pressure (turgor
pressure) prevents further water influx.
➢ Maintaining the balance of water and solutes is very important to the health of the
plant. If a plant is not watered, the extracellular liquid will become isotonic or
hypertonic, causing water to move out of the plant cells. This results of the loss of
the turgor pressure, which you have likely seen as wilting.
➢ Under hypertonic conditions the cell membrane, in the plant cell, may actually
detach itself from the cell wall and constrict the cytoplasm, a state called
plasmolysis.
15
Active uptake/ transport
❖ This is the movement of particles through a cell membrane from a region of lower
concentration to a region of higher concentration using energy from respiration.
❖ Plants and animals use active uptake to move substances when the concentration
gradient does not allow diffusion, cells need to provide energy to achieve this
movement.
There are two big differences between diffusion and active uptake;
1. The direction of movement is down the concentration gradient in diffusion and up
the concentration gradient in active uptake.
2. Energy is needed in active uptake but no energy is used in diffusion.
Examples of active uptake are shown in the table below;
Site of active uptake
Root hair cell
Walls of intestines
Substance
Mineral ions e.g phosphorus
Glucose
Kidney (nephron)
Glucose
16
Description
Soil to roots
From small intestines to
blood stream
From nephron into blood
capillaries
ENZYMES
What are enzymes?
➢ Enzymes are proteins that function as biological catalysts.
➢ A catalyst is a chemical substance which speeds up a chemical reaction but remains
chemically unchanged.
➢ A catalyst alters /changes the rate of a reaction (by increasing the reaction rate ) and
remain unchanged. For example; lipase, amylase, maltase etc
➢ All chemical reactions taking place inside bodies of living organisms are controlled by
catalysts.
➢ These catalysts which are found in living organisms are special proteins called
enzymes ( i.e biological catalysts )
There two types of enzymes
1. Intracellular enzymes; enzymes are made inside cells and perform their function
inside the same cells that made them.
2. Extracellular enzymes; enzymes are made inside cells and leave the cell to perform
their function outside the cells
Naming enzymes
➢ Named according to the substance they catalyse
➢ Names of enzymes usually end in /-ase/. For example ; lipase , amylase etc
➢ Enzymes that break down carbohydrates are called carbohydrases, those that break
down lipids are called lipases and those that break down proteins are called
proteases.
Substrate / end product
A chemical reaction always involves one substance changing to another.
➢ The chemical substance which an enzyme works on is called the substrate
➢ The substance made by the reaction is called end- product
Properties of enzymes
➢ Reading assignment ; Macmillan Biology for Southern Africa, page 48.
➢ Read and write down the properties of enzymes
Enzyme action - how do enzymes work ?
➢ The “lock and key” hypothesis is used to explain enzyme action
➢ Key – enzymes
➢ Lock – substrate
17
➢ Each enzyme has an active site into which its substrate fits exactly ( see fig. 3.2, page
48)
➢ The substrate has a reactive site which fits into the active site of the enzyme
➢ The enzyme and substrate bond together through the reactive site and the active
site to form the enzyme – substrate complex (this is the most important stage )
➢ The reaction then occurs rapidly
➢ The complex then breaks down, the product of the reaction is released and the
enzyme remains unchanged and is capable of facilitating another reaction of the
same kind (see fig. 3.3, page 49)
What are the factors that affect enzyme activity?
➢ There are a number of factors that can affect the enzyme activity. Remember that
the enzyme activity affects the overall reaction rate. Some of the factors are as
follows;
1. Temperature
2. pH
3. Enzyme concentration
4. Substrate concentration
➢ We are going to study the effects of temperature and pH (look at how the other two
affect the enzyme action on your own)
Effect of Temperature on enzyme activity
➢ Most chemicals reactions occur faster at a higher temperature
➢ The temperature increases until it reaches the optimum temperature for the
reaction i.e the temperature at which the activity of the enzyme is at its maximum
➢ For most human enzymes the optimum temperature is about 37 oC
➢ Increasing temperature above optimum ( above 40 oC ) results to enzyme denaturing
(deforms the active site of the enzyme such that the enzyme cannot make the
perfect fit with its substrate molecule)
➢ There are other enzymes whose optimum temperature is much high. For example;
those that are found in bacteria that live in hot springs
➢ Low temperatures make enzyme controlled reactions go slow- enzyme activity not
initiated at low temperature
➢ See fig. 3.4 , page 49
Effect of pH on enzyme activity
➢ Each enzyme has a specific range of pH within which it will function and an optimum
pH at which it will function at its best.
➢ Most enzymes function at neutral environments (pH 7)
➢ Pepsin found in human stomach functions at pH 2
18
➢
➢
➢
➢
Salivary amylase found in mouth of humans function at pH 6 – 8
Pancreatic amylase found in duodenum functions at pH 9
Extreme pH changes can denature the active site of the enzymes
See fig,3.6 , page 51
19
NUTRITION
✓ Obtaining the organic substances and mineral ions from which organisms gain their
energy and the raw materials for growth and tissue repairs
✓ The two types of nutrition are ; heterotrophic feeding and autotrophic feeding
Nutrients
Why do we need nutrients?
✓ To repair worn out tissues
✓ To fight infections
✓ For growth
✓ To obtain energy
There are seven kinds of nutrients
✓
✓
✓
✓
✓
✓
✓
Carbohydrates
Proteins
Fats
Vitamins
Minerals
Water
Roughage /dietary fibre
Note ; carbohydrates, proteins and fats are called macro nutrients,,,, why are they called
macro nutrients?
The following table shows a summary food nutrients
Nutrients
Carbohydrates
Proteins
Elements present
Carbon, hydrogen,
oxygen
Carbon, hydrogen,
oxygen, nitrogen,
traces of sulfur and
phosphorus
Function
Source of energy
Making hair and nails
Repair worn out
tissues
Make haemoglobin
Broken down to give
energy
Make enzymes
Make hormones
20
Good food source
Bread , rice
porridge, sweets
Eggs, meat, fish
Lipids / fats/oils
Make antibodies
Insulate the body
against heat
Carbon, hydrogen,
oxygen
Cheese, peanuts,
milk, butter,
Source of energy
Make hormones and
cell membranes
Insulate nerve fibres
Synthesis of carbohydrates proteins and fats from smaller basic units
✓ The synthesis process is called dehydration synthesis ( also called a condensation
type reaction)
✓ As one molecule of a compound is bonded to another molecule, a molecule of water
is formed
✓ Examples include synthesis of glycogen, starch, fats and proteins
Synthesis of starch and glycogen
✓ These molecules are made up of long chains of smaller units of monosaccharides
like glucose
✓ The monosaccharides are held together by a chemical bond
✓ See fig.4.18, page 74
Synthesis of proteins
✓ Proteins are made of long chains of amino acids that are chemically bonded together
✓ See fig.4.20 page 75
Synthesis of fats
✓ fats are made of three units of fatty acids chemically bonded to glycerol molecule
✓ see fig 4.19 page 75
Food tests
The following table shows a summary of food tests
Food tested
Starch
Name of test
Starch test
Method/procedure
Crush food sample
into smaller pieces
Add a few drops of
iodine solution to the
21
Results (positive)
The iodine solution
changes from brown
to blue-black
Reducing sugars
Benedict’s test
crushed food pieces
If food sample is solid,
crush it into smaller
pieces and put them
into a clean test tube
containing water
The Benedict’s
solution changes
from blue to orange
or brick- red.
For liquid sample,
pour 1cm3 into a clean
test tube
if a small amount of
reducing sugar is
present the colour
changes from blue
to green
Then add 2cm3 (10
drops ) of Benedict’s
solution into the test
tube
Proteins
Biuret test
Heat the mixture or
solution in a hot water
bath for 3-5 minutes
and observe the
colour changes
If food sample is solid,
crush it into smaller
pieces and put them
into a clean test tube
containing water
The blue colour
changes to purple or
violet
For liquid sample,
pour 1cm3 into a clean
test tube
Then add 1cm3 of
Sodium Hydroxide and
1 cm3 of Copper
Sulfate solution, drop
by drop to the food
sample
Fats
Emulsion test
Shake well and allow
the mixture to stand
for 5 minuters
Crush the food sample
into smaller pieces
and put them into a
clean test tube
Add 1cm3 of ethanol
22
A white emulsion is
formed
to dissolve any fat in
the food
Vitamin C
DCPIP
Pour the food (after
dissolving ) into a test
tube containing water
Grind the food sample
into smaller pieces
Add a few drops of
DCPIP solution
The DCPIP loses its
blue colour
(becomes colourless)
in the presence of
vitamin C
Micro / minor nutrients
The following table shows other micro nutrients
Nutrient
Vitamin C (ascorbic
acid)
Function
Needed to maintain
the skin and gums
Synthesis of bones,
connective tissues
Effect on deficiency
Scurvy – bleeding
gums and pain in
joints and muscles
Good food source
Citrus fruits
Green vegetables
Guavas
Tomatoes
Disorder of teeth,
lose teeth
Increase resistance
to diseases
Vitamin D
Calcium
Increase ability of
wound to heal
Needed to maintain
hard bones and teeth
Helps in absorption
of calcium in small
intestines
Formation of strong
bones and teeth
Rickets (soft bone
that become
deformed)
Rickets
Slow blood clotting
Normal clotting of
blood
Iron
Muscle contraction
Formation of
haemoglobin in red
Anaemia –constant
tiredness , lack of
23
Milk
Cheese
Egg yolk
Made by skin when
exposed to sun light
Milk
Cheese
Fish
Green vegetables
Red meat
Liver
blood cells
Iodine
Roughage
energy
Activation enzymes
in respiration process
Formation of
Goitre
hormone thyroxine
Slow metabolic rate
This cellulose
Dehydration
Kidney
Green vegetables
Sea food
Table salt
Drinks fruits
Vegetables
It adds bulk to
undigested food
passing through the
intestines
Maintains peristalsis
Prevent constipation
Plant nutrition
❖ Plants feed through the process of photosynthesis
❖ This is autotrophic feeding and they are called autotrophs (they make their own
food)
What is photosynthesis?
❖ Photosynthesis is the fundamental process by which green plants manufacture
simple sugars from carbon dioxide and water in the presence of light energy.
❖ Photo = light
❖ Synthesis = manufacture
❖ The organic food molecules in plants are made using raw materials carbondioxide
and water, using light energy which is trapped using chlorophyll, products are
glucose and oxygen
❖ This means that carbondioxide, water, light energy and chlorophyll are very
necessary for the process of photosynthesis to take place in plants
Photosynthesis can be represented using equations
Word equation
Carbon dioxide + water chlorophyll
glucose + oxygen
Sunlight
24
Symbol equation
6 CO2
+
6 H2O
chlorophyll
C6 H12 O6 + 6 O6
Sunlight
How the process of photosynthesis takes place?
❖ Photosynthesis takes place in leaves of plants
❖ Green plants take in carbon dioxide through stomata on their leaves by diffusion
❖ Root hair cells absorb water in roots of plants by osmosis and the water is
transported to leaves by the xylem vessels
❖ Chloroplasts that contains chlorophyll are found in green leaves of plants and are
responsible for trapping the light energy
❖ The light energy is used to break down water molecules and bond the carbon dioxide
with the hydrogen to form glucose
❖ Light energy is converted to chemical energy (glucose) during photosynthesis
❖ The oxygen released as by product of the process is used by the plant in respiration
What are the uses of the glucose produced in the plant?
❖ The glucose can be combined with oxygen during respiration to release energy for
the plant
❖ The glucose may be converted to starch for storage- glucose is readily soluble so
must be converted insoluble starch for use later
❖ The glucose may be converted to other parts of the plant in the form of sucrose
❖ The glucose may be used to make organic substances like cellulose, fats and amino
acids
❖ Note that respiration takes place all the time in both plants and animals to release
energy yet photosynthesis require light for initiation
Factors affecting the rate of photosynthesis
They are temperature, light intensity and carbon dioxide’
Temperature
❖ Chemical reaction of photosynthesis only take place slowly at low temperatures
❖ Plant photosynthesis is faster on a warm day than cold day
❖ Photosynthesis rate increases as temperature increases upto a certain point
❖ Temperatures that are too high causes the stomata of the leaf to close in order to
prevent excessive water loss from the plant- might lead to death of plant
25
Light intensity
❖ The rate of photosynthesis increases with an increase in light intensity
❖ In the dark photosynthesis cannot take place
❖ As light intensity increases the rate of photosynthesis increases upto a point where it
cannot increase any further (there might another factor that is in short supplylimiting factor)
❖ A limiting factor is an external factor which restricts the effect of others when a
number of factors are needed; it is the one in shortest supply
Carbon dioxide
❖ The more carbon dioxide a plant is given faster the plant makes its own food
❖ The photosynthesis rate increases only to a certain point where it cannot increase
any further due to other limiting factors like light and temperature
Carbon dioxide enrichment, optimum light and optimum temperature in greenhouse
systems
❖ Greenhouse/glasshouses are used in some countries to control conditions for plant
growth when growing conditions outside are not ideal
❖ The atmospheric conditions inside a greenhouse can be controlled
❖ Crop production is important for food supply
❖ The greater the rate of photosynthesis in a plant, the greater the plant productivity
❖ A productive plant will gain more dry mass in the form of the different nutrients e.g
proteins
❖ In green houses optimum temperature, optimum light and carbon dioxide
enrichment are ensured to maximise crop productivity
❖ Carbon dioxide enrichment can be achieved through burning fossil fuels or releasing
pure carbon dioxide from gas cylinders
❖ Optimum light can be provided through the use of artificial lights (in winter)
❖ Optimum temperature can provided through the use of heating systems like heaters
( in winter)
Testing a leaf for starch
❖ A test for starch in a leaf can tell us whether photosynthesis has taken place or not.
❖ Starch is stored in the leaves as a product of photosynthesis
❖ Iodine is used to test for starch in a leaf
26
The procedure is laid down in the following table
Stage
Boil the leaf in water for
about 30 seconds
Put leaf in ethanol
Put the leaf in hot water
Spread the leaf on a white
tile
Add iodine solution to the
leaf
Reason
Kills the leaf. Break the cell
membrane and make the leaf
permeable to iodine
To decolourize the leaf.
Chlorophyll dissolves in
ethanol
To evaporate the ethanol
together with the chlorophyll
Easy observation of test
results
To test for presence of starch
27
Safety point
Danger of scalding
Put out any open flames to
avoid fire
Danger of scalding
Avoid skin contact with
iodine
Adaptation of a leaf for photosynthesis
Adaptation of a leaf
1. Leaf has a large surface area (broad)
2. Leaf is thin
3. Epidermis is transparent and has no
chloroplasts
4. Stomata are found in the epidermis
5. There are many chloroplasts in the
palisade mesophyll cells and they can
move
6. There are fewer chloroplasts in the
spongy mesophyll and there are
larger air spaces between the cells
7. Network of veins provide a good
water supply to photosynthesizing
cells, veins are found right next to
the mesophyll cells
Reason for the adaptation
This is to provide a large surface area for the
leaf to absorb as much sunlight as possible
This is to allow gases and light to reach the cells
in the centre of the leaf as quickly as possible
This outer layer lets a lot of light through into
the inner part of the leaf. There is nothing to
get into the way of light
These pores allow gases to pass into and out of
the leaf
This means that the chloroplasts in the cells can
absorb as much light as possible
These cells do not receive as much light and so
need fewer chloroplasts. The air spaces
between the cells allow gases to easily diffuse
through the leaf.
This means water, which is needed for
photosynthesis, can easily be transported to the
cells, and food, which is made by
photosynthesis, can easily be carried away to
other parts of the plant
Note; although photosynthesis takes place mainly in the leaves, any part of the plant which
contains chlorophyll will photosynthesize. Many plants have green stems in which
photosynthesis takes place
Leaf structure
✓ You need to be able to identify the cellular and tissue structure of a leaf and relate
the features to their functions
✓ See figure 4.14 a, b & d
Parts of a leaf and their functions
Parts of leaf
Cuticle
Upper epidermis
Details
Made of wax, waterproofing the leaf. It is secreted by the cells of the
upper epidermis
These cells are thin and transparent to allow light to pass through. No
chloroplasts are present. They act as a barrier to diseases organisms
Main region for photosynthesis
Palisade
mesophyll
Spongy mesophyll Cells are more spherical and loosely packed. They contain chloroplasts
but not as many as in palisade cells. Air spaces between cells allow
28
Vascular bundle
Lower epidermis
Stomata
gases
This is a leaf vein, made up xylem and phloem. xylem vessels bring
water and minerals to the leaf. Phloem vessels transport sugars and
amino acids away from the leaf ( this is called translocation)
Acts as a protective layer. Stomata are present to regulate the loss of
water vapour ( this is called transpiration)
Each stomata is surrounded by a pair of guard cells. These can control
whether the stoma is open or closed. Water vapour passes out during
transpiration. Carbon dioxide diffuses in and oxygen diffuses out during
photosynthesis
Mineral requirement in plants
Nitrate ions
✓ Needed in plants for synthesis of proteins
✓ Plants must first make amino acids by combining sugars with nitrates during
photosynthesis
✓ Proteins are then used to make cytoplasm of cells and enzymes for growth
✓ Nitrate ions deficiency in plants results to slow growth
✓ Stems become weak, the lower leaves turn yellow and die
✓ The upper leaves turn pale green
Magnesium ion
✓
✓
✓
✓
✓
✓
Needed in plants for synthesis of chlorophyll
Each chlorophyll molecule contains a magnesium atom
Plants need chlorophyll to trap sunlight energy for photosynthesis
Magnesium deficient plants will not be able to make chlorophyll
Plant growth will be stunted due to reduced photosynthesis
Chlorosis (yellowing of lower leaves)
Nitrogen fertilizers
✓ Added to the soil to increase crop yields
✓ Repeatedly farming the same piece of land results to nitrate depletion from the soil
Nitrates can be replaced in 3 ways;
✓ Applying animal manure
✓ Adding artificial fertilizers e.g ammonium nitrate and ammonium phosphates
✓ Crop rotation- growing leguminous plants such as beans, peas every two or three
years. These plants develop nodules containing nitrogen fixing bacteria
29
Dangers of overuse of nitrogen fertilizers
✓ Wilting and death of plants – applying too much nitrogen fertilizers can result in
water being drawn out of the plant roots by osmosis, the plant wilts and dies.
✓ Eutrophicatiobn – this is the destruction of life in nearby rivers or lakes.
Eutrophication follows the following sequence;
Leaching - soluble nitrates washed into nearby rivers and lakes
Rapid algal growth - extra nitrates promote rapid growth of water plant i.e algae
Death of algae – bottom algae dies because of shading from the surface i.e sunlight
blocked
Decay by bacteria – dead algae decomposed by bacteria aerobically (using up all
available oxygen ) leading to reduced oxygen concentrations in the water
Death of aquatic animals – plants and animals die due to lack of oxygen
30
Transport in plants
Transport systems
✓ There are two transport systems found in plants
1. Xylem vessels
2. Phloem vessels
vascular bundle
✓ The xylem vessels carry water with dissolved minerals
✓ The phloem carry vessels carry food minerals which the plant has made
Xylem vessels / tissues
✓
✓
✓
✓
✓
Made of hollow dead cells joined end to end
The end walls have completely disappeared so that long open tubes formed
Xylem vessel individual cells contain no cytoplasm and no nuclei
Cell walls of xylem vessel cells are lignified ( made of lignin)
Lignin is a very strong substance, lignified xylem vessel cells help to keep the plant
upright (mechanical support of the plant )
✓ Xylem vessels run from the roots to the stem and branch to the leaves
✓ See fig. 5.3 a page 102 / photo 1
Phloem vessels / tubes
✓ Made up of many cells joined end to end
✓ Their end walls have not completely broken down, instead, they form sieve plates
with holes in them
✓ The cells are called sieve tubes elements
✓ Phloem cell contains the cytoplasm but there is no nucleus
✓ Each element has a companion cell next to it
✓ The companion cell contains nucleus and other vital organelles and it supplies the
element with most of the cell requirements
✓ See fig 5.4 a page 103 photo 1
The vascular bundle is found in the stem and root
✓
✓
✓
✓
✓
✓
✓
Know the different distributions of vascular bundles in root and stem
see fig.5.5 b root page 104 & fig5.7 stem page 105
In root the vascular bundles are found in the centre
the xylem is star shaped in a root and the phloem is situated between the arms
the vascular bundles form a ring in the stem
the stem has a pith at the centre
there is no pith in roots
31
Water uptake in plants
✓ roots absorb water in plants and also anchor the plant firmly into the soil
✓ roothair cells grow on the root to increase surface area of the root and make it more
efficient in absorbing water
✓ roothairs are long finger-like extensions found on the surface of the root
✓ water passes through the cells of the root by osmosis and reach the xylem at the
centre of root
✓ water travels up the stem through the xylem all the way up to the leaves
✓ minerals are also transported in the xylem dissolved in water
Mechanism of water uptake
✓ see fig 5.6 page 105
✓ water is absorbed by roothair cells through osmosis
✓ this happens when water potential in the soil (surrounding the root ) is higher than
in the roothair cell
✓ as water enters the cell, the water potential of that cell becomes higher than the
water potential of the next cell, leading to water moving to the next cell by osmosis
✓ the process repeats itself until the water reaches the xylem
✓ the water moves in two routes i.e symplastic and apoplastic routes (refer to fig 5.6)
Water movement up the stem
✓ see fig 5.8 page 107
✓ water moves up the stem through the xylem vessel
✓ the water moves through molecular cohesion or capillary, adhesion and
transpiration pull or suction force
✓ this is due a high water potential in the roots than in the leaves
✓ the water moves until it reaches the leaves where it is eventually lost through the
stomata during the process of transpiration
✓ transpiration produces a tensional pull from above creating a water potential
gradient in xylem drawing cohesive water molecules up the plant
✓ cohesion- attraction and sticking of water molecules to each other as they move up
through the xylem
✓ adhesion – tendency of water molecules to stick to the inside walls of the xylem
vessels as they rise up xylem of stem
✓ avoid saying that water moves through xylem by osmosis
32
Transpiration
✓ transpiration is the loss of water vapour from the leaves through the stomata by
diffusion
✓ the rate of transpiration is related to ; surface area of the leaf, stomata and
distribution of the air spaces in the leaf
✓ the larger the surface area of the leaf, the higher the rate of transpiration and vice
versa
✓ the more there are stomata in a leaf the faster the rate of transpiration
✓ the more the air spaces in a leaf, the faster the rate of transpiration. More water will
evaporate from the surface of the mesophyll cells into the intercellular air spaces
Environmental factors affecting the rate of transpiration
Factor
Temperature
Air movement
(wind speed )
Humidity
Light intensity
Water supply
Explanation
Transpiration increases as temperature increases. The kinetic energy of the
water molecules increases , so they diffuse faster
Transpiration increases as the wind speed increases. On a windy day water
evaporates more quickly than on a still day. An increase in air movement
removes water molecules as they pass out of the leaves making a steeper
concentration gradient for diffusion to take place faster
The rate of transpiration decreases as humidity increases. The higher the
humidity the less water evaporates from the leaves. Decrease in humidity
results in a lower concentration of water molecules outside the leaf,
making a steeper concentration gradient for diffusion to occur faster
Stomata open to allow gaseous exchange for photosynthesis, so water
vapour can diffuse out of the leaf
If water is in short supply the plant closes its stomata. This will cut down
the rate of transpiration. Transpiration decreases when water supply
decreases below a certain point
Wilting
✓ young plant stems and leaves rely on the turgidity of their cells
✓ plant cells become flaccid if more water is lost in the leaves than is absorbed by the
roots
✓ flaccid plant cells no longer press against each other so the stems and leaves lose
firmness and wilt
✓ wilting in plants does not mean the plant is dead, when water is supplied the plant
become again ( consider behaviour of spinach leaves between noon and in the
afternoon)
33
Measuring the rate of transpiration
✓ the rate of transpiration can be determined by measuring the rate of water uptake in
a stem
✓ the instrument used to measure the rate of transpiration is called the photometer
(see photo)
✓ it is not easy to measure how much water is lost from the leaf of a plant
✓ it is however easier to measure how fast the plant takes up water.
✓ The rate at which the plant takes up water depends on the rate of transpiration
✓ The faster the plant takes up water, the faster the plant transpires
✓ The photometer can be used to compare the rates of transpiration in different
conditions by recording how fast the water bubble moves along the capillary tube.
✓ You can compare how fast the plant takes up water in different conditions
Ways in which plants cut down water loss
Closing stomata
✓ Many plants lose more water through the stomata
✓ Plants close their stomata when it is very hot and dry or when they cannot
photosynthesize such as at night
Waxy cuticle
✓ Many leaves are covered with thick waxy cuticle made by the upper epidermal cells
✓ The wax waterproofs the leaves and reduce the amount of water lost
Hairy leaves
✓ Some plants have a hairs on their leaves
✓ The hairs trap a layer of moisture next to the leaves and reduce the amount of water
lost in the leaf
Stomata on the underside of the leaf
✓ There are more stomata on the lower side of the leaf than on the upper side
✓ The lower surface is usually cooler than the upper surface so less water will
evaporate
Cutting down on the surface area
✓ The smaller the surface area of the leaf, the less water will evaporate from it
✓ This will slow down the rate of transpiration
34
Adaptation of roots, stem and leaf to different environments
Most modifications are adaptations to very dry (arid ) environments. Plants modified to
cope with lack of water are called xerophytes
Plant
Ammophilia
(marram grass,
bent grass,
beachgrass )
Modifications
Have very long roots to search for water deep down in sand dunes
Leaves role up in dry weather to increase humidity around stomata
Sunken stomata to create high humidity and reduce the rate of
transpiration
Opuntia
(prickly pear/
cactus aloe)
Fine hairs around stomata, reducing air movement so humidity builds up
and transpiration reduced
Leaves had been reduced to spines /thorns. This reduces the surface area
for transpiration and also acts as defence against herbivores
Reduced number of stomata
Stomata close during the day
Pinus (pine
trees )
Fleshy green stems to store water
Leaves are needle- shaped to reduce the surface area for transpiration
and to resist wind development
Sunken stomata to create high humidity and reduce transpiration
Thick waxy cuticle on the epidermis to prevent evaporation from the leaf
surface
NB; add more examples of local plants
Translocation
✓ Translocation is the movement of sucrose and amino acids from regions of
production or of storage to regions of utilisation in respiration or growth
Translocation of applied chemicals
✓ chemicals can be sprayed on the leaves of plants because they can be absorbed and
enter the plant transport system
✓ once in the leaf, they are transported through the phloem to other parts of the plant
by translocation
35
Systemic chemicals
✓ systemic chemicals are applied, in the same way as above, and translocated to the
sap of the plant cells
✓ If an animal feeds on the plants while pesticides are in the sap, the animal will take in
the pesticides and become poisoned.
✓ In this way insect pests such as aphids and caterpillars can be controlled and the
crop yield can increase
Differences in the role of transpiration and translocation in the transport of materials
Translocation
Transport of sucrose and amino acids from
leaves to regions of utilisation or storage
Occurs in phloem tissue
Occurs by active uptake
Transpiration
Transport of water
Causes uptake of water by xylem
Movement of water in xylem is through
passive process
36
Animal nutrition
Balanced diet
A diet which contains all the main nutrients in correct amounts and proportion to
sustain a healthy life
Unbalanced diet leads to a deficiency disease or to a disorder such as obesity
Factors affecting energy intake
Dietary requirements depend on age, gender and activity
Energy needed in the body is mainly supplied by carbohydrates and fats
Males need more energy than females. why?
Females need more iron than males. Why ?
Children need more proteins than adults. Why ?
Pregnant woman need extra nutrients. Why?
Effects of malnutrition
Malnutrition is the result of not eating a balanced diet
There may be too much nutrients or too little nutrients In the food or the food may
be lacking one or more key nutrients
1. Obesity ; too much carbohydrates, fats or proteins in a diet can lead to
obesity. Obesity is dangerous to health. Obese people are more likely to get
heart diseases, stroke and diabetes.
2. Too much saturated fats lead to coronary heart diseases
3. Too little food can result to starvation. Extreme sliming diets such as those
avoiding carbohydrates result in a disease called anorexia nervosa (see video
posted in whatsapp platform)
4. The lack of dietary fibre /roughage in the diet causes constipation. This can
lead to bower / colon cancer and piles. Vitamin and mineral deficiency
diseases are all the result of malnutrition
37
Digestion
The human alimentary canal
Digestion; the breakdown of large insoluble food molecules into smaller soluble
molecules
Mechanical digestion; the breakdown of food into smaller pieces without chemical
change to food molecules (what breaks the food down ?)
Chemical digestion; breakdown of large, insoluble food molecules into smaller,
soluble ones using enzymes
Ingestion ; the intake of food into the mouth
Absorption ; the process of passing digested food molecules across the walls of the
intestines into the blood or lymph (what is lymph ?)
Assimilation ; use of food molecules by cells in the process of growth, reproduction
and repair ( i.e building up of the cell / incorporating into the cell)
Egestion ; the passing out of undigested food, in the form of faeces, through the
anus
The gross structure of the human alimentary canal
see fig 4.27 on page 85
The table below shows parts of the alimentary canal and their functions
Part/ organ
Mouth
Function
Food is ingested here
It is where mechanical digestion by cutting, chewing and grinding takes place
by action of teeth
Starch is chemically digested by salivary amylase into maltose
Oesophagus Bolus of food passes through by peristalsis from the mouth to the anus
Stomach
Muscular walls squeeze on food to make it semi solid
Gastric juices secreted contains protease to digest proteins into polypeptides
and peptides
Juices also contain hydrochloric acid to maintain optimum pH (1-2) for the
enzymes.
Duodenum
The acid also kill bacteria that may be found in food
First part of small intestines. Receives pancreatic juices that contains
protease, lipase and amylase that digests proteins, fats and starch
The juice also contain sodium hydrogen carbonate which neutralizes the acid
in the food from the stomach producing an optimum pH 7-8 for efficient
38
Pancreas
enzyme activity.
Secrete pancreatic juice into the duodenum (see above )
Liver
Makes hormones insulin and glucagon to regulate blood sugar concentrations
Makes bile that is stored in gall bladder. Bile contains salts and pigments
The salts emulsify fats, forming droplets with large surface area to make
digestion by lipase more efficient.
Digested food materials are assimilated here.
Excess glucose is stored here as glycogen, excess amino acids are deaminated
here.
Second part of small intestines.
Ileum
Secretes maltase and peptidase which break down peptides and maltose
Allows efficient absorption of digested food ( presence of villi )
First part of large intestine
Colon
Where water re-absorbed from undigested food
Rectum
Also absorbs bile salts and pass them back to the liver
The second part of the large intestine
Anus
Stores faeces until they are egested.
This has muscles to control faeces when they are egested from the body
Digestion in the alimentary canal
Mechanical digestion
digestion makes food easier to swallow and absorb
teeth break down large insoluble pieces of food into smaller soluble pieces
no chemical change in food is involved
action of teeth in food increases the surface area of food for enzyme activity
achieved by chewing the food in the mouth
Chemical digestion
involves a chemical change of the food from one sort of molecule to another
enzymes are involved to speed the process
enzymes work efficiently at body temperature (370 C ) and a suitable pH
the mouth, stomach and small intestines (duodenum and ileum) are the places
where chemical digestion takes place
39
the liver and the pancreas are important in secreting digestive juices (bile and
pancreatic juice ) to aid digestion
Chemical Digestion in alimentary canal
Enzyme
Site of action
Amylase
Protease
Lipase
Substrate
End- product
Mouth
Special
conditions
Neutral
Starch
Maltose
Duodenum
Stomach
Slightly alkaline
Acidic
Starch
Proteins
Maltose
Peptides and polypeptides
Duodenum
Slightly alkaline
Proteins
Duodenum
Slightly alkaline
Fats
Peptides and poly
peptides
Fatty acids and glycerol
Starch digestion
in the mouth starch is broken down by enzyme salivary amylase into maltose
in the duodenum starch is broken down into maltose by the enzyme pancreatic
amylase
in the ileum maltose is broken by enzyme maltase into glucose (simple sugars)
the glucose is then absorbed into the blood stream
Fats digestion
in the duodenum, emulsified fats are broken down by enzyme lipase into fatty acids
and glycerol
in the ileum the fatty acids and glycerol are absorbed into lacteals, which are part of
the lymphatic system
Proteins digestion
in the stomach proteins are broken down into polypeptides by enzyme pepsin
in the duodenum, proteins and polypeptides are broken down into amino acids by
enzyme trypsin
in the ileum, polypeptides are broken down into amino acids by enzyme peptidase
amino acids are then absorbed into the blood stream
Absorption of digested food molecules
the main region for the absorption of digested food is the ileum
Adaptation of the ileum for absorption
see fig 4.38 page 92
40
the ileum is very long and folded to increase the surface area for absorption
the ileum has villi (finger like projections which further increase the surface area for
absorption)
ileum has a network of blood capillaries with thin walls, allowing absorbed food to
pass through
Adaptation of the villi for absorption
see fig 4.39 page 93
inside each villus are blood capillaries that absorb amino acids and glucose
there are lacteals in each villus that absorb that absorb fatty acids and gklycerol
micro villi are also present to increase the surface area for absorption
epithelial lining of the villi are one cell thick to increase the ratye of diffusion
the epithelial cells also contain mitochondria to release energy for absorption of
nutrients against a concentration gradient
note;
❖ food molecules are mainly absorbed by diffusion but some can be
absorbed through active uptake e.g glucose
❖ hepatic portal vein transport absorbed food from the ileum to the
liver
❖ after meals the hepatic portal vein contains high concentrations of
glucose and amino acids as well vitamins and minerals
❖ the liver reduces (regulates ) the level of glucose back to normal
❖ see fig 4.40 page 94
The role of the liver in assimilation
excess glucose in blood is converted into glycogen for storage or broken down
through respiration in liver cells releasing energy
excess amino acids deaminated (nitrogen containing part of the amino acids is
removed to form urea, the remainder is used to release energy)
The role of fats in the body
body cells take up reformed fat molecules
fats can be used in respiration as a source of energy or stored, fats are a good
storage compound
fats insulate the body skin
fats also form the myelin sheath of nerve cells to prevent impulses from leaking out
41
Emulsification
bile salts emulsify fats turning them into smaller droplets with a large surface area
Chewing
performed by the teeth and it helps to mix food with saliva
the food particles also become smaller and it becomes easy to swallow
chewed food present an increased surface area
Peristalsis
see fig 4.34
it is a way in which food moves along the alimentary canal
the canal has a layer of circular muscles and longitudinal muscles
circular muscles contract behind food bolus and relax infront of food bolus
the food is pushed further down the canal
constrictions in one region are followed by another just below it in a wave-like
motion
the circular and longitudinal muscles are antagonistic
Diarrhoea
caused by bacteria e.g E coli, viruses and parasites
poisonous food, medication and stress can also cause diarrhoea
sometimes it may be due to underlying medical conditions
It is usually due to increased secretion of fluid into the small intestine or rapid
passage of undigested food through the rectum
Symptoms of diarrhoea include abdominal pain, especially cramping. Other
symptoms depend on the cause of the diarrhoea. Complications include
dehydration, electrolyte or mineral abnormalities and irritation of the anus
Treatment ; dehydration caused by diarrhoea can be treated with oral rehydration
solution (ORS).
Homework – how is ORS made at home??
42
Types and function of human teeth
The following table shows different human teeth and their functions
Type
Position in
mouth
Description
Incisor
Front
Chisel – shaped
Function
Cutting and
biting food
See fig.4.30 page 88
Canine
Either sides of
incisor
More pointed
Tearing food
Premolar
Behind canine
Molar
At the back
Have one or two
cusps and roots
Grinding food
Have 3 or 4
cusps and roots
Chewing and
grinding food
Structure of human tooth
See fig 4.31 page 88
You need to be able to identify the cement from a given diagram of a tooth
Functions of parts of human tooth
Enamel
Outermost part of the human tooth
Hardest part of the tooth- very difficult to break or chip
Can be dissolved acids
Dentine
Found just beneath the enamel
Hard like the borne but not as hard as the enamel
Have channels containing cytoplasm
Pulp cavity
Found in the middle of the tooth
Contain nerves
Contains blood vessels which supply the cytoplasm with foo and oxygen
Cement
Covers the root of the tooth
Has fibres growing out of it
Fibres attach tooth to the jaw bone but allow it to move slightly when biting or
chewing
Causes of tooth decay
What is tooth decay?
43
Food deposits and bacteria form a layer on the surface of the tooth called plague
Bacteria on the plaque feed on the sugars contained in the food and produce an acid
The acid slowly corrodes the enamel forming a hole
When the hole reaches the dentine, the acid dissolves more quickly because it is
weaker than the enamel
If the hole reaches the pulp cavity the bacterial infection can get to the nerves,
resulting to a tooth ache
Food for thought ;Why does it hurt when the hole reaches the pulp cavity in a
decaying tooth ?????
Ways of taking proper care of teeth/ prevention of tooth decay
Clean or brush your teeth regularly atleast three times a day (after every meal) to
remove plaque
Avoid sugary food, especially between meals, so bacteria cannot make an acid
Use dental floss/ toothpick to remove pieces of food and plaque trapped between
the teeth
Use a fluoride toothpaste (or drink fluoridated water). Fluoride hardens the enamel
Visit the dentist regularly, at least once every six months to make sure any tooth
decay is treated very early and plaque is removed
Do not use teeth for cracking hard nuts and bones
Eat crispy vegetables and fruits e.g apples and carrots and chew sugar free gum.
Fluoride
Fluoride help to fight bacteria, strengthen the teeth and prevent plaque formation
It also neutralises the any acid formed
Children get fluoride from the diet and also from toothpaste
It becomes part of the enamel of the developing teeth and makes it more resistant
to tooth decay
Advantages of adding fluoride to public water supplies
Tooth decay in the local population of children decrease
There is no need to buy fluoride toothpaste
Disadvantages of adding fluoride to public water supplies
It is a form of mass medication people have no choice about whether they want the
treatment or not
Fluoride can cause mottling of teeth fluorosis
If people are taking proper care of their, fluoridation is unnecessary
Fluoride is a benefit for growing children only but adults donot benefit
44
Transport in humans
The blood circulatory system
✓ This is a system of a pump and blood vessels , with valves to ensure one way flow of
blood
✓ The pump is the heart; blood vessels are the capillaries, arteries and veins
✓ The system transport blood around the body
✓ The heart keeps the blood moving and the valves ensure one way flow of blood
✓ Valves are found in the heart and veins and they keep the blood flowing in one
direction (prevent backflow of blood)
✓ Blood circulation in humans is known as the double circulatory system
Double circulatory system
✓ This means that blood passes through the heart twice for each complete circulation
✓ Pulmonary circulation- deoxygenated blood is pumped at low pressure from the
heart to the lungs of oxygenation then back to the heart
✓ Systemic circulation- oxygenated blood flows from the heart to the body and then
back to the heart
✓ The blood drops off oxygen as it as it passes through the organs of the body and it
becomes de-oxygenated
The structure and function of the human heart
✓ See fig 5.17 and fig5.18 on page 113
✓ the heart is the pump of the circulatory system, so its muscles (cardiac muscles )
constantly need energy
✓ coronary arteries provide the heart with glucose and oxygen
✓ the heart has two sides ; right side and left side
✓ the right receives deoxygenated blood from the body and pump it to the lungs for
oxygenation
✓ the left side receives oxygenated blood from the lungs and pump it to the body
✓ there are four chambers of the heart; left and right atria (singular-atrium), left and
right ventricles
✓ the atria receive blood from the veins and the ventricles squeeze blood to the
arteries
✓ there are valves in between the atria and ventricles (atrio-ventricular valves ) which
prevent the backflow of blood from the ventricles to the atria
✓ the tricuspid valve separates the right atrium and right ventricle while the bicuspid
valve separates the left atrium and left ventricle. Semi lunar valves lie between the
ventricles and the arteries that carry blood away from the heart( prevent backflow of
blood )
45
✓ the walls of the left ventricle are thicker than those of the right ventricle because
they have to pump blood much further to the rest of the body
✓ there are four main blood vessels found in the human heart; vena cava, pulmonary
artery, pulmonary vein and aorta
✓ What are the roles of the blood vessels mentioned above in blood circulation?
✓ Note ; generally arteries carry blood away from the heart and veins carry blood
towards the heart ( can you think of an exception ? )
The effect of exercise on heart
✓ a heartbeat is a contraction. Each contraction squeezes blood to the lungs and body
✓ the heart beats about 72 times a minute, more if you are younger and the rate
becomes lower the fitter you are
✓ during exercise the heart beat rate increases to pump more blood with more glucose
and oxygen to muscles – for muscles to release more energy using aerobic
respiration
✓ regular exercise is important for keeping the heart muscles in good tone- the heart
becomes more efficient in maintaining blood pressure and reduce the risk of
coronary heart diseases
✓ coronary heart diseases have got something to do with the blockage of the coronary
heart arteries and stroke
Coronary heart diseases
✓ see fig 5.30 page 119
✓ coronary heart diseases occur when the coronary arteries become blocked , this is
called atherosclerosis
✓ this happens when fatty substances become deposited on the inner walls of the
coronary arteries, decreasing the diameter of the lumen
✓ blood has to be pumped harder to get through the blood vessels to deliver oxygen
and glucose to the heart muscles
✓ there is also a risk of clot formation known as thrombosis inside artery walls
✓ the heart muscle will therefore not have enough energy to contract , and the heart
stops beating. This is called cardiac arrest or heart attack
✓ sometimes thrombosis may lead to chest pain, shortness of breath and hypertension
Causes of heart attack and preventive measures
Cause
Diet with too much saturated
animal fat
Lack of exercise
Explanation
Leads to cholesterol building up
in arteries eventually blocking
the blood vessels or allowing a
blood clot to form
Leads to obesity, being
46
Preventive measure
Eat cholesterol free
diet/ avoid diet with
too much saturated
animal fats
Take regular exercise
overweight puts extra strain on
the heart and makes it more
difficult for the person to
exercise
Smoking
Stress
Genetic disposition
Age
The heart muscle loses its tone
and becomes less efficient in
pumping blood
Nicotine damages the heart and
blood vessels
Tend to increase blood pressure
which in turn increases the risk
of coronary heart diseases
Coronary heart diseases are
more common in some families
than others. Conditions
transferred through genes
People aged 65 and older are
much likely to suffer from
coronary heart diseases. Aging
can cause changes in the heart
and blood vessels
Stop smoking
Avoid stress
n/a
Lead a healthy lifestyle
High blood pressure (HBP)
✓ normal blood pressure is less than 120/80 mmHg
✓ the numerator denotes pressure in arteries during contraction (systolic pressure)
and the denominator denotes pressure in arteries during relaxation of heart muscles
(diastolic pressure )
✓ any blood pressure that is higher than120/80 mmHg is high blood pressure
✓ this condition is also known as hypertension
Causes
Effects
Preventive
measures
Blood vessels
✓ there are three types of blood vessels
1. arteries
2. veins
3. capillaries
✓ they have different structures and functions
✓ see fig 5.20 page 115
47
Control
measures
Special diet for
HBP patients
Summary of structure and functions of blood vessels
Blood vessel
Function
Structure
Artery
Transport blood
away from the heart
Thick tough and
elastic walls
How structure is
related to function
Carries blood at high
pressure. Thick
muscle walls prevent
bursting.
Narrow lumen
Vein
Transport blood
towards the heart
Thin tough and
elastic walls
Maintains blood
pressure
Carries blood at low
pressure. No threats
of bursting of the
walls
Have valves
Prevent backflow of
blood as it moves at
low pressure
Wide lumen
Capillary
Transport blood to
cells of organs
Reduce resistance of
blood as it flows at
low pressure
Permeable one cell
Allows diffusion of
thick (very thin) walls materials between
capillary and
surrounding tissues
Blood
✓ see fig 5.27 page 118
✓ blood is the transport medium of dissolved substances around the body
✓ blood has the following components
1. plasma
2. red blood cell
3. white blood cell (lymphocyte and phagocyte)
4. platelets
✓ plasma is the liquid part of blood where most of raw materials and waste products
are dissolved e.g glucose and urea
✓ the components (blood cells) float in the blood plasma
48
Summary of the blood cells and their functions
Blood cell
Red blood cell
Lymphocyte
Structure
Nucleus absent in cytoplasm.
Haemoglobin present in
cytoplasm
Large nucleus
Phagocyte
Lobed nucleus
Platelet
Small fragments made by
born marrow cells
Function
Transport oxygen all
around the body
Produce antibodies to
fight bacteria and other
foreign bodies
Fight diseases by
engulfing, digesting and
killing bacteria
Responsible for blood
clotting to prevent
excessive blood loss after
a cut
Function of blood
1.
2.
3.
4.
clotting
transport of materials e.g glucose and urea
fight infections
maintains a constant body temperature
Main components of blood plasma/ substances transported in blood plasma
Substance
Amino acids
From
Small intestines (ileum)
Carbon dioxide
Glucose
Respiring tissue
Ileum
Urea
Heat
Hormones
Liver
Liver and muscles
Endocrine glands
To
Site of growth and tissue
repair
Lungs for excretion
All tissue for release of
energy in respiration
Kidney for excretion
All tissues
Target organs
Transport of oxygen
•
•
•
•
oxygen diffuses in the moist lining of the alveoli, through the epithelium and diffuses
through the capillary wall to the red blood cells in the lungs
oxygen combines with haemoglobin in red blood cells to form oxyhaemoglobin
oxygenated blood goes to the heart and then pumped through the arterioles and
capillaries to the body cells e.g muscle cells
Oxygen reacts with glucose in cells to release energy during respiration
49
Blood clotting
• See fig 5.29
• When there is a cut on the skin, fibrinogen (soluble protein ) is converted to fibrin
(insoluble )
• Fibrin is in the form of fibres and it forms a net across the cut where platelet cells are
trapped to make a blood clot
• Blood clot prevent excessive loss of blood and prevents entry of pathogens through
the cut
Capillaries and tissues
•
•
•
•
•
As blood enters the capillaries from arterioles, it slows down
This allows substances in plasma (like oxygen) to diffuse through the capillary wall
into the surrounding tissues
Plasma also leaves the blood vessels and it is now called tissue fluid (see fig 5.31)
Waste products diffuse from the cells into the plasma through the capillary walls
Tissue fluid that fails to diffuse back into the blood vessels is collected as lymph and
collected by the lymph vessels to join the lymphatic system (see fig 5.32)
The immune system
•
•
•
Immune system is the body’s defence against foreign bodies or pathogens
A pathogen is a disease causing organism
The body defence takes 3 forms ;
1. Antibody production;
• antibodies are produced by lymphocytes which are formed in the
lymph nodes. Lymphocytes produce the antibodies in response to the
presence of pathogens, eg bacteria
• pathogens have antigens on their surface. A different antibody is
produced for each antigen
• once the antibody has been made, it remains in the blood for long
term protection
• lymphocytes multiply when there are pathogens present
2. phagocytes ;
• phagocytes have the ability to move out of the blood capillaries to the
site of infection
• they then engulf and digest the bacteria and kill them
3. tissue rejection;
• transplant involves replacing a damaged organ with a donor organ
• the body treats the replacement as an invading organism and triggers
an immune response
50
•
•
•
•
the donor organ is rejected as a result of the production of the
antibodies to fight the foreign tissue
to prevent tissue rejection, the donor organ needs to be of similar
tissue type to that of the patient eg from a close relative
immunosuppressive drugs are used to switch off the immune system
this puts the patients at risk of dying from any disease so they must
be kept in isolation
There are two types of immunity
➢ active immunity;
✓ involves your body’s response to an unknown pathogen
✓ it is the production of antibodies specific to the antigen of a particular
pathogen
✓ this type of immunity also include vaccinations whereby the person is
injected with a weakened form of a disease causing pathogen and starts
producing antibodies against that pathogen (see fig 5.35 page 123)
✓ its disadvantage is that it takes time to develop, usually several weeks
✓ an extreme response to an antigen, resulting from active immunity is called
an allergic reaction
✓ examples of active immunity is fighting off cold
➢ passive immunity ;
✓ immune which involves antibodies obtained outside the body
✓ antibodies are obtained from another human being or animal and injected
into a person to counteract antigens suck as snake venom, rabies etc
✓ the advantage of this type of passive immunity is that it offers immediate
protection
✓ passive immunity builds up resistance to a disease due to immunizations
✓ examples of passive immunity is passing of antibodies from a pregnant
mother to a foetus
The differences between active and passive immunity
Active immunity
Can be gained after an infection or contact
with a pathogen or vaccinations
Lasts for a long time / provides long term
immunity.
Lymphocytes remain as memory cells. the
body can produce antibodies against the
same pathogen
Develops after a long time
Passive immunity
Can be gained through acquiring antibodies
from another individual
Lasts for a few days / provides short term
immunity
Memory cells are not produced. The body
remains passive and cannot produce
antibodies against the same pathogens
Develops immediately
51
Respiration in humans
What is respiration?
✓ Respiration is the release of energy from food substances in living cells
Types of respiration
✓ There are two types of respiration; aerobic respiration and anaerobic respiration
Aerobic respiration
✓ This is the breakdown of glucose in the presence of oxygen to release energy in cells
Anaerobic respiration
✓ Breakdown of glucose in the absence of oxygen to release energy in cells
What happens to the energy released in cells?
✓ The energy released in cells is stored in the form of ATP (Adenosine Triphosphate ).
✓ The energy can be lost in the form of heat (urine / faeces )
Aerobic respiration - Word equation
✓ Glucose + oxygen
water + carbondioxide + energy
Aerobic respiration – symbol equation
✓ C6H12O6 + 6 O2
6 H2 O + 6 CO2 + energy
Anaerobic respiration ( muscles ) – word equation
✓ Glucose
lactic acid + energy
Anaerobic respiration (muscles ) – symbol equation
✓ C6H12O6
2C3H6O3 +
energy (there is no carbondioxide produced )
Anaerobic respiration (in yeast ) – word equation
✓ Glucose
carbon dioxide + ethanol + energy
Anaerobic respiration (yeast ) – symbols
✓ C6H12O6
2CO2 + 2C2H5OH + energy
52
Similarities between aerobic and anaerobic respiration
✓ ATP is made in both types
✓ Energy is made from the breakdown of glucose
✓ Some energy is lost as heat
Differences between aerobic and anaerobic respiration
Aerobic respiration
Uses oxygen gas
Large amount of energy is released
Carbondioxide is always made
No alcohol or lactic is produced
Anaerobic respiration
Does not use oxygen gas
Little or small amount of energy is released
Carbon dioxide is sometimes made
Alcohol or lactic acid is produced
Uses of energy released during respiration
✓
✓
✓
✓
✓
✓
✓
Contraction of muscles to cause movement
Maintaining a constant body temperature
Cell division
Protein synthesis
Active transport
Growth organism
Passage of nerve impulses
Investigating the uptake of oxygen by respiring organisms, such as arthropods and
germinating seeds
✓ a simple respirometer is used
✓ a respirometer is a device used to measure the rate of respiration of a living
organism, by measuring its rate of exchange of oxygen and or carbon dioxide
Procedure
✓ a living arthropod (eg locust ) is placed in a boiling tube (test tube ) and a dead body
of the same organism is put in another test tube
✓ soda lime ( KOH) is placed in each test tube to absorb all carbondioxide
✓ to prevent contact between the organism and the soda lime, a cotton wool or wire
gauze is used
✓ a bubble of water is introduced in a capillary tube by touching it against a liquid
✓ the capillary is rested against a ruler and the position of water bubble noted
✓ after a minute, the new position of the water bubble is recorded
53
Results
✓ the water bubble moves towards the organism
Interpretation
✓ movement of water towards the organism shows that it is taking in air (oxygen)
✓ the rates can be compared with a range of organisms and germinating seeds
Anaerobic respiration in muscles
✓ muscles respire anaerobically when exercising vigorously because the blood cannot
supply enough oxygen to maintain aerobic respiration
✓ this leads to the formation of lactic acid
✓ the build-up of lactic acid in the muscles causes cramps (muscle fatique)
✓ muscle cramps stop an athlete from running
✓ At the end of the race, a sprinter has to pant to get sufficient oxygen to the muscles
to convert or oxidize the lactic acid back to harmless carbon dioxide and water.
Gaseous exchange
Human respiratory system
➢ See fig 6.11 page 138
Breathing
➢ Breathing also known as pulmonary ventilation
➢ The phases of breathing are ; inhalation, gaseous exchange, exhalation
Inhalation / inspiration/breathing in
➢ Two sets of intercostal muscles are attached to the ribs
➢ They are ant agonistic in nature that is they work to produce opposite effects
➢ When the external intercostal muscles contract, they cause the ribcage to move
upwards and outwards, increasing the volume of the thorax.
➢ The diaphragm is a tough fibrous layer or sheet of muscles at the base of the thorax
➢ When the diaphragm contracts, it moves downwards or flattens increasing the
volume of the thorax
➢ This reduces the air pressure in the thorax cavity
➢ As the air pressure outside the body is higher, air rushes into the lungs through the
mouth or nose
54
Gaseous exchange process
➢ The process involves the passage of gases such as oxygen into cells and
carbondioxide out of cells or transport system
➢ The air needs to be In contact with the gaseous exchange surface
➢ This is achieved by breathing
➢ Gaseous exchange relies on diffusion; concentration of oxygen in the air in the
alveoli is higher than in the capillaries, so a concentration gradient is created then
oxygen diffuses into the blood
➢ Draw fig 6.13 b) page 139
Breathing out/ exhalation/expiration
➢ When breathing out, the thoracic volume decreases so air pressure becomes greater
than outside the body
➢ Air rushes out of the lungs to equalise the pressure
➢ Internal intercostal muscles contract, ribs move downwards and inwards
➢ The diaphragm muscles relax and the and the diaphragm move up (become dome
shaped )
Features of gaseous exchange
1. Have thin epithelium/ thin walls ensure a short distance for gases to diffuse
faster
2. Are moist/ film of moisture to allow the gases to dissolve
3. Have a large surface area for gases to diffuse faster
4. Have a good blood supply – have a network of blood capillaries
5. Have a good ventilation with air
Differences between exhaled and inhaled air
Inhaled air
Large concentration of oxygen
Contains a small concentration of carbon
dioxide
Contain less moisture
It is less warm
Exhaled air
Smaller concentration of oxygen
Contains a large concentration of carbon
dioxide
Contain more moisture
It is warm
55
The composition of inspired and expired air
Gas
Nitrogen
Inspired air
79%
Expired air
79%
Oxygen
21%
16%
Carbondioxide
0.04%
4%
Water vapour
Variable
Saturated
Explanation
Not used or produced by
body
Produced in the process of
respiration
Produced in the process of
respiration
Produced in the process of
respiration, moisture
evaporates from the
surface of alveoli
Testing for carbondioxide
➢ lime water and hydrogen carbonate indicator solutions are used to test the presence
of carbon dioxide
➢ these solutions change colour when the gas is bubbled through
➢ if the gas bubbled through lime water is carbondioxide, the lime water turns milky
➢ if the gas bubbled through hydrogen carbonate indicator is carbondioxide , the
indicator changes from red to yellow
The effects of physical activity on breathing rate
➢ a respirometer is machine that can be used to measure the amount of air breathed
in and out over a period of time
➢ the volume of air breathed in and out during a normal relaxed breathing is about 0.5
litres
➢ this is called the tidal volume and the breathing rate is about 12 beats per minute
➢ during exercise the breathing depth increases and the volume increases to about 5
litres , depending on age , sex and fitness of the person
➢ the maximum amount of air breathed in and out in one breath is called the vital
capacity
➢ the breathing rate can increase to over 20 beats per minute during exercise
➢ the air in lungs is never completely emptied out, the air that remains in the lungs is
called residual air
➢ physical activity requires more energy and is obtained from high respiration rate
which requires more oxygen which results to increased oxygen demand
56
Effects of tobacco smoke on the respiratory system
➢ tobacco smoke contains a large number of toxic chemicals
➢ the main ones are carbon monoxide, nicotine, smoke particles and tar
➢ nicotine and carbon monoxide enter the blood stream, tar and smoke particles do
not- they stay in the lungs
Chemical
Carbon monoxide
Nicotine
Effect on respiratory system
Poisonous gas. Combines
with red blood cells
preventing them from
transporting oxygen
Addictive, results in the
continuation of smoking
exposing the lungs to
harmful substances
Effect on other systems
Increases the risk of
thrombosis which can lead
to a heart attack
Raises blood pressure and
heart attack.
Causes thrombosis and lead
to a stroke
Stimulates the brain
Can pass to blood of foetus
from its mother resulting in
reduced birth weight
Smoke particles
Irritate the air passages
causing inflammation and
increased mucus production
resulting to chronic
bronchitis
Coughing in the presence of
smoke particles
Tar
In the alveoli can lead to
emphysema
A carcinogen increases the
risk of lung cancer (cells start
to divide out of control)
It lines the air passages
increasing mucus
production, paralysing and
damaging cilia causing
bronchitis.
57
EXCRETION IN HUMANS
➢ excretion is the removal of toxic materials and waste products of metabolism from
organisms
➢ NB; faeces are not an example of excretion , egestion is not excretion. Faeces are
mainly undigested food materials that have passed through the gut, but which have
not been made in the body. The only excretory materials in faeces are the bile
pigments
Three main excretory products in humans
1. Carbondioxide;
• Produced by all cells during respiration and excreted by the lungs
2. Urea
• Produced by the deamination of excess amino acids in the liver and excreted
by the kidneys
3. Bile pigments
• Produced by breakdown of haemoglobin in the liver and excreted in the
faeces
Formation of urea, breakdown of alcohol, drugs and hormones in the liver
✓ Surplus amino acids in blood cannot be stored
✓ They are deaminated by the liver as follows; The nitrogen containing part of the
amino acid is removed by the liver to for urea, the sugar residue is respired to
produce energy
✓ The urea is returned to the blood stream and filtered out when it reaches the
kidneys. A small amount if urea is excreted in sweat
✓ The body treats alcohol as a poison. The liver breaks down poisons like alcohol
✓ Prolonged and excessive use of alcohol damages the liver and may cause it to fail
✓ Overdose of drugs such as paracetamol can result in death due to liver failure,
because the liver cannot cope with breaking down such a high concentration of the
chemical
✓ The liver also converts hormones into inactive compounds. These are filtered off the
blood by the kidneys
Other functions of the liver
1. Controls the amount of glucose in the in the blood with the help of hormones insulin
and glucagon
2. Stores carbohydrates as the polysaccharide glycogen
3. Make bile by breaking old red blood cells, storing the salts and excreting the remains
of the pigment of the bile
4. Stores vitamin A and D and iron
58
5. Makes cholesterol which is needed to make and repair cell membranes
The human excretory /urinary system
✓ the kidneys are part of the excretory system
✓ two kidneys are found in humans at the back of the abdomen behind the intestines
✓ draw fig 7.4 page 152
The human kidney
✓ draw fig 7.5 page 152
✓ the kidney has 3 parts ;
1. cortex
2. medulla
3. pelvis
✓ the ureter leads from the pelvis. It carries urine that the kidney has made to the
bladder
✓ kidneys are made of millions of nephrons
✓ each nephron begins in the cortex, loops down into the medulla, back into the cortex
and then goes back into the medulla, to the pelvis and finally to the ureter
The nephron
✓ daw fig 7.7 page 153
There are three main functions of the kidney
1. it removes urea formed through deamination
• the kidney removes or take out unwanted substances form the blood and
pass them into the bladder to be excreted
2. removes excess water, they maintain the correct concentration of blood by bringing
about osmoregulation (maintenance of water and salt in the blood )
3. removes hormones and drugs broken down by the liver
Formation of urine
✓ urine is formed by two processes in the kidneys (nephron)
1. ultra- filtration
2. reabsorption
✓ ultra-filtration is filtration under high pressure,
• it occurs in the bowmans capsule (cup shaped)
• there are thousands of bowmans capsules in each kidney
• the bowmans capsule has a network (knot ) of capillaries in the middle
• the renal artery brings blood into the bowmans capsule
59
•
✓
✓
✓
✓
water, salts , glucose and urea are squeezed out of the blood into the
bowmans capsule (known as the glomerular filtrate )
• proteins and blood cells remain in the blood ( too big to pass through walls of
blood capillary)
as the glomerular filtrate passes through loop of Henle, reabsorption of essential
substances back into the blood takes place.
• Water is reabsorbed through osmosis while glucose and salts pass back into
the blood by diffusion and active uptake
• Amount of water reabsorbed depends on the state of hydration of the body
and is controlled by the secretion of Anti-Diuretic Hormone (ADH)
• ADH is produced by the hypothalamus in the brain, it increases water
reabsorption, reducing the amount of water passed out in the urine
Filtered blood returns to the vena cava via the renal vein
Formed urine passes down the ureter into the bladder for temporal storage
Sphincter muscles control the release of urine through the urethra
Dialysis and its application in kidney machine
✓ dialysis is a method of removing one component from a solution using the process
of diffusion.
✓ the principles of dialysis is used in a kidney dialysis machine to clean blood
✓ a patient with kidney failure need to have toxic materials removed from the blood,
for them to stay alive
✓ blood enters the kidney machine from the patient’s vein in the arm and it is kept
moving through the dialysis tubing in the machine using a pump
✓ the tubing (sermi –permeable ) is very long to provide a large surface area
✓ the dialysis fluid has a composition similar to blood plasma, this makes sure that the
essential useful substances in the blood do not move out to the dialysis fluid (e.g
glucose)
✓ waste product , however, are not contained in the dialysis fluid so that they can
easily diffuse out of the blood to the dialysis fluid (e.g urea)
✓ urea, uric acid, excess salts and used hormones are removed from the blood by
diffusion into the dialysis fluid
✓ the cleaned blood is then returned to the patient by passing it through a bubble trap
to remove any air bubbles
✓ draw fig. 7.9 page 155
60
Advantages and disadvantages of dialysis treatment
Advantages
treatment starts immediately after diagnosis
treatment can continue for a long time
there are few complications with treatment
it is not as expensive as kidney transplant
Disadvantages
patients are attached to a machine
throughout the treatment
it may be too expensive for many people
the nearest dialysis machine may be too far
away to visit regularly
side effects e.g nausea and feeling cold
there are dietary restrictions
It is time consuming
✓ some kidney failure patients may have operations to replace damaged kidney(s).
✓ advantages and disadvantages of kidney transplant are as follows
Advantages and disadvantages of kidney transplant
Advantages
Patients are free from a machine
The patient has a good quality of life
There are few dietary restrictions
The patient has better overall health
Disadvantages
Surgery is required
It is very expensive
There has to be a tissue match with donor
There may be organ rejection
There are not many donors
The patient must be on life- long medication
61
Coordination and response
➢ this is the ability to detect and respond to internal and external stimuli
Hormones
➢ chemical secreted by an endocrine gland, transported in blood stream and affecting
a target organ
➢ nerves (neurones) carry electrical messages (impulses) very quickly form one part of
the body to another but animals also use chemical messages
➢ endocrine glands have many blood capillaries running right through them
➢ when the endocrine glands make hormones, they release the hormones directly into
the blood stream
➢ the hormones are carried in the blood to all parts of the body, dissolved in plasma,
affecting only specific parts of the body
➢ used hormones are broken down in the liver and lost in urine
➢ examples of hormones are;
1. adrenaline (animal hormone)
2. auxin (plant hormone)
Chemical control of metabolic action by adrenaline
➢ metabolism refers to all the chemical reactions that take place in the body of living
organisms
➢ adrenaline is sometimes called the danger hormone
➢ adrenaline is secreted by the adrenal glands which are found above the kidneys
➢ this hormone is secreted in large amounts when one is frightened, excited or
stressed
➢ the brain sends impulses along the neurones to adrenal glands which then secrete
adrenaline into the blood
➢ the adrenaline prepares the body for fight or flight
➢ adrenaline has the following effects;
1. causes heart rate to increase, so that muscles are supplied with blood
containing glucose and oxygen more quickly to prepare muscles for working
2. reduce blood supply to the skin and digestive organ, so that blood is diverted
to vital organs e.g heart
3. stimulate the liver to convert glucagon to glucose ( used in respiration)
62
Uses of chemicals in food production
Animal hormones
➢ farmers sometimes use hormones to make their animals grow faster or produce
more of a particular product e.g meat and milk
➢ bovine somatotropin (BST) is a hormone naturally produced by cattle. However if
cows are given extra BST they produce more milk
Plant hormones
➢ gardeners use hormones to improve looks of their gardens and to increase yields
from the plants
➢ weedkillers contain plant hormones auxin and they selectively destroy broadleaved
plants
➢ ethane gas is used to help fruits grow large and ripen well or fast (e.g banana,
mangoes, tomatoes apples etc)
how weedkillers are effective in killing weeds
➢ when weedkillers are sprayed on weeds, the weeds respond by growing very fast,
exhausting all the nutrients in their food reserves due to high respiration rate then
they die leaving more space, nutrients and water for the crop to grow
63
coordination in plants
Tropic responses
Tropism
➢ directional growth response
phototropism
➢ a plant growth in response to light
gravitropism
➢ a response in which parts of a plant grow towards or away from gravity
there are two stimuli for a plant
1. light
2. gravity
phototropism
➢ photo means light
➢ there are two main parts of a plant i.e shoot and roots
➢ the shoot always grows towards the light sources and that response is called
positive phototropism
➢ the roots also respond to light by growing away from light sources and this response
is called negative phototropism
gravitropism
➢ plants can respond to gravity either by growing toward or away from the pull of
gravity
➢ this is called gravitropism
➢ the shoot tend to grow away from the pull of gravity and this called negative
gravitropism
➢ roots always grow into the soil towards the pull of gravity and this is called positive
gravitropism
control of plant growth by auxin
➢ auxins are plant growth substances
➢ referring to auxins as hormones is not very accurate as they are not secreted in
glands and not transported in blood
➢ auxins are produced by tips of shoots and tips of roots of growing plants
64
➢ in shoot accumulation of auxins results to stimulation of growth cells whereas when
they build up in roots they slow down cell growth
phototropism and gravitropism ( see page 166 – 167)
➢ auxins are responsible for growth of cells in shoots of plants
➢ when light shines onto a shoot from all around the auxins are distributed evenly
around the tip of the shoot
➢ the cells will grow at about the same rate so the shoot grows straight upwards
➢ this is what happens in plants growing outside
➢ if light shines from one direction in to a plant the auxins tend to accumulate on the
shady side, the cells on the shady side lengthen faster than those on the enlightened
side (see fig.8.6 page 166)
➢ the cells in the two region / sides elongate at different rates resulting to differential
growth leading to the shoot bending bending towards the light as it grows
➢ this is called positive phototropism
➢ if a shoot is placed horizontally on the ground in the absence of light the auxins
accumulate on the lower side of the shoot due to the pull of gravity
➢ this makes the cells on the lower side of the shoot to grow more quickly than the
cells on the upper side , so the shoot bends upwards
➢ this is called negative gravitropism
➢ if a root is placed horizontally in the absence of light, auxins also accumulate on the
lower side of root due to gravity
➢ however, this makes the cells on the lower side of the root to grow more slowly
than those on the upper side resulting to differential growth , so the root bends
downwards
➢ this is called positive gravitropism
➢ see fig. 8.88 page 167
taxis / taxic response
➢ movement of an organism in response to an external stimulus
➢ these are non-directional responses made by invertebrate animal
➢ the animals move randomly until it escapes from an unpleasant stimulus eg
paramecium, woodlouse
➢ some animals are attracted to the stimulus e.g moths moving towards an electric
lamp/ light bulb at night
65
Nervous control in animals
➢ the way in which receptors pick up the stimulus and then pass the messages
(impulses/ electrical messages) to the effectors is called coordination
➢ effectors can be muscles and glands
➢ most animals have two methods of sending messages from receptors to effectors
➢ the fastest one is by means of nerves
➢ receptors and muscles make up the animal nervous system
➢ a slower method is by means of chemicals called hormones. Hormones are part of
the endocrine system
➢ the nervous system consists of receptors, nerves, brain and spinal cord
➢ the nervous system is made up of two parts; see fig. 8.11 page 169
1. central nervous system (CNS) i.e the brain and spinal cord
2. peripheral nervous system (PNS) i.e nerves and receptors
➢ the nerves connect all parts of the body to the CNS
➢ sense organs are connected to the peripheral nervous system
➢ sense organ is a group of receptor cells responding to specific stimuli e.g light, sound
temperature, chemicals, touch
Examples of sense organs and the stimuli they respond to
Sense
Hearing
Sense organ
Ear
Stimulus
Sound, body movement
(balance)
Sight
Eye
Light
Smell
Nose
Chemicals
Taste
Tongue
Chemicals
Touch
Skin
Temperature , pain, touch,
pressure
➢ information picked up by receptors is sent along nerves to the CNS.
➢ Inside the CNS, information coming from different receptors and information
generated within the brain itself is processed and coordinated
➢ Messages are then sent out along nerves to muscles or glands to tell them what to
do ( those muscles and glands are known as effectors)
➢ Effectors carry out actions in response to messages from the CNS (see fig.8.10
page 168)
➢ Both the peripheral and CNS contain special cells called the nerve cells neurones
The reflex arc
➢ The path along which a nerve impulse travels in a reflex action is called a reflex arc
➢ reflex arc start at the receptor, travel via a sensory neurone to the spinal cord (or
brain), across a relay neurone and leave the spinal cord (or brain ) via the motor
66
➢
➢
➢
➢
➢
➢
➢
neurone, which carries the impulse to an effector such as muscle (see fig. 8.19 page
172)
a reflex action is an automatic response to a stimulus , the route involves the parts
mentioned above
receptors; receive the stimuli. They consists of nerve endings in the skin
sensory neurones; these carry impulses from receptors to the spinal cord i.e they
pass electrical signals from receptors to the CNS. They have a long head called
Dendron and an axon. There are several shorter threads of the cytoplasm called
dendrites. Their function is to pick up the messages from the cells
relay neurones; carry impulses from the upper part to the lower part of the spinal
cord. The whole of this neurone is found inside the spinal cord. It has many dendrites
motor neurones; carry impulses from the spinal cord to the muscles. It has a long
axon which stretches out from the cell
effectors; respond to the impulses reaching them accordingly. These are usually
biceps , triceps and glands
synapse
• an impulse from the finger tip has to pass at least 3 neurones before reaching
the brain and produce a conscious sensation
• the impulse pass from one neurone to another
• the regions where impulses cross from one neurone to another are called
synapses
• a synapse is a junction between two neurones
structure of a sensory neurone
➢ draw fig. 8.14 a page 170
structure of a motor neurone
➢ draw fig.814 b page 170
structure of a relay neurone
➢ draw fig.814 c page 170
structure of a synapse
➢ draw fig.8.15 page 170
functions of the myelin sheath
1. it insulates neurone
2. it makes transmission of impulses more efficient and quickly
3. prevents the leakage of electrical signals from the axon
67
functions of the cytoplasm
1. passes electrical signals along
2. it is elongated to carry impulses for a longer distance
3. it is modified to form dendrites
Differences between sensory and motor neurones
Sensory neurone
Has a short axon and one long dendron
Cell body found along the side of the
neurone and has no dendrites
Has a receptor
Motor neurone
Has a long axon and many short dendrites
Cell body found at the one end with
dendrites
Has no receptor
Voluntary and involuntary actions
Voluntary action
➢
➢
➢
➢
action that one does as one wishes
one consciously think, then make decisions about what to do
it involves the brain
examples; walking, talking, smoking, laughing etc
involuntary action
➢ also known as reflex action
➢ action that automatically occurs, one does not think about it
➢ it is means of automatically and rapidly integrating and coordinating stimuli with
responses
➢ examples; blinking, sneezing, breathing, snoring etc
Antagonistic movement of muscles
➢ antagonistic means opposite effects
➢ examples: muscles in the arm are of 2 types
1. biceps
2. triceps
bones that are associated with the muscles in the arm
➢
➢
➢
➢
➢
upper arm - humerus
lower arm - radius and ulna
bones and muscles are joined together by bone fibres called tendons
muscles which action to produce opposite effects are called antagonistic muscles
muscles bending a limb are called flexors
68
➢ muscles straightening a limb are called extensors
The central nervous system (CNS)
➢ made of the;
1. brain
2. spinal cord
the nervous system
draw fig. 8.11 page 169
the brain
draw fig. 8.12 page 169
The structure of the brain
➢ the brain is the enlarged front end of the central nervous system (CNS)
➢ it controls everything that goes on inside the body
➢ it receives information from the external and internal environment and makes
decisions about what to do and how to respond to this information
➢ it then sends instructions to the parts of the body that will carry them out
Different parts of the brain and their functions
➢ cerebrum
▪ largest part of the brain
▪ involved in; memory, learning, reasoning, conscious thought, feelings and
emotions
➢ cerebellum
▪ coordinates voluntary movements such as running, walking, dancing and playing
soccer
▪ also balances the body, for example when riding a bicycle
➢ medulla oblongata (brain stem)
▪ regulates involuntary actions such the heart rate and breathing rate of the body
▪ also involved in other reflex actions like swallowing, sneezing and vomiting
➢ hypothalamus
▪ regulates body temperature and water balance in the body
▪ also controls the endocrine system
➢ pituitary gland
▪ part of the endocrine system and secretes many different hormones
▪ it regulates the other endocrine glands (it is the master gland )
69
▪
the pituitary gland produces;
1. anti- diuretic hormone (ADH) which causes kidneys to reabsorb water
2. thyroid stimulating hormone which causes the thyroid to produce
thyroxine
3. growth hormone which stimulates growth
Comparing nervous and hormonal system
Nervous system
Made of neurones
Information is transmitted in the form of
electrical signals or impulses
Information transmitted along nerve fibres
Effect of a nerve impulse usually last for a
very short time
Hormonal system
Made of secretary cells
Information is transmitted in the form of
chemicals (hormones)
Chemicals are carried, dissolved in blood
plasma. Chemicals travel more slowly
The effect of a hormone may last longer
The structure of the human eye
Draw fig. 8.24 page 174
Functions of parts of the human eye
➢ sclera
• keeps the spherical shape of the eye
• protects the eyeball
➢ conjunctiva
• thin transparent membrane, sensitive layer on the surface of the cornea
• stops the entry of dust particles and protects the eye from diseases
➢ cornea
• transparent tissue at the front of the eye, it refracts light rays entering the
eye helping to focus them
➢ iris
• a coloured muscular diaphragm that controls how much light enters the eye
(i.e controls the size of the pupil )
➢ lens
• a soft ,transparent, convex shaped, flexible, jelly like structure found behind
the pupil.
• It refracts light rays that enter the eye to focus them on the retina
➢ Aqueous humour
• Transparent, colourless water liquid found at the front of the eye
• Maintains the shape of the cornea (front part of the eye)
70
➢ Ciliary muscle
• Circular muscle that changes the shape of the lens to allow focusing of light
on the retina
➢ Suspensory ligament
• Holds the lens in place or attaches the lens to the ciliary body so that the lens
is held in place
➢ Vitreous humour
• Jelly like clear substance in the eye that gives the eyeball its shape
➢ Retina
• Inner layer of the human eye, composed of light sensitive cells called rods
and cones
• Converts light energy into nerve impulses where eyeball image is formed
➢ Optic nerve
• Transmit nerve impulses to the brain from the retina
➢ Blind spot
• This is where the optic nerve leaves the eye
• There are no rods or cones here so no image can be formed in this spot
➢ Fovea
• Part of the retina formed only of cones
• Place of clearest vision
➢ Pupil
• Hole through which light enters the eye (hole between iris muscles)
• It controls the amount of light reaching the retina
➢ Choroid
➢ Dark pigmented layer that absorbs light so that the light does not get
scattered around the inside of the eye and has blood vessels that bring
nutrients to the eye
Functions of the human eye
1. Vision
2. Accommodation
3. The rest of the eye helps to focus light on the retina
➢ The eyelashes and eyebrows help to stop dirt from landing on the surface of the eyes
➢ The retina contain two sets of cells
1. Rods
 Lets you see in black and white
2. Cones
 Gives colour vision but only in bright light
➢ When light falls on the receptor cells on the retina , the cell sends a message along
the optic nerve to the brain
➢ The brain sorts out all the messages from each receptor cell and build up an image
71
➢ Receptor cells are packed in the fovea (yellow spot) – this is where light is focused
when you look straight at an object
➢ All receptor cells in the fovea are cones
➢ There are no receptor cells in the blind spot (part where the optic nerve leaves the
eye)
➢ If light falls on the blind spot , no message will be sent to the brain, hence no image
formed
➢ Behind the retina is the choroid which absorbs all light after it has been through the
retina, so it does not get scattered around the inside of the eye.
Differences between rods and cones
Cells
Rods
Cones
Function
Sensitive to low light
intensity
Distribution
Found scattered
throughout the
retina but not in the
fovea
Detect shades of
grey, black and white
images
Sensitive to high light Concentrated in the
intensity
fovea
Detect colour, donot
operate in the dark
Comments
Provide us with night
vision where we can
recognise shapes but
not colours
There are three
types of cones
sensitive to red,
green and blue light
How light is focused onto the retina
➢ For the brain to see images, there must be a clear image focused on to the retina
➢ Light rays must be bent or refracted so that they focus exactly on the retina
➢ The cornea is responsible for most of the bending of the light (the lens is also
involved in bending of the light and make fine adjustments)
➢ The image formed is upside down (inverted )
➢ The brain interprets it so that it is seen the right way up
➢ Draw fig. 8.27 page 176
Accommodation
➢ The adjustment in the shape of the lens to focus the light coming from different
distances is called accommodation
➢ The amount of focusing needed by the lens depends on the distance of the object
being viewed
➢ Light from nearer objects require a more convex lens that light from distant objects
➢ The shape of the lens needed to accommodate the image is controlled by the ciliary
body which contain a ring of muscles
72
•
Distant objects
✓ Ciliary muscles relax, become larger in diameter
✓ Suspensory ligament become tight
✓ Tight suspensory ligament pulls the lens
✓ The lens becomes thinner (less convex)
✓ The thinner the lens the lens, the longer the focal length, and the
object is clearly focused onto the retina
• Near / close object
✓ The ciliary muscles contract, become smaller in diameter
✓ Suspensory ligament become slack
✓ Slack suspensory ligament stop pulling on the lens
✓ The lens become thicker ( more convex)
✓ The thicker the lens, the shorter the focal length, and the near object
is clearly focused onto the retina
➢ See fig. 8.28 page 177
The pupil reflex
➢ Infront of the lens is a circular piece of muscle tissue called the iris
➢ The iris contains pigments (coloured substance which absorb excess light and stop it
from getting through the retina)
➢ In between the two iris muscles is a hollow space called the pupil
➢ The size of the pupil can be adjusted, the wider the pupil size the more light can get
into the retina
➢ The pupil reflex changes the size of the pupil to control the amount of light
➢ When there is too much light the iris closes and makes the pupil small to stop too
much light from getting into the eye and damage the retina
➢ The iris contain muscles which allow it adjust the size of the pupil
➢ Circular muscles go in circles around the pupil and radial muscles run outwards from
the edge of the pupil
➢ When circular muscles contract they make the pupil get smaller or constrict
➢ When the radial muscles contract, they make the pupil get larger / wider/ dilate
➢ This response of the iris to a change in light intensity is an example of a reflex action
➢ Nb; circular and radial muscles affect the size of the pupil . ciliary muscles affect the
size and shape of the lens
➢ Draw fig. 8.26 page 176
73
Homeostasis
➢ Maintenance of a constant internal environment
The human skin
➢
➢
➢
➢
➢
➢
➢
➢
➢
➢
➢
➢
➢
the human skin is made up of two layers
the top layer is called the epidermis and the lower layer is called the dermis
draw fig. 9.8 page 190
all cells are surrounded by tissue fluid
the temperature and concentration of this fluid must not change no matter how the
outside environment changes the body keeps the tissue fluid at 370 C with the right
amount of water and food dissolved in it
all warm blooded animals have a way of controlling their body temperature, water,
Ions/ salt levels and breathing mechanisms
each of these body functions are kept at a constant level by a homeostatic system
several organs in the body are involved in homeostasis
the kidneys, under the control of the hypothalamus, regulate the amount of water in
the tissue fluid
the liver and pancreas keep the level of glucose constant
the corrective mechanism that function to bring any change in the body back to
normal level is called a negative feedback
positive feedback is rare (not often) in living organisms under normal conditions ,
and when it occurs it become difficult to reverse and may result to death
see fig.9.10 page 191 (example)
➢ maintaining a constant internal environment is vital for organisms to stay healthy
➢ increase in temperature, water level and nutrient concentration could lead to death
Temperature control in humans
➢ mammals and birds are warm blooded animals, they maintain a constanat body
temperature of 37 0C
➢ the skin has mechanisms to lose heat when we get too hot and ways of retaining
heat when we get too cold
Role of fats in the body
➢ fats insulates the body, preventing heat from escaping from the body
➢ the human skin is the largest sense organ and can detect several types of
environmental changes through the basic sense of touch
74
➢ the sense of touch allows us to detect skin sensations, these include pressure, pain,
and temperature
Temperature receptors (thermoreceptors) and temperature
➢ Temperature are able to detect heat and cold and are found throughout the skin
inorder to allow sensory reception throughout the body
➢ Heat receptors are closer to the skin surface while cold receptors are found deeper
in the dermis
➢ The part of the brain that controls body temperature is called the hypothalamus
➢ There are also thermocereptors within the brain itself (in the hypothalamus)
➢ The hypothalamus processes this information and sends impulses to the effectors (
e.g sweat glands, hair muscles, muscles in the arterioles) which a response to the
stimulus
➢ The responses produced by the effectors help us to maintain a constant body
temperature. For example, when the hypothalamus senses that the body
temperature is too high, it sends impulses to the muscles in the arterioles supplying
the capillaries with blood in the skin, causing them to relax, then the arterioles dilate
Mechanisms used by the human skin to regulate body temperature
1. Sweating
✓ When the body feels too hot sweat is released.
✓ Sweat is a liquid made up of water, some salt and urea
✓ Sweat glands in the skin secrete sweat through sweat pores on the
skin surface
✓ As the water in the sweat evaporates, it removes heat from the skin,
cooling it in the process
✓ When the body is too hot, the volume of sweat released increases
✓ Prolonged sweating can lead to dehydration and shortage of salts,
when the body is too cold, the amount of sweat produced is reduced
2. Vasodilation
✓ When the body feels hot, heat is transported around the blood
stream
✓ When blood passes through the capillaries near the skin surface, heat
is lost by radiation
✓ Arterioles (small arteries) are involved. these have muscles in them,
when the body feels too hot, the muscles relax creating a wide lumen
through which a lot of blood pass
✓ The mechanism is called vasodilation
✓ More heat is radiated so the body cools down
75
3. Vasoconstriction
✓ When the body feels too cold, muscles in the arterioles contract,
creating a narrow lumen through which little blood can pass
✓ Less heat is radiated and this is called vasoconstriction
4. Shivering
✓ When the body gets overcooled, shivering occurs to generate heat
✓ Shivering involves contraction of erector muscles
➢ Draw fig. 9.9 page 190
Control of glucose content in blood
➢
➢
➢
➢
➢
➢
➢
➢
➢
➢
➢
Cells in the pancreas constantly monitor the concentration of glucose in the blood
These cells detect extra glucose in blood and secrete a chemical (insulin)
Insulin is a hormone and is carried in the blood stream all over the body
When insulin reaches the liver, it stimulates the liver cells to take up the glucose
from the blood
The liver cells use the glucose for respiration and the liver cells also convert some of
the extra glucose to fats and some to glycogen for storage
The glycogen is sored glucose and is stored in the liver( glycogen is easy to store
because it is not readily soluble like glucose-glycogen is insoluble )
When the level of glucose falls below normal, the secretion of insulin stops
When the levels of glucose goes on lower than normal, the liver cells will be
stimulated by glucagon hormone (secreted in pancreas) to break down some of the
glycogen they have stored back to glucose
The glucose will be released back to the blood stream and the level of glucose
returns back next to normal
Very high glucose level or very low glucose level in the blood can damage the brain
leading to a coma and possibly death
NB; insulin is a protein, so it is usually given as an injection to patients’ blood stream
to individuals who require it. If taken orally, it would be digested by protease( in the
stomach) into amino acids
Control of blood sugar concentration in a person with sugar diabetes
➢ What is sugar diabetes?
➢ The following can be practiced to control the concentration of blood sugar in a
person with sugar diabetes
1. Exercise to reduce weight which will make the insulin secreted to be
sufficient
2. Use insulin injection which promotes the oxidation of glucose or use pills (the
pills don’t have insulin but have chemicals that stimulate secretion of insulin
76
3. Reduce carbohydrates intake to reduce the sugar / glucose absorbed
Long term effects of sugar diabetes
➢ Long term effects of sugar diabetes include
✓ Damage to blood vessels
✓ Heart attack
✓ Stroke
✓ Problems with kidneys, eyes, gums, feet and nerves
77
DRUGS
*Drugs – any substance taken into the body that modifies or affects chemical reactions
There are two types of drugs;
1. Medicinal drugs ( commonly known as medicines) ;
▪
Drugs that can be obtained with a prescription from a doctor e.g ARV drugs
▪
Can also be drugs that are bought over the counter from chemists and
supermarkets e.g paracetamol, asprin etc
NB: medicinaldrugs help the body to fight diseases or to treat injuries or pain
2. Non-medicinal drugs ( recreational drugs) – these are drugs that are not medicines
NB: people take non-medicinal drugs just to make themselves feel good
Eg alcohol
There are two kinds of drug;
1. Legal drugs
2. Illegal drugs
Different types of medicinal drugs can be used to treat different types of diseases and
symptoms.
The following table shows some examples of medicinal drugs and their uses.
Drug name
Uses of drug
Painkiller( also known as analgesics)
Used to reduce pain. Examples are
*Paracetamol, and asprin
Antacids
Treat indigestion (or heartburn).
They basically reduce the discomfort caused
by acids in the stomach. Eg Rennies
Antibiotics
Used to treat infections caused by bacteria
and viruses.* Penicillin and Streptomycin are
examples of antibiotics. Penicillin is derived
from a fungus called Penicillium notatum.
Some people are however allergic to
penicillin, so they show some allergic
78
reactions. People allergic to penicillin must
wear a medical alert bracelet.
Fungicides
Used to treat fungal infections like thrush
and athletes foot
Antidepressants
These drugs help people who are feeling
depressed(too sad) and who may even think
of taking their own lives. This drugs makes
them feel better and want to live again.
Example is Prozac.
Some drugs can be legal and non-medicinal, for instance tobacco and alcohol. While other
drugs can be illegal and non-medicinal, for instance herion, solvents and dagga (increasingly
made legal in most parts of the world including SA).
Drug abuse, whether legal or illegal, can lead to a variety of problems in the lives of the drug
abusers. The problems can either be personal, social and or financial.
What is drug abuse?
This is the use of drugs in amounts or methods which are harmful to the individual or
others.
The effects and dangers of abuse of some drugs
Drug name
Effects and danders
Alcohol
Short term: Loss of concentration, loss of
coordination, poor judgement, mood swings
raised blood pressure, passing out, vomiting
Long term: brain damage, memory loss, loss
of attention span, trouble learning, alcoholic
hepatitis, liver fibrosis steatosis(fatty
liver)high blood pressure, stroke irregular
heart beat
NB: continued excessive drinking can result
to many health problems.
79
Tobacco
Solvents
Dagga
Hereoin
Home work
1. use your books + syllabus+ internet to complete the table
2. discuss the effects of performance –enhancing drugs in sports
80
Reproduction in living things
Reproduction – producing offspring, preventing extinction of species
Two types of reproduction
1. Sexual reproduction –a process involving the fusion of the nuclei of male and female
Gametes resulting in the production of offspring that are genetically different.
2. Asexual reproduction- This is the process resulting in the production of genetically
identical offspring from one parent.
Differences between sexual and asexual reproduction
Sexual
Asexual
Involves two parents
Involves one parent
Produces offspring that are genetically
different from the parent
Produces offspring that are identical to the
parent
Involves gametes or fertilisation
No gametes involved, offspring produced
from somatic or body cells , no fertilization
Genetic mixing from the parents, so there is
variation within species
There is no genetic mixing , so there is no
variation within species
Long generation period
Short generation period
Sexual reproduction
Advantages of sexual reproduction;
1. There is variation within the offspring , so adaptation to a new or changing
environment is likely to enable the survival of the species
2. In flowering plant, seeds are dispersed at different places, reducing competition for
nutrients, space and light.
3. New varieties can be created which are resistant to diseases
Disadvantages of sexual reproduction
1. Competition for nutrients if the plants are grown on the same land
2. Long generation period
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3. Usually two parents are needed ( though some plants can be self- pollinated)
Asexual reproduction
Advantages of asexual reproduction
1. Only one parent is needed
2. The process is quick, there is rapid multiplication
3. No gametes involved
4. Good characteristics of the parents can be passed on to the offspring
Disadvantages of asexual reproduction
1. If the parent has no resistance to diseases none of the offspring will have
2. There is little variation, so adaptation to a changing environment is unlikely
3. Lack of dispersal of seeds leads to competition for nutrients
Examples of species undergoing asexual reproduction include;
1. Bacteria
2. Fungi
3. Potatoes
4. Sugar cane propagation
Bacteria
Bacteria reproduce asexually by a process called binary fission. During this process DNA is
replicated, the cell then divides into two daughter cells each containing a copy of the DNA.
See fig.12.3 page 225
Fungi
Produces spores which are found in structures called sporangia. When the sporangia get
ripe, they burst open and release the spores. If conditions are favourable, the spores
germinate to form new individuals.
See fig. 12.4 (a) page 225
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Potatoes
Reproduce by vegetative propagation. Potatoes are stem tubers. The parent plant
photosynthesises and stores the food in the form of starch in underground stem. The stem
swells up to form tubers. These contain starch, and buds (the eyes) form on the surface. In
suitable conditions, the bud uses the stored food in the tubers to form shoots. Each tuber
forms a new plant. Other examples of plants that undergo this type of reproduction are
cassava and sweet potatoes.
See fig. 12.5 (a) (b) (c) page 226
Sugar cane
Reproduce by vegetative reproduction. The sugar cane stem with buds on the nodes (rings
around stem) are planted in furrows. Roots and shoots appear on the nodes and grow to
form new plants.
See fig. 12.6 page 226
Sexual reproduction in flowering plants
There are two groups of plants
1. Flowering plants
2. Non-flowering plants e.g pine ferns, moses
The main reproductive organ in a flowering plant is the flower.
➢ Flowers can either be bisexual or unisexual
➢ Bisexual flowers contain both the male and female reproductive parts
➢ Unisexual flowers contain one reproductive parts either male /female
➢ Flowers can be from dicotyledonous plant e.g hibiscus plant, or from
monocotyledonous plant e.g grass
Structure of the flower and its functions
Parts of a flower
see fig.12.11 page 229
1. Sepals – they protect and enclose the flower while in bud phase
2. Petals –they attract insects to the flower for pollination to occur. Petals may have
guidelines to guide insects to the nectar
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3. Anthers –produce pollen grains
4. Filament-hold the anthers which contain the male gamete upright
5. Nectary – makes a sugary liquid which insects feed on.
6. Ovary – produce ovules for fertilisation
7. Ovules- contain the female gamete
8. Stigma – carries / traps pollen grains
9. Style – supports the stigma. Provides a passage for pollen nucleus moving into the
ovary
10. Flower stalk/ petiole- supports the flower so that it can be easily seen by insects.
Helps the flower to be able to withstand the wind .
NB: The main function of a flower is to ensure that fertilisation occurs.
Pollination
This is the transfer of pollen grains from the anther to the stigma of a flower
There are two types of pollination;
✓ Self-pollination- the transfer of pollen grains from the anther to the stigma of the
same flower or another flower of the same plant.
NB; A plant undergoing this type of pollination results to offspring with no variation.
✓ Cross-pollination- this is the transfer of pollen grains from the anther to the stigma
of another flower of a different plant of the same species.
NB; this type of pollination results to variation within the species
Agents of pollination
There are two types of agents that transport pollen;
➢ Insects
➢ Wind
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Structural adaptations of insects and wind pollinated flowers
Insect pollinated
Wind pollinated
Bright coloured and large petal. Petals may
have guidelines and scent
Petals are dull coloured and small. They have
no guidelines and no scent.
Have nectar produced in nectaries
Small or no nectar
Have shorter filament
Long filament, mostly found hanging outside
the petals
Anthers are small and firmly attached to the
filament
Anthers are large and loosely attached to
the filament
Stigma is sticky and small found inside the
flower
Stigma is large and featherly, hangs outside
the flower
Pollen grains are large and spiky
Pollen grains are small and smooth
Pollen grains are produced in small amounts
Pollen grains are produced in large amount
Fertilisation
See 12.18 page 233
➢ The pollen grains contain the male gametes i.e pollen nucleus. The ovule contains the
female gamete i.e ovule nucleus.
➢ After pollination, each pollen grain on the stigma germinates and forms a pollen
tube. The pollen nucleus moves down the style through the pollen tube.
➢ The pollen nucleus secretes enzymes to digest the pathway through the style.
➢ The pollen tube grows through one micropyle into the ovule (the pollen nucleus
travels along the pollen tube )
➢ When the pollen nucleus reaches the ovule nucleus, the two nuclei fuse together
➢ This is called fertilisation.
➢ One pollen grain fertilises one ovule
➢ After fertilisation, the ovule develops into a seed and the ovary into a fruit
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There are two types of seeds
✓ Endospermic seeds- seeds that contain large amount of endosperm tissue which
stores food for the developing embryo plant, E.g maize
✓ Non-endospermic seeds- store food for developing plant in the cotyledons, e.g been
seed
See fig 12.19 (a) (draw)
page 234
Fruits and seed dispersal
➢ Dispersal is means of moving fruits or seeds away from the parent plant.
➢ Dispersal reduces competition among individual of same species
Structural adaptation of seed / fruits for wind, animal and explosive dispersal
Wind dispersal
1. Parachute seeds- have feathery hairs that project out of the seeds e.g dandelion.
2. Winged fruits – have wing- like extensions which make them spin as they fall from the
tree thus being carried far away by wind e.g Jacaranda.
Animal dispersal
1. Hooks (hooked fruits)- the hooked bracts that surround the fruit attach to the fur of
animals or clothes of human e.g black jack
2. Succulent fruits - bright coloured, juicy and nutritious, fruits e,g guavas, blackberries
when eaten , the hard part containing the seed pass through the animal gut withouit
digested and deposited with the animal faeces which may be away from the parent plant
Explosive dispersal
1. Explosive fruits- e.g bean fruit , some members of the pea family , have tough fibres in
the pericarp ( fruit walls). When the fruit dries up the fibres in the wall shrink creating
tension. The tension created helps in flicking all the seeds as the walls violently split apart.
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Environmental conditions affecting seed germination
Environmental condition
Explanation
Water
When a seed germinates, it absorbs water
from the soil and increase in size.
The water is absorbed through the micropyle
until the radicle forces its way out of the
testa.
The water is needed to activate enzyme
amylase which convert the insoluble starch
into soluble glucose that can be used during
respiration
Oxygen
This is needed for respiration to release
energy for growth and the chemical changes
necessary for growth (metabolism)
Suitable temperature
Enzymes work best at an optimum
temperature.
Generally , the higher the temperature (up
to 40 oC ) the faster the rate of germination
Seeds remain dormant at low temperatures
Growth and development in plants
Growth is due to an increase in the number of cells, produced by mitosis. In animals, it is
controlled by hormones and in plants it is controlled by growth substances like auxins.
Dry mass is often used as measure for growth because wet mass (fresh) varies from day to
day. Fresh mass contains water. The value of dry mass is obtained by drying out the
organism in an oven, but this involves killing it.
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To monitor the growth of a plant, many individuals have to be germinated at the same time
and under the same conditions. The samples are then taken and dried at various times
during the growth period.
See fig. 12.28 (a)
page 238
NB; from the graph above: there is a small drop in dry mass as the seed germinates. This is
because some of the food stored in the cotyledons is being used in respiration.
Dry mass increases as soon as the plumule starts to photosynthesize and foliage (leaves )
starts to form to continue the process.
Dry mass decreases at the end of the growth period because of the loss fruits or as the
leaves die.
Development
This is the increase in complexity of an organism as it grows. The number of cells increases,
they become differentiated (become specialized to carry out different tasks). This involves
changes in shape to adapt for a specific function e.g xylem cells are elongated and lose their
cell content, with cell walls becoming lignified, so they conduct water efficiently.
Growth curve for an annual plant
See hand out #1
❖ A-B - The seed is dormant.
❖ B-C – Germination begins and seed increases in mass as it absorbs water.
❖ C-D – Seed loses mass as it uses up the stored food to release energy for growth.
❖ D-E – The plant is photosynthesizing building up new cells.
❖ E-F – The plant loses mass quickly as its flowers and produces seeds and dies.
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Sexual reproduction in humans
There are two types of gametes (sex cells)
1. Female gamete – ovum (egg)
2. Male gamete – sperms
The eggs are produced from the female reproductive part called the ovary. Sperms are
produced in the male reproductive part called the testes.
For fertilisation to take place, the two sex cells fuse to form a single cell known as the
zygote. The zygote divides by mitosis until a new organism is formed. In humans, the body /
somatic cells contain chromosomes (strands of DNA made up of genes)
During the formation of the gametes, the number of chromosomes in each gamete is halved
(this is called reduction division). Each gamete contains 23 chromosomes. A body cell has a
diploid nucleus (contains 46 chromosomes). A gamete has a haploid nucleus. The process by
which gametes are formed is called meiosis.
Illustration of gamete formation in humans
See hand out #2
A sperm and an egg
See fig.12.31 page 241
Differences between a sperm and an egg
Sperm
Egg
Produced in testes
Produced in ovaries.
Produced continuously
One or sometimes two produced every
month
Produced in very large numbers
Very few are produced
One sperm is small in size
Eggs are large in size because they have to
store nutrients needed for the development
of the fertilized egg
Sperm have a tail and can swim- it needs to
swim to an egg to fertilize it
Eggs don’t have a tail and can’t swim
All animals are either male or female (few exceptions )
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Structure and function of the human male reproductive system
See fig. 12.29 (a) & (b) page 239
Part
Function
Testes
Make sperms
Produce the hormone testosterone
Held by the scrotum
Scrotum
Carries the testes outside the body- this
helps to keep temperature of the testes
cooler than body temperature
Epididymis
It stores and nourishes the developing
sperms-it is a mass of tubes
Sperm duct
It is a long mascular tube which convey
sperms to the urethra
Penis
Used during sexual intercourse-it can
become erect and be inserted into the
vagina of the female to transfer sperms
Prostate gland
Secretes seminal fluid
Seminal vesicle
Also secrete seminal fluid and some
nutrients to the sperm to form semen
Urethra
Males have urinogenital system which
carries urine and semen at different times
Structure and function of female reproductive system
See fig. 12.30 (a) & (b)
Part
Function
Cervix
A ring of muscles that separate the vagina
from the uterus
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Oviduct
Carries the ovum from the ovaries to the
uterus
Walls have tiny hair like structure to propel
the egg
It is where fertilisation takes place
Ovary
Contain follicles in which ova are produced
Secretes the hormone oestrogen
Urethra
Carries urine from the bladder
Uterus
Where the fertilised egg is implanted and
where foetus develops
Vagina
Receives the male penis during sexual
intercourse
Sex hormones
These are responsible for the development of sex organs and secondary sexual
characteristics at puberty. The time when a person approaches maturity is called
adolescence. The time or point when maturity is reached is called puberty.
Puberty is when the sex organs (ovaries in girls, testes in boys ) become matured and start
to secrete hormone as well as mating gametes sperms /ova. Puberty happens at 10-14 years
of age but varies from person to person. This is earlier in girls than in boys.
Testosterone – hormone secreted by testes causing the changes in boys.
Oestrogen- hormone secreted by ovaries causing changes in girls
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Secondary sexual characteristics that appear at puberty
Male
Female
Voice become lower and deeper
Breasts grow and nipples enlarge
Hair start to grow on chest, face armpits and
pubic areas
Hair grow under armpit and pubic areas
Body become more muscular
Hips become wider and more round
Penis become larger
Uterus and vagina enlarges
Testes start to produce sperms
Ovaries start to release eggs and periods
begins
Summary of the sex hormones
Hormone
Site of production
When it is secreted
Function
Testosterone
Testes
In small amounts
throughout life
Control development
of male organs
In large amounts
from puberty
onwards
Control the
secondary sexual
characteristics
Small amounts
throughout life
Control the
development of
female sex organ
Oestrogen
Ovary
In large amounts
from puberty
onwards, when
follicle is developing
in ovary
Controls the
secondary sexual
characteristics
Causes the lining of
uterus to get spongy
and thick
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Progesterone
Corpus leteum
After ovulation
Throughout
pregnancy
Maintains the lining
of the uterus. If not
secreted , a
miscarriage occurs
The menstrual cycle
There are two hormones involved;
1. Follicle stimulating hormone (FSH) – It stimulate the follicle to develop in the ovary and
stimulate the ovary to secrete oestrogen. FSH is secreted by the pituitary gland
2. Luteinising hormone (LH)- Secreted by the pituitary gland. It causes ovulation and
stimulates the ovaries to secrete the hormone called progesterone from the corpus luteum.
After the egg has been released, the follicle which contains the egg develops into a body
called the corpus luteum.
Physical changes that happen during the menstrual cycle
1. First, a follicle develops inside the ovary. The developing follicle secretes a hormone
called oestrogen. This hormone makes the lining of the uterus thick and spongy
2. When the follicle is fully developed, ovulation takes place. The follicle then stops
secreting oestrogen. It becomes a body called corpus luteum. This starts to secrete another
hormone called progesterone
3. The progesterone keeps the uterus lining thick and spongy and well supplied with blood
in case the egg is fertilised. If it is not, the corpus luteum gradually disappears.
Progesterone is not secreted anymore and so the lining of the uterus breaks down,
menstruation occurs. This lasts for a period of about 4-7 days.
4. A new follicle starts to develop in the ovary and the cycle begins again. The cycle lasts for
28 days. If the egg is fertilized the corpus luteum does not degenerate so quickly. It carries
on secreting the progesterone until the embryo sinks into the uterus wall and a placenta.
The placenta secretes the progesterone throughout the pregnancy.
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The human menstrual cycle
See hand out #3
NB: the numbers in the cycle represent days
Formation and development of a foetus
Sexual intercourse- involves the erect or firm penis into the vagina of the female. When
stimulated, the spongy tissue in the penis become filled with blood and become erect. As
the male climax, semen is ejaculated from the penis to the neck of the vagina. Muscles in
the walls of the sperm duct helps to propel the semen forward by contracting.
Using their tails, the sperms swim from the vagina through the cervix and uterus to the
oviduct. Sperms are attracted to the ovum by hormones. Sperms swim using energy from
respiration.
Fertilisation in humans
Fertilisation may occur if there is an ovum passing down the oviduct. A single sperm
penetrates the membrane of the ovum by secreting a protease enzyme. The sperm nucleus
fuses with the ovum nucleus to form a zygote. A zygote is a single diploid cell formed as a
result of the fusion of the gametes.
The zygote starts to divide by mitosis to form a ball of cells called a blastula. It continues to
move down the oviduct until it reaches the uterus.
Implantation occurs when a blastula embeds itself in the lining of the uterus.
Development of the foetus
The blastula develops into an embryo and some of the cells form the placenta to link the
embryo with the uterus lining.
Organs such as the heart develop and after 8 weeks the embryo develops into foetus.
Growth of the foetus requires a good supply of nutrients and oxygen. This is achieved
through the link between the mother and the placenta.
Dietary requirements of a pregnant mother
Pregnant women should increase the following nutrients in their diet;
1) Protein – for making tissues for the baby
2) Calcium – for the development of strong bones for the baby
3) Vitamin D – helps in the calcification of bones of the foetus
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4) Iron – for the synthesis of blood and red blood cells for both the mother and the foetus
Role of the placenta
1. For the exchange of materials e.g glucose , oxygen, antibodies, urea, carbon dioxide,
water, amino acids etc
2. For physical attachment between the foetus and uterus / mother
3. Prevents blood mixing/ allow the blood systems of the mother and the foetus to be close.
4. Protects the entry of some pathogens (diseases-causing organisms like bacteria)
Function of the chorionic villi in placenta
Chorionic villi are the main functional units of the placenta. The chorion is a layer that
separates the mother from the baby. The chorionic villi are projections of the chorion that
develops as a way to get nutrients from the mother to the foetus. They eventually develop
into arteries.
The chorionic villi are threaded through with foetal blood vessels. The mother’s blood
pressure forces blood around the villi. The chorionic villi can absorb and pass needed
nutrients and antibodies for immunity to the baby.
Why foetal blood and maternal blood should not mix
1. The blood may be different / incompatible blood groups / risk to damage to red blood
cells of foetus
2. To prevent transfer of pathogens / toxins / drugs
3. Maternal blood pressure much higher than that of foetus/ could damage foetal blood
vessels.
See hand out # 4
Roles of the amniotic fluid
1. Protects the foetus from physical damage
2. Maintain a constant environment for the foetus
3. Allows free movement of foetus
4. Protects the foetus from temperature changes / fluctuations
5. Protects the foetus from drying out
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Roles of the amniotic sac
1. Secretes / produce amniotic fluid
2. Encloses / contains the amniotic fluid
Stages leading to birth
✓ The first stage of the process of birth is called labour. It is triggered by the hormone
oxytocin. During labour.
✓ The muscular walls of the uterus start to contract.
✓ The pressure breaks the amniotic sac, releasing the amniotic fluid ( this is known as
the waters breaking )
✓ Contractions gradually become more frequent, pushing the baby down towards the
cervix, which becomes dilated to allow the baby to pass through.
✓ The vagina stretches to allow the baby to be born
✓ The baby is still attached to the placenta by the umbilical cord, so this is cut and tied.
✓ The placenta breaks away from the wall of the uterus and passes out (this is known
as the after birth.
Summary; contraction of uterus (labour) , dilation of cervix, breaking of amniotic sac and
release of amniotic fluid and lastly the passing out of after birth.
Advantages of breast milk (breastfeeding) over bottled milk
Breast milk
Formula milk
There are antibodies present in breast milk,
giving the baby protection against infections
It does not contain antibodies
Food nutrients are present in correct
proportions
Food nutrients may not be in the correct
proportions
There is no risk of allergic reactions to breast
milk
It can cause allergies to cow’s milk and other
It is free
It is expensive
It is clean and sterile
Formula milk can be infected by
microorganisms
It is at the right temperature for the baby
It is difficult to get formula milk at the
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correct temperature
It promotes brain growth ( breastfed babies
are thought to have high IQs)
It does not promote brain growth
The physical connection helps the mother to
bond with the baby
There is not as much of physical connection,
so the bond might not be as strong
Methods of birth control (contraception)
There are 4 main groups of birth control methods:
1. Natural
2. Chemical
3. Mechanical
4. Surgical
Type
Examples
Details
Comments
Natural
Abstinence
No sexual
intercourse
The best of avoiding
an unwanted
pregnancy
Withdrawal
The penis is taken
out from the vagina
before ejaculation
Very unreliable.
Some semen is
released before
ejaculation.
Rhythm
The time of
ovulation is
predicted and
intercourse is
avoided around the
date of ovulation
Time of ovulation
vary , so not always
reliable
Contraceptive pill
Contains
progesterone and
oestrogen which
prevents ovulation.
Usually very reliable
when taken
regularly
Chemical
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or progesterone
only which prevents
implantation
Mechanical
Spermicide
Kills sperms in
vagina
Contraceptive
injections
Given to women
every 3 months.
Contain the
hormone
progesterone which
stops the ovaries
from releasing eggs
Contraceptive
implant
A small, flexible
tube that contains
progesterone. The
progesterone stops
a woman from
ovulating
It functions for up
to three years.
Menstruation may
be irregular or it
may stop
altogether.
Intrauterine device
(IUD)
A plastic-coated
copper coil is
surgically inserted
into the walls of the
uterus
Prevents
implantation of the
blastula; reliable
Male condom
Rubber sheath
placed over the
penis to stop from
entering the vagina
Also prevents
transmission of
sexually transmitted
diseases; reliable if
used with a
spermicide
Femidom (female
condom)
Thin plastic sheath
placed inside the
vagina
Also prevents
transmission of
sexually transmitted
diseases
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Should only be used
with a condom or
diaphragm
Surgical
Vasectomy
Sperm ducts are
tied or cut, so no
sperm can leave the
testes
Not normally
reversible;
extremely reliable
Tubal ligation (
laparotomy)
Oviducts are tied or
cut, so no eggs can
pass down them
Not normally
reversible;
extremely reliable
Infertility treatment
Infertility in men is due to:
➢ Problems in producing enough sperm
➢ Production of abnormal sperm ( for example no tail )
Infertility in women is due to:
➢ Problems with ovulation
➢ Blocked oviducts
➢ Problems with the uterus ( for example fibroids)
In vitro fertilisation
If a woman has a problem of blocked oviducts, a doctor can collect the ova produced by FSH
and LH treatment. Some of the ova are fertilised in a Petri dish using the male partner’ s
sperm ( the others may be stored in case the process is not successful ). The early embryos
produced are then inserted into the uterus to achieve pregnancy. The treatment is quite
expensive, and not always successful.
Social aspects of artificial insemination
Artificial insemination (AI) is a way of increasing the chances of a woman having a baby
when the male partner is infertile. It involves using sperm from a donor, stored in a sperm
bank. The sperm are inserted into female partner’s uterus around the time of ovulation.
The baby will not carry any of the genetic characteristics of the male in the relationship, and
it is argued that the child has the right to know who the real father is (the sperm donor).
However, many sperm donors wish to remain anonymous.
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Surrogacy
A surrogate is a woman who becomes pregnant with the baby of an infertile couple.
An egg, from the infertile female, is fertilised with a sperm outside the body and the embryo
is implanted in the endometrium of the surrogate.
When the surrogate gives birth to the child, she hands it to the infertile couple who she is
helping. Any costs associated with the pregnancy are covered by the infertile couple.
HIV and sexually transmitted infections (STI)
Examples of STIs;
✓ Gonorrhoea
✓ HIV /AIDS
✓ Herpes
A sexually transmitted infection is an infection passed on through a sexual intercourse. It is
unprotected sexual intercourse between an infected person and an uninfected person.
Gonorrhoea
Signs and symptoms
Effects
Treatment
Male:
Damage to urinary and
reproductive organs
Antibiotics ( as gonorrhoea
is caused by a bacterium)
Sores on penis/ painful or
swollen scrotum
Sterility
Yellowish discharge from
penis
Blindness in a baby born to a
mother with the disease
Pain when urinating
Female:
Yellowish discharge of pus
from vagina, but not always
obvious
Abdominal pain
Production of antibodies
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Burning sensation when
urinating
*Often no symptoms in
women
HIV /AIDS
What is HIV?
HIV – stand for human immuno-deficiency virus. It is the germ that causes AIDS. It is found
in lymph nodes and body fluids of an infected person. These are;
✓ Blood
✓ Sex fluids
✓ Breast milk
What is AIDS?
This is a name given to a condition when the body is nolonger able to fight off infectiins
because of the damage done to the immune system by the HIV virus. AIDS stands for
immune deficiency syndrome.
For HIV to be passed on from one person to the next, two conditions must be present;
1. Exchange of body fluids containing HIV
2. An opening on the skin or membrane
Methods of transmission of HIV
1. From infected mother to child
✓ Through breastfeeding
✓ During delivery
✓ While still in womb
2. Unprotected sexual intercourse with an infected person
3. Sharing unsterilized surgical instruments or drug use involving sharing a needle used
by an infected person
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4. Blood transfusion of unscreened blood (not tested blood)
Ways of preventing the spread of HIV
1. Prevention of mother to child transmission of HIV (PMTCT)
✓ Pregnant mothers undergo routine HIV counselling and testing
✓ HIV positive mothers reduce maternal viral load by using ARVs in prophylaxis
Prophylaxis: ARVs are given to pregnant HIV positive mother before delivery. The positive
mother takes one tablet on the onset of labour and it should be in blood stream for 2hrs.
The baby is put on ART for four to six weeks after birth to reduce the risk of infection from
any HIV that may have entered the baby’s blood during delivery.
2. Breastfeeding
✓ HIV positive mothers are not encouraged to breastfeed
✓ They are encouraged to use bottle milk
3. Early testing for everyone
4. Use of antiretroviral drugs (ARVs) by HIV positive pregnant mothers.
5. The use of condoms for sexual intercourse
6. Male circumcision also reduces the risk of HIV infection
➢ The foreskin is delicate and easily bruises during sexual intercourse.
➢ When it is removed, the penis hardens and does not easily bruise, reducing
chances of entry of the virus.
➢ Also when the foreskin is absent, the virus is not harboured for a long time
giving it more chances of penetration.
How HIV affects the immune system
✓ HIV attacks the B lymphocytes ( a type of white blood cells ) found in the blood.
✓ The HIV prevents or stops the lymphocytes from producing the antibodies.
✓ The immune system is then weakened and we say that you have AIDS
✓ The body loses existing immunity and therefore cannot defend against diseases/
become less resistant to pathogens
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✓ The body is vulnerable to many sicknesses like pneumonia and tuberculosis
✓ There is no cure for AIDS but a suppressive therapy is used world – wide
NB; there are new scientific advances developed to better fight HIV/AIDS
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INHERITANCE
What is inheritance?
Inheritance is the transmission of genetic information from generation to generation,
leading to continuity of, and variation within, the species.
Genetics is the study of how characteristics are passed from one generation to the next.
Definition of terms
✓ Chromosome – a thread of DNA, made up of genes
✓ Gene – a section of DNA, which codes for the formation of a protein, controlling a
specific characteristic of the organism
✓ Allele – an alternative form of a gene
✓ Haploid nucleus – a nucleus containing a single set of unpaired chromosomes e.g in
sperm and ovum.
✓ Diploid nucleus – a nucleus containing pairs of chromosomes e.g in somatic (body)
cells
✓ Genotype - genetic make- up of an organism
✓ Phenotype – characteristics visible in an organism controlled by genotype and the
environment
✓ Homozygous – having a pair of identical alleles controlling the same characteristic
✓ Heterozygous – having a pair of dissimilar alleles for a characteristic
✓ Dominant gene – a gene that always shows in the phenotype of an organism
whether the organism is heterozygous or homozygous
✓ Recessive gene – a gene that only has an effect on the phenotype when the
organism is homozygous
Chromosomes
➢ Human body cell contains 23 pairs (46) chromosomes
➢ Sperm cells and ova (gametes ) contain 23 chromosomes – the chromosomes
comprises one chromosome from each pair
➢ Each pair is made up of a number of genes coding for the information of different
proteins which give us our characteristics e.g height , complexion, eye colour, shape
of ear lobe, etc
104
➢ The gene responsible for a particular characteristic is always on the same relative
position (locus) on the chromosome.
➢ The pairing of bases of the DNA is such that Adenine always pairs with Thymine,
Guanine with Cytosine
➢ DNA ( deoxyribonucleic acids) carries the hereditary information of organisms
See fig 13.3 page 266
DNA is the molecule that carries the information about how organisms will look like.
The monomers (single units) used to build nucleic acids are nucleotides. These are referred
to by the single letter abbreviated A, C, G, and T
DNA is composed of two long strings (polymers) of nucleotides twisted around each other to
form spiral or helical structure. It is a double helix formed by base pairs attached to a sugar
phosphate backbone. The twisted molecules are arranged in a particular manner with the
specific nucleotides always found across from each other.
The nucleotide containing A (adenine ) always pair with the nucleotide containing T
(thymine) likewise G (guanine ) always pair with C(cytosine) ; A –T, G- C .
Inheritance of sex in humans
➢ Out of the 23 pairs of chromosomes in each human body cell, one pair is the sex
chromosomes. These determine the sexes of the offspring.
➢ Male have XY genotype and females have XX genotype
➢ The presence of a Y chromosome results in male features developing
105
The diagram below shows sex is inherited
Parental phenotype
male
Parental genotype
XY
Gametes
X
x
female
x
XX
Y
X
X
F1 genotype
XX
XX
XY
XY
F1 phenotype
female
female
male
male
Ratio
male : female
2
:
2
1
:
1
NB: the possibility of getting a boy or a girl is 50% in each case.
Cell division
There are two types of cell division
➢ Mitosis
➢ Meiosis
Mitosis
This is a form of cell division used for making new cells to enable new growth and
replacement of old or damaged cells.
Asexual reproduction involves mitosis. During the process, all chromosomes are copied and
split into 2 nuclei with the same number of chromosomes as the parent cell ( the diploid
number of the chromosomes is maintained). At the end of the mitotic cell division, the
number of cells is doubled
The daughter cells produced are identical to each other and to the parent cell.
106
Meiosis
Sex cells are formed in the gonads (ovaries and testes) by meiosis. The gametes produced
are haploid but are formed from diploid cells, so meiosis involves halving the normal
number of chromosomes.
The pair of chromosomes are separated. Four daughter nuclei are produced at the end of
the process. The cells produced are not identical to the parent cell
Meiosis results to variation within the species. When the ova produced or formed, they all
carry the X chromosome. When sperms are produced, half will carry the X chromosome and
half will carry the Y chromosome.
Female body cell
male body cell
XX
X
XY
X
X
Y
Monohybrid inheritance
This is the study of how a single gene can be passed on from one generation to the next (
from parents to offspring)
It is easier to predict the outcome of a monohybrid cross using two ways ;
➢ Punnet square
➢ The traditional way
Writing up a genetic diagram or solving genetic problems in an exam.
A standard procedure in working out the answer and presenting it is a follows ;
✓ Read the question through twice carefully
✓ Decide whether or not one gene is dominant over the other
✓ Decide on the symbols to use, make sure you state what the symbols represent e.g
T = tall
t = short
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Usually we use a capital letter of the first letter for the dominant characteristic . The small
version of this letter is for the recessive characteristic. For example, if red colour is
dominant over the white colour, you will write;
R = red
r = white
✓ Write out in words the phenotypes of the parents
✓ Write out the symbols of the genotype of the parents
✓ Write out the contents of the gametes circled to show that meiosis has occurred
✓ Write out the F1 offspring genotypes that result after the cross (fertilisation)
✓ Write out the F1 offspring phenotypes with the phenotypic ratio
Examples of genetic crosses
Example 1
Inheritance of sex in humans (see notes above)
Using a punnet square
Parental phenotype
male
Parental genotype
XY
Gametes
x
female
x
X
XX
Y
X
X
F1 genotype
2
XX ,
2
Y
XY
Male : female
2:2
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X
Other examples of genetic crosses
All the examples below involve pea plants which can be tall or short. Tallness is dominant
over shortness
✓ A cross between a pure breeding tall pea plant and a pure breeding short pea plant.
Let T = Tall
t = short
Using the traditional way;
Phenotype of a parent
tall
x
short
Parental genotype
TT
x
tt
Parental gametes
T
F1 genotype
Tt
Tt
Tt
Tt
F1 phenotype
tall
tall
tall
tall
T
t
Phenotypic ratio: all tall
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t
✓ A cross between a heterozygous tall pea plant and short pea plant.
Key; T = tall
t = short
Parental phenotype
tall
x
short
Parental genotype
Tt
x
tt
Parental gametes
T
t
t
F1 genotype
Tt
tt
Tt
tt
F1 phenotype
tall
short
tall
short
Phenotypic ratio
tall : short
2 : 2
1: 1
110
t
✓ A cross between two heterozygous tall pea plants
Parental phenotype
tall
x
tall
Parental genotype
Tt
x
Tt
Parental gamete
T
F1 genotype
TT
Tt
Tt
tt
F1 phenotype
tall
tall
tall
short
Phenotypic ratio
tall : short
t
T
t
3 : 1
NB: a ratio of 1 : 1 in the offspring indicates a cross between a heterozygous parent and
homozygous recessive parent.
A ratio of 3 : 1 in the offspring indicates a cross between two heterozygous parents .
If the ratio is given in numbers, simplify it by dividing with the smallest number
From the ratio we can get the genotypes of the parents.
Monohybrid inheritance cross involving sex linkage
Genes that are located in the sex chromosomes are called sex-linked genes. These genes
may cause certain disorders. Since the Y chromosome is much shorter than the X
chromosome, only the X chromosome carries the disorder. A sex linked characteristic is
therefore more common in one sex than the other.
Colour blindness is an example of a sex-linked characteristic. In colour blindness the
affected people lack light sensitive receptors or have defects in the light receptors. The
defective gene is a receptive gene that is found on the X chromosome. One X chromosome
is enough to cause the defect in male, as a result females with one defective gene do not
suffer from the disorder, but are carriers. Females need two defective alleles to suffer from
the condition.
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✓ A cross between a colour blind man and a normal woman
Let XcXc = colour blind woman
XcX = carrier woman
XcY = colour blind man
XY
= normal male
XX
= normal female
(draw genetic diagram- traditional cross diagram)
✓ A cross between a colour blind man and a carrier woman
(Draw genetic diagram – traditional cross diagram)
A colour blind daughter therefore must have a colour blind father and a mother who is a
carrier who has passed on the ‘faulty gene’ to her daughter). If her father is not colour blind,
the daughter will not be blind but become a carrier.
A daughter can become a carrier with one of two ways;
➢ She can acquire the gene from a carrier mother or
➢ She can acquire the gene from a colour blind father. This is why red/green colour
blindness is far more in men than in women.
Codominance and inheritance of humans blood groups
Codominance describes a pair of alleles that are equally dominant, neither of which is
dominant over the other. Their effect is seen on heterozygous organisms.
Example: human blood groups and hair colour of several domestic animals like dogs, cats
and cattle. In examples of genetic crosses of organisms showing codominance for certain
characteristics, it is likely to find a ratio of 1:2:1
Inheritance of blood groups
✓ There are four blood group ; A , B, AB and O.
✓ These are controlled by a single gene normally represented by the letter I.
✓ The gene I has 3 alleles that are represented by the superscript letter A, B, O
(antigens).
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✓ Alleles A and B are codominant, they are both dominant to O. The four blood
groups have the following genotype;
Phenotype
Blood group
Genotype
A
IA IA IA IO
B
IB IB IB IO
AB
IA IB
O
IO IO
Inheritance of blood group O
Example: a person with blood group A could have a genotype IA IA or IA IO. This has an
implication when having children because if both parents caring the IO allele, a child could
be born with the genotype IO IO (blood group O) even though neither of the parents has this
phenotype
The parents have blood groups A and B and the father is I A IO and the mother is IB IO
(draw traditional genetic cross using the information given above)
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VARIATION
Variation means observable differences within a species. Examples include height, weight,
blood groups etc.
There are two types of variation
1. Continuous variation
2. Discontinuous variation
Continuous variation
This type of variation shows a complete range of the characteristics within a population
caused by both genes and the environment.
The environmental influence for plants may be;
1. Availability of nutrients
2. Competition for nutrients
3. Light and water
4. Exposure to diseases
Environmental influence in plants may be;
1. Availability of nutrients ( a balanced diet in humans)
2. Exposure to diseases
3. Availability of health services for humans
Examples of continuous variation
1. Height
2. Body mass
3. Intelligence
4. Complexion
When the frequency is plotted on a graph, a smooth curve is produced with the majority of
the population sample grouped together and only small members at the extremes of the
graph.
(Draw diagram, fig. 13.24 page 279)
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Discontinuous variation
It refers to the distinct differences between organisms. There is always a choice between
one characteristic/ feature and another. This type of variation is usually influenced by genes
and no environmental influences.
Examples of discontinuous variation are;
1. Blood groups
2. Gender
3. Hair colour
4. Eye colour
When the frequencies are plotted on a graph, the bars produced cannot be linked with a
smooth curve.
(Draw diagram, fig. 13.25 page 279)
Mutation
This is a spontaneous change in a gene or a chromosome.
Mutations are a source of variation in the population, however, they are usually harmful
and produce a feature or an organism very different from the parents.
Mutation can be caused by;
1. Faulty copying when DNA is replicated
2. Faulty separation of chromosomes during cell division
3. Exposure to radiations such as X-rays
4. Exposure to some chemicals such as tobacco tar
Examples of mutations include sickle cell anaemia and Down’s syndrome
Down’s syndrome
This is an example of a chromosome mutation. When ova are produced in the ovaries, the
chromosome number is halved, during meiosis, one of the chromosomes in the pair,
number 23, sticks to its partner.
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This results in the ovum having 24 chromosomes. This ovum is still viable. If fertilised, the
foetus formed will have 47 chromosomes instead of 46chromosomes. The presence of the
extra chromosome causes unusual features to develop in the body. These include;
1. Lowered life expectancy
2. Mental retardation (although some children with Down’s syndrome are intelligent)
3. Early puberty
4. A distinctive round face
5. A short neck
6. Slanted eyes
Effects of radiation and chemicals on the rate of mutation
✓ Refer to hand out.
Sickle cell anaemia and its incidence in relation to that of malaria
✓ Refer to hand out.
Importance of variation
✓ Variation is important in survival of species.
✓ A wide range of variation within a species increases chances of surviving an
environmental or biological disaster
✓ Example; Mammals with a thicker layer of fat under their skin and those with a
higher rate of metabolism are most likely to survive very cold temperature (sudden
change in temperature) and pass their genes to the next generation.
✓ Variation is also important in natural selection and evolution.
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SELECTION
There are two types of selection;
1. Natural selection
2. Artificial selection
Artificial selection
✓ This is a method used by humans to produce varieties of animals and plants that
have an increased economic importance.
✓ Examples;
1. A variety of cattle may have a higher than average milk yield . another
variety may have a very high meat yield. If the two varieties are cross- bred,
a new breed could be artificially produced that has the benefits of both
parental varieties ( high milk production in females, high meat production in
males)
2. Wild varieties of plants sometimes have increased resistance to fungal
diseases, but have poor fruit yield. Cross – breeding wheat plants can result
in the formation of varieties that have both high resistance to diseases and
high seed yield.
✓ Human modify plant or animal species to make sure that traits which are desirable
appear in successive generations.
✓ Through artificial selection, farmers and breeders can improve the quantity of yields
resulting in increased profits
Natural selection
✓ The passing on of genes by the best adapted organism.
✓ Only the best adapted organisms survive and reproduce (passing their genes to the
next generation) due to natural factors such as predators or shortage of food
✓ Natural selection can lead to evolution.
Development of an antibiotic resistant strain of bacteria
The development of strains of bacteria such as the Multiple Drug Resistant Tuberculosis
(MDR- TB) is an example of natural selection.
Multiple drug resistance is a condition enabling a disease-causing organism to resist drugs or
chemicals of a wide variety of structure and function targeted at eradicating the organism.
117
Organisms that display multiple drug resistance can be pathogens such as tuberculosis
bacteria (TB). Completing a full course of antibiotics medication is very important, failure to
complete the medication results in mutation making some strains of bacteria to be resistant
to the antibiotics. The mutated bacteria strains will not be killed by the antibiotics, they will
survive and reproduce passing on their antibiotic resistant genes to the next generation.
This is how MDR- TB develops by natural selection.
118
BIOTECHNOLOGY AND GENETIC ENGINEERING
Biotechnology is the use of living organisms, their components or processes to make things
that help to make our lives better e.g enzymes, hormones and antibiotics.
Roles of enzymes in our everyday life
✓ Biological washing powders contain lipase and protease.
✓ Lipase digest greasy or fatty stains eg butter, margarine or mayonnaise into fatty
acids and glycerol
✓ Protease digest protein stains like blood and egg into amino acids
✓ The enzymes break down these stains into produce smaller soluble molecules which
easily dissolve in water
✓ Enzymes are also used in the food industry e.g the use of enzymes like cellulase,
pectinase and amylase in fruit juice production to give a better juice yield and
superior quality of the fruit juice
Uses of microorganisms and fermenters to manufacture enzymes for use in biological
washing powders
➢ Two types of microorganisms are used; bacteria and fungi
➢ A nutrient rich medium like molasses, cornsteep liquor and ammonium salts, is put
in large sterile vessels called fermenters
➢ The fermenter should be sterile to exclude other microorganisms that can compete
for nutrients and release products that will contaminate the enzymes.
➢
The bacteria or fungi are added into fermenter
➢ Inside the fermenter there is a stirrer to keep the microorganisms in contact with the
nutrients
➢ suitable temperature and pH conditions are carefully monitored inside the
fermenter
➢ The temperature is maintained at 26 0C and the pH is kept between pH 5 – 6
➢ The enzymes formed are then extracted and purified
(Draw fermenter ,,, hand out)
119
The use of microorganisms in the food industry
Yoghurt making
✓ During yoghurt making, bacteria are added to pasteurized milk at 40 0C.
✓ The bacteria respire anaerobically breaking down lactose sugar to lactic acid.
✓ This acid lowers the pH of the milk and causes it to coagulate.
✓ When fermentation is finished, the yoghurt is stirred and cooled to 5 0C.
Bread making
✓ Yeast is mixed with water , sugar and flour
✓ The enzymes in yeast convert sugar to ethanol and carbon dioxide.
✓ The carbon dioxide gets trapped inside the dough and makes the dough to rise. This
makes the dough to be light in texture.
✓ A high temperature kills the yeast cells and evaporate the ethanol
Brewing
✓ Yeast is added to the source of sugar eg fruit juice, kept in warm conditions
✓ When yeast respires anaerobically, it converts the sugar to ethanol and carbon
dioxide.
✓ The ethanol makes the drink alcoholic and the carbon dioxide makes the drink
fizzy.
Cloning
✓ This is the process of producing an identical copy of an organism by manipulation or
biotechnology.
✓ This results to the production of a similar population of genetically identical
organisms.
✓ An ovum is selected from a female organism and the DNA removed from any cell in
the body of the organism to be reproduced.
✓ The DNA is then injected into the empty ovum.
✓ The ovum is returned into the uterus of the female organism where it grows.
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GENETIC ENGINEERING
Genetic engineering is changing the genetic material of an organism by removing, changing
or inserting individual genes. One famous example of genetic engineering is the production
of human insulin using bacteria, as follows;
1. Human cells with genes for healthy insulin are selected
2. A chromosome ( which is a thread of DNA ) is removed from the cell
3. The insulin gene is cut from the chromosome using restriction endonuclease enzyme
4. A suitable bacterium cell is selected. Some of its DNA is in the form of circular
plasmids
5. All the plasmids are removed from the bacterial cell
6. The plasmids are cut open using the same restriction endonuclease enzyme
7. The human insulin gene is inserted into the plasmids using ligase enzyme
8. The plasmids are returned to the bacterial cell ( only one is shown in the diagram)
9. The bacterial cell is allowed to reproduce in the fermenter with the right conditions
for growth and reproduction. All the cells produced contain plasmids with the
human insulin gene
10. The insulin produced by these bacteria could then be collected and given to people
suffering from diabetes mellitus.
(draw fig.13.36 page 288)
Reasons why insulin produced this is better than insulin extracted from dead animals
✓ Insulin produced using this method is identical to the insulin that we produce
ourselves (as opposed to the insulin produced by animal).
✓ It is also cheaper to produce insulin using this method, it can be produced in large
qualities without slaughtering the animals
✓ The insulin produced is very pure
✓ Insulin produced using this method can be acceptable to people with a wide range of
religious beliefs who may not be allowed to use insulin from animals such as cows or
pigs
121
Reasons for using bacteria in genetic engineering
1. Bacteria have the required DNA, especially those that have plasmids. Plasmids are
readily isolated from bacteria and cultured.
2. Bacteria reproduce fast and so it easy to produce a genetically identical bacteria
population in a short time.
3. Inexpensive.
4. Bacteria have restriction enzymes that are used to cut up DNA.
5. Bacteria can be grown and manipulated without ethical concerns.
6. They have genetic information that is the same as other organisms, so genes from
other animals or plants can be successfully transferred into bacterial DNA.
Genetically Modified Organisms (GMOs)
Plants or animals that contain genes from another organism are called genetically modified
organisms. Biotechnology companies spend a lot of money on developing genetically
modified crops that contain genes that improve them.
Advantages and disadvantages of genetic engineering (GMOs)
Should companies continue to spend more money and time on developing new crops using
genetic engineering?
Advantages of genetic engineering;
✓ It is much quicker to produce plant crops and domestic animals with the
characteristics that we want by using genetic engineering rather than selective
breeding
✓ GM crops can be produced that are resistant to diseases and pests and can grow in
harsher environments. This means that we can produce a greater amount of food
✓ Many GM food crops have a longer shelf life. This means that less food is wasted.
✓ Many GM food crops have been modified to produce more nutrients, such as
vitamins. These food crops therefore provide better nutrition.
✓ Using gene therapy, we could cure many of the human diseases that affect so many
people in the world and give people a better quality of life.
122
Disadvantages of genetic engineering
✓ Introduced genes from GM crop plants could move into wild plants through
pollination. This could reduce the genetic diversity of wild plants, which could
create ecological problems in the future
✓ Genetic engineering is a new field. There could be irreversible side effects of
genetically altering plants, animals and humans that will only become apparent in
the future.
✓ There are risks associated with transferring genes from plants into animals and
animals to plants. One of these could be the creation of new diseases or poor
health
✓ Many people think that genetically altering organisms is unethical
✓ Genetic engineering could be used to produce biological weapons.
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BIODIVERSITY
Biodiversity is the existence of many different species of plants and animals in an
environment, and differences within a species.
The importance of biodiversity
✓ Medicinal purposes
❖ Many of our most important medicines are derived from plants and animals.
❖ Antibiotics, anti-cancer drugs, blood clotting agents and thinners, cardiac
regulators and fever suppressants are among the drugs we obtain from wild
biodiversity.
✓ Ecological roles
❖ All species provide some kind of function to an ecosystem.
❖ The different species can capture and store energy, produce organic material,
decompose organic material, help to cycle water and nutrients throughout
the ecosystem or help regulate climate.
❖ The different species also help to maintain food chains.
Threats to biodiversity
1. Habitat change
2. Alien invasion species
3. Unsustainable resource
4. Wild fires
5. Climate change
6. Soil erosion
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ECOSYSTEMS
Food chains and food webs
Definition of terms;
✓ Ecology – the study of the relationship between organisms and their environment
✓ Environment – all conditions in the surroundings of an organism that may affect it
✓ Ecosystem – a community of interdependent organisms and their environment
✓ Community – different populations of organisms in the environment
✓ Population – a group or a number of organisms usually of the same species
✓ Habitat – a place where an organism lives, feeds and breeds
✓ Food chain – a way of showing linear feeding relationships between organisms and
the direction of energy flow
✓ Food web – a group of interlinking food chains that shows the feeding relationship
between them.
✓ Trophic level- an organism’s position in a food chain, food web or pyramid
✓ Producer – an organism that makes its own food using energy from sunlight through
the process of photosynthesis
✓ Consumer – an organism that feeds on other organisms
✓ Herbivore (primary consumer) – an animal that eats plants
✓ Carnivore (secondary or tertiary consumer) - an animal that eats other animals
✓ Decomposer – an organism that obtains its food by breaking down dead organisms
Energy flow
➢ The sun is the principal source of energy input in all biological ecosystems
➢ All organisms directly or indirectly get their energy from the sun
➢ Energy is passed from one organism to another in a food chain.
➢ Unlike water and other nutrients, like carbon and nitrogen, energy does not return in
a cycle ( energy in non-cyclical in nature)
➢ Energy gained by organisms is lost to the environment.
125
Food chains
Producer
primary consumer
secondary consumer
tertiary consumer
Decomposer
Examples of food chains
Grass
cow
Grass
locust
man
lizard
hawk
When writing a food chain;
➢ We do not include the sun
➢ A food chain starts with a photosynthesizing plant (which gains energy from the sun)
➢ The arrows always point towards the eater and away from the plant.
Trophic level
Grass
First trophic level
cow
man
second trophic level
third trophic level
Energy is lost at each trophic level in a food chain. About 90% is lost and 10% is passed on to
the next organism. (refer to page 300 – 301)
Energy can be lost through the following ways:
❖ Through respiration, in the form of heat
❖ Energy is used up during movement (to search for food, find a mating partner and to
escape from predators)
❖ Warm blooded animals lose heat energy in faeces and urine
❖ Some of the materials in organisms being eaten are not used by the consumer e.g a
locust does not eat the roots of maize and some parts are not digestible.
126
Even plants do not use all the light energy available because light:
1. Is reflected off shinny leaves
2. Has a long wavelength for chlorophyll to trap it
3. Passes through the leaves without passing through the chloroplast
4. Does not fall onto the leaves
In long food chains, very little energy is available to the carnivore. Short food chains have an
advantage because more energy will be available for the last consumer there is increase in
efficiency in feeding crop plants to animals and green plants as human food.
Food web
Example
baboon
leopard
Scorpion
Locust
lion
impala
Grass
Food web is the most accurate way of showing feeding relationships than food chains
because most animals can have more than one food source e.g in the above example, the
leopard can be placed in two different trophic levels; as a quaternary consumer feeding on
baboons or as a secondary consumer when feeding on the impala.
If one population of organisms in the food web disappears, the organisms having more than
one kind of food can still survive
Organisms in the food chain/ food web disappear / die due to;
✓ Over predation/ hunting
✓ Lack of food (and other sources )
✓ Diseases
✓ Use of pesticides
✓ Destruction of habitat
✓ Pollution
127
Food pyramids
Each trophic level is represented by a horizontal bar, with the width representing;
❖ the number of organisms,
❖ the amount of biomass at that trophic level
❖ the amount of energy available at that trophic level
The base represents the producer; the second bar is the primary consumer and so on.
1) The pyramid of numbers
❖ Usually the producers have the largest number and form the widest bar.
❖ There will be fewer primary consumers and fewest secondary consumers so a
pyramid shape is formed
❖ E.g
Lion
Antelope
grass
However this is not always the case. There is a different pyramid of numbers like the one
below.
Fleas
Owl
Blue tits
Caterpillars
Oak tree
In the above food pyramid, the food chain is supported by a single tree (oak tree). Many
caterpillars feed on its leaves. Only a single owl has many fleas which suck its blood.
128
2) Pyramid of biomass
❖ The amount of living material biomass is measured at each trophic level in a
food chain.
❖ A normal shaped pyramid is usually obtained as shown below;
Fleas
Owl
Blue tits
Caterpillars
Oak tree
3) Pyramid of energy
❖ Indicates the total amount of energy in all the organisms at each trophic level
in a food chain
❖ A normal shaped pyramid is always produced because there is a reduced
amount of energy at each successive level
❖ Data collection for pyramids of numbers involves killing and burning the
organisms in order to measure their energy content
(draw example of pyramid of numbers)
129
NUTRIENT CYCLES
❖ There is a fixed amount of carbon , hydrogen, oxygen and nitrogen on earth
❖ These elements must be recycled and reused over and over again.
❖ They continuously move from the environment to living organisms and back again in
cycles
❖ This cyclic movement of the elements is called nutrient cycling
❖ Examples of nutrient cycles include water cycle, carbon cycle and the nitrogen cycle
Carbon cycle
✓ Living organisms need carbon to make carbohydrates proteins and fats (carbon is a
main constituent of these nutrients)
✓ Carbon cycle is the continuous movement of the carbon on earth between the
atmosphere, living organisms, the land and back again.
✓ The carbon cycle is driven by the processes of photosynthesis, respiration and
decomposition.
(Draw fig.14.13 page 306)
Fig 14.13 shows the parts of the carbon cycle as follows;
1. There is a small amount of carbon dioxide available in the atmosphere
2. During photosynthesis, plants absorb carbon dioxide from the atmosphere and turn it
into carbohydrates such as glucose and starch
3. Respiration takes place in plants, breaking some of the carbohydrates into carbon dioxide
and gets released back into the atmosphere
4. Animals feed on plants taking up the rest of the stored carbohydrates in plants
5. Respiration takes place in the bodies of the animals, breaking down some of the
carbohydrates, releasing carbon into the atmosphere
6. Decomposition takes place on remains of dead bodies of organisms and wastes of plants
and animals.
7. Decomposers return carbon dioxide to the atmosphere during respiration.
8. Carbon stored as fossil fuels such as coal.
9. When fossil fuels are burnt, combustion, carbon dioxide is returned to the atmosphere.,
130
NB; carbon dioxide is also added to the atmosphere when wood and other plant or animal
matter is burnt.
Human influence on the carbon cycle
The two main human activities that affect the carbon cycle are;
1. The burning of wood and fossil fuels ( fuel combustion)
❖ These fuels release large volumes of carbon dioxide into the atmosphere.
❖ This contributes to global warming ( CO2 is one of the greenhouse gases).
2. The cutting down of trees (deforestation)
❖ This reduces the volume of carbon dioxide that is absorbed from the atmosphere
for photosynthesis, and consequently leads to reduced oxygen concentration in
the atmosphere ( animals rely on oxygen produced by plants for respiration)
❖ Trees are large, natural carbon sinks ( naturally absorb large amounts of carbon
dioxide from the atmosphere)
NB; read about global warming on pages 309- 310
Nitrogen cycle
✓ Nitrogen is one of the main components of proteins, including enzymes
✓ This nutrient is also a major constituent of DNA.
✓ The nitrogen cycle describes the way that nitrogen continuously moves from the
atmosphere to the soil and living organisms, and back again.
✓ The three main types of bacteria involved are
1. Nitrogen – fixing bacteria.
•
Convert nitrogen gas into compounds of ammonia.
2. Nitrifying bacteria.
•
Convert compounds of ammonia into nitrates
3. Denitrifying bacteria.
•
Break down nitrates into nitrogen gas.
( draw the nitrogen , fig14.21 , page 311)
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The processes in fig.14.21 can be discussed as follows;
1. Nitrogen, in the form of nitrogen gas, is abundant in the atmosphere.
2. Lightning changes nitrogen gas into nitrates in the soil.
3. Nitrogen fixing bacteria turn nitrogen gas into nitrates or ammonia salts through the
process of nitrogen fixation. Some of these bacteria are found in the roots of legumes.
4. Man –made inorganic fertilisers; nitrogen gas turned into nitrates and ammonium salts.
5. Plants turn absorbed nitrates and ammonium salts into proteins.
6. Animals feed on plants and other animals and use nitrogen gained to make their own
proteins.
7. Decomposers get nitrogen from dead plants and animals and other waste products like
urine.
8. Ammonification- decomposition of plants and animals.
9. Nitrification – nitrifying bacteria turn ammonium salts into nitrates.
10. Denitrification- denitrifying bacteria turn nitrates into nitrogen gas.
NB; sometimes nitrates get leached out of the soil to nearby river systems, or ground water,
out of the reach of the plant roots.
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POLLUTION
Pollution is the build-up of substances such as chemicals, which damage the environment,
due to human activity.
Water pollution by sewage and chemical waste
Sewage; see page 233
❖ Sewage can result to eutrophication ( like over use of fertilisers)
❖ This is because sewage contains high concentrations of nutrients like phosphates,
organic matter and bacteria
❖ Phosphates act as fertilizers of algae, while the bacteria feed on the organic matter and
reproduce rapidly, using up oxygen in respiration.
❖ Untreated sewage can lead to diseases.
Chemical waste
❖ Chemical wastes such as heavy metals, i.e mercury, and nickel) can be dumped in low
concentrations into river systems.
❖ Bio-accumulations; organisms feeding on those which have consumed the contaminated
water might die. Poisons such as mercury damage the central nervous system and can
lead to death
❖ This reduces the organisms in the next trophic level.
Air pollution by sulfur dioxide
❖ Sulfur dioxide is released into the air when fossil fuels are burnt ( coal and oil).
❖ Power stations burn large amounts of fossil fuels, sulfur dioxide dissolves in the water
vapour in the clouds forming sulfuric acid, leading to acid rain.
Problems caused by acid rain
1. Damage to plant leaves, eventually killing the plants.
2. Acidification of lakes ; water animals can not survive, they die.
3. Increased risk of asthma attack and bronchitis in humans.
4. Corrosion of stone work on buildings( limestone)
5. Release into soil of soluble ions that are toxic to fish when washed into lakes
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Ways of reducing incidence of acid rains
1. Changing the types of power stations that generate electricity from coal and oil, to
gas or nuclear power stations or using more renewable sources like wind.
2. Using scrubbers in power station chimneys, it removes most of the sulfur dioxide
present in waste gases
3. Using catalyst converters in car exhaust, these convert oxides of nitrogen into
harmless nitrogen
Pollution by insecticides, herbicides and nuclear fallout
✓ When insecticides are applied to kill some insects and pests, they also kill all the
insects exposed to them.
✓ These include useful insects that are needed to pollinate crops.
✓ Food webs are also affected.
✓ Herbicides may also kill rare plant species near the fields being sprayed
✓ Nuclear fall out may be a result of nuclear leak from a nuclear power station or from
a nuclear explosion.
✓ Radioactive particles are carried by the wind or water and gradually settle in the
environment. If the radiation has a long half- life, it remains in the environment and
absorbed by living organisms.
✓ The radioactive materials accumulate in food chains and can cause cancer in top
carnivores.
NB: read about non- biodegradable substances and their effects to the environment,
CONSERVATION
Conservation is maintenance and protection of the habitat and or species. Conservation
also include the management of natural resources (e.g water, sunlight, minerals, etc)
Conservation is concerned with;
1. Conserving species biodiversity.
2. Conserving habitat biodiversity.
3. Conserving natural resources.
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Sustainable development is development providing for the needs of an increasing human
population without harming the environment.
Resource conservation
We depend on natural resources to live and to make the things we need.
Natural resources are classified into;
1. Renewable resource – resources that can be replaced by natural processes relatively
quickly. These can be used for a long period of time if we dont use them faster than
they are replaced ( solar energy, tides, flowing water etc)
2. Non-renewable resources- resources that are replaced by natural processes
relatively slowly. It takes too long for these resources to be replaced compared to
the human life span that we consider them to be irreplaceable once they have been
used up (e.g fossil fuels, minerals )
✓ Non-renewable resources like fossil fuels must be conserved because once
they are all used up, they will not be replaced in our life time, and we will
have to use alternative sources of energy.
✓ Some minerals, however, can be recycled from waste and used repeatedly.
For example, metals such as copper and tin, as well as silica in glass can be
recovered from waste and recycled.
✓ Other substances that can be recycled include paper and plastic
Conservation is based on the principle of sustainable resource use. To use resources in a
sustainable way we must not use them at a faster rate than they can be replaced. In this
way the resources are continuously available over time and they are never used up.
Reasons for conserving species
1. Many species of plants and animals are in danger of extinction, due to factors such
as habitat destruction, the introduction of other species and pollution.
✓ Many different species means complex, stable food webs. If one species of
become extinct, the one that rely on it for food or shelter will also die.
✓ Most countries in southern Africa are concerned about the conservation of
black rhinos. Rhinos are hunted and killed for their horns, which are cut off
and sold for high prices.
2. Lose of species also means that its genes are lost. These may be important in the
future for genetic engineering and the production of useful chemicals such as
medicines.
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3. The presence of rare species can be an important source of money for poor
countries through tourism
4. The species may play an important role in food chain. Its loss could endanger other
species.
Note: conservation of habitats is as important as conservation of individual specie- if
habitats are lost, so are the species which live in them. Habitat destruction poses a great
threat to the survival of species.
Conservation of endangered species
1. Placing species in nature reserves/ game parks/sanctuary
2. Protecting species, habitat reconstruction, fencing
3. Controlling predators/grazers/parasites/ diseases
4. Supplying food to the conserved species
5. Preventing hunting/ reducing poaching/ reducing fishing
6. Educating local population
7. Providing breeding sites or captive breeding
8. Ban trades involving threatened species.
Good luck with your study and final exams!!!!!!
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