1. CELL STRUCTURE AND ORGANISATION
1.1 PLANT AND ANIMAL CELL
(a) examine under the microscope an animal cell (e.g. from fresh liver) and a plant cell (e.g. from Elodea,
a moss, onion epidermis, or any suitable, locally available material), using an appropriate temporary
staining technique, such as iodine or methylene blue
(b) draw diagrams to represent observations of the plant and animal cells examined above
(c) identify, from fresh preparations or on diagrams or photomicrographs, the cell membrane, nucleus
and cytoplasm in an animal cell
(d) identify, from diagrams or photomicrographs, the cellulose cell wall, cell membrane, sap vacuole,
cytoplasm, nucleus and chloroplasts in a plant cell
(e) compare the visible differences in structure of the animal and the plant cells examined
(f) state the function of the cell membrane in controlling the passage of substances into and out of the cell
(g) state the function of the cell wall in maintaining turgor (turgidity) within the cell
Most living things are made of cells. Cell shape varies according to its function. Plant and animal cells differ
in size, shape and structure (plants cells are usually larger than animal cells).
The basic unit of life or building blocks of life is a cell.
Similarities and differences between animal cell and plant cell
All animal cells have cytoplasm and cell surface membrane which completely surrounds the cells. Most
animal cells and also have a nucleus. Red blood cells, however, are unusual and do not have a nucleus.
CELL MEMBRANE- all cells have an outer covering called cell membrane, which is made up of proteins and
lipids. The cell membrane is semi-permeable. It means that it allows certain substance to pass through while
prevent other substances. Controls in and out of substances to the cell. In general, oxygen, food and water
are allowed to enter; waste products are allowed to leave and harmful substances are kept out.
CYTOPLASM – cytoplasm is a jelly-like substance present in all living cells. The term cytoplasm refers to all
the living substances of a cell except nucleus. Cytoplasm is composed of 65%with as much as a billion
molecules contained within the cytoplasm of a single cell. In the cytoplasm all the chemical reactions of cell
(metabolic reactions) takes place. The cytoplasm contains enzymes, and dissolved nutrients like amino acids
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and sugars. Cytoplasm contains tiny living structure called organelles (such as, mitochondria, ribosomes
and chloroplasts).
NUCLEUS - nucleus is a round or oval shaped. The nucleus appears dark because nucleus takes stain more
than cytoplasm. The nucleus is double membrane structure. Nucleus contain rod shape or thread like
structures called chromosomes, which carries hereditary characters from one generation to the other.
Controls the cell activity by the production of enzymes. The nucleus also control cell division.
MITOCHONDRIA – the mitochondria are tiny organelles present in plant and animal cells. They may be
spherical, rod-like or elongated. They are most numerous in regions of rapid chemical activity and are
responsible for producing energy from food substances.
Plant cells are often easier to see than animal cells, at least partly because they are often quite a bit bigger.
You can see that it has several structures that animal cells don’t have. These are cell wall, chloroplast and
large vacuole containing cell sap.
ELL WALL – only plant cell have cell wall. A tough and rigid layer membrane completely surrounds the cell
membrane of a plant cell. It is made up of cellulose. It provides structural support and protects against
damage caused by osmotic intake of water. The cell wall is freely permeable to water and dissolved
substances.
VACUOLE – vacuole is present mostly in plant cells. Vacuole is a space in the cytoplasm which is filled with
some fluid. Normally animal cells have small and temporary vacuoles. Plant cells have a large and permanent
vacuole. Vacuole contains water necessary to provide turgor pressure and may store ions and molecules.
CHOLOROPLAST – chloroplast are small disc-shaped organelles lying in the cytoplasm of a plant cells.
Composed of double layer of modified membrane contains pigment called chlorophyll which absorbs light
energy for photosynthesis. Chloroplast produces the enzymes necessary for the production of glucose by
photosynthesis.
Mnemonic
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THE LIGHT MICROSCOPE
Cells are too small to see with the naked eye so a microscope is used to study them. If a very thin slice of a
plant stem or root is cut and studied under a microscope, it can be seen that the stem consists of
thousands of tiny, box-like structures. These structures are called cells.
Here is the example;
This is a thin slice taken from maize root and photographed through microscope. Photographs like this are
called photomicrographs. Thin slices of this kind are called sections.
If you cut along the length of the structure, you are taking a longitudinal section.
If you cut across the structure you make a transverse section.
SIZE OF SPECIMENS
Many of the structure we study in biology are too small to be seen by just using our eye. We can use
magnifying glasses and microscopes to examine details of plant and animal cells and to take picture and
draw the diagrams.
The magnification is equal to the size divided by the actual size.
Magnification =
𝑜𝑏𝑠𝑒𝑟𝑣𝑒𝑑 𝑠𝑖𝑧𝑒
𝑎𝑐𝑡𝑢𝑎𝑙 𝑠𝑖𝑧𝑒
If we look at something that we know is 0.5 mm long using a microscope, and the image we see is 20 mm
long then we can calculate that the Magnification.
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When we use a microscope to examine a specimen, we can work out the size of a structure as long as we
know the magnification we are using
𝑜𝑏𝑠𝑒𝑟𝑣𝑒𝑑 𝑠𝑖𝑧𝑒
Actual size = 𝑚𝑎𝑔𝑛𝑖𝑓𝑖𝑐𝑎𝑡𝑖𝑜𝑛
So if you look at the cell using magnification of 400 and the image we see has a diameter of 6 mm then we
know that the cell has an actual diameter of 0.015 mm.
HOW TO PREPARE AN ONION CELL SLIDE
Tissue from an onion is a good first exercise in using the microscope and viewing plant cells. The cells are
easily visible under a microscope and the preparation of a thin section is straight forward. An onion is made
of layers, each separated by a thin skin or membrane. In this exercise you will make a wet mount on a
microscope slide and look at the cells of the onion membrane magnified by the high power, compound
microscope.
1. First add a few drops of water or solution on the microscope slide to avoid dryness and wilting
2. Take a small piece of onion and using forceps (tweezers), peel off the membrane from the
underside (the rough side).
3. Lay the membrane flat on the surface of the slide
4. Add a drop of Iodine solution to the onion epidermis.
5. Using a pin, lower the thin glass cover slip or cover glass onto the slide. Make sure there are no air
bubbles.
6. Transfer the slide for viewing.
HUMAN CHEEK CELLS
Materials
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Glass microscope slides
Plastic cover slips
Paper towels or tissue
Methylene Blue solution (0.5% to 1% (mix approximately 1 part stock solution with 4 parts of water))
Plastic pipette or dropper
Sterile, individually packed cotton swabs
Methods
1. Take a clean cotton swab and gently scrape the inside of your mouth.
2. Smear the cotton swab on the centre of the microscope slide for 2 to 3 seconds.
3. Add a drop of methylene blue solution and place a coverslip on top. Concentrated methylene blue is
toxic if ingested. Wear gloves and do NOT allow children to handle methylene blue solution or have
access to the bottle of solution.
4. Remove any excess solution by allowing a paper towel to touch one side of the coverslip.
5. Place the slide on the microscope, with 4 x or 10 x objective in position and find a cell. Then view at
higher magnification.
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1.2 SPECIALISED CELLS, TISSUES AND ORGANS
(h) state, in simple terms, the relationship between cell function and cell structure for the following:
• absorption – root hair cells
• conduction and support – xylem vessels
• transport of oxygen – red blood cells
(i) identify these cells from preserved material under the microscope, from diagrams and from
photomicrographs
(j) differentiate cell, tissue, organ and organ system as illustrated by examples covered in sections 1 to
12, 15 and 16.
CELL DIVISION
When plants and animals grow, their cells increase in number by dividing. During cell division each cell
divides to produce two daughter cells. Both daughter cells may divide again, but usually one cells grows
and changes its shape and structure and adapted to do one particular job – or becomes specialized. At the
same time it loses its ability to divide anymore. The other cell is still able to divide and so continue the
growth of the tissue.
SPECIALISED CELLS:
In UNICELLULAR organisms, one cell must be able to carry out all the functions of living organisms. In
MULTICELLULAR organisms, different types of cell have particular structure designed to help them to carry
out one main function – they have become specialized.
THERE IS A RELATIONSHIP BETWEEN THE STRUCTURE OF A CELL AND ITS FUNCTION.
Here are examples of cells and their functions in tissues.
1. Ciliated cells in respiratory tract
Ciliated cells are specialized animal cells. We have ciliated cells in the lining of our trachea and bronchiole. Cilia are
tiny extensions of the cell. Cilia can move. They help to sweep mucus up the bronchi and trachea towards the back of
the throat. The mucus trap bacteria and dirt particles in the air that we breathe in.
Features: tiny hairs called cilia which can move mucus.
Function: waft mucus with bacteria and dust away from the lungs.
2. Muscle cells
Muscles are found in many different animals, including humans. Like all animal cells, muscle cells have a
cell membrane, cytoplasm and a nucleus – but each muscle cell has many nuclei rather than just one. They
are made up of many strand protein arranged in pattern. This strand of protein can slide between each
other, making the cell much shorter. This is called contraction.
Features: cells merge together to form fibres that can contract
Function: cause movement
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3. Red blood cells
Red blood cells are small (7 µm × 2 µm) and they are many, so they have a very large surface area for
oxygen absorption. They have a cell membrane and cytoplasm, but no nucleus, leaving more space for
haemogolobin. The cytoplasm is filled with the pigment haemoglobin, which carries oxygen. They have a
biconcave shape, making their surface area for absorption even larger. Being very flexible, allowing them to
be pushed easily through small blood vessels (Capillaries).
Features: have no nucleus, contain hemoglobin
Function: transport oxygen around the body
4. Root hair cell (plants)
Root hair cells are specialized plant cells. They are found on the outside of the plant roots just a little way up
from the root tip. Their functions are to help to anchor the plant in the soil, and to absorb water and mineral
ions from the soil. The outer part of its cell wall (i.e. the part in direct contact with the soil) is in the form of
long, tubular extension (the root hair) which increases the surface area for the absorption of materials.
Features: the hair gives a large surface area
Function: absorb water and mineral ions; anchor the plant firmly in the soil
5. Xylem cells
Xylem cells are another type of specialised plant cell. They strangest of all, because they are
completely empty and dead. They began as a normal, living plant cell, but then their cell walls gradually
filled up with a substance called lignin. The cell has no cytoplasm so water can pass freely. No end wall,
so that many cells can form a continues tube. Walls are strengthened with waterproof substance called
lignin
Features: long, thin cells arranged end-to-end to form vessels (tubes). The cells lack end wall and
cell contents such as cytolplasm and nucleus. The walls become lignified (woody).
Function: conduction (transport water and mineral ions from roots to leaves)
support (Ligmin provides strength for the stem).
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TISSUES, ORGANS AND ORGAN SYSTEMS
Cells are organized to form tissue, organs, and organ systems. In a healthy organism, all the systems work
together.
SPECIALIZED CELLS
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A specialized cell is designed to do a particular job.
Nerve cells have long fibers to carry massages.
Muscle cells can contract and relax.
White blood cells attack bacteria.
Platelets help clotting.
TISSUES
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Large numbers of specialized cells make up tissue.
Muscles, blood and nerves are all tissues.
Blood tissue contains red cells for carrying oxygen, white cells for destroying harmful bacteria, and
platelets to cause clotting in cuts
ORGANS
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Various tissues together make up an organ.
Each organ has its own specific job.
The heart, the stomach and the brain are all organs.
The heart has to pump blood around the body. It is made up of muscle tissue, blood
vessels and nerves.
Arteries and veins are usually thought of as organ as they consist of several tissue layers.
ORGAN SYSTEMS
Various organs together make up an organ system. E.g. the circulatory system carries blood to
all parts of the body. It is made up of heart, arteries, veins, capillaries and blood.
ORGANISM
Various organ systems together make up an organism.
A human organism has:
 Respiratory system
 Digestive system
 Circulatory system
 Nervous system
 Endocrine system
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LEVELS OF ORGANISATIONS
Key definitions
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Organells: a structure within a cell (e.g. nucleus, vacuole, cytoplasm and chloroplast are all organelles
of a plant cell).
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Tissue: a group of cells with similar structures, working together to perform a shared function.
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Organ: a structure made up of a group of tissues, working together to perform specific functions.
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Organ system: a group of organs with related functions, working together to perform body functions.
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Organism: a collection of systems working together produce an organism, an independent plant or an
animal
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2. DIFFUSION AND OSMOSIS
Cells need food materials which they can oxidize for energy or use to build up their cell structure. They also
need salts and water which play a part in chemical reactions in the cell. Finally, they need to get rid of
substances such as carbon dioxide, which if they accumulate in the cell, would upset some of the chemical
reactions and even poison the cell. In another word, for plant and animals to stay alive, chemicals must be
able to move easily:
- From one part of a cell to another
- Into and out of a cell
- From one cell to another
Substance may pass through the cell membrane either passively by diffusion, or actively by some form of
active transport.
2.1 DIFFUSION
(a) define diffusion as the movement of molecules from a region of their higher concentration to a region
of their lower concentration, down a concentration gradient;
All substance are made up of tiny particles called atoms. In some substances, these atoms have lost or
gained on e or more electrons, to become ions. In other substances, the atoms are grouped together to form
molecules.
Atoms, ions and molecules in liquids and gases are never still. They keep moving and bumping into each
other all the time. Molecules and ions in a liquid or a gas move continuously. The movement of particles is
due to their own kinetic energy. Before diffusion can occur, there must be a concentration gradient of the
molecules – a region of (relatively) high concentration next to a region of (relatively) low concentration.
We can see molecules move by adding a drop of ink to water. Ink spreads because ink molecules move into
the spaces between water molecules, and water molecules move into the spaces between ink molecules.
These mixing of molecules are called diffusion.
DEFINITION
Diffusion is the movement of molecules from a region of their higher concentration to a region of their lower
concentration, down a concentration gradient.
For living cells, the principle of the movement down a concentration gradient is the same, but there is one
problem:
The cell is surrounded by a cell membrane, which can restrict the free movement of the molecules --> This
is a selective permeable membrane: the composition of the membrane (lipid and protein) allows some
molecules to cross with ease, but others with difficulty or not at all. The simplest sort of selection is based on
the size of the molecules.
SOME ADAPTATIONS TO SPEED UP DIFFUSION
DIFFUSION DISTANCES ARE SHORT – the membrane of the lungs are very thin so that O2 and CO2 can
diffuse between the blood and the lungs air spaces.
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CONCENTRATION GRADIENT ARE MAINTAINED- glucose molecules that cross from the gut into the
blood are quickly removed by the circulating blood.
DIFFUSION SURFACES ARE LARGE – the surface of the placenta is highly folded to increase the surface
area for the diffusion of molecules between pregnant female and fetus.
SIZE OF THE MOLECULES - the smaller the better.
TEMPERATURE - molecules have more kinetic energy at higher temperature.
IMPORTANCE OF GASEOUS AND SOLUTE DIFFUSION
Diffusion helps living organisms to:
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obtain many of their requirements
get rid of many of their waste products
gas exchange for respiration
EXAMPLES OF DIFFUSION IN PLANT
- CO2 uses by plants for photosynthesis is diffuses from the air into the leaves, through the stomata
(pores at the surface of leaves). There is a lower concentration of CO2 inside the leaf, as the cells
are using it up. O2 (waste product of photosynthesis diffuses out in the same way).
- Flowering plants use diffusion to attract pollinators like bees.
- Mineral ions from the soil solution are absorbed by plant roots by diffusion
- Movement water vapor during transpiration
EXAMPLE OF DIFFUSION IN ANIMALS
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From the lungs, O2 enters the blood by diffusion
Glucose and amino acids pass from inside the gut into the blood by diffusion
The movement of carbon dioxide into the blood
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IMPORTANCE OF WATER AS A SOLVENT
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Most cells contain about 75% of water.
Many substances move around a cell dissolved in water.
Many important reactions take place in water.
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2.2 OSMOSIS
(b) define osmosis as the passage of water molecules from a region of higher water potential to a region
of lower water potential, through a partially permeable membrane
(c) describe the importance of a water potential gradient in the uptake of water by plants and the effects
of osmosis on plant and animal tissues
DEFINITION
OSMOSIS as the passage of water molecules from a region of higher water potential to a region of
lower water potential, through a partially permeable membrane
Osmosis is a special form of diffusion and always involves the movement of H2O across a membrane.
Osmosis is:
- the movement of H2O
- across a selectively permeable membrane
- down a water potential gradient.
IN THE PICTURE BELOW
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The concentration of sugar molecules is higher on the concentrated solution (L) and lower on
the diluted one (R).
The concentration of water molecules is higher on the (R) and lower on the (L) (a lot of place is taken
up by sugar molecules).
It is confusing to talk about the 'concentration of water', so we can say that a diluted solution (R) has
a high water potential and a concentrated solution (L) has a low water potential.
There is a water potential gradient between the 2 sides. The water molecules diffuse down this gradient,
from a high water potential (R) to a low water potential (L).
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CELL MEMBRANES
- partially permeable (let some substances pass through, but not others).
- separate 2 solutions: cytoplasm and solution around the cell.
- If the solutions are of different concentrations, osmosis will occur.
EFFECT OF OSMOSIS ON PLANT AND ANIMAL CELLS
1. WHEN PLACED IN WATER:
Concentration of H2O outside the cell is higher than inside it. Cells will take in H2O by osmosis:
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plant cells become turgid (swollen) but do not burst (have tough cell wall which is fully permeable).
As water enters the plant cell, the vacuole increases in volume. It presses the cytoplasmic lining of
the cell against the flexible, box-like cell wall. This pressure is called TURGOR pressure, and helps
to make plant cells firm.
TURGIDITY IN PLANT CELLS HELPS:
 To keep stems upright
 To keep leaves flat so they can better absorb sunlight.
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animal cells will burst (no cell wall).
If an animal cell is placed in water, it starts to take in water by osmosis. Since there is no cell wall to
resist the increased pressure that results, the cell bursts.
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2. WHEN PLACED IN CONCENTRATED SUGAR OR SALT SOLUTIONS:
Concentration of H2O inside the cell is higher than outside it. H2O get out of the cells by osmosis:
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plant cells become flaccid (soft and limp), cytoplasm is no longer pressed against the cell wall. The
plant loses it firmness and begin to wilt.
The cells lose their turgor because the cytoplasm is no longer being forced against the cell wall. They
become flaccid. If the cells remain in the solutions of lower water potential, so much water will be
drawn from the vacuole that the cytoplasm will pull away from the cell wall. This condition is called
plasmolysis.
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animal cells shrink, become crenated.
Animal cells placed in solution of lower water potential lose their shape and turgidity as water moves
out of their cytoplasm. A red blood cell shrinks in size and its cell membrane becomes unevenly
creased.
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2.3 ACTIVE TRANSPORT
(d) define active transport as the movement of ions into or out of a cell through the cell membrane, from
a region of their lower concentration to a region of their higher concentration against a concentration
gradient, using energy released during respiration
(e) d iscuss the importance of active transport as an energy-consuming process by which substances are
transported against a concentration gradient, as in ion uptake by root hairs and glucose uptake by cells in
the villi.
DEFINITION
Active transport as the movement of ions into or out of a cell through the cell membrane, from a region of
their lower concentration to a region of their higher concentration against a concentration gradient, using
energy released during respiration
Sometimes substances are required to be moved against the Concentration Gradient, or faster than they
would by Passive Transport. In these cases, Active Processes are used, which require energy.
There are many occasions when cells need to take in substances which are only present in small
quantities around them.
EXAMPLES OF ACTIVE TRANSPORT
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root hair cells in plants take in nitrate ions from the soil. Their concentration are often higher inside
the root hair cell than in the soil, so the diffusion gradient is from the root hair à the soil. Despite
this, the root hair cells still can take nitrate ions in, by active transport.
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in the small intestine of an animal, when digested food (such as glucose) is absorbed by the cells of
the villi by active transport.
THIS ACTIVE TRANSPORT
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requires energy as ATP from respiration to 'drive' the molecules 'uphill'
is affected by factors affecting respiration (temperature, O2 concentration)
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The importance of active transport: energy-consuming process by which substances are transported
against a concentration gradient, e.g. ion uptake by root hairs and glucose uptake by epithelial cells of villi.
Two big differences between diffusion and active transport:
- direction of movement (down or up a gradient)
- use of energy for movement
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The active transport is carried out by ‘carrier proteins’ in the membrane, which bind to the solute
molecule, change shape and carry the molecule across the membrane.
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3. ENZYMES
3.1 ENZYME ACTION
(a) define catalyst as a substance that speeds up a chemical reaction and is not changed by the
reaction
(b) define enzymes as proteins that function as biological catalysts
(c) explain enzyme action in terms of the ‘lock and key’ hypothesis
Enzymes are proteins that act as biological catalyst. A catalyst is a substance that speeds up the rate of
a chemical reaction, but is not itself changed by the reaction. A catalyst can be used over and over again.
Living organisms have thousands of different chemical reactions, called metabolic reactions, taking
place inside them. Some of these reactions, such as those involved in respiration, digestion and
photosynthesis.
Each kind of enzyme can catalyse only one particular kind of reaction. So our bodies contain many
different enzymes, one for each of the many different metabolic reactions that must take place for us to
stay alive.
ENZYMES ARE CLASSIFIED ACCORDING TO THE SUBSTRATE ON WHICH THEY ACT ON
Eg: digestive enzymes are divided into groups according to the foods which they digest;
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amylase is a group of enzymes which break down starch to glucose
lipase is a group of enzymes which break down fats and oils to their component fatty acids and
glycerol
protease is a group of enzymes which break down proteins to amino acids
SOME PROPERTIES OF ENZYMES ARE:
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They are all protein molecules
They are made in the cytoplasm
Each enzyme works at its fastest rate at one particular temperature known as optimum
temperature
Each enzyme works at its fastest rate at one particular pH, known as optimum pH
HOW ENZYME WORK - THE ‘LOCK AND KEY’ HYPOTHESIS
Each enzyme is a molecule with a specific shape. On part of its surface is the active site (the ‘lock’) – a
section where its substrate molecule (the ‘key’) fits exactly. When the substrate molecule is in position in
the active site, the enzyme slightly stress the substrate, splitting it into two products. The product
molecules drift away from the enzyme molecule, leaving its active site free to operate again.
Key:
M – substrate
N – active site
O – enzymes
P - products
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Enzymes and reactions
most enzyme names end in –ase, e.g. lipase, protease, amylase, lactase, maltase, peptidase.
3.2 EFFECTS OF TEMPERATURE AND PH
(d) investigate and describe the effects of temperature and of pH on enzyme activity.
THE EFFECT OF TEMPERATURE ON ENZYMES
Enzymes can only work if their molecules are exactly the right shape. If the enzyme molecule losses its
shape, then its substrate won’t fit into its active site. If an enzymes molecules gets very hot, it starts to
lose its shape. This is called denaturing. A denatured enzyme cannot act as a catalyst.
At low temperatures, the enzyme molecules and the substrate molecules are moving very slowly. As the
temperature increases, their kinetic energy increases and they move faster. The higher the temperature,
the faster they move around and more frequently they collide and with each other. What’s more, they have
more energy when they collide and so it is easier for the reaction to take place. So, as temperature rises,
the rate of reaction also increase.
But when we get a temperature above about 40oC, you can see that the rate of reaction begins to slow
down. This is because the enzymes molecules are beginning to be denatured. They have lost their shape
and substrate no longer fits into the active site. By a temperature of 60oC, the enzyme molecules are all
completely denatured and no reaction is taking place at all.
The enzyme activity gradually increases with temperature up to around 37ºC, or body temperature. Then,
as the temperature continues to rise, the rate of reaction falls rapidly as heat energy denatures the
enzyme. Most enzymes are denatured above 500C.
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THE EFFECT OF pH ON ENZYMES
The pH of a solution is a measure of how acid or alkaline it is. The scale runs from 1 to 14. A pH of 7 is
neutral. A pH below 7 is acid, and a pH above 7 is alkaline.
pH also affects enzyme activity since changing the acid or base conditions around an enzyme molecule
affects three-dimensional shape and can denature the enzyme.
For most enzymes, there is a small range of pH in which their molecules are exactly the right shape to
catalyse their reaction. Above or below this pH, their molecule lose their shape, so their substrate cannot
fit into the active sites.
Changes in pH also alter an enzyme’s shape and slow down its activity, but this can usually be reversed if
the optimum pH is restored. An extreme pH can denature enzymes – the active site is deformed
permanently.
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The pH of a solution is how acidic or alkaline it is.
Different enzymes work best at different pH values.
The optimum pH for an enzyme depends on where it normally works.
It is around neutral (pH= 7) for most enzymes but there are some exceptions.
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ROLE OF ENZYMES IN GERMINATING SEEDS
Seeds contain stored food in the cotyledons to provide energy and materials for growth. This is usually
in the form of starch – a large, insoluble molecule (long chain of glucose), that keeps the food immobile.
The starch needs to be changed into a soluble molecule (sugar) with help of enzymes for the seeds to
make use of.
Things to remember:

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
In the presence of H2O, Gibberellin or gibberellic acid (GA) stimulates the production of amylase.
Amylase breaks down starch to maltose, allowing for the formation of ATP (via glucose).
The energy produced in the embryo is used to facilitate germination.
The glucose produced may also be used to synthesis cellulose - for cell wall formation.
Warmth helps speed up the process.
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USE OF ENZYME IN BIOLOGICAL WASHING POWDERS
Biological washing powders contain protease and lipase to remove protein stains and fat/grease from
clothes. The enzymes break down proteins or fats on the fabric, forming water-soluble substances that
can be washed away.
Example: Blood contain the red protein Haemoglobin (Hb). The Proteases in biological washing powder
break Hb molecules into smaller molecules, which are not coloured and which dissolve in water and can
be washed away.
This makes the washing powder more effective than detergent alone, especially at lower temperatures.
This save energy (no need to boil water), but if the temperature is too high, the enzyme will be denatured.
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USE OF ENZYMES IN THE FOOD INDUSTRY
Enzymes are an integral component of modern fruit juice manufacturing and are highly suitable for
optimising processes. Fruit juices are extracted using an enzyme called pectinase.
Pectin is a substance which helps to stick plant cells together. Fruits like apple or orange contain a lot of
pectin. The braking down of pectin makes it much easier to squeeze juice from the fruit.
Pectinase is widely used in order to:
• increase extraction of juice from raw material
• increase processing efficiency (pressing, solid settling or removal)
• generate a final product that is clear and visually attractive
Enzymes are sometimes used when making baby foods. Proteases are used to treat some high-protein
foods, they break down proteins to polypeptides and amino acids for young baby to absorb the
food easier.
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USE OF MICROORGANISMS AND FERMENTER TO MANUFACTURE ENZYMES
We obtain many enzymes from microorganisms. The enzymes that are used in industry are usually
obtained from microorganisms. These include bacteria and microscopic fungi, such as yeast. The
microorganisms are grown inside large vessels called fermenters.
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Inside the fermenter, the microorganisms are provided with everything they need to grow and
reproduce, e.g.:O2, supply of nutrients, a suitable pH and temperature.
The microorganisms make the enzymes and release them into the liquid in which they are
growing.
The liquid can then be collected from the fermenter, and the enzymes purified before use.
Closer look at fermenter


The fermenter is a large, sterile container with a stirrer, a pipe to add feedstock* (molasses* or
corn-steep liquor), and air pipes to blow air into the mixture.
The microorganisms are added and the liquid is maintained around 260C and a pH of 5-6.
The enzymes produced by the microorganisms may be extracellular or intracellular:
1. Extracellular enzymes are extracted from the feedstock by filtering.
2. To extract intracellular enzymes the microorganisms are filtered from the feedstock, then crushed and
washed with water. The enzymes are now in solution.
Explain words:
* Feedstock: Raw material (input) fed into a process for conversion into something different (output).
* Molasses (syrup): Thick, dark brown, uncrystallized juice obtained from raw sugar during the refining
process.
*Corn-steep liquor: a concentrated fluid obtained by soaking corn grains in water (containing
0,2% SO2) for 36 — 40 hours at 46 — 50°C.
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4. PLANT NUTRITION
4.1 PHOTOSYNTHESIS
(a) understand that photosynthesis is the fundamental process by which plants manufacture
carbohydrates from raw materials
(c) state the equation (in words or symbols) for photosynthesis
(f) describe the intake of carbon dioxide and water by plants
(g) understand that chlorophyll traps light energy and converts it into chemical energy for the
formation of carbohydrates and their subsequent storage
(h) explain why most forms of life are completely dependent on photosynthesis
PHOTOSYNTHESIS
Photosynthesis is the fundamental process by which plants manufacture food molecules
(carbohydrates) from raw materials (CO2 and H2O) using energy from light, which is absorbed by
chlorophyll. The byproduct of photosynthesis is oxygen.
Things needed for photosynthesis
There are four things necessary for photosynthesis. They are sunlight, carbon dioxide, water and
chlorophyll. Out of this sunlight, carbon dioxide and water are obtained from outside. They are also
known as the raw materials for photosynthesis. Chlorophyll is the green pigment, which is present in
the chloroplasts.
Sunlight - Sunlight is absorbed from the sun by the chlorophyll. Sunlight provides the energy for
photosynthesis
Water - Water enters the leaf through root from the soil by osmosis. It travels up to the leaf through the
xylem vessels.
Carbon dioxide - enters the leaf, by diffusion, through the open pores (stomata) on the lower surface of
the leaf, from the atmosphere.
Chlorophyll - the green substance, which is found in the chloroplasts and which, makes the leaf green.
It absorbs the light energy for photosynthesis.
The word equation of photosynthesis
The following equation summarizes the process of photosynthesis. During photosynthesis carbon
dioxide
The balanced equation for photosynthesis shows that to produce one molecule of glucose, six molecules
of carbon dioxides and six molecules of water are needed. In addition in the same process six molecules
of oxygen are released.
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Mechanism of photosynthesis
The light energy trapped by the chlorophyll pigments present in the chloroplast is used to split water to
hydrogen and oxygen atoms. The hydrogen combines with carbon dioxide and glucose is produced,
whereas the oxygen is excreted as a by-product of photosynthesis. The enzymes convert glucose into
sucrose, which is transported through the phloem tubes to the storage organs. This sucrose may be
converted into starch and stored in the plant.
Fate of photosynthesis
The products of photosynthesis are glucose and oxygen. The oxygen been a byproduct is released into
the surrounding. There are many things that happen to the glucose.
Some of the glucose: Is used up in respiration to release energy.
 Is converted to starch and stored. The storage organs of the plant include the leaves, the roots
and the stems.
 Is converted to sucrose to be transported to other parts of the plant.
 Is converted to cellulose to build cell walls.
 Is used to make proteins, lipids and etc.
Importance of photosynthesis
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During photosynthesis the green plants make food, which is eaten by herbivores and man. So
green plants supply food to all organisms in the biological word.
Green plants absorb the carbon dioxide released by the modern industry and replace it with
oxygen so purify the atmosphere.
Green plants release oxygen as a by-product of photosynthesis so life exists on earth.
The fossil fuels, which we use today, have come from plants, which were fixed in photosynthesis
several million years ago.
PHOTOSYNTHESIS INVESTIGATIONS - PRINCIPLES AND STARCH TEST
4.1 PHOTOSYNTHESIS
(b) investigate the necessity for chlorophyll, light and carbon dioxide for photosynthesis, using
appropriate controls
(d) investigate and state the effect of varying light intensity, carbon dioxide concentration and
temperature on the rate of photosynthesis (e.g. in submerged aquatic plants)
(e) understand the concept of limiting factors in photosynthesis
Experiments can be used to find out what factors (CO2, light, chlorophyll) are needed for
photosynthesis. But first of all you need to destarch the plants. To be certain that they
are thoroughly destarched, test a leaf for starch before you begin your investigation.
Principles of investigations
1. Investigations need controls
Control plant (or leave) has all substances it needs.
Test plant lacks one substance (light/chlorophyll/CO2)
2. Plants must be destarched
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
It is very important that the leaves you are testing should not have any starch in them at the
beginning of the experiment.
So, first of all, you must destarch the plants. Leave them in the dark for 48 hours. The plants use
up all stores of starch in its leaves.
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3. Starch test with Iodine solution
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After a few hours, carry out the starch test on both plants: Iodine solution is used; a blue-black
colour on the leave is positive.
Boil the leaf in water for 30 second. This kill the cells in the leaf à break down the
membrane à iodine solution gets through cell membrane to reach starch inside the chloroplasts
and react with them.

Boil the leaf in alcohol (ethanol) in a water bath: The green colour of the leaf and the brown
iodine solution can look black together, so you need to remove chlorophyll by dissolving it out
with alcohol. Leave it until all the chlorophyll has come out of the leaf.


Rinse the leaf in water: Boiling the leaf in ethanol makes it brittle, the water softens it.
Spread the leaf out on a white tile à easy to see the result.
Add iodine solution to the leaf à blue- black colour is positive, starch is present.

EXPERIMENTS TO SEE WHETHER CARBON DIOXIDE, SUNLIGHT AND CHLOROPHYLL ARE NECESSARY FOR PHOTOSYNTHESIS
To show that carbon dioxide is necessary for photosynthesis
APPRATUS: two well-watered de-starched potted plants
polythene bag to fit over one of the pots
cotton (to tie the polythene bag over the pot and around the stem)
a large piece of flat glass
two bell jars
petroleum jelly (Vaseline)
a small beaker containing concentrated sodium hydroxide (soda lime)
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METHOD:
Destarch two potted plants.
Water the two plants and place bell jars over the plants as shown:
the two plants are left side-by-side in sunlight. After about eight hours, a leaf is taken
from each plant and tested for the presence of starch.
RESULT: The leaf, which had no carbon dioxide, does not turn blue black. The one from the Jar B stains
blue/black. Starch present.
CONCLUSION: The fact that starch was made in the leaves, which had carbon dioxide but not in the
leaves, which had no carbon dioxide, suggests that this gas must be necessary for photosynthesis.
To show that light is necessary for photosynthesis
APPARATUS: a well-watered, desatrched, potted plant
aluminum foil,
paper clips and iodine solution.
METHOD: cut a simple shape from a piece of Aluminum foil to make a stencil and attach it to a
destarched leaf. After four to eight hours of daylight remove the leaf and test it for starch.
RESULT: only the areas, which had received light, go blue black with iodine.
CONCLUSION: As starch has formed in the areas which received light, it seems that light is needed for
starch formation and thus for photosynthesis.
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To show that chlorophyll is necessary for photosynthesis
APPARATUS: a potted plant that is well-watered, de-starched and variegated
METHOD:
Expose to sunlight for eight hours.
Remove one leaf from the plant.
Draw it carefully to show where the chlorophyll is (i.e. the green plants)and test for starch
RESULT: Only the parts, which were previously, green, turn blue black with iodine. The parts that were
white would stain brown.
CONCLUSION: Since starch is present only in the parts, which originally contained chlorophyll, it is
believed that chlorophyll is needed for photosynthesis.
Effect of Light intensity on the rate of Photosynthesis
Plants need light energy to make the chemical energy needed to create carbohydrates. Increasing the
light intensity will boost the speed of photosynthesis. However, at high light intensities the rate
becomes constant.
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Place a pond weed Elodea upside in a test tube containing water.
Place the tube in a beaker of fresh water at 25°C. This helps to maintain a constant temperature
around the pond weed.
Place excess sodium bicarbonate (NaHCO3) in the water to give a constant saturated solution of
CO2.
Place the lamp (the only light source) at distance from the plant.
Count the number of oxygen bubbles given off by the plant in 1 minute period. This is the rate of
photosynthesis at that particular light intensity.
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The gas should be checked to prove that it is indeed oxygen - relights a glowing splint.
Repeat at different light intensities by moving the lamp to different distances.

Graph the results placing light intensity on the x-axis.
Explanation
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Light energy absorbed by chlorophyll is converted to ATP and H+
At very low light levels the plant will be respiring only not photosynthesising.
As the light intensity increases, the rate of photosynthesis increases. However, the rate will
not increase beyond a certain level of light intensity.
At high light intensities the rate becomes constant, even with further increases in light intensity,
there are no increases in the rate.
The plant is unable to harvest the light at these high intensities and the chlorophyll system can
be damaged by very intense light levels.
Effect of Carbon Dioxide on the Rate of Photosynthesis
When the concentration of CO2 is low the rate of photosynthesis is also low (the plant has to spend time
waiting for more CO2 to arrive). Increasing the concentration of CO2 increases the rate of
photosynthesis.
Experiment


Place a pond weed Elodea upside in a test tube containing water at 25°C.
Place the tube in a beaker of fresh water.
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Place excess sodium bicarbonate (NaHCO3) in the water to give a constant saturated solution
of CO2.
Place the lamp (the only light source) at a fixed distance from the plant.
Maintain the room temperature at 20°C.
Count the number of oxygen bubbles given off by the plant in a one -minute period. This is the
rate of photosynthesis at that particular concentration of CO2.
The gas should be checked to prove that it is indeed oxygen - relights a glowing splint.
Repeat at different lower CO2 concentrations by using different dilutions of a saturated solution.
Graph the results placing CO2 concentration on the x-axis.
Explanation


The rate of photosynthesis increases linearly with increasing CO2 concentration (from point A
to B).
The rate falls gradually, and at a certain CO2 concentration it stays constant (from point B to C).
Here a rise in CO2 levels has no effect as the other factors such as light intensity become
limiting.
Effect of Temperature on the Rate of Photosynthesis
When the temperature rises the rate of photosynthesis rises also. There is an optimum temperature at
which the rate of photosynthesis is maximum. Beyond this temperature, the reaction quickly comes to a
halt.
Experiment

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


Place a pond weed Elodea upside in a test tube containing water at 25°C.
Place the tube in a beaker of fresh water.
Place excess sodium bicarbonate (NaHCO3) in the water to give a constant saturated solution of
CO2.
Place the lamp (the only light source) at a fixed distance from the plant.
Maintain the room temperature at 20°C.
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
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Count the number of oxygen bubbles given off by the plant in a one -minute period. This is the
rate of photosynthesis at that particular temperature.
The gas should be checked to prove that it is indeed oxygen - relights a glowing splint.
Repeat at different temperatures: 0°C - surround the beaker with an ice jacket; greater than room
temperature (25°C, 30°C, 35°C, 40°C, 45°C, etc.,) by using a hot plate.
Graph the results placing temperature on the x-axis.
Explanation


At low temperature, the enzyme does not have enough energy to meet many substrate
molecules, so the reaction is slowed.
When the temperature rises, the particles in the reaction move quicker and collide more, so the
rate of photosynthesis rises also.

At the optimum temperature, the enzyme is most efficient and the rate if maximum.

At temperatures above 40°C the rate slows down. This is because the enzymes involved in the
chemical reactions of photosynthesis are temperature sensitive and destroyed
(denatured) at higher temperatures.
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Limiting Factors In Photosynthesis
Limiting factor is something present in the environment in such short supply that it restricts life
processes. Three factors can limit the speed of photosynthesis – light intensity, carbon dioxide
concentration and temperature.
If a component is in low supply then productivity is prevented from reaching maximum.
Sunlight
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Light energy is vital to the process of photosynthesis. It is severely limiting at times of partial light
conditions, e.g. dawn or dusk.
As light intensity increases, the rate of photosynthesis will increase, until the plant is
photosynthesising as fast as it can. At this point, even if light becomes brighter, the plant cannot
photosynthesise any faster.
Over the first part of the curve (between A and B), light is a limiting factor. The plant is limited
in how fast it can photosynthesise because it does not have enough light.
Between B and C, light is not a limiting factor. Even if more light is shone on the plant, it still
cannot photosynthesise any faster.
Carbon dioxide


In photosynthesis CO2 is a key limiting factor. The usual atmospheric level of CO2 is 0.03%. In
perfect conditions of water availability, light and temperature this low CO2 level holds back the
photosynthetic potential.
The more CO2 a plant is given, the faster it can photosynthesise up to a point, but then a
maximum is reach.
Temperature
The chemical reactions of photosynthesis can only take place very slowly at low temperature, so a plant
can photosynthesise faster on a warm day than on a cold one.
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Optimum conditions for photosynthesis in Green house
When plants are growing outside, we cannot do much about changing the conditions that they need for
photosynthesis. But if crops are grown in glasshouses, then it is possible to control conditions so that
they are photosynthesising as fast as possible.
CO2 enrichment
CO2 concentration can be controlled. CO2 is often a limiting factor for photosynthesis, because its
natural concentration in the air is so very low (0.04%). In a closed glasshouse, it is possible to provide
extra CO2 for the plants, e.g. by burning fossil fuels or releasing pure CO2 from a gas cylinder.
Optimum light
Light also can be controlled. In cloudy or dark conditions, extra artificial lighting can be provided, so that
light is not limiting the rate of photosynthesis. The kind of lights that are used can be chosen carefully so
that they provide just the right wavelengths that the plants need.
Optimum temperature
In some countries where it is too cold for good growth of some crop plants, the heated greenhouses can
be used. This is done, for example, with tomatoes. The temperature in the glasshouse can be kept at the
optimum level to encourage the tomatoes to grow fast and strongly, and to produce a large yield of fruit
that ripens quickly.
The temperature can be raised by using a heating system. If fossil fuels are burned, there is also a
benefit from the CO2 produced.
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4.2 LEAF STRUCTURE
(i) identify and label the cuticle, cellular and tissue structure of a dicotyledonous leaf, as seen in
cross section under the microscope, and describe the significance of these features in terms of
function, i.e.
• distribution of chloroplasts – photosynthesis
• stomata and mesophyll cells – gas exchange
• vascular bundles – transport
EXTERNAL STRUCTURE OF A LEAF
The leaf consist of a broad, flat part called the lamina, which is joined to the rest of the plant by a leaf
stalk or petiole. Running through the petiole are vascular bundles, which then form the veins in the
leaf.
THE EXTERNAL ADAPTATION OF A LEAF FOR PHOTOSYNTHESIS



The leaf is broad and flat. This increases the surface area of the leaf for maximum absorption of
light and carbon dioxide
Most leaves are thin. This allows carbon dioxide to diffuse quickly and light to penetrate easily to
all the cells.
The lower surface of the leaf has many stomata. This enables the leaf to have efficient gaseous
exchange.
THE INTERNAL STRUCTURE OF A LEAF
Although a leaf looks thin, it is made up of several layers of cells. You can see these if you look at a
transverse section (cross-section) of a leaf under a microscope.
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Cuticle
Upper epidermis
Chloroplast
Cytoplasm
Palisade
layer
Vacuole
Mesophyll
(photosynthetic
tissue)
Xylem vessel
Water and salts
Sugar made by photosynthesis
Spongy
layer
Phloem sieve tube
Guard cell
Sieve plate
Pore
Part of the leaf
Air spaces
Structure
Cuticle
Waxy non-cellular covering to help protect
the leaf
Upper
epidermis
A single layer of cells that secretes the
cuticle. Stomata not present.
Chloroplasts
Where photosynthesis takes place inside
cells
Palisade
mesophyll
Consists of closely packed long cylindrical
cells arranged at right angles to the upper
epidermis. Contains a large number of
chloroplast which absorbs maximum light.
Spongy
mesophyll
Air spaces
Vascular tissue
Irregular shaped cells containing fewer
chloroplasts. Cells are loosely packed with
inter cellular air spaces.
Vascular tissue consists of xylem and
phloem.
Lower
epidermis
Guard cells
stomata
One cell thick layer. Do not contain
chloroplasts except the guard cells.
Consists of many stomata.
Functional Adaptations
- Waterproof layer
- Transparent to allow light to enter
- Prevents the loss of water and entry of bacteria into
the leaf
- Upper epidermis has no chloroplasts allowing light
to reach the mesophyll cells.
- Protects the middle layers of the leaf.
- Contain chlorophyll
- Large surface area for uptake of carbon dioxide
- Usually convert glucose to starch and store it
temporarily
- In dim light, may more near to the illuminated
surface of the cell
- Contain largest number of chloroplasts. These are
the most active cells in photosynthesis.
- Main site of photosynthesis.
-For diffusion of CO2 and O2 in and out of the leaf.
- Walls are coated with a water film
- In some cells photosynthesis occurs.
- Provides a pathway for gases to travel inside the
leaf.
- Xylem carries water and mineral salts to the
photosynthesizing cells.
- Phloem transport food made by photosynthesis
away from the leaves to all the parts of the plant.
- Protects the middle layers of the leaf.
- May be coated with a thin waxy cuticle
- Occur in pairs
- Controls the opening and closing of the stomata.
- The site of gas exchange.
 Water vapour passes out during transpiration
 CO2 diffuses in and O2 diffuses out during
photosynthesis
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THE INTERNAL ADAPTATIONS OF A LEAF TO CARRY OUT PHOTOSYNTHESIS

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

The palisade cells are cylindrical (column shaped) and are arranged vertically in rows so light
can pass through the long axis and more chlorophyll can trap light energy.
Large air spaces between spongy cells enable easy diffusion of gases in and out of the cells.
A branching network of ylem brings a ready supply of water.
A branching network of phloem carries away the food which is formed in the leaf to other parts of
the plant
MINERAL NUTRITION IN PLANT
Plants need about 10 major elements and 5 trace elements. The major elements are indispensable and
are required in large amounts. Trace elements are needed in traces (i.e., in extremely small amounts).
Plant is in need for mineral ions to control chemical activities, grow, and produce materials. The most
important minerals are Magnesium ions and Nitrates.
Nitrate ion
Plant absorb nitrate ions from the soil, through their root hairs. Nitrate ions combine with glucose and
form amino acids, then link the amino acids together to form proteins.
Magnesium ion
Plant absorb magnesium ions from the soil solution, through their root hairs. Magnesium ions used for
the manufacture of chlorophyll. Each chlorophyll molecule contains one magnesium atom.
The following table shows two minerals their functions and their deficiency symptoms
MINERAL
Nitrates,
NO3
Magnesium,
Mg2+
WHY IT IS NEEDED
DEFICIENCY SYMPTOMS
Is important for protein synthesis, for the
formation of amino acids and nucleic
acids which are essential for growth and
development of plant and the synthesis of
chlorophyll
- Results in extremely stunted growth
- yellowing of leaves,
- leaves become smaller and the stem
becomes thinner and weaker
For chlorophyll formation. It also activates
enzyme.
- Chlorosis (poor growth and very pale
yellow of leaves) from bottom upward
- reduction in photosynthesis
- insufficient carbohydrates are
manufactured
- respiration rate is slow down and
-few proteins can be made
-growth is therefore limited
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5. ANIMAL NUTRITION
5.1 NUTRIENTS
(a) list the chemical elements that make up: • carbohydrates • fats
• proteins
(b) describe tests for:
• starch (iodine in potassium iodide solution)
• reducing sugars (Benedict’s solution)
• protein (biuret test)
• fats (ethanol emulsion test)
(c) list the principal sources of, and describe the dietary importance of carbohydrates, fats, proteins,
vitamins (C and D only), mineral salts (calcium and iron only), fibre (roughage) and water
(d) name the diseases and describe the symptoms resulting from deficiencies of vitamin C (scurvy),
vitamin D (rickets), calcium (rickets) and iron (anaemia)
All living organisms need food. In all plant and animals, food is used for growth, as a source of energy and
for replacement of worn and damaged tissues.
CLASSES OF FOOD
There are seven main types of food: carbohydrates, lipids (fats and oils), proteins, vitamins and minerals,
water and roughage (fibre). They each have different chemical composition, different properties, and
different functions in living organisms.
MAIN NUTRIENTS: CARBOHYDRATES, FATS AND PROTEINS
 Carbohydrate
Carbohydrates are the cheapest and most readily available source of energy to the body. Carbohydrates
are made up of components like carbon, hydrogen and oxygen. Sugar and starch are important
carbohydrates. Sugary carbohydrates- e.g: Jam, honey, ice cream, biscuits, chocolates, etc. Starchy
carbohydrates- e.g: potato, bread, maize, rice, noodles, etc. carbohydrates are classified in to;
o
Monosaccharide: Carbohydrates which has only one glucose molecule. They are sweet, soluble and
crystalizable. E.g. Glucose (C6 H12 O6), galactose, and fructose.
o
Disaccharide: Carbohydrates which are having two glucose molecules. They are also sweet, soluble
and crystalizable. E.g. Sugar, Sucrose (cane sugar), Lactose (milk sugar) and Maltose (malt sugar
of barley).
Polysaccharide: Carbohydrates which are having many glucose molecules. They are not sweet,
insoluble and uncrystalizable. E.g. Starch, glycogen and cellulose.
o
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 Lipids (fats and oils)
Fat is a nutrient which gives energy to the body. They help the body to maintain the body temperature. Fat
is present in the cell membrane in the form of lipids. Fat is made up of carbon, hydrogen and oxygen. E.g.
Oil, cheese, fatty meat, avocadoes, egg yolk
 Protein
Proteins are necessary for the growth of tissues and for the formation of structural proteins. (protoplasm,
cell membrane, melanin, keratin) and functional proteins (enzymes, hormones, antibodies, nucleic acids).
Protein deficiency causes Marasmus and Kwashiorkor. Protein is made up of components like carbon,
hydrogen, oxygen and nitrogen. E.g. Meat, peas and beans, fish, egg white and peanuts.
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Other Nutrients: Vitamins, Minerals, Fiber and Water
 Minerals
Humans require about fifteen different mineral elements in their diet. Minerals have no energy value but
they do have important function in the body.
Functions of minerals
Constituent
Iron
Calcium
Source of
minerals
liver, red
meat,
spinach
milk, cheese,
flour
Function in the body
- for haemoglobin – the oxygen
carrying pigment in red blood
cells.
- for healthy bones and teeth
- for muscle action and blood
clotting
Disease and symptoms
caused by lack of minerals
- the deficiency disease is
anaemia – a person feel tired
and weak.
- shortage in the diet leads to
rickets. Bones become brittle
and do not form properly,
 Vitamins
Vitamins are essential for the body to be able to use other nutrients efficiently. They are not digested or
broken down for energy. They are needed in very small amounts. There are 13 major vitamins: A, C, D, E,
K, and eight different B vitamins.
Functions of vitamins
Constituent
Vitamin C
Vitamin D
Source
of Function of vitamin
vitamin
oranges,
- helps wounds to heal
lemons, black
- needed for healthy gums
current and
and teeth.
green
vegetables
liver, butter,
- enables the body to absorb
cheese, egg,
calcium and phosphorous
and fish.
from food.
Disease and symptoms
caused by lack of vitamin
- causes scurvy, a disease in
which the gums become soft,
teeth grow loose, and
wounds fail to heal properly.
- cause rickets, soft weak
bones, which bend under
pressure. Causing bow-legs
or knock-knees.
 Water
At least two-thirds of the human body consists of water. Water has no energy value, but it is still one of the
most essential components of living matter. The most important functions of water is;



to act as the medium in which all the chemical reactions of metabolism take place.
It is used in temerature regulation in many animals
It is the means of transporting chemicals in plants and animals
 Dietary fibre (roughage)
Dietary fibre is the indigestible part of food, largely cellulose from the cell walls. Fibre forms bulk in the
intestines. This gives the muscles of peristalsis something to push against, preventing constipation. Fibre
also reduces the amount of fat absorption and reduces the risk of bowel cancer. Sources are fruits,
vegetables and nuts.
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TEST TO SHOW THE PRESENCE OF CARBOHYDRATES, FATS AND PROTEINS
Starch
Chemical
(‘reagent’)
used
IODINE
SOLUTION
Glucose
(Reducing
sugar )
BENEDICT’S
SOLUTION
Fat
ETHANOL
Protein
BIURET
SOLUTION
How test is carried
Result
Take the sample solution in a test-tube. Add
little amount of Iodine solution and shake it
well.
Blue/black colour if
starch is present
Take some amount of sample solution in a
clean test-tube. Add some amount of
Benedict’s solution and shake it well. Then
heat the solution in a hot water bath for
some time.
Take some amount of sample (cooking oil) in
a clean test-tube. Add little amount of
alcohol into the tube and shake well. Keep
the test-tube undisturbed for some time. We
can see two layers separated. Add top layer
to a test-tube having water.
Take some amount of sample (egg white) in
a clean test-tube. Add little amount of
sodium hydroxide solution (Na OH solution)
and shake well. Then add little amount of
copper sulphate solution (Cu SO4 solution)
and shake well.
MILANDHOO SCHOOL / SH.MILANDHOO / FIRST SEMESTER 2017 / BIOLOG5090 / NOTES/ ANIMAL NUTRITION
(brown if starch is
absent).
Red, orange yellow or
green if either of sugar
is present
(blue if not)
The water turns
cloudy if fat is present.
The water remains
clear if it is not.
A purple colour
indicates that protein
is present
(blue if it is absent).
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5.2 DIET
(e) understand the concept of a balanced diet
(f) explain why diet, especially energy intake, should be related to age, sex and activity of an individual
(g) state the effects of malnutrition in relation to starvation, heart disease, constipation and obesity
A BALANCED DIET
A diet which has the correct amount of each constituent is called a balanced diet.
Good health depends on to a large extent eating the correct amount of food, and the correct proportions of
each type of food. The amount of food eaten each day should provide no more and no less than the
amount of energy used during that day. The amount of energy a person uses each day varies according to
age, sex, body size, occupation, and special condition such as pregnancy.
Age, occupation
Energy used in 1 day
males
females
15 years
12600 kj
9600 kj
Adult (light work)
11500 kj
9450 kj
Adult (moderate work)
12100 kj
10500 kj
Adult (heavy work)
15000 kj to 20000 kj
12600 kj
A balanced diet is different for each person, and depends on their life style, age and sex.
Type of person
Special requirements
reason
Child
Protein
Carbohydrate
Calcium
For growth
For energy
For bones and teeth
Active adult
Carbohydrate
Protein
For energy
To build muscles
Pregnant women
Iron salts
Calcium
Protein
For blood
For baby’s bone
For making baby’s cells
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PROBLEMS CAUSED BY AN UNBALANCED DIET

Malnutrition (constituent is incorrect)
Constipation is a result of insufficient fibre in the diet. A diet lack in fibre may, over several years, lead to
bowel cancer.
Obesity is caused when energy input as a result of eating is greater than energy used. Eating too much
can lead to weight increase and body becomes inflated with stored food. Extra fat, carbohydrates and
proteins could converted to body fat. Obesity may result to heart disease, high blood pressure, diabetes,
stress on joints, gall bladder cancer, cancer of the bowel in both sexes, and cancer of the breast and womb
lining in women and social rejection.
Heart disease can occur when the animal fats and cholesterol form deposits called ATHEROMA on the
walls of the coronary artery. Atheroma forms a blockage in the artery and restricts blood flow, decreasing
oxygen supply to the heart muscles. In severe condition the artery may become blocked, leading to a heart
attack.

Starvation (insufficient quantity)
Protein energy malnutrition (PEM) is a term used to describe diets which lack proteins, and energy-giving
carbohydrates. Kwashiorkor and marasmus are diseases which is caused by PEM.
Kwashiorkor: symptoms include swelling of the body, specially the belly, flaking skin, and red hair
Marasmus: symptoms include thinness and poor muscles development, so that bones show through the
skin.
Starvation results in very restricted growth and development, particularly of muscles, leading to weakness.
Resistance to disease is severely reduced, and death eventually follows.
Starvation is often the result of famine, a lack of adequate amounts of food to support the population.
5.3 WORLD FOOD SUPPLIES
(h) discuss the problems that contribute to famine (unequal distribution of food, drought and flooding,
increasing population)
PROBLEMS OF WORLD FOOD SUPPLIES AND THE CAUSES OF FAMINE
There is not always enough food available in a country to feed the people living there. A severe food
shortage can lead to famine.
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It has been calculated that more than enough food is produced on Earth to provide every single person with
more than enough for their needs. Yet many people do not got enough food. Each year, many people die
because they have an inadequate diet.
The fundamental problem is that food is distributed unequally on our planet: while some parts of the
world produce more than enough food for the people that live there, in other part of the world not enough
food is produced.
Although large amounts of food are transported from one area to another, this is still not sufficient to supply
enough food to everybody.
If food prices rise too high, many people may not be able to afford to buy it.
Famine can occur for many different reasons:







Climate change and natural disaster such as drought and flooding that prevent crops from
growing.
Increasing population: population may grow so large that the land on which they live can no longer
provide enough food for them.
Unequal distribution of food.
Poverty
Crop failure due to disease
Poor farming techniques
War/political instability
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5.4 HUMAN ALIMENTARY CANAL
(i)
identify the main regions of the alimentary canal and the associated organs: mouth (buccal) cavity,
salivary glands, oesophagus, stomach, duodenum, pancreas, gall bladder, liver, ileum, colon,
rectum and anus
(j) describe the main functions of these parts in relation to ingestion, digestion, absorption, assimilation
and egestion of food, as appropriate
(k) identify the different types of human teeth and describe their structure and functions
(l) state the causes of dental decay and describe the proper care of teeth
HUMAN ALIMENTARY CANAL
The alimentary canal is a long tube which runs from the mouth to the anus. It is part of the digestive
system. The digestive system also includes the liver and the pancreas.
Main regions of the alimentary canal and associated organs are:







Mouth, salivary glands
Oesophagus
Stomach
Pancreas, liver, gall bladder
Small intestine (duodenum + ileum)
Large intestine (colon +rectum)
Anus.
nasal cavity
palate
tongue
salivary duct
bolus of food
epiglottis
salivary gland
trachea
oesophagous (gullet)
oesophagous
liver
diaphragm
gall bladder
sphincter muscles
bile duct
sphincter muscles
stomach
pancreas
pancreatic duct
duode
num
small intestine
ileum
colon
caecum
large intestine
rectum
appendix
anus
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The journey of the food from the mouth to the anus through the alimentary canal includes 5 steps:
Ingestion
Intake of substances (food, drink…) into the body through the mouth
Digestion
The break-down of large, insoluble food molecules into small, watersoluble molecules using mechanical and chemical process.
Absorption
Movement of digested food molecules across the wall of intestine into the
blood or lymph.
Assimilation
Movement of digested food molecules into the cells where they are used,
becoming part of the cells (uptake and use of food molecules by cells).
Egestion
Passing out of undigested food as faeces, through the anus
Note:- Don’t confuse egestion with excretion, excretion is to get rid of waste products of metabolism.
The alimentary canal (gut or digestive tract) is made up of several organs working together to perform
all the processes mentioned above. Starting with the mouth and ending with the anus.
Functions of the regions of the alimentary canal
ORGAN
FUNCTION
Mouth
Food is mechanically digested here by cutting, chewing and grinding of
teeth. Saliva is added – this contains amylase to begin the digestion of
starch
Oesophagous
Boluses (balls) of food pass through by peristalsis, from mouth to stomach.
Stomach
Muscular walls squeeze on food to make it semi-liquid. Gastric juice
contains protease to digest protein and hydrochloric acid (HCL) to
maintain an optimum pH (1-2, 5). The acid also kills bacteria.
Duodenum
This is the first part of the small intestine, it receives pancreatic juice
containing protease, lipase and amylase. The juice also contains sodium
hydrogen carbonate, which neutralizes acid from the stomach, producing a
pH of 7-8.
Pancreas
Secretes pancreatic juice into the duodenum, also makes the hormones
insulin and glucagon.
Liver
Makes bile, which is stored on the gall bladder. Bile contains salts that
emulsify fats, forming droplets with a large surface area to make digestion
by lipase more efficient. Digested foods are assimilated here. For example,
glucose is stored as glycogen, surplus amino acids are deaminated.
Ileum
The second part of the small intestine. Enzymes in the epithelial lining break
down lactose and peptides. Its surface area is increased by the presence
of villi which allow the efficient absorption of digested food molecules.
Colon
The colon absorb water, salt and vitamins. For more effective absorption,
its wall are folded to increase its surface area. Infections of the colon lead to
diarrhea.
Rectum
This stores faeces until it is egested.
Anus
This has muscles to control when faeces is egested from the body.
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HUMAN TEETH AND DENTAL DECAY
There are four types of teeth in human (incisors, canines, premolars and molars), each specialised for
different funtions.
T YPES OF MAMMALIAN TEETH:
Incisors:
They are 4 in front of each jaw.
They act like a blade to cut food (eg. To cut a bite of a sandwich) they have a (chisel-like surface).
Canines:
They are two in each jaw.
They are very pointed, in humans they are used for the same purpose as incisors.
However in carnivores they are longer and sharper and used to kill the prey.
Premolars:
4 on the sides of each jaw.
The surface of each tooth has two projections (‘cusps’)
They are used to crushing and grinding food.
Molars:
They are 6 at the back of
Each jaw, 2 of them are wisdom teeth. They have the same use as Premolars.
The tooth surface is square with four cusps.
They are used to crushing and grinding food.
The tooth is divided into three parts, the crown, neck and the root.
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STRUCTURE OF TOOTH
Enamel: Made of calcium salts, it is very strong.
Dentine: It is covered by the enamel and surrounds the pulp cavity.
The pulp cavity: It contains the nerves and blood vessels.
The part of the tooth above the gum is called the crown, the part buried in the jawbone is called the root.
The enamel covers the crown, the root is covered by cement. And the tooth is held in place by fibres.
CAUSES OF DENTAL DECAY
When we eat, some food particles stay in our mouth. Bacteria are present on the surface of our teeth. Food
deposits and bacteria form a layer called plaque. Bacteria on the plaque feed on sugars, producing acid.
This acid dissolves enamel, forming a hole.
Dentine underneath the enamel is softer – it dissolves more rapidly. If the hole reaches the pulp cavity,
bacterial infection can get to the nerve. This results in toothache and possibly, an abscess (an infection in
the jaw).
METHODS OF PREVENTING TOOTH DECAY:
➢ Reduce sugar intake to prevent bacteria respiring
➢ Brush teeth to remove the plaque layer of bacteria and saliva on our teeth and nuetralise mouth
➢ Use toothpaste or water containing fluoride because it is absorbed by the teeth and helps to stop the
attack by acid
➢ Pay regular visits to the dentist.
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5.5 CHEMICAL DIGESTION
(m) describe peristalsis
(n) explain why most foods must be digested
(o) describe:
• digestion in the alimentary canal
• the functions of a typical amylase, protease and lipase, listing the substrates and end-products
MECHANICAL AND CHEMICAL DIGESTION
Food that we ingest is mainly made up of large, insoluble molecules that cannot be absorbed through the
gut wall. It needs to be changed into small, soluble molecules.
Mechanical digestion is the physical process of preparing the food for chemical digestion. It involves
chewing (in the mouth), mixing, churning (in the stomach and intestine) and segmentation (in the
intestine).
Large pieces of food are breaking down into smaller pieces which increases the surface area of the food.
Bile physically digests fats by emulsifying them – turning them into small droplets with a large surface area.
DIGESTION IN THE MOUTTH
The mouth performs several functions:
Mechanical Digestion: The action of the teeth biting a small piece of food from a large one is considered
mechanical digestion, the teeth also tears and grinds the food into a bolus to give it larger surface area for
faster chemical digestion.
Chemical Digestion: beneath the tongue lies a salivary gland which secrets saliva into the mouth, this
saliva contains water and mucus to lubricate the food bolus and amylase enzyme that breaks down starch
in the food into maltose. After this the tongue pushes the food bolus into the oesophagus. Salivary glands
secrete saliva into the mouth. The teeth chew the food and break them down to small pieces. At the same
time the tongue mixes the food thoroughly with saliva. Saliva contains:
Mucus:- which lubricates the food.
Water: which act as a solvent
Mineral salts:- (usually sodium bicarbonate), helps to maintain a pH between7 to 7.5 in the
saliva. The optimum pH for the enzyme salivary amylase is between7 to 7.5.
Salivary amylase:- an enzyme, which breaks down starch to maltose
Since the food is kept in the mouth for a short time all the starch in the food is not converted to maltose.
Some starch will remain as it, without change. After the food is thoroughly mixed with saliva the tongue rolls
the food into a ball called bolus and take it to the back of the mouth to be swallowed.
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THE OESOPHAGUS:
This is a tube that transports the food from the mouth deep into the body to the stomach. As the ball of food
(bolus) formed in the mouth enters the pharynx, a reflex action is initiated. This produces slow, wave-like
contractions in the walls of the esophagus and later along the whole length of the tract (peristalsis). The
oesophagous has two types of muscles. Circular muscles in the inside and longitudinal muscles in the
outside. These two muscles alternatively relax and contract to send the food to the stomach. This way the
food is passed to the stomach by a wave like muscular movement known as peristalsis.
Peristalsis
Peristaltic waves involve the contraction of the circular muscle fibres behind the bolus (A) and their
relaxation in front of the bolus.
Longitudinal muscles provide the wave-like action. The two functions together push the ball down the tract (B).
DIGESTION IN THE STOMACH
The stomach is a bag of muscles. Its walls have got gastric
glands, which secrete a juice called gastric juice.
The gastric juice contains;
Hydrochloric acid - which keeps the stomach
contents acidic and kills the bacteria, which comes
into the stomach with the food.
Pepsin- the enzyme which break down proteins to
polypeptides
Rennin- an enzyme that break down milk protein. It
is usually present in the young mammals.
Once in the stomach the food is thoroughly mixed with gastric juice by the muscular actions of the stomach
and is converted to a creamy liquid called chime. The food remains in the stomach for about 3 to 4 hours
and little by little the food enters the duodenum.
DIGESTION IN THE DUODENUM
Once the food enters the duodenum, it is mixed with two liquids,
which comes to the duodenum from outside. One liquid known as
bile comes from the liver. It is produce in the liver, stored in the gall
bladder and pass to the duodenum through the gall bladder. The
other liquid which comes to the duodenum is the pancreatic juice.
This liquid comes from the pancreas through the pancreatic duct.
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Bile contains;
Bile salts: - which emulsify large lipid globules. Lipids, as they are not soluble in water are difficult to digest.
Hence, they have to be broken down physically to simple droplets before the enzymes come can work on it.
Therefore, the bile salts emulsify them. Emulsification is the breakdown of large lipid globules to tiny
droplets. This is a type of physical digestion. Emulsification increases the surface area of the lipids. This
would enable the enzymes to break it down efficiently. Bile salts also make the fat-soluble vitamins to
water-soluble, thereby making them easy to digest.
Bile salts in bile
Large fat globule- relatively
small surface area
Many small fat droplets –
relatively large total surface
Pancreatic juice contain:area
Mineral salts:- helps to neutralize the acidic chime, which comes from the stomach. Also provides
an alkaline medium of pH between7.5 – 8.5, for the enzymes in the small intestine to work
efficiently.
Pancreatic amylase:- converts starch to maltose
Trypsin:- converts polypeptides to peptides
Peptidase:- converts peptides to amino acids
Lipase converts lipids to fatty acids and glycerol
DIGESTION IN THE ILEUM
After leaving the duodenum the food enters the ileum. In the ileum the digestion of the food is completed.
The walls of the small intestine produce a juice called intestinal juice. This juice contains:Mineral salts: - helps to neutralize the acidic chime, which comes from the stomach. Also provides
an alkaline medium of pH between7.5 – 8.5, for the enzymes in the small intestine to work
efficiently.
Intestinal amylase:- which converts starch to maltose
Maltase:- which converts maltose to glucose
Sucrose:- which converts sucrose to fructose and glucose
Lactase:- which converts lactose to galactose and glucose
Erepsin:- which converts peptides to amino acids
THE LARGE INTESTINE:
Once all the soluble food products are absorbed the rest of the materials left in to digestive system enters
the large intestine. Mainly this material will consist of undigested food materials like roughage, dead
bacteria, dead cells, water and salts. When this material moves along the colon, most of the water and
salts, present in it, are absorbed back into the body. By the time this material reaches the rectum it would
be solidified and turned to faeces. The feaces would be stored in the rectum for a short while and then
would be egested.
THE PRODUCTS OF DIGESTION
After digestion all the carbohydrates would be converted into monosaccharaides, all the proteins will be
converted to amino acids and all the lipids will be converted to fatty acids and glycerol. These final products
of digestion are soluble and in the simplest forms and they are ready to be absorbed.
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Chemical digestion
Involves breaking down large, insoluble molecules into small, soluble ones.
Enzymes speed up the process. They work efficiently at body temperature (370 C) and at suitable pH.
The main places where chemical digestion happens are the mouth, stomach and small intestine.
5.6 ABSORPTION AND ASSIMILATION
(p) describe the structure of a villus, including the roles of capillaries and lacteals
(q) describe the significance of villi in increasing the internal surface area
(r) state the function of the hepatic portal vein as the route taken by most of the food absorbed from
the small intestine
(s) state:
• that large molecules are synthesised from smaller basic units:
glycogen from glucose
proteins from amino acids
lipids (fats and oils) from glycerol and fatty acids
• the role of the liver in the metabolism of glucose and amino acids
• the role of fat as a storage substance
• that the formation of urea and the breakdown of alcohol occur in the liver.
ABSORPTION
Once the food is digested the foods to be absorbed. Absorption mainly occurs from the ileum. The ileum is
very long and folded. It is about 5m long. The inner folding of the ileum has finger like projections called villi.
When the food moves along the ileum the microvilli moves and enables the food to enter the epithelial cells
of the villi. From here the amino acids and monosaccharide are taken into the blood capillary system
surrounding the villi, by active transport. The fatty acids and glycerol enter the lacteal, recombine to form
small droplets of lipids which are carried by the lymph to the main lymphatic system and finally to the veins
in the blood system.
The adaptation of the ileum for absorption
The folded internal surface of the ileum is converted with the numerous finger like projections called
villi (singular villus), to increase the surface area for absorption.
The surface area of each villus is further increased by the microvilli, which are tiny microscopic
projections from the epithelial cells of the villus.
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The long length of the ileum also increases the surface area for absorption.
Each villus contains a dense capillary network, close to the epithelium, to carry away the absorbed
food substances as quickly as possible.
The epithelium of the villus is one cell thick, allowing the digested food to diffuse rapidly over a short
distance into the blood capillaries of the villus
ASSIMILATION OF THE ABSORBED FOOD MOLECULES:
After the food molecules are absorbed from the alimentary canal, it is transported to the liver by a special
blood vessel called The Hepatic Portal Vein. The liver is an organ that is considered a gland too. It carries
out several jobs to “sort out” the food molecules it receives. Each type of nutrient has its own fate in the
liver.
Glucose: when the absorbed glucose reaches the liver, the liver allows as much as needed by the body to
pass to the circulatory system to be used for respiration or other processes. The excess glucose is
converted to glycogen and stored in the liver cells, when the blood is short in glucose, glycogen will be
converted back into glucose and secreted to the blood. Some glucose will also be converted to fats as an
energy reserve. These functions are controlled by the Insulin and Glucagon hormones which are made in
the pancreas.
Amino Acids: some amino acids will be used by the liver cells to make proteins, the rest will be allowed
into the blood stream to be absorbed by the body cells which also convert it to proteins. If the body contains
enough amino acids, the excess will undergo a process called Deamination, this involves the breakdown
of amino acids into carbohydrates and amino group, which is then converted to ammonia then converted
into urea, which is part of the waste product of the body, urine. Part from sorting out food molecules, the
liver performs the following jobs too:
•Dealing with old red blood cells:
The liver changes dead red blood cells to iron and bile. Iron is stored in the liver, large amounts of iron give
it the red colour and used to build up new red blood cells. The bile is stored in the gall bladder to be used in
digesting food again.
•Detoxification:
The liver breaks down toxic materials such as alcohol which damages cells to fats. Alcoholics are known to
have liver diseases.
•Helps in generating heat:
The liver contains a very large number of cells, which means a lot of metabolic reactions take place in it
producing lots of energy to warm the blood.
•Making fibrinogen:
This is a plasma protein which helps in blood clotting when the skin is cut.
Fat metabolism
The liver does not play a major part in fat metabolism. Once in the blood, fatty acids and glycerol recombine to form tiny fat droplets. Fats at body temperature are liquid form, so the word LIPID is used to
cover both fats and oils.
Lipids are stored in in special storage cells in the skin (‘adipose’ tissue), and around the kidneys.
Fat is a good insulator, or protector, against physical damage and low temperature, and is a very efficient
energy store. But fat is also heavy, and can lead to obesity.
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6. TRANSPORT IN FLOWERING PLANTS
6.1 WATER AND ION UPTAKE
(a) relate the structure and functions of root hairs to their surface area and to water and ion uptake
Root hairs and water uptake by plants
Plants take in water from the soil, through their root hairs:



At the very tip is a root cap. This is a layer of cells which protects the root as it grows through the
soil.
The rest of the root is covered by a layer of cells called the epidermis.
The root hairs are a little way up from the root tip. Each root hair is a long epidermal cell. Root
hairs do not live for very long. As the root grows, they are replaced by new ones.
Root hair cells, as seen under the light microscope:
The hair is an extension of the cell and not a separate cellular structure.
Functions of root hair cells


Increase the external surface area of the root for absorption of water and mineral ions (the hair
increases the surface area of the cell to make it more efficient in absorbing materials).
Provide anchorage for the plant.
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6.2 TRANSPIRATION AND TRANSLOCATION
(b) state that transpiration is the evaporation of water at the surfaces of the mesophyll cells followed
by the loss of water vapour from the leaves through the stomata
(c) describe:
• how water vapour loss is related to cell surfaces, air spaces and stomata
• the effects of air currents (wind), and the variation of temperature, humidity and light intensity
on transpiration rate
• how wilting occurs
(d) investigate, using a suitable stain, the pathway of water in a cut stem
(e) explain the movement of water through the stem in terms of transpiration pull
(f)
identify the positions of xylem and phloem tissues as seen in transverse sections of
unthickened, herbaceous, dicotyledonous roots, stems and leaves
(g) state the functions of xylem and phloem.
Transport In Plants - Functions Of Xylem And Phloem
Plants have transport systems to move food, water and minerals around. These systems use continuous
tubes called xylem and phloem:

Xylem vessels carry water and minerals from the roots to the leaves

Phloem tubes carry sugar & other organic nutrients made by plant from the leaves to the rest of
the plant.
The movement of sugar and amino acids around a plant is called TRANSLOCATION.
Structure Of The Xylem Tissue
Xylem vessels consist of dead cells. They do not have nucleus, cytoplasm and cell membrane. They have
a thick, strengthened cellulose cell wall with a hollow lumen. Xylem contains, xylem vessels and xylem
fibres. The end walls of the cells have disappeared, so a long, open tube is formed. The walls of the xylem
vessel contains holes called pits which water enters through. The xylem vessel is specialized to transport
water and dissolved minerals from the root up to all the other parts of the plant, and also to help
supporting the stem and strengthening it.
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Structure Of The Phloem Tissue
This is a long tube that runs alongside the xylem tissue. They are made of long narrow tubes with
perforated sieve plates along the thin length. The function of the phloem tissue is to transport food
nutrients such as glucose and amino acids from the leaves and to all other cells of the plant, this is called
translocation. Unlike the xylem, the phloem tissue is made of columns of living cells, which contains a
cytoplasm but no nucleus, and its activities are controlled by a companion cell next to it which has a
nucleus, but companion cells have no function in translocation.
Scanning electron micrograph of a sieve plate in a phloem tube (x1300)
Distribution Of Xylem And Phloem In Roots, Stems And Leaves



In the roots, xylem and phloem are in the centre to withstand stretching forces.
In the stems, they are arranged in bundles near the edge to resist compression and bending forces.
They are grouped together into veins and vascular bundles as they pass through leaves.
The positions of xylem and phloem tissues as seen in transverse sections of unthickened, herbaceous,
dicotyledonous roots, stems and leaves:
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Root:
Stem:
Leaf:
Passage Of Water Through Root, Stem And Leaf
Three causes water to rise up a plant. They are:
A root pressure


Water enters root hair cells by osmosis. This happens when the water potential in the soil
surrounding the root is higher than in the cell so water diffuses from the soil into the root hair, down
its concentration gradient.
As the water enters the cell, its water potential becomes higher than in the cell next to it, e.g. in the
cortex. So water moves, by osmosis, into the next cell. Some of water may also just seep through
the spaces between the cells, or through the cell walls, never actually entering a cell.
B Capillarity
Once in the xylem of the stem, water is carried upwards by a second force, called ‘capillarity’.
Capillarity is the movement of liquid s upward through very narrow tubes. Xylem vessels have a
microscopic bore, which can be responsible for carrying water 20cm or more up a plant.
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C Transpiration pull


Water vapour evaporating from a leaf crates a kind of suction, its pressure at the top of the vessels
is lower than that at the bottom and water move up the stem in the xylem, more water is drawn into
the leaf from the xylem. This creates a transpiration stream, pulling water up from the root. Mature
xylems cells have no cell contents, so they act like open-ended tubes allowing free movement of
water through them. Roots also produce a root pressure, forcing water up xylem vessels.
Water moves from xylem to enter leaf tissues down water potential gradient. In the leaves, water
passes out of the xylem vessels into the surrounding cells.
Mechanism of water movement through a plant
Water molecules are attracted to each other (cohesion), and water vapour evaporating from a leaf creates a
kind of suction, pressure of water at the top of the vessels is lower than that of the bottom. Water move up
the stem in the xylem, more water is drawn into the leaf from the xylem. This creates a transpiration
stream, pulling water up from the root.
Transpiration In Plants And Factors Affecting Transpiration Rate
Transpiration is the evaporation of water at the surfaces of the mesophyll cells followed by the loss of
water vapour from the leaves through the stomata.
Transpiration takes place in the following ways:


In the leaves, water molecules leave the xylem vessels and move from cell to cell. They move
through the spongy mesophyll layer by osmosis along a concentration gradient. This water film is
for dissolving carbon dioxide for use during photosynthesis.
This creates a high concentration of water molecules. Water then evaporates into spaces behind
the stomata and diffuses through the stomata into the surrounding air.
How wilting occurs
Young plant stems and leaves rely on their cells being turgid to keep them rigid. If the amount of water
lost from the leaves of a plant is greater than the amount taken into the roots by the plant will have
a water shortage in cells become flaccid (soft) and will no longer press against each other. Stems and
leaves lose their rigidity, and wilt.
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The Rate Of Transpiration Can Be Affected By Several Factors:
condition
1. Temperaturestomata
T
Effect
Warm air can hold more water vapour than cold air. Thus
evaporation or transpiration will take place more rapidly into warm
air.
When the sun shines on the leaves, they will absorb heat as light.
This warms them up and increases the rate of evaporation of
water.
closed
300C

0
C

2. Humidity
T
If the air is very humid, i.e. contains a great deal of water vapour,
it can accept very little more from the plants and so transpiration
slows down. In dry air, the diffusion of water vapour from the leaf
to the atmosphere will be rapid.
H
3. Light intensity
T
stomata closed
Light absorbed
An increasing temperature increases rate of evaporation of
water inside the leaf. This further increases transpiration
But temperature should not be more than 300C


Air inside the leaf saturated with water vapour
A decreasing humidity increases the concentration
gradient. This increases rate of transpiration
Light itself does not affect evaporation, but in daylight the stomata
of the leaves are open. This allows the water vapour in the leaves
to diffuse out into the atmosphere. At night, when the stomata
close, transpiration is greatly reduced.
Transpiration speeds up when light intensity increases because
the stomata respond to changes in light intensity.
Sunlight may warm up the leaves and increase evaporation.



When light intensity increased, guard cells become turgid
The stomata opens, increasing rates of transpiration
When light intensity is reduced, the stomata closes
Air movement
In still air, the region round a transpiring leaf will become saturated with water vapour so that no more can
escape from the leaf. In these conditions, transpiration would slow down. In moving air, the water vapour
will be swept away from the leaf as fast as it diffuses out. This will speed up transpiration.
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The opening and closing of the stomata is controlled by the guard cells.


In light, guard cells take up water by osmosis and become turgid. Because their inner walls are rigid
they are pulled apart, opening the pore.
In darkness water is lost and the inner walls move together closing the pore.
Because of this, the transpiration rate is increased by an increase in light intensity.
* Most of the factors that result in a change in transpiration rate are linked to diffusion. When writing
explanation, try to include references to the concentration gradient caused by a change in the factor.
STOMATA
Stomata open









Day time (light)
Photosynthesis
Glucose collects in the guard cell
causing an increase in
concentration of the cell sap
Osmosis of water into the guard
cell
Guard cell become turgid
Start to swell
Thin outer wall stretches more than
thick inner wall
Pore form between guard cellsstoma
Effect: increases rate of gaseous
exchange and transpiration
Stomata close



Night time (darkness)
No photosynthesis
Glucose concentration drops

Osmosis of water out of the cell


Guard cell become flaccid
Shrinks

Close pore between cells

Effect: no gaseous exchange or
transpiration
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Adaptations Of The Leaf, Stem And Root To Different Environments
Plants which live in extreme environments have adaptations to control their transpiration rate. Most
modifications are adaptations to very dry (arid) environments. Water plants have no problem of water
shortage. They do not need adaptations to conserve water as desert plants.
Adaptation of plants to reduce water loss by transpiration
 Small, spiny, hairy leaves to reduce surface area exposed to evaporation
 Thick, waxy cuticle
 Reduction in the number of stomata
Plants modified to cope with a lack of water are called xerophytes. Living in deserts where water is scarce
and evaporation is rapid, or in windy habitats where evaporation can also be rapid, they have to cut down
water loss.
1. Marram grass (Ammophila)




Very long roots to search for water deep down in sand dunes.
Leaves that roll up in dry weather to increase humidity around stomata, reducing transpiration.
Sunken stomata to create high humidity and reduce transpiration.
Fine hairs around stomata, reducing air movement so humidity builds up and transpiration is reduced.
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2. Prickly pear cactus (Opuntia)




Leaves reduced to spines – this reduces the surface area for transpiration and also acts as a defence
against herbivores.
Reduces number of stomata.
Stomata cloesed during the day- when conditions for transpiration are most favourable.
Fleshy stem - to store water.
3. Pine tree (Pinus)



Leaves needles-shaped to reduce surface area for transpiration and to resist wind damage.
Sunken stomata to create high humidity and reduce transpiration.
Thicsk waxy cuticle on the epidermis to prevent evaporation from leaf surface.
Water plants may have stomata on the tops of their leaves
Water hyacinth (Eichhornia csassipes)




Roots do not attach to to the bed of the river or pond where they grow, but just float freely in the water.
The stems and leaf stalks have hollow spaces in them, filled with air à help to float on the top of the
water where they can get plenty of light for photosynthesis.
Leaves and stomata are on both surfaces, not just on the underside as in most plant à allow to
absorb CO2 from the air, for photosynthesis.
The cuticle on the upper and lower surfaces of the leaves is much thinner than in plants that don't live
in water, there is no need to prevent water loss from the leaves.
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Although transpiration can leading to wilting, it also has the following advantages:
It maintains a constant supply of ions to the leaves.
It brings water to the mesophyll cells for photosynthesis.
It helps to supply water to all cells for metabolic process and for turgidity.
It helps to cool leaves – important in very hot climates.
To show that the water travels up a stem in the xylem
Apparatus
 A beaker
 Food colouring
 A soft-stemmed dicotyledonous plant
Method
Cut the plant stem about 1 cm above the root. Place the stem in water containing food colouring and leave
it, as shown in fig. for about six hours
Remove the stem from the beaker and carefully cut it through at 2-3 cm from its base.
cut stem of plant
water plus food
colouring
Xylem stained with
food colouring
Results
The vascular bundles will have been stained by the food colouring. Using a razor blade, carefully cut a very
thin section from the stem, and view it under a microscope. It will be seen that the coloured region of the
vascular bundle is in the position occupied by the xylem.
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7. TRANSPORT IN HUMANS
7.1 CIRCULATORY SYSTEM
(a) describe the circulatory system as a system of tubes with a pump and valves to ensure one-way
flow of blood
(b) describe the double circulation in terms of a low pressure circulation to the lungs and a high
pressure circulation to the body tissues and relate these differences to the different functions of the
two circuits
CIRCULATORY SYSTEM
The main transport system of human is the circulatory system, a system of
tubes (blood vessels) with a pump (the heart) and valves to ensure oneway flow of blood. Its functions:



To transport nutrients and oxygen to the cells.
To remove waste and carbon dioxide from the cells.
To provide for efficient gas exchange.
The right side of the heart collects deoxygenated blood form the body and
pumps it to the lungs.
The left side collects oxygenated blood from the lungs and pumps it to
the body.
THE DOUBLE CIRCULATION
Beginning at the lungs, blood flows into the left-hand side of the heart, and then out to the rest of the body. It
is brought back to the right-side of the heart, before going back to the lungs again.
This is call a double circulation system, during one complete
circulation of the human body, blood travels twice through the
heart. Blood arrives at the heart from the other organs of the body,
and then travels to the lungs. From the lungs, blood travels back to
the heart, then to the other organs of the body.
One circuit links the heart and lungs (low pressure circulation)
Pulmonary circulation, which conveys blood to and from lungs.
From right ventricle (with less pressure), deoxygenated blood
pumps to the lungs through pulmonary artery and from the lungs
oxygenated blood flows to the left atrium through pulmonary vein
The other circuit links the heart with the rest of the body (high
pressure circulation).
Systemic circulation, which conveys blood to and from all other
parts of the body. From left ventricle (with high pressure),
oxygenated Blood pumps to all parts of the body through aorta
(main artery) and from all parts of the body deoxygenated blood
flows to the right atrium through vena cava (main vein)
The importance of a double circulation


Oxygenated blood is kept separate from deoxygenated blood. The septum in the heart ensures this
complete separation. Oxygenated blood flows through the left side of the heart while deoxygenated blood
flows through the right.
The blood pressure in the systemic circulation is kept higher than that in the pulmonary circulation.
The left ventricle, with a thicker wall, pumps blood under higher pressure to the body and delivers
oxygenated blood effectively to all parts of the body. The right ventricle has a thinner wall and pumps
blood to the lungs under lower pressure, thereby avoiding any lung damage.
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(c) name the main blood vessels that carry blood to and from the heart, lungs, liver and kidneys
(d) describe the structure and function of the heart in terms of muscular contraction and the working of
valves
STRUCTURE AND FUNCTION OF THE HEART
The function of the heart is to pump blood around the body.
The right ventricle pumps blood to the lungs and the left ventricle pumps
blood to the rest of the body. In the human body the heart is situated
slightly to the left of the middle of the thorax, behind the breastbone. It is
enclosed by a sac known as the pericardium and is surrounded by the
lungs. It is made up mostly muscle. Heart muscle is very special. Unlike all
the other muscles in the body, the heart muscle cannot afford to get tired
THE HEART AND HOW ITS FUNCTIONS
i.
ii.
iii.
iv.
v.
vi.
It has four chambers, all with similar volumes when full. Two
atria ‘on top’ of two ventricles
Atria (singular: ‘atrium’) have thin walls and receive the blood
Ventricles have thick muscular walls to pump [the blood out of
the heart under pressure. The left ventricle has the thickest
walls, to send blood round the body
A system of valves ensures one-way flow of blood through the
heart
A wave of contraction (called systole) passes over the heart
from atria to ventricles. It forces blood from atria into the
ventricles, then forces blood out of the ventricles. As the
ventricles contract, the mitral and tricuspid valves are slammed
shut causing the ‘lubb’ sound of the heartbeat.
The heart muscles then relaxes (diastole). As the ventricles
relax, the semilunar valves close to stop blood being drawn
back into the ventricles. The closing the valves causes the ‘dupp’ sound.
Muscular contraction
The heart is made of a special type of muscle called cardiac muscle which contracts and relaxes regularly,
throughout
life.
The heart’s muscle is constantly active, so it needs its own blood supply, through the coronary artery, to
provide it with oxygen and glucose.
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Working of the valves
Valves in the heart prevent blood from being pushed backwards up into the atria when the heart ‘beats’.
blood
from the
lungs
blood from
the body
The valves close to stop
blood flowing backwards.
The ventricles contract
forcing the blood to leave
the heart.
At the same time, the atria
are relaxing and once again
filling with blood.
The heart beat begins when the
heart muscles relax and blood
flows into the atria.
Vena cava
Right atrium
Right ventricle
Tricuspid valve
Pulmonary
arteries
Pulmonary vein
Left atrium
Bicuspid valve
Left ventricle
Aorta
Semilunar valves
The atria then contract and
the valves open to allow
blood into the ventricles.
the main vein of the body; returns deoxygenated blood from the head and lower
body to the right atrium
receives deoxygenated blood from the vena cava.
receive deoxygenated blood to from right atrium and pumps blood to the pulmonary
artery
three flaps; prevent blood flowing back from ventricle to atrium during contraction
carry deoxygenated blood to the lungs
Returns oxygenated blood from the lungs. A vein from each lung joins together
before entering the left atrium
receives oxygenated blood returning from the lungs. Atria have thin walls since they
need only pump blood to the ventricles
Two flaps; prevent back flow of blood from ventricle to atrium
Thick muscular wall and pumps blood through the arteries to all the tissues of the
body
The main artery of the body; carries oxygenated blood out to the tissues. Blood
pressure is at its highest in the aorta, and the strongest pulse is felt here.
Prevent blood running back into the ventricles when pressure falls during relaxation
(e) compare the structure and function of arteries, veins and capillaries
ARTERIES, VEINS AND CAPILLARIES - STRUCTURE AND FUNCTIONS
There are 3 main kinds of blood vessels – arteries, veins and capillaries.

Arteries carry blood away from the heart. They divide again and again, and eventually form very
tiny vessels called capillaries. A large artery is called an aorta; a small one is called an arteriole.
Some arteries are; Pulmonary artery, Hepatic artery and Renal artery.

The capillaries gradually join up with one another to form large vessels called veins.

Veins carry blood towards the heart. A large vein is a vena cava; a small one is a venule. Some
veins are; Pulmonary vein, Hepatic vein, Hepatic portal vein and Renal vein.
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Plan of the main blood vessels in the human body
The ARTERY
 Take blood from the
heart
 Blood under high
pressure
 Blood flows in pulses
 Thick muscular walls
and small lumen
 No semilunar valves
 Carry oxygenated
blood (except
pulmonary artery)
The VEIN
 Take blood to the
heart
 Blood under low
pressure
 No pulses
 Thinner muscular
walls and large lumen
 Semi-lunar valves
 Carry deoxygenated
blood (except
pulmonary vein)
The CAPPILARY
 Take blood from arteries to
veins
 Pressure rises then gradually
falls as blood flows from
arteries to veins
 Pulse gradually disappears
 Walls are one cell thick; where
substances are exchange
 No semi-lunar valves
 Blood slowly losses its oxygen
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The comparison of blood vessels structure and functions
Function
Arteries
Carry blood away from
the heart at high pressure
Structure of
wall
- Thick, strong
- Contain muscles, elastic
fibres and fibrous tissue
Lumen
- Narrow
- Varies with heartbeat
(increases as a pulse of
blood passes through)
(-)
Valve
How
structure
fits function
- Strength and elasticity
needed to with stand the
pulsing of the blood,
prevent bursting and
maintain pressure wave
- Helps to maintain high
blood pressure,
preventing blood flowing
backwards
Capillaries
- Supply all cells with their
requirements
- Take away waste products
Very thin, only one cell thick
- Very narrow
- Just wide enough for a red
blood cell to pass through
Veins
Returns blood to the heart
at low pressure
- Thin
- mainly fibrous tissue
- Contain far less muscle
and elastic tissue than
arteries
widw
(-)
(+)
Prevent backflow
- No need for strong walls, as
- No need for strong walls,
most of the blood pressure has as most of the blood
been lost
pressure has been lost.
- Thin walls and narrow lumen - Wide lumen offers less
bring blood into close contact
resistance to blood flow
with body tissue, allowing
diffusion of materials between
capillary and surrounding
tissues.
- White blood cells can
squeeze between cells of the
wall
(h) identify red and white blood cells as seen under the light microscope on prepared slides, and in
diagrams and photomicrographs
(i) list the components of blood as red blood cells, white blood cells, platelets and plasma
(j) state the functions of blood:
• red blood cells – haemoglobin and oxygen transport
• white blood cells – phagocytosis, antibody formation and tissue rejection
• platelets – fibrinogen to fibrin, causing clotting
• plasma – transport of blood cells, ions, soluble food substances, hormones, carbon dioxide, urea,
vitamins and plasma proteins
BLOOD CELLS - STRUCTURE AND FUNCTIONS
Blood consists of cells floating in plasma.

Most of the cells are red blood cells.
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

A much smaller number are white blood cells.
There are also fragments formed from special cells in the bone marrow, called platelets.
Blood as seen through a microscope:
Red and white blood cells as seen
under a light microscope.


Functions of blood cells



1.
The largest cells are white cells.
The others are all red cells.
There are also a few platelets.
Red blood cells transport oxygen.
White blood cells protect against disease.
Blood platelets help the blood to clot.
Red blood cells (erythrocytes)

Human red cells are tiny bi-concave discs. They measure
0.008 mm in diameter and are 0.002 mm thick
 They have no nucleus. This is one reason why they live for
only about four months
 They are broken down in the liver and some of their
component like iron, are re-used to make new RBC
 The new red cell are made in the bone marrow , particularly
at the ends of long arm, leg bones, in the rib and in the vertebrae
 They are made of spongy cytoplasm enclosed in an elastic cell memebrane. In their cytoplasm
contains the red iron- containing protein called haemoglobin
 They are flexible, so they can pass through the very narrow capillaries
 There are 4,000,000 – 5,000,000 RBCs per mm3 of blood
 Their microscopic size, biconcave shape and very large numbers provided an enormous surface
area for the function given below
 The uptake and carriage of oxygen, by the haemoglobin in the form of oxyhaemoglobin from lungs
to all respiring tissues.
2. White blood cells (leukocytes)




Made in the bone marrow and in the lymph nodes.
Have a nucleus, often large and lobed.
Can move around and squeeze out through the walls of blood capillaries into all parts of the body.
There are many different kinds of white blood cells. They all have the function of fighting
pathogens (disease-causing bacteria and viruses) and to clear up any dead body cells in your body:
a. Phagocytes:



Have lobed nuclei and granular cytoplasm.
Can move out of capillaries to the site of an infection.
They carry out phagocytosis. That is, they ingest potentially
harmful bacteria, to prevent or overcome infections.
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b. Lymphocytes: produce antibodies to fight bacteria and foreign materials.



Have large nuclei
Responsible for immunity
They produce antibodies which ‘stick’ to the bacteria and clump them together ready for being
ingested by phagocytes. Some antibodies are in the form of antitoxins, which neutralise poisons in
the blood
3. Platelets (thrombocytes)




Fragments of cells
Made in bone marrow
There are 250,000 per mm3 of blood
They play a part in blood clotting and help to block holes
in damaged capillary walls
PLASMA




Pale yellow watery fluid
Contains the following materials in solution
Digested foods (amino acids, glucose), vitamins, excretory materials (urea, CO2), hormones, heat, fat
droplets, ions(salts), plasma proteins (e.g. fibrinogen), red and white blood cells and platelets
The PLASMA carries all materials from where there are produced or absorbed to the parts of the body
where they are needed or excreted. E.g. Plasma carries CO2 from the cells of the body to the lungs
Functions of the blood
 Transportation of R.B.C’s, W.B.C’s, oxygen, food nutrients, hormones, and waste products.
 Defence against disease, by white blood cells phagocytosis and production of antibodies.
 Supplying cells with glucose to respire and keep a constant temperature.
(k) describe the transfer of materials between capillaries and tissue fluid.
THE TRANSFER OF MATERIALS BETWEEN CAPILLARIES AND TISSUE FLUID
As blood enters capillaries from arterioles (small arteries), it slows down. Capillaries leak, so some – but not
all – of materials in plasma can escape. All the blood cells, except phagocytes, are too large to leave the
capillaries. By their own effort, phagocytes are able to squeeze out between the cells in the capillary walls.
Most plasma protein molecules are too large to pass out of the capillaries. All the smaller molecules in solution
pass out to bathe the cells in the tissue fluid and from tissue fluid to the body cells
Diffusion is responsible for the transfer of materials between capillaries and tissue fluid.
Tissue fluid = blood without red cells, plasma proteins and some white blood cells
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BLOOD CLOTTING
Blood platelets and damaged tissues form enzyme thrombokinase that converts insoluble prothrombin to
thrombin. Thrombin converts soluble FIBRINOGEN to insoluble fibrin.
This fibrin forms a mesh which traps blood cells and becomes a CLOT- prevent the entry of bacteria. The
clot dries and hardens to form a scab, which covers the wound until the skin beneath has repaired. When an
injury causes a blood vessel wall to break, platelets are activated. They change shape from round to spiny,
stick to the broken vessel wall and each other, and begin to plug the break.
Necessity for blood clotting




Prevent excessive blood loss from the body when there is a damage of the blood vessel.
Maintain the blood pressure.
Prevent the entry of microorganism and foreign particles into the body.
Promote wound healing.
(f) investigate and state the effect of physical activity on pulse rate
(g) describe coronary heart disease in terms of the occlusion of coronary arteries and state the
possible
causes (diet, stress and smoking) and preventive measures
EFFECT OF EXERCISE ON HEARTBEAT AND CAUSES OF A CORONARY HEART
DISEASE



A heartbeat is a contraction. Each contraction squeezes blood to the lungs and body. The heart beats
about 70 times a minute, more if you are younger, and the rate becomes lower the fitter you are.
During exercise the heart rate increases to supply the muscles with more oxygen and glucose and allow
the muscles to respire aerobically à they have sufficient energy to contract.
Regular exercise is important to keep the heart muscle in good tone and heart is more efficient in maintaining
blood pressure and risk of coronary heart disease and stroke.
Coronary arteries
the muscles of the heart are so thick that the nutrients and oxygen in the blood
inside the heart would not be able to diffuse to all the muscles quickly enough.
The heart muscles needs a constant supply of nutrients so that it can keep
contracting and relaxing. The coronary arteries supply this.
If a coronary artery gets blocked – e.g. by a blood clot – the cardiac muscles
run short of oxygen --> they cannot respire --> cannot obtain energy to
contract --> heart stops beating. This is called a heart attack or cardiac
arrest.
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Blockage of the coronary arteries is called coronary heart disease.
Main causes of a coronary heart disease and preventive measures
Heart disease may occur; the diet we use, obesity, smoking, stress and poor exercise.
DIET
Diet is important for a healthy heart, but like all muscles, the heart benefits from exercise.
Heart disease can occur when animal fats and cholesterol form deposits called ATHEROMA on the walls of
the coronary artery. ATHEROMA forms a blockage in the artery and restricts blood flow, decreasing oxygen
supply to the heart muscle. In severe cases, the artery may become blocked, leading to a cardiac arrest
(heart attack)
OBESITY
Obesity leads to high blood pressure and heart disease. It is often the result of eating too much animal fat,
and the heart has to work harder to move the body’s excess weight.
CIGARETTE SMOKING
Nicotine increases the tendency for blood to clot. The coronary artery may therefore not supply enough blood
to the heart muscle.
STRESS
People who live stressful lives are also at a risk of heart disease. Stress causes the release of raised levels
of the hormone adrenaline, which constricts artery walls.
To decrease the risk of heart disease:





Restrict the intake of animal fats and cholesterol
Avoid obesity
Do not smoke
Settle for a less stressful lifestyle
Take regular exercise
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8. RESPIRATION
8. RESPIRATION
(a)
(d)
define respiration as the release of energy from food substances in all living cells
state the uses of energy in the human body: muscle contraction, protein synthesis, cell division,
active transport, growth, the passage of nerve impulses and the maintenance of a constant body
temperature
RESPIRATION RELEASES ENERGY FROM FOOD
Respiration is the chemical reactions that break down nutrient molecules in living cells to release
energy.
In humans, our cells need energy (ATP) for:
 muscle contraction
 making protein molecules: linking together amino acids into long chains
 cell division: to repair damaged tissues and so that we can grow
 active transport
 transmitting nerve impulses
 maintenance of constant body t°
All this energy comes from the food we eat. Water soluble molecules are absorbed from the intestine into
the blood.
The main energy–providing nutrient: glucose (contains a lot of chemical energy).
There are 2 types of respiration:
8.1 AEROBIC RESPIRATION
8.2 ANAEROBIC RESPIRATION
(b)
(c)
(e)
(f)
define aerobic respiration as the release of a relatively large amount of energy by the breakdown
of food substances in the presence of oxygen
state the equation (in words or symbols) for aerobic respiration
define anaerobic respiration as the release of a relatively small amount of energy by the
breakdown of food substances in the absence of oxygen
state the equation (in words or symbols) for anaerobic respiration in humans and in yeast
AEROBIC AND ANAEROBIC RESPIRATION
Respiration releases energy from food.
There are 2 kinds of respiration. Aerobic and anearobic respiration.
The main difference between them is that aerobic respiration
involves oxygen and anaerobic respiration does not!
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A. Aerobic respiration
The release of a relatively large amount of energy in cells by the breakdown of food substances in
the presence of O2.
B. Anaerobic respiration
Anaerobic respiration: the release of a relatively small amount of energy by the breakdown of food
substances in the absence of O2.
Anaerobic respiration in muscles during exercise:
Anaerobic respiration in yeast:
(g)
describe the effect of lactic acid production in muscles during exercise
Muscles respire anaerobically when exercising vigorously, because the blood cannot supply enough oxygen
to maintain aerobic respiration. However, the formation and build-up of lactic acid in muscles causes cramp
(muscle fatigue).
In the liver, lactic acid is oxidized after the exercise by the extra oxygen provided by fast breathing. An oxygen
debt is created because oxygen is needed to convert lactic acid back to a harmless chemical (pyruvic acid).
Aerobic respiration provides most of the energy we need. During exercise we need more energy so the rate
of aerobic respiration increases. As the level of activity rises, the blood flow through the muscles increase to
provide more glucose and oxygen, and to remove carbon dioxide and the heat created by the reaction.
The breathing rate increase to increase gaseous exchange;
The breathing rate increase both in terms of number of breaths per minute and the volume of air are taken in
with each breath. Blood leaving the lungs is always fully saturated with oxygen but the increase in lungs
activity compensate for the smaller time the blood spends in the lungs when the heart rate increase.
The heart rate increase to increase blood flow;
The heart rate increase, meaning that the number of beats per minute increases and the volume of blood
pumped with each beat increases. The effect is to move blood more rapidly through the body.
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(i)
investigate and state the effect of physical activity on rate and depth of breathing
Effects of physical activity on breathing
* tidal volume: amount of air during normal, relaxed breathing
vital capacity; maximum amount of air breathed in or out in one breath
During normal breathing:
- depth (tidal volume) : ≈ 0.5ℓ
- rate: 12 breaths/ minute
During exercise:
- depth: ≈ 5ℓ (depending on age, sex, size & fitness of person)
- rate: over 20 breaths/ minute
The total lung volume is greater than vital capacity (some air always remains in the lungs). If not, alveoli
walls would stick together, the lung would collapse.
Link between physical activity and rate and depth of breathing









when you run, muscles in your legs use up a lot of energy.
cells in the muscles need a lot of O2 very quickly.
they combine O2 + glucose as fast as they can, to release energy for muscle construction ---> a lot
of O2 is needed
you breath deeper and faster to get more O2 into your blood.
your heart beast faster to get O2 to the leg muscles as quickly as possible.
a limit is reached - the heart and the lung cannot supply O2 to the muscles any faster.
some extra energy (not much) is produced by anaerobic respiration: some glucose is broken
down without combing with O2:
 Glucose ---> lactic acid + energy.
CO2 and lactic acid concentration in tissue and in the blood ↑ ---> blood pH ↓
Brain sense the change ---> nerve impulses sent to the diaphragm and the intercostal muscles,
stimulating them to contract harder and more often ---> faster and deeper breathing.
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(h)
know the percentages of the gases in atmospheric air and investigate and state the differences
between
inspired and expired air
THE DIFFERENCES BETWEEN INSPIRED AND EXPIRED AIR
Inspired air (air we breath in)
Expired air (air we breath out)
20% oxygen
16% oxygen
0.04% carbon dioxide
4% carbon dioxide
relatively dry
saturated
at air temperature
at body temperature
relatively dirty
relatively clean
THE COMPOSITION OF INSPIRED AND EXPIRED AIR
Testing for CO2
To investigate the differences in composition between inspired and expired air, we
use limewater because it change colour when the gas is bubbled through, from colourless to milky.
There is more CO2 present in expired air ---> it makes limewater change colour more quickly (than
inspired air).
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8.3 HUMAN GAS EXCHANGE
(j)
identify on diagrams and name the larynx, trachea, bronchi, bronchioles, alveoli and associated
capillaries
The lungs are enclosed in the thorax. They are joint to the back of the mouth by the trachea. The trachea
divides into two smaller tubes called bronchi, which enter the lungs and divide into even smaller branches
called bronchioles. These fine branches end in masses of thin walled air sac called alveoli.
The diaphragm is the sheet of tissue which separate the thorax from abdomen when relaxed, it is domed
slightly upwards. The ribs are moved by the intercostal muscles. The external intercostal muscles push
them upward and outwards. The internal intercostal muscles pull them downward and inwards.
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(k)
state the characteristics of, and describe the role of, the exchange surface of the alveoli in gas
exchange
Gas exchange usually involves 2 or more gases transferred in opposite directions across a respiratory
surface.
1.
Structure of the breathing system: the larynx, trachea, bronchi, bronchioles, alveoli and
associated capillaries.
Gaseous exchange relies on diffusion. To be efficient, the gaseous exchange surface must:
2.
- thin – shorter distance to diffuse
- moist – allow gases to dissolve
- large surface area
- have a concentration gradient across surface – maintained by movement of air and transport/
use of gas.
How the alveoli are adapted for the process of gaseous exchange.
o
The millions of alveoli provide a large surface area for gaseous exchange.
o
The walls of the alveoli are covered with a layer of water to dissolves the gases.
o
The walls are only one cell thick for quick and easy diffusion of gases in solution.
o
They are richly supplied with capillaries for rapid transport of the gases.
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(l)
describe the role of cilia, diaphragm, ribs and intercostal muscles (external and internal) in
breathing.
Keeping the lungs clean (The role of mucus and cilia)
Air around us contain dust particles and bacteria. The pathway that the air takes as it goes down into our
lungs are constructed so that not too many of these unwanted particles
The lining of trachea contains two kind of cells. Some cells are goblet cells. They make sticky, slimy mucus,
many of the dust particles and bacteria in the air get trapped in the mucus. The other cells have tiny,
microscopic ‘hair’ on them called cilia. They sweep the mucus upwards, towards back of the throat. Then the
mucus swallowed, together with its all trapped dust particles and bacteria.
- Inside the nose, thin turbinal bones are covered with a layer of cells. Some of which are goblet cells.
- Goblet cells produce a liquid (water + mucus) ---> evaporate ---> moisten nose.
- Cilia: tiny hair-like projections; constantly moving
- Bacteria + dust particles are trapped by cilia and mucus as to not move further inside the gas exchange
system.
Breathing (inspiration and expiration)
Oxygen enters the blood from the lungs. Breathing is a muscular, pumping action that takes in air from the
atmosphere and moves it to the lungs. Breathing in is responsible for presenting air with its oxygen to the
surface in the lungs where gaseous exchange will take place. Breathing out pushes the air, now containing
waste carbon dioxide, back into the atmosphere.
During inspiration
The external intercostal muscles contract while internal intercostal muscles relax. This causes the ribs
swing up and outwards, increasing the volume of the thorax.
The muscles of the diaphragm contract, pulling it flat further increasing the volume of the thorax.
The resulting increase in volume of the thorax decreases its pressure.
During expiration
The external intercostal muscles relax while internal intercostal muscles contract. This causes the ribs
swing down and inwards, decreasing the volume of the thorax.
The muscles of the diaphragm relax and the diaphragm domes upwards again.
The action decrease the volume of the thoracic cavity, increasing its pressure. Air is forced back out into
the atmosphere.
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9. EXCRETION
METABOLIC WASTE PRODUCTS
(a) define excretion as the removal of toxic materials and the waste products of metabolism from
organisms
(b) describe the removal of carbon dioxide from the lungs
Great number of chemical reactions take place inside the cells of an organism in order to keep to alive. These
reactions are called metabolic reactions. The product of some of these reactions are waste products and are
poisonous and must be remove from the body.
Examples;
o
o
o
Break down of glucose during respiration produce CO2. This carried away by the blood and removed
in the lungs.
Urea, which is made in the liver from excess proteins. And then excrete by the kidneys.
Water, which is sometimes in excess in the body and is removed by the kidneys.
Excretion is defined as the removal of toxic materials and the waste products of metabolism from
organisms
Excretory organ
skin
Excretory substance
removes sweat from the body
lungs
removes carbon dioxide from the body
liver
removes bile from the body
kidneys
removes excess water, nitrogenous waste and unwanted salts from the body
*The removal of faeces from the alimentary canal is not regarded as excretion
UREA PRODUCTION AND EXCRETION
Surplus amino acids in the bloodstream cannot be stored. They are removed by the liver and broken down
into the urea (which is the nitrogen-containing part of the amino acid) and a sugar residue, which can be
respired to release energy. The breakdown of amino acids is called DEAMINATION. Urea is returned to the
bloodstream (into the hepatic vein) and filtered out when it reaches the kidneys.
The body treats alcohol as a poison. The liver removes poisons, such as alcohol and drugs, from the blood
and breaks them down. Prolonged and excessive use of alcohol damages the liver and may cause it to fail.
An 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 filterd out of the blood by the kidneys.
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9.1 STRUCTURE AND FUNCTION OF KIDNEYS
(c)
identify on diagrams and name the kidneys, ureters, bladder, urethra and state the function of
each (the function of the kidney should be described simply as removing urea and excess salts
and water from the blood; details of kidney structure and nephron are not required)
The kidneys are two red-brown bean-shaped organs lying dorsally in the abdominal cavity. They are
supplied with blood via the renal artery, which branches from aorta. Blood returns to the rest of the
circulation by the renal vein to the vena cava.
The material removed from the blood by each kidney are sent down the ureter to the bladder where they
are stored. Relaxation of the bladder sphincter muscles allows them to leave the body as a solution
called urine via the urethra.
Renal artery
Contains blood with higher urea concentration
Renal vein
Contains blood with lower urea concentration
Ureter
Carries urine from kidney to bladder
Bladder
Stores up to about 500cm3 of urine before expelling it from body
Sphincter
Ring of muscle which controls flow of urine from bladder to urethra
Urethra
Carries urine from bladder to outside
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FUNCTION OF THE KIDNEY - FILTRATION AND REABSORPTION
The function of the kidney is to filter blood, removing urea and excess H2O, reabsorbing glucose, some
H2O and some mineral salts.
The role kidneys carry out high pressure filtration of the
blood, during two functions have to be achieved
The removal of urea and toxins from the blood
The maintenance of a constant concentration of
blood plasma (osmoregulation)
Osmoregulation may be achieved either:
By the removal (if it is in excess) or the retention of
water, or
By the removal (if they are in excess) or the
retention of ions.
If a diabetic’s person has an excess of glucose in their
blood, the kidneys will remove some of the glucose as
well.
9.2 KIDNEY DIALYSIS
(d) describe dialysis in kidney machines as the diffusion of waste products and salts (small molecules)
through a membrane; large molecules (e.g. protein) remain in the blood.
If a person’s kidneys stop working properly (‘fail’), there will be a build-up of urea and toxins in their blood
which will eventually prove fatal. A kidney transplant may be possible if a donor with a suitable tissue type is
available. Otherwise, kidney dialysis may be used.
The dialysis machine contains a tank having dialysis liquid. A long coiled, celluloid dialysis tube is suspended
in the dialysis liquid. The dialysis liquid contains water, glucose and essential salt the glucose and essential
salt concentration will be same like that of the blood. When the patient blood is passed into the dialysis
machine through the dialysis tube, the toxic materials like urea and unwanted salts present in the blood
diffuse out of the dialysis tube into the dialysis liquid. The dialysis fluid is constantly changed through the
outlets present in the dialysis tank. The pure blood which is not having the urea is returned to the patient’s
body.
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10. HOMEOSTASIS
HOMEOSTASIS
(a) define homeostasis as the maintenance of a constant internal environment
Definition
Homeostasis is the maintenance of a constant internal environment.
Importance of Homeostasis in Mammals
 metabolic reactions are controlled by enzymes
 enzymes work best in a narrow range of temperature & pH only
 important to keep internal environment as steady as possible
Parts Of The Body Involved In Homeostasis
Kidneys-
Which remove substances that might poison the enzymes. The kidneys also control the level of
salts, water and acids in the blood. The composition of the blood affects
the tissue fluid which in turn affects the cells.
Liver- Which regulates the level of glucose in the blood. The liver stores
any excess glucose if the concentration in the blood gets too lows.
Lungs -
The lungs play a part in homeostasis by keeping the
concentrations of oxygen and carbon dioxide in the blood at the best
level for the cells chemical reactions, especially respiration.
Skin- The skin regulates the temperature of the blood. If the cells were
get too cold. The chemical reaction would become too slow to maintain life. If they become too hot, the
enzymes would be destroyed.
NEGATIVE FEED BACK IN HOMEOSTASIS
(b) explain the concept of control by negative feedback
A system which automatically brings about a correction, regardless which side of the optimum the change has
occurred, is called negative feedback.
Temperature, blood glucose level and osmoregulation involve negative feedback.
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•
Regulate water potential in Tissue Fluid

Control Of Blood Glucose Content
The control of glucose concentration in the blood is a very important part of homeostasis.
Two hormones (insulin and glucagon) control blood glucose levels.
Both hormones are secreted by the pancreas and are transported to the liver in the bloodstream.
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When blood glucose levels get too high or too low, a person may:
- lose consciousness
- fall into a coma
- die
Too little glucose ---> Cells can not release enough energy they need. Brain cells are especially dependent
on glucose for respiration, and die quite quickly if they are deprived of it.
Too much glucose in the blood ---> water moves out of cells and into the blood by osmosis ---> Cell has too
little water to carry out normal metabolic process.
The control of blood glucose concentration is carried out by the pancreas and the liver.
Pancreas secretes insulin and glucagon: 2 hormones that work side-by-side.
Left-side: When glucose levels drop below normal, glycogen is broken down to glucose, which is released
into the bloodstream.
glucagon: glycogen ---> glucose
Right-side: Excess glucose is stored in the liver and muscles as the polysaccharide glycogen (animal starch).
insulin:
glucose
---> glycogen
↑ respiration rates ---> cells consume more glucose
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- a change from normal conditions (body temperature, blood glucose levels…)
- triggers a sensor,
- stimulates a response in an effector.
Glucose blood levels regulation



If glucose levels rise, the sensor will instruct an effector (the pancreas) to secret insulin ---> glucose levels
drop below normal.
If glucose levels drop, the sensor will instruct the pancreas to stop secreting insulin ---> glucose levels rise.
This is negative feedback – the change is fed back to the effector.
Temperature regulation




All the time, the hypothalamus is monitoring small changes in the temperature of your blood.
If temperature rise above normal, actions take place that help to reduce it.
If temperature is lower than normal, the hypothalamus stops these actions and start actions that help
to raise the blood temperature.
This is negative feedback - the information that the blood has cool down stop the hypothalamus making
your skin to increase heat loss.
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STRUCTURE AND FUNCTION OF THE SKIN
(c)
identify, on a diagram of the skin, hairs, sweat glands, temperature receptors, blood vessels and
fatty
tissue
Functions of Our Skin






protect the body (epidermis)
temperature regulation (hair)
excretion of sweat (sweat gland)
store fats (fatty layer)
sensation (numerous receptors )
production of vitamin D under ultra-violet light (inner epidermis)
EPIDERMIS
- dead outer layer;
 protect the underlying tissues
o to prevent mechanical injury
o to prevent bacterial entry
o to reduce water loss
- middle layer;
 made up of living cells
 become dead as they approach the surface
- black inner layer;
 with pigment (melanin) to absorb ultra-violet ray for sunlight
 have cell division to repair the lost outer layers
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DERMIS
 Blood capillaries
– to nourish the cells of the skin
– branch into superficial blood capillaries
 Sweat gland
– surrounded by a network of capillaries
– secrete sweat (consists of water, mineral salts, urea & some waste materials
 Hair follicles & Hairs
– each hair has a nerve & a capillary attached to it
– nerve: receives stimuli
– capillary: supply food & oxygen
– hairs reduce heat loss & assist in temperature regulation
 Erector muscle
– controls the hair movement for temperature regulation
 Oil gland
– secretes oily substance
• to make the skin waterproof
• to prevent bacterial entry
 Receptors
– detect pain, pressure, temperature & touch
THE PART PLAYED BY THE SKIN IN TEMPERATURE REGULATION
(d)
describe the maintenance of a constant body temperature in humans in terms of insulation and
the role of temperature receptors in the skin, sweating, shivering, blood vessels near the skin
surface and the coordinating role of the brain.
Control Body Temperature in Hot Conditions
 More sweat is produced by sweat glands
– evaporation of sweat takes away heat which produces a cooling effect
 Vasodilation of skin arterioles
– arterioles near the surface of the skin dilates
– to let more blood flows near the skin surface
– to have more heat lost by conduction & radiation.
 Erector muscles relax
– hairs lie flat on the skin
– reduce thickness of air trapped among the hairs
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 Decrease metabolic rate & muscle contraction
– gain less heat
Control Body Temperature in Cold Conditions
 Vasoconstriction of skin arterioles
– arterioles near the surface of the skin constrict
– to let less blood flows near the skin surface
– to have less heat lost by conduction & radiation
 Erector muscles contract
– pull hairs erect for trapping more air
– thicker layer of air acts as a good insulator of heat
 Less sweat is produced by sweat glands
– reduce heat loss by evaporation
 Increase metabolic rate & muscle contraction (shivering)
– releases more heat (gain more heat)
SHIVERING
If the temperature of the blood falls below 37oC, muscles in the body start to contract and relax rhythmically,
which releases heat energy. This reaction is called shivering.
To help raise their body temperature, a person may take warm drinks, increase the insulating layer of air
around their body by wearing clothes, and do some exercise.
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11. COORDINATION AND RESPONSE
The various organs of the body must work in coordination if an organisms is to survive effectively in its
environment. All living things, including plants, are able to detect changes in their environment and to respond
to them. These changes are called stimuli (eg; light, sound, smell, taste and touch). The parts of the body that
detect the changes are called receptors (eg; eyes, ears, nose, tongue and skin). The parts of the body that
respond to them are called effectors (eg; glands and muscles).
The components of coordinated behavior;
stimulus
receptor
coordinator
effector
response
11.1 Nervous System
(a)
(b)
(c)
state that the nervous system (brain, spinal cord and nerves) serves to coordinate and regulate
bodily functions
identify, on diagrams of the central nervous system, the cerebrum, cerebellum, pituitary gland
and hypothalamus, medulla, spinal cord and nerves
describe the principal functions of the above structures in terms of coordinating and regulating
bodily functions
The NS is made up of the central nervous system and peripheral
nervous system (system of nerves).
The body has a series of receptors which pass information about the
environment to a coordinating center called central nervous system.
Central nervous system is made up of the brain and the spinal cord.
After receiving the information, the CNS directs and response in the
appropriate effectors (muscles or glands). Nerve carries impulses
between receptor organs (eg: Eye) to the effector (muscles or glands).
Peripheral nerves contain sensory and motor neurones (nerve cells).
THE BRAIN AND THE SPINAL CORD (Central Nervous System)
The functions of the major part of the brain
cerebrum
hypothalamus
pituitary gland
cerebellum
medulla
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CEREBRUM
The cerebrum is in the form of two matching halves- known as cerebrum hemispheres – and is responsible
for:
o The coordination of the organs of the body
o The control of voluntary action
o The reception of sensation
o At the very front of cerebrum is responsible for money and moral
o At the back region is responsible for sight
CEREBELLUM
The cerebellum is the region of balance and
instinct.
MEDULLA
The medulla joins the brain to the spinal cord. It
controls unconscious activities such as heartbeat,
peristalsis and breathing.
HYPOTHALAMUS
The hypothalamus lies under the cerebrum and is
the part of the brain responsible for monitoring
changes, particularly in the blood. It may be regarded as the ‘homeostat’ of the body.
PITUITARY GLAND
Situated beneath the hypothalamus, the pituitary gland is made up partly of nerve tissues. It is some time
called the ‘master’ gland because it manufactures chemicals called HORMONES and release them into blood.
These hormones control the activity of many other glands and other organs throughout the body, such as those
responsible for growth (e.g. of bones) and development (e.g. sexual development). Therefore pituitary gland
has a very important part to play in coordination. It is regularly instructed by the hypothalamus.
The Spinal cord
In the same way that a series of nerves (cranial nerves) serve the brain, impulses are relayed to, and conducted
from the spinal cord by nerves called spinal nerves. Spinal nerves are connected with receptors and effectors
in parts of the body other than the head.
In emergency situations, the spinal cord can receive and transmit impulses to bring about rapid, often protective
responses called REFLEX actions. The central region of the spinal cord (the grey matter) contains nerve cells
(relay neurons) involved solely in this process. The outer region of the spinal cord (the white matter) contains
nerve cells involved in either supplying sensory information to the brain, or passing impulses on to muscles
which are instructed by the brain (i.e. voluntary actions).
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11.2 RECEPTORS
(d)
(e)
describe the gross structure of the eye as seen in front view and in horizontal section
state the principal functions of component parts of the eye in producing a focused image of near
and distant objects on the retina
The Eye
The eye is one of the most important of the receptors. It provides us with information on dimensions, colors
and the distance of object in our environment.
o
The eyebrow stops sweat running down into the eye.
o
Eyelashes help to stop dust blowing on to the eye.
o
Eyelids can close automatically (blinking is a reflex)
to prevent dust and other particles getting ton to the
surface of the cornea.
o
Blinking also helps to keep the surface moist by
moving liquid secretions (tears) over the exposed
surface. Tears also contain enzymes that have an
antibacterial function.
o
Sclera - the tough outer coat which protects the eye against damage. The muscles that move the eye
in its socket attach to the sclera.
o
Cornea - a transparent layer responsible for most of the refraction (bending)of the light rays that
enters the eye.
o
Vitreous humour - a jelly-like substance which helps to keep the shape of the eyeball, supports the
lens and keeps the retina in place at the back of the eye.
o
Aqueous humuor- watery fluid which supports the cornea and front chamber of the eye.
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o
Lens - is the transparent, curved front of the eye which helps to converge the light rays which enter
the eye.
o
Ciliary body- has suspensory ligaments that hold the lens in place. It secretes the aqueous humour,
and contains ciliary muscles that enable the lens to change shape, during accommodation (focusing
on near and distant objects).
o
Iris – the colored part of the eye which can expand and contract to control the amount of light that
enters the eye.
o
Pupil – the circular opening which lets light into the eye.
o
Choroid – a darkly colored layer which reduces reflections inside the eye and contain blood vessels
which helps to nourish the cell of the retina.
o
Retina – contains the light-sensitive cells, rods and cones.
o
Fovea – a part of the retina that is directly opposite the pupil and contains only cone cells. It is
responsible for good visual acuity (good resolution).
o
Blind spot – is where the bundle of sensory fibres form the optic nerve; it contains no light-sensitive
receptors.
o
Optic nerve – composed sensory neurons which are carry nerve impulses to the brain.
How the eye produces a focused image
o
Light rays from an object enters the transparent cornea.
o
The cornea refracts the light rays in towards one another.
o
o
Light rays pass through aqueous humor and pupil.
The transparent, elastic LENS is altered in shape. It is made:
 Fatter to decrease its focal length
 Thinner, to increase its focal length
The relatively small amount of refraction now produced by the lens brings the rays to focus on the
o
RETINA.
o
The retina contains light sensitive cells
 rods which work well when light intensity low
 cones which detect color
These cells stimulated by the light of the image, and are converted into light energy into electrical
energy.
o
Electrical energy, in the form of impulse, travels along the optic nerve to the brain.
o
The brain de-codes the impulse to produce the sensation of sight.
Accommodation
The ability of lens to change shape and focus on objects at different distance is called accommodation. Thos
ability depends on:
•
•
•
The elasticity of lens
The existence of ciliary muscles which are used to alter the shape of the lens
The suspensory ligaments which transfer the effect of the ciliary muscles to the lens
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Viewing a near object
Viewing a near object
The (circular) ciliary muscles contract, reducing
their circumference.
The (circular) ciliary muscles relax, increasing their
circumference.
They reduce pull on the (elastic) suspensory
ligaments.
The suspensory ligaments pulled tight.
With less force on the lens, its elasticity allows it to
become wider decreasing its focal length.
the lens, stretched to become longer and thinner,
increasing its focal length.
Rays from near object produce a focused image on
the retina.
Rays from distant object brought to focus on the
retina.
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11.3 REFLEX ACTION
(f)
(g)
(h)
describe the pupil reflex in response to bright and dim light
outline the functions of sensory neurones, relay neurones and motor neurones
discuss the function of the brain and spinal cord in producing a coordinated response as a result
of a specific stimulus (reflex action)
THE ‘PUPIL’ REFLEX
Bright light could seriously damage the delicate light-sensitive cells of the retina. The intensity of light that falls
on the retina is therefore controlled by the IRIS. It has an antagonistic arrangement of circular and radial
muscles.
IN DIM LIGHT
IN BRIGHT LIGHT
Light-sensitive cell in the retina detect the light
intensity.
Light-sensitive cell in the retina detect the light
intensity.
Impulses are sent along the optic (a sensory)
nerve to the brain.
Impulses are sent along the optic (a sensory) nerve
to the brain.
The brain returns impulses along a motor nerve to
the radial muscles of the iris.
The brain returns impulses along a motor nerve to
the circular muscles of the iris.
The radial iris muscles contract while the circular
iris muscles relax.
The circular iris muscles contract while the radial iris
muscles relax.
The diameter of the pupil increases, allowing more
light to enter.
The diameter of the pupil decreases, allowing less
light to enter.
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NERVES
A nerve is like a telephone cable: it contains a large number of small “wires” called neurons. Each neurons is
an individual nerve cell with its own cytoplasm, cell membrane and nucleus.
Neurons are insulated by a fatty sheath. They are long, they target the exact area to be affected they
conduct there impulses very quickly.
TYPES OF NEURONS
Sensory neuron - Neurons which conduct impulses from sensory receptors to the brain or spinal cord. They
have long dendron and short axon. Their cell body are found outside the CNS in the dorsal root of spinal
cord.
Motor neuron - Neurons which conduct impulses from the brain or spinal cord to effectors (muscles/gland).
They have long axons and short dendrons. Their axons branch repeatedly in the muscles.
Relay neuron - Neurons which then direct those impulses directly from sensory to motor neurons in the
CNS. They occur in the brain and spinal cord where they are link the sensory neuron with the motor neurons.
REFLEX ACTION
A reflex action is a coordinated response to a specific stimulus. When the spinal cord alone directs the
response, the action is describe as a spinal reflex. Eg; when we quickly remove our finger from hot object.
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Sequence of events in spinal reflex is:
1
A stimulus is received by the sensory receptor (in the example given above, the hot object provides
the stimulus and the sensory receptor is located in the finger).
2
An impulse is generated and carried along by sensory neurones towards the spinal cord.
3
The sensory neurones become part of a spinal nerve.
4
The impulse travels towards the spinal cord along the dorsal root. The dorsal root is part of the
linking pathway between outside stimuli and the spinal nerve.
5
Impulses arrive at the nerve endings of the sensory neurone in the grey matter of the spinal cord.
6
The nerve endings release a chemical which diffuses across a gap – the SYNPSE – between the
sensory neurone and the nerve endings of a relay neurone. The chemical stimulates the relay
neurone to produce an impulse
7
Another synapse links the relay neurone with a motor neurone.
8
The impulse travels along motor neurones away from the spinal cord along the ventral root. The
ventral root is part of the linking pathway between the spinal nerve and the effector.
9
The nerve endings of the motor neurone are applied to the effector. (the biceps muscle in this case)
10
A response is produced. (as the biceps muscle contracts to lift the hand clear of the stimulus).
A reflex action is an automatic response to a stimulus.
A reflex arc describes the pathway of an electrical impulse in response to a stimulus.
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Voluntary and involuntary actions
Knee jerk is an involuntary reflex.
Two types of action controlled by the human nervous system are : voluntary and involuntary actions. The
peripheral nerves transmit both of them.
Comparison of voluntary and involuntary actions
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11.4 HORMONES
(i)
(j)
(k)
(l)
define a hormone as a chemical substance, produced by a gland, carried by the blood, which
alters the activity of one or more specific target organs and is then destroyed by the liver
state the role of the hormone adrenaline in boosting the blood glucose concentration and give
examples of situations in which this may occur
state the role of the hormone insulin in controlling blood glucose concentration
describe the signs (increased blood glucose concentration and glucose in urine) and treatment
(administration of insulin) of diabetes mellitus.
Hormone is a chemical substance, produced by endocrine gland, carried by the blood, which alters the
activity of one or more specific target organs and is then destroyed by the liver.
Credit: biologie.uni-hamburg.de
Hormone molecules must be relatively small, soluble and diffuse easily, so they can pass quickly from the
cells that make them, into blood capillaries. The endocrine glands that produce hormones have no ducts to
carry the hormones. They pass their hormones directly into the blood. These gland are called as ductless
glands.
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Gland
Situated
Hormone produced
Adrenal
above the ADRENALINE
(the liver
kidneys
‘fight, fright and flight’
hormone)
heart
Islets
of in
the INSULIN
Langerhans pancreas
Target organ
Effect of hormone
Turns glycogen into glucose to boost
blood sugar levels in emergency*
heart beats faster – more oxygen to
brain and muscles
tire less easily
voluntary
muscles
liver
and promotes the uptake of glucose by cells
muscles
promotes the conversion of glucose to
glycogen for storage
*Example of emergencies
The moments before the start of competitive events, when being chased by an angry dog and during a
heated argument
Other effect of adrenaline
Increasing blood pressure
Diverting blood away from the intestines and towards the muscles about to be used
Increasing air flow to the lungs
Chemical control of metabolic activity by adrenaline
Adrenaline is a hormone secreted by adrenal glands. When you are frightened, excited, your brain sends
impulses along a nerve to your adrenal glands. This makes them secrete adrenaline into the blood.
Adrenal gland is situated above each kidney.
Adrenaline helps you to cope with danger:
1. ↑ heart rate → supply O2 to brain and muscle more quickly →↑ energy for action (fighting, running…).
Contract blood vessels in skin and digestive system → they carry very little blood → supplies blood back to
vital organs (brain and muscles).
2. Stimulate liver to convert glycogen to glucose, ↑ glucose release into the blood by liver → extra glucose
for muscle →help muscle to contract.
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Examples of situations in which adrenaline secretion increases
Adrenaline is needed and secreted in a “fright, fight or flight” situation.
E.g.: When you are facing danger, for example, a masked man with a gun is approaching you.
- Your brain sends a signal to the adrenal glands, to start secreting and pumping adrenaline into the
bloodstream.
- the actions of the adrenaline is listed above
- this gets you ready to either stand and fight or run away from the man.
Comparison of nervous and hormonal control systems
Diabetes
If the person’s islet of Langerhans cells do not produce enough insulin, the level of glucose in their body will
rise. Glucose will present in their urine. The increased concentration of their blood plasma will draw water
from their cells by osmosis, making them thirsty, tired and causing them to urinate more frequently.
If insulin production is not seriously reduced, it may be possible to treat by restricting the person’s intake of
carbohydrate.
In more extreme cases, however, the treatment will include regular injection of insulin. The carbohydrate intake
must then be regulated to match the amount of insulin injected.
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SKELETAL SYSTEM
12. SUPPORT, MOVEMENT AND LOCOMOTION
Skeletal system is made up of bones and muscles. There are about 206 bones in our body. Muscles and
bones are joined together and form a frame work called the skeleton.
A human skeleton consist of
o
o
o
A vertebral column- support the skull
Twelve pairs of rib- attached upper part of vertebral column
Limbs are attached by means of girdles;
- The hip (pelvic girdle) is joined rigidly to the lower end of vertebral column.
- The shoulder (pectoral girdle) is not rigidly fixed to the vertebral column but held in placed by
muscles- consists of pair of collar bones and shoulder blade
Function of the skeleton
o
Support - refers to the skeleton and its role in holding up the body structure and giving its shape.
o
Movement - refers to the changing position of one part of the body in relation to another part.
o
Locomotion - refers to the movement of entire body from one place to another.
o
Protection - the brain is protect from injury by being enclosed in the skull.
- the heart, lungs and the liver are protected by the rib cage.
o
Storage - both calcium and phosphate are stored in the bone.
o
Production of blood cells - The marrow inside some of the bones make blood cells.
Eg; vertebrae, ribs, breast bone and the heads of the ling bone, produce both red and white blood
cells.
12.1 BONES
(a)
identify and describe, from diagrams, photographs and real specimens, the main bones of the
forelimb (humerus, radius, ulna and scapula) of a mammal.
Bone is very hard and very strong, and it is made up of hard tissues that is formed by living cells, strong fibres
made from protein called collagen and crystals of calcium, phosphate which gives bone its hardness. Bone is
penetrated by blood vessels which keep the cell alive, allow growth and for repair.
Structure of the human arm
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12.2 JOINTS
(b)
describe the type of movement permitted by the ball and socket joint and the hinge joint of the
forelimb
Movement is possible because of joints. Joint is a part of skeleton where two bones are meet.
Types of joints
o
Ball and socket joint
Hip and shoulder which allows free movement in many planes (forwards, backwards and sideways).
o
Hinge joint
At the elbow and knee, which allows movement in one plane or one direction.
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12.3 ANTAGONISTIC MUSCLES
(c)
describe the action of the antagonistic muscles at the hinge joint.
How Muscle Move bones at a Joint
Muscles move in the following way:
o
They can pull but not push.
o
They pull only when they contract.
o
When they contract, they decrease in length.
o
When returning to their original, they relax.
o
They are attached to the bones by TENDONS which do not stretch. They are arranged in
ANTAGONISTIC PAIRS, and only apply their force other side of the bone they are required to move.
o
One muscle of the pair (the FLEXOR) contracts to bend the limb at the joint. As it does so , the other
muscle in the pair (the EXTENSOR) relaxex.
o
The extensor contracts to straight the limb at the joint, and as it does so, the flexor relaxes.
When stimulated, muscles contract get shorter). The biceps and triceps are antagonistic muscles - they have
opposite effects when they contract.
The biceps is attached to the scapula (shoulder blade) and the radius. Contraction of the biceps pulls on the
radius, moving the lower arm toward the scapula. This results in the arm bending (flexing) at the below - the
arm is raised.
The triceps is attached to the scapula, humerus and ulna.
Contractions of the triceps pulls on the ulna, straightening (extending) the arm. In doing so, the triceps pulls
the biceps back to its original lengths.
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13.1 ANTIBIOTICS
(a)
13. THE USE AND ABUSE OF DRUGS
define a drug as any externally administered substance that modifies or affects chemical
reactions in the body
describe the medicinal use of antibiotics for the treatment of bacterial infection
(b)
A drug is an externally-administered substance which modifies or effects chemical reactions in the body.
Drug used in medical care, or to relieve mild pain, are very helpful to us.
Drug may be used for beneficial effects:
o
o
o
For pain relief (aspirin, paracetamol and morphine).
For treatment of disease.
Drug also used for their mood influencing effect. This can be useful for treating patients with
emotional disorders such as depression.
However, some people misuse drugs, so that they cause harm to themselves and to others around them.
Antibiotics kill bacteria in the body
Antibiotics are substances that kill bacteria or prevent their growth, but do not harm other living cells. Most
of them are made by fungi. It is thought that the fungi make antibiotics to kill bacteria living near them –
bacteria and fungi are both decomposers, so they might compete for food. The first antibiotic to be
discovered was penicillin. It is made by the fungus Penicillium.
Since the discovery of penicillin in 1928, many more antibiotics have been developed and used to treat
bacterial infections. Some bacteria have mutated and become resistant to antibiotics, but new drugs are
constantly being developed and tested.
ADVANTAGES OF USING ANTIBIOTIC
Useful in the treatment of infectious disease caused by bacteria. Antibiotic inhabits or kill bacteria that make
it past our immune systems and starts reproducing inside our bodies. Antibiotics act only on the bacteria and
have little or no effect on the good cells or organism taking the drug.
DANGERS OF USING ANTIBIOTICS TO TREAT INFECTIONS
If the course of treatment is incomplete, some bacteria will continue to survive and develop to become more
resistant to the antibiotic. This makes future treatment of bacteria using the same antibiotic ineffective.
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13.2 EFFECTS OF HEROIN
(c)
describe the effects of the abuse of heroin: a powerful depressant, problems of addiction,
severe withdrawal symptoms and associated problems such as crime and infection, e.g. AIDS
Heroin is a powerful depressant that has a sedative effect. It removes
feeling of anxiety, and creates a sense of extreme well-being. Heroin is a
drug to which the body shows tolerance. This means that progressively
increased dosages are needed to maintain the feelings
of well-being.
The person using the drug may end up in a state of dependence, where
they crave the drug and cannot face life without it. If they cannot get
further supplies, they suffer severe withdrawal symptoms, like diarrhoea,
vomiting, muscular pain, shaking and hallucination.
These are signs that abuse of the drug has led to addiction. Addiction can
lead to the user into a life of crime to get money and /or regular
supplies of drug.
Heroin is a drug normally taken by injection into a vein. If several addicts
use the same unstrelised needles, they are at high risk of contracting
blood-borne diseases such as hepatitis and AIDS.
13.3 EFFECTS OF ALCOHOL
(d) describe the effects of excessive consumption of alcohol: reduced self-control, depressant, effect on
reaction times, damage to liver and social implications
Effects of excessive consumption of alcohol
o
o
o
o
o
o
o
o
o
Alcohol is a depressant, create a sense of wellbeing.
Larger amounts slow down the reaction times. (slows the transmission of electrical impulses in the brain)
Poor judgments may leads to criminal activity and sexual promiscuity.
Long-term excessive drinking can lead to addiction (alcoholism).
This can lead to financial difficulties and family problems.
As the liver removes alcohol from the blood, heavy drinking can lead to liver damage such as cirrhosis.
Drinking can cause brain damage, ulcers in the stomach and obesity.
Drinking during pregnancy can damage the fetus, increase the risk of miscarriage or premature birth,
and reduce the average birth weight.
When consumed in excessive quantities it leads to loss of self control.
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13.4 EFFECTS OF TOBACCO SMOKE
(e) describe the effects of tobacco smoke and its major toxic components (nicotine, tar and carbon
monoxide) on health: strong association with bronchitis, emphysema, lung cancer and heart disease,
and the association between smoking during pregnancy and reduced birth weight of the baby
(f) recognise the fact that many people regard smoking as no longer socially acceptable.
Tobacco smoke contains following harmful components;
NICOTINE
Is the drug of addiction present in cigarette smoke. This drug has the following effects:
o Is a poison increases the heart rate and blood pressure.
o Blood clotting, increase the risk of thrombosis this may lead to heart ‘attach’
o Heart beat faster
o Vein constrict
o Blood pressure increases
o Adrenal glands pump out adrenaline
o Metabolic rate increases
TAR
o
o
Forms a layer over the walls of the alveoli, restricting gaseous exchange.
Tar is a carcinogen and prolonged exposure to it may lead to lung cancer.
CARBON MONOXIDE
Carbon monoxide is taken up, permanently, by haemoglobin in preference to oxygen (forming
carboxyhaemoglobin). It greatly reduces the ability of the blood to carry oxygen.
IRRITANT CHEMICALS
o
o
o
Increase the production of mucus in the bronchi and bronchioles. These chemicals also destroy the
cilia lining in the trachea.
The build-up of mucus is relieved only by continual coughing. Persistent coughing may damage the
walls of the alveoli, allowing them to become over-stretched. This may lead to emphysema.
Irritant chemicals also cause inflammation of the bronchi and may increase the risk of secondary
bacterial infection of the bronchial walls.
PREGNANT WOMAN
o
o
Less oxygen reaches the baby as a result of the effect of carbon monoxide, and nicotine can pass
from mother’s blood to baby’s blood.
Babies born to mothers who smoke during pregnancy have been shown to be underweight, perhaps
less intelligent, and there is a great risk of miscarriage.
PASSIVE SMOKING
Evidence now exists that breathing the smoke from other people’s cigarettes can be harmful. Cigarette
smoke certainly an irritant to the eyes and leaves a lingering smell in clothes. Smoking is therefore
increasingly becoming a socially unacceptable habit.
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14. MICROORGANISMS AND BIOTECHNOLOGY
All organisms are collections of chemical molecules which, when working together, show what are known as
the ‘characteristics of life’. These are: respiration, reproduction, excretion, nutrition, sensitivity, growth,
movement and a cellular structure.
Nobody knows how many different kinds, or species, of living organisms there are on Earth. About 1.4 million
species have been described and named. But many biologist think this may be only about one-tenth of all the
species on Earth. We have almost certainly discovered most of the large land animals, but there are probably
many animals living in the deep oceans which have never been seen by humans. And biologists estimate that
there are millions of insects and smaller animals and plants that have not yet been discovered.
14.1 MICROORGANISMS
Microorganisms are organisms which are studied only with the aid of a microscope. Often, they are made up
of one cell only (i.e. they are unicellular).
(a) list the main characteristics of the following groups: viruses, bacteria and fungi
VIRUSES
Viruses are simple organism that biologists don’t regard them as truly living.
Viruses have the following characteristics
o
o
o
o
o
o
o
o
They are less than 300nm in size around 50 times smaller than a bacterium.
They can be seen only with an electron-microscope.
They contain nucleic acid.(DNA or RNA)
The nucleic acid is surrounded by a coat of protein (known as the capsid).
They do not have a cell wall and cell membrane.
They can reproduce only inside living (‘host’) cells.
They are parasites, and cause disease like influenza, measles and AIDS.
Viruses are not affected by antibiotics.
BACTERIA
Bacteria are the simplest form of truly living organisms.
Bacteria have the following characteristics
o
o
o
They have a size in the range of 0.5 – 5 µm.
They have a cell wall and cell membrane.
They don’t have true nucleus.
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o
o
o
o
o
o
They have single chromosomes consisting of circular DNA.
Some bacteria have filament, called flagella, which help in
moving bacteria.
Some bacteria need oxygen for their respiration and some
bacteria don’t need oxygen for respiration.
They may be PARASITES or they may be
SAPROTROPHS feeding on dead and decayed organic
matter.
Some may be involved in NITROGEN FIXATION.
They are killed by antibiotics.
FUNGI
Fungi are usually much larger organisms, visible to the naked eye.
Fungi have the following characteristics
o
o
o
o
o
o
They have no chlorophyll, and thus have heterotrophic nutrition; digesting large molecule with
enzymes and absorbing the soluble products. They are parasites or saprotrophs.
They have a cell wall made up of chitin.
They reproduce by producing spores.
They are usually made of large number of tubular threads (hyphae) intertwined to forma mycelium.
Hyphae are not divided into individual cells. The lining of cytoplasm has many nuclei and the central
space in the hyphae is a vacuole full of (vacuolar) sap.
If they store carbohydrate, they store glycogen.
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(b) outline the role of microorganisms in decomposition
THE ROLE OF MICRO-ORGANISMS IN DECOMPOSITION
The micro-organisms like bacteria and fungi plays an important role in decomposing the dead materials. They
do external digestion by releasing the enzyme on to the dead organic matter. These enzymes digest the
carbohydrate, protein, and fats present in the dead materials and changed into glucose, amino acid and fatty
acids which are then absorbed by the micro-organisms.
Some of these end-products are absorbed by the microorganisms for use in their own metabolism. For
example;
Amino acids for building up proteins during growth
Sugars for energy release during respiration
Fats for energy storage.
Gradually, the dead matter is broken down, releasing its mineral ions which are returned to the soil for recycling
as they are taken up for use by plant.
14.2 FOOD BIOTECHNOLOGY
(c) explain the role of yeast in the production of bread and alcohol
(d) outline the role of bacteria in yoghurt and cheese production
BREAD PRODUCTION
Flour and water are used to make a dough, then yeast and a little sugar are added. Yeast start to respire
anaerobically and release alcohol and CO2. The mixture is left in a warm place for around half an hour for
the dough to rise. The CO2 gas causes the dough to rise giving a little texture. The dough is than baked at
high temperature (180ºC) in an oven. The high temperature cooks the bread and also evaporates the alcohol
produce during fermentation.
* Although alcohol is produced by the anaerobic respiration of the yeast, it is the carbon dioxide which is
important.
ALCOHOL PRODUCTION
Yeast is a fungus that is added to a sugar solution to make alcohol. For example, to make wine, yeast is
added to fruit sugar from grapes; to make beer, it is added to maltose from barley. The yeast is allowed to
FERMENT the sugar at a controlled temperature in a vessel called a fermenter. The optimum temperature
for the growth of Yeast is around 20ºC. The yeast converts the sugar to alcohol by anaerobic respiration,
with CO2 evolve as a waste product. As the concentration of alcohol rises, it eventually kills the yeast, which
must then be filtered from the liquor to produce yeast free alcoholic drink.
YOGHURT PRODUCTION
Yoghurt is produce by using milk. The Milk is heated to 90ºC and cool down to about 40ºC. A culture of bacteria
(lactobacillus) is added and stirred gently. Then the milk is kept at normal temperature for about 24-36 hours.
During these time the bacteria converts milk sugar (lactose) into lactic acid by anaerobic respiration
(fermentation). The lactic acid curdles the milk to produce the characteristics texture and sharp flavor of
yoghurt.
Flavourings such as sweeteners or fruit can be added to the yoghurt. It is then packed into sterlised containers
ready for sale.
* Usually, the milk is sterilized first by heating to a high temperature, to kill any other bacteria that might already
be in the milk and might spoil the flavor of the yoghurt.
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CHEESE PRODUCTION
Milk is heated and kept warm at 40ºC and a culture of bacteria (streptococcus) is added. After four to five hours
an enzyme called rennin is added into the milk. The lactic acid which is produce by bacteria reduces the pH of
milk and increase the function of the enzyme rennin, and it makes the milk to curdle. The solid part (the curd)
is separated from the liquid (the way). The curd are pressed and moulded and left to mature, or ripen.
14.3 INDUSTRIAL BIOTECHNOLOGY
(e) describe the use of fermenters for large-scale production of antibiotics and single cell protein
(f) describe the role of the fungus Penicillium in the production of penicillin.
Industrial biotechnology is the use of microorganisms in industrial purposes, for example, in the manufacture
of antibiotics and single-cell protein. Large quantities of antibiotic and single-cell protein are required, so the
microorganisms involved are grown in a very large containers called fermenters. A maximum rate of growth of
the microorganism within the fermenter can be achieved by careful control of;
o
o
o
o
The micro-organisms are encouraged to grow and multiply by providing nutrients such as glucose, with
added salts and, possibly, vitamins.
Oxygen or air, is bubbled through the culture if the reaction is aerobic, or excluded if the process is
anaerobic.
An optimum pH and temperature are maintained for the species of microbe being cultured.
Fermenters must be kept sterile to prevent the growth of unwanted species of microorganism which
might contaminate the end-products.
LARGE SCALE PRODUCTION OF ANTI-BIOTIC PENICILLIN
o
o
o
o
o
o
o
o
o
o
For penicillin production the fermenter size is usually 100,000 to 150,000 liters.
The fermenter is filled with nutrient (culture medium), for the growth of fungus Peniciilium.
The main fundamental carbohydrate sources in a culture medium is lactose.
The other main nutrients include an organic nitrogen sources and other mineral salts.The pH is
maintained between 5 and 6 at 20° C in temperature.
Aeration is important for optimum growth of Peniciilium, air is blown in to the fermenter and the
medium is stirred constantly.
Relevant Peniciilium strains is added to culture medium. Medium conditions are maintained for rapid
growth of fungus.
There’s a little Peniciilium production at this stage. As they growth slows down, Peniciilium production
begins.
If anti-biotic production cannot be maintained effectively as the conditions of culture medium
becomes unstable for the growth of fungus, which affects the rate of penicillin synthesis.
At the correct time, the nutrients growth containing penciling is filtered off and penciling is extracted
by crystallization.
Sterilized conditions are essential throughout this process, otherwise micro-organisms contaminate
the culture medium and the whole process is disrupt.
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SINGLE-CELL PROTEIN
Bacteria and fungi contains cytoplasm and a major constituent of cytoplasm is protein. Therefore, large-scale
production of bacteria and fungi involves the large-scale production of protein. The micro-organism can be
grown in a fermenter harvested and used as a protein source known as SCP (single cell protein). If the microorganisms involved as fungi, then more accurately the protein is known as myco-protein.
The fungus is grown on waste from flour making in a large metal containers called fermenters. As the fungus
grows, it forms long threads called hyphae. There is no stirrer in the fermenter, because this would break and
tangle up the threads.
The hyphae are collected from the fermenter and pressed together to form fibrous substance that can be used
in making processed food or cut into blocks to be sold. It is very high in protein and very low in fat.
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15. RELATIONSHIPS OF ORGANISMS WITH ONE ANOTHER AND WITH THE ENVIRONMENT
ECOSYSTEM
An ecosystem is a group of living organisms and their environment. A pond for example, and all the things
that live n it is an ecosystem. There are probably many different species of living organism in the pond. There
may be fish, frogs, water beetles, snails and plants. All these different species of organisms make up the
pond community.
All individuals of one species of organism make up a population. For example all the individuals of one
species of fish. The pond is the habitat of all the organisms that live in it. A habitat is a place where an
organism lives. The pond community and the pond itself make up the pond ecosystem.
We can define an ecosystem as:
A unit containing all of the organisms and their environment, interacting together in a given area.
The pond ecosystem consists of all the animals and plants living in it, plus the pond water, the mud on the
bottom, the stones in the and the gases such as oxygen and carbon dioxide that are dissolved in the water.
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15.1 ENERGY FLOW
(a) state that the Sun is the principal source of energy input to biological systems;
(b) describe the non-cyclical nature of energy flow;
The Sun is the principal source of energy input to biological systems. The Earth receives 2 main types of
energy from the Sun: light (solar) and heat. Photosynthetic plants and some bacteria can trap light energy
and convert it into chemical energy.
Non-cyclical nature of energy flow
Heterotrophic organisms obtain their energy by eating plants or animals that have eaten plants. So all
organisms, directly or indirectly, get their energy from the Sun. a plant’s chemical energy is passed on to an
animal when the animal eats the plant. If that animal is eaten by another animal, the energy is passed again.
In this way, the sun’s energy enters and flows through biological ecosystems, and is gradually lost to the
environment as it passes from one organism to the next. unlike water and elements such as carbon and
nitrogen, energy does not return in a cycle. It is nerve recycled.
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15.2 FOOD CHAINS AND FOOD WEBS
(c) define the following terms and establish the relationship of each in food webs:
• producer – an organism that makes its own organic nutrients, usually using energy from
sunlight through photosynthesis;
• consumer – an organism that gets its energy by feeding on other organisms;
• herbivore – an animal that obtains its energy by eating plants;
• carnivore – an animal that obtains its energy by eating other animals;
• decomposer – an organism that obtains its energy from dead or waste organic matter;
• food chain – a chart showing the flow of energy (food) from one organism to the next,
beginning with the producer (e.g. mahogany tree → caterpillar → songbird → hawk);
(d) describe energy losses between trophic levels and infer the advantages of short food chains;
(e) describe and interpret pyramids of numbers and of biomass;
DEFINITION
A FOOD CHAIN is a sequence of organisms, starting with a photosynthesizing organism (usually a
green plant), through which energy is passed as one organism is eaten by the next in the sequence.
Food chain is a chart showing the flow of energy (food) from one organism to the next beginning with
a producer.
Examples:
mahogany tree ---> caterpillar ---> song bird ---> hawk
maize ---> locust ---> lizard ---> snake
 A food chain usually starts with a photosynthetic plant, which gains its energy from the Sun.
 The arrows used to link each organism to the next represent the direction of energy flow. They always
points towards the ‘eater’, and away from the plant.
 The feeding level is known as the trophic level.
 Plant are producers (they make/produce food for other organisms).
 Animals that eat plants are primary consumers (a consumer is an ‘eater’). They are also called
herbivores.
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DEFINITION
A FOOD WEB is made up of interlinked food chains involving organisms within the same ecosystem.
Food web is a network of interconnected food chains showing the energy flow through part of an ecosystem.
These are a more accurate way of showing feeding relationships than food chains, because most animals have
more than one food source. For example, in the food webs in figure below, the leopard feeds on baboons and
impala.
The leopard can be placed at 2 different trophic levels:
 Secondary consumer (feeding on imlala)
 Quaternary or fourth level consumer (feeding on baboons).
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Another example of food web.
Food webs are easily unbalanced, especially if one population of organisms in the web dies or disappears.
This may happen for a number of reasons, including:







over–predation or hunting
disease
pollution
Another example of food web.
use of pesticides
lack of food (or other resources)
emigration.
For example, in the food web here, if all the baboons were killed by hunters the leopard would have only
impala to eat. So the impala population would decrease. The scorpion population may increase because of
less predation by baboons, but if there are more scorpions they will eat more locusts, reducing the locust
population, and so on.
 producer – an organism that makes its own organic nutrients, usually using energy from sunlight
through photosynthesis. E.g. green algae.
 consumer – an organism that gets its energy by feeding on other organisms. E.g. mosquito larvae,
small fish, heron.
 herbivore (primary consumer) – an animal that obtains its energy by eating plants. E.g. mosquito
larvae.
 Secondary consumer – consumers which feed directly on the herbivore. E.g. small fish.
 Tertiary consumer – consumers which feed on secondary consumer. E.g. heron
 carnivore – an animal that obtains its energy by eating other animals. E.g. small fish, heron.
 decomposer – an organism that obtains its energy from dead or waste organic matter. E.g. bacteria,
fungi.
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Energy lost along a food chain
Energy is lost at each level in the food chain, as in the examples below.
 Energy lost through the process of respiration (as heat)
 Energy used up for movement (to search for food, find a mate, escape from predators…).
 Warm-blood animals (birds and mammals) maintain a standard blood temperature – they lose heat
to the environment.
 Warm-blood animals lose heat energy in faeces and urine.
 Some of the material in the organism being eaten is not used by the consumer, for example a locust
does not eat the roots of maize, and some of the parts eaten are not digestible.
Even plants do not make use of all the light energy available to them. This is because some light:




is reflected off shiny leaves
is the wrong wavelength for chlorophyll to trap
passes through the leaves without passing through any chloroplasts
does not fall on the leaves.
On average, about 90% of the energy is lost at each level in a food chain. This means that in long food
chains, very little of the energy entering the chain through the producer is available to the top carnivore. So
there tend to be small numbers of top carnivores. The food chain below shows how energy reduces through
the chain. It is based on maize obtaining 100 units of energy.
maize --->
locust --->
lizard
100 units
10 units
1 unit
--->
snake
0.1 unit
On shorter food chains, less energy is lost.
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Food pyramids of numbers, biomass and energy
A food pyramid shows the relative sizes of different components at the various trophic levels of a food chain.
There are three types of ecological pyramid we use: numbers, biomass and energy.
In a food pyramid, each trophic level in a food chain is represented by a horizontal bar, with the width of the
bar representing the number of organisms, the amount of biomass or the amount of energy available at
that level. The base of the pyramid represents the producer; the second level is the primary consumer; and so
on.
1. PYRAMIDS OF NUMBERS
A pyramid of numbers shows the relative number of organisms at each stage of a food chain.
There is a decrease in the number of individuals from the lower to the higher trophic levels. The number
pyramid varies from ecosystem to ecosystem. There are three of pyramid of numbers:
•
•
•
Upright pyramid of number
Partly upright pyramid of number and
Inverted pyramid of number.
Upright Pyramid of Number
In this type of pyramid number, there are numerous autotrophs which support lesser herbivores which in turn
support smaller number of carnivores and hence this pyramid is upright.
Example 1: clover → snail → thrush → hawk
Clover is a plant and it is the producer in this food chain. Its bar goes at the bottom of the pyramid:
A lot of clover is needed to support the snail population. A thrush eats lots of snails, and a hawk eats lots of
thrushes, so the population of hawks is very small.
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Partly Upright pyramid of Number
This could happen if the producer is a large plant such as a tree, or if one of the animals is very small.
Remember, though, that whatever the situation, the producer still goes at the bottom of the pyramid.
Here are two examples like this:
Example 2: Oak tree → Insects → Woodpecker
An oak tree is very large so many insects can feed on it.
Example 3: Grass → Rabbit → Flea
Fleas are very small and lots of them can feed on a rabbit.
Inverted Pyramid of Number
This type of ecological pyramid is seen in parasitic food chain where one primary producer supports
numerous parasites which support more hyperparasites.
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2. PYRAMIDS OF BIOMASS
Sometimes a pyramid of numbers is not the best way to represent a food chain. In this case a pyramid of
biomass (the dry mass of an organism) is a better diagram to use. It shows the total mass of organisms
at each stage of a food chain. The biomass here the net organisms collected from each feeding level and
are then dried and weighed.
This dry weight is the biomass and it represents the amount of energy available in the form of organic matter
of the organisms.
In general, all producers have a higher biomass than the primary consumer, so a pyramid will always be
produced.
The total energy (and biomass) present at a lower tier of the pyramid, must be greater than the higher tiers
in order to support the energy requirements of the subsequent organisms.
Pyramid of numbers and pyramid of biomass.
3. PYRAMIDS OF ENERGY
Pyramid of energy shows amount of energy trapped per unit time and area at each stage of a food chain.
This pyramid shows the flow of energy at different trophic levels. It depicts the energy is minimum as the
highest trophic level and is maximum at the lowest trophic level. At each trophic level, there is successive
loss of energy in the form of heat and respiration, etc.
A normal-shaped pyramid is always produced because there is a reduced amount of energy at each
successive level.
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15.3 CARBON CYCLE
(f) describe and state the importance of the carbon cycle;
Most of the chemicals that make up living tissue contain carbon. When organisms die the carbon is recycled
so that it can be used by future generations. Four main processes are involved: photosynthesis,
respiration, decomposition and combustion.
1. The grass and plant carry out photosynthesis. During photosynthesis, glucose and oxygen are produced
from carbon dioxide and water using light energy from the sun, which absorbed by chlorophyll by grass and
tree. Glucose is converted into carbohydrates for storage. Plant itself respire and release CO2 back to the
atmosphere.
2. Animals (cattle) feed on the grass (plant) passing the carbon compounds along the food chain. Most of
the carbon they consume is exhaled as CO2 formed during respiration. The animals and plants eventually die.
3. The dead organisms are eaten by decomposers and the carbon in their bodies is returned to the
atmosphere as CO2. The decomposition of excretory waste and faeces of the animal (cattle) by decomposers
(bacteria and fungi) produces CO2 and nutrients for healthy growth of the grass.
4. In some conditions decomposition is blocked. The plant and animal material may then be available
as fossil fuel in the future for combustion. Combustion of fossil fuels increases the CO2 level in the
atmosphere for photosynthesis.
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15.4 NITROGEN CYCLE
(g) describe the nitrogen cycle in making available nitrogen for plant and animal protein, including the
role of bacteria in nitrogen fixation, decomposition and nitrification (details of denitrification and the
names of individual bacteria are not required);
Nitrogen is essential for the formation of amino acids to make proteins. The nitrogen cycle describes the
ways in which nitrogen is recycled. The element nitrogen is a very unreactive gas. Plants are not able to
change it into nitrogen compounds, but it is needed to form proteins.
There are three ways that nitrogen gets “fixed”. Nitrogen compounds become available for plants in
the soil in a number of ways, including:
(a) Atmospheric Fixation (lightning)
The enormous energy of lightning breaks nitrogen molecules apart and enables the nitrogen atoms to
combine with oxygen forming nitrogen oxides (N2O). Nitrogen oxides dissolve in rain, forming nitrates.
Nitrates (NO3) are carried to the ground with the rain.
(b) Industrial Fixation
Under great pressure, at a temperature of 600 degrees Celsius, and with the use of a catalyst, atmospheric
nitrogen (N2) and hydrogen are combined to form ammonia (NH3). Ammonia can be used to make fertilizer
such as ammonium nitrate.
(c) Biological Fixation (nitrogen fixing bacteria)
Live in the soil, or in little swellings on the roots of some kinds of plants. In particularly, leguminous plants
such as peas and beans contain these bacteria. Nitrogen fixixng bacteria change nitrogen from the air
spaces in the soil into ammonia.
Decomposition includes the conversion by bacteria of proteins to amino acids, and the conversion of
amino acids and urea to ammonium ions.
Nitrifying bacteria in the ground first combine ammonia with oxygen to form nitrites. Then another group
of nitrifying bacteria convert nitrites to nitrates which green plants can absorb and use.
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Plants absorb nitrates into their roots by active uptake. The nitrates are combined with glucose (from
photosynthesis) to form protein. Proteins are passed through the food chain as animals eat the plants.
When animals digest proteins the amino acids released can be reorganized to form different proteins.
Some soil bacteria - denitrifying bacteria- break down nitrogen compounds and release nitrogen back into
the atmosphere. This is a destructive process, commonly occurring in waterlogged soil. Farmers try to
keep soil well drained to prevent this happening – a shortage of nitrates in the soil stunts the growth of crop
plants.
Nitrates and other ammonium compounds are very soluble, so they are easy leaches out of the soil and
can cause pollution.
Farmer can increase the fertility (nitrogen compound concentration) of their soil by:
 adding artificial fertilisers
 adding manure or compost
 growing leguminous plants, then digging the roots (with their nodules) into the soil.
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15.5 PARASITISM
(h) understand the role of the mosquito as a vector of disease;
(i) describe the malaria pathogen as an example of a parasite and describe the transmission and control
of the malarial pathogen (details of the life cycle of the pathogen are not required);bacteria in nitrogen
fixation, decomposition and nitrification (details of denitrification and the names of individual bacteria are
not required);
DEFINITION
A parasite can be defined as an organism which obtains its food from another, usually larger living
organism (‘host’); the host always suffering in the relationship.
Pathogens are therefore parasites. One such pathogen is the unicellular organism plasmodium which
causes malaria.
MALARIA
Malaria is a disease caused by a single-celled microorganism called plasmodium which lives in red blood
cells. It is carried from person to person by the female Anopheles mosquito. The mosquito is described as
the vector, or carrier, of the microorganism.
A parasite is an organism living in or on another organism (the host). The parasite derives food from its
host.
A vector is an organism that acts as an intermediary host for a parasite. Most importantly the vector transfers
the parasite to the next host. Good examples of vectors are the mosquito in transmitting malaria.
CAUSES OF MALARIA
Malaria is caused by the Plasmodium parasite. The parasite can be spread to humans through the bites of
infected mosquitoes. There are many different types of plasmodium parasite, but only five types cause
malaria in humans.
THESE ARE;
 Plasmodium falciparum
 Plasmodium vivax
 Plasmodium ovale
 Plasmodium malariae
 Plasmodium knowlesi
HOW MALARIA IS SPREAD
The plasmodium parasite is spread by female Anopheles mosquitoes, which are known as "night-biting"
mosquitoes because they most commonly bite between dusk and dawn. Usually at night, while the host is
asleep, she injects her saliva into a (healthy) person before she starts to suck the blood which she needs for
her developing eggs. The saliva contains a chemical to stop the blood from clotting. If a mosquito bites a
person already infected with malaria, it can also become infected and spread the parasite on to other people.
Once you're bitten, the parasite enters the bloodstream and travels to the liver. The infection develops in the
liver before re-entering the bloodstream and invading the red blood cells.
Malaria can also be spread through blood transfusions and the sharing of needles, but this is very rare.
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CONTROL OF MALARIA
Malaria can be controlled in three ways:
 By controlling the mosquito vector
 By avoiding mosquito bites
 By treating the parasite in the blood
By controlling the mosquito vector
•
Covert he water tanks with netting to stop mosquitoes laying their eggs in the water
•
Drain swamps where mosquitoes lay their eggs
•
Introduce fish such as Tilapia into the swamps to feed on mosquito larvae
•
Cover the surface of the water with light oil
•
Use insecticides or mosquito coils to kill or repel adult mosquitoes inside buildings
Avoiding mosquito bites
•
Place nets over doors and windows
•
Wear clothes which cover wrists and ankles, especially in the evening
•
Use insect repellent sprays
•
Sleep under mosquito nets
Protection against the parasite
•
Take drugs regularly to kill the parasite if it enters the bloodstream
•
Treat patients suffering from malaria with a higher dosage of anti-malarial drug, and isolate them to
prevent spreading of the disease
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15.6 EFFECTS OF HUMANS ON THE ECOSYSTEM
(j) describe the effects of humans on the ecosystem with emphasis on examples of international
importance (tropical rain forests, oceans and important rivers);
(k) describe the consequences of deforestation in terms of its effects on soil stability, climate and local
human populations;
The human animal is as much part of the ecosystem in which it lives as any other organism in that ecosystem.
But humans can be far more destructive than any other organism.
Burning fossil fuels increased the concentration of carbon dioxide in the atmosphere, leading to global
warming. Cutting down forests reduces the amount of photosynthesis and therefore the rate at which carbon
dioxide is removed from the atmosphere. Destroying tropical rainforests, where huge number of different
species of plants and animals lives, is causing extinction of many species. A spill from a giant oil tanker can
spread over a large area of the ocean, and kills seabirds and other life at sea and also along the shore.
Building dams to provide water for expanding human populations often ruins river ecosystems and makes it
impossible for species to live there.
DEFORESTATION
Deforestation, clearance or clearing is the removal of a forest or stand of trees where the land is thereafter
converted to a non-forest use.
Natural woodland has been (and is being) destroyed for the following reasons;
 To harvest timber for building houses and making furniture
 To make way for roads and industrial development
 To create agricultural land for the growth of crops and the rearing of livestock
 trees are cut down to be used or sold as fuel (sometimes in the form of charcoal)
 used in war to deprive the enemy of cover for its forces and also vital resources.
 deforestation may include corruption of government institutions
THE DANGER OF DEFORESTATION
A
the loss of soil stability
B
the effect on climate
C
the effect on local human population
A
The loss of soil stability
(i)
the loss of humus in the soil.
Leaves fall to the ground where they decompose, forming humus in the soil. Humus provides a steady
supply of ions. It acts as a sponge, soaking up and holding water in the soil, and helps to bind the soil
together, preventing soil erosion.
(ii)
the loss of protection from excessive sun, wind and rain.
Trees form a canopy which keeps the powerful sun’s rays off more delicate organisms. The canopy
also protects the soil from the force of tropical rainfall, and protects the soil, smaller plants and animals
from the full force of high winds. Tree roots also help to bind the soil. Removal of trees means there
are no roots to hold soil, which can result in soil erosion and leaching of minerals and carried into
rivers may lead to flooding further downstream as it is deposited on the bed of the river as silt.
Leaching of nutrients into lakes and rivers can lead to eutrophication. Desertification can eventually
occur.
B
the effect on climate
Trees supply enormous quantities of water to the atmosphere through transpiration. Transpiration
leads to the formation of clouds. Clouds are carried by the prevailing winds and eventually produce
rain, usually in an area some distance away from where the vapour was released. Deforestation can
there for lead to distant regions receiving reduced rainfall. In the most extreme cases, relatively fertile
areas can become deserts.
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On a global scale, deforestation can reduce the amount of carbon dioxide taken in for photosynthesis.
The levels of carbon dioxide in the atmosphere rise, acting as a thermal blanket’ over the planet,
preventing the natural escape of heat from our atmosphere. This is known as the greenhouse effect.
It is believed to lead to global warming, which may affect the distribution of plants and animals (and
eventually melt the ice caps).
C
the effect on local human population
Deforestation is usually motivated by financial gain. Those who benefit may live outside the country
where the deforestation is occurring. Many local residents lose their homes and see their culture
destroyed along with the trees. Many People find it difficult to adapt to lifestyles which are geared to
commercial success. Reduction of habitats or food sources for animals, which can result in their
extinction.
15.7 POLLUTION
(l) evaluate the effects of:
water pollution by sewage, by inorganic waste and by nitrogen-containing fertilisers;
air pollution by greenhouse gases (carbon dioxide and methane), contributing to global warming;
air pollution by acidic gases (sulfur dioxide and oxides of nitrogen), contributing to acid rain;
pollution due to insecticides;
POLLUTION
Apart from the effects of deforestation, humans are also responsible for polluting the environment in a number
of ways.
THE POLLUTION OF WATER BY SEWAGE
THE POLLUTION OF WATER BY INORGANIC WASTE
AIR POLLUTION
POLLUTION DUE TO INSECTICIDE
A
THE POLLUTION OF WATER BY SEWAGE
Large human settlements create a considerable amount of sewage. Tipping sewage directly into streams and
rivers can have these harmful effects:
 Sewage contains pathogenic organisms. If the water is used for human consumption, then disease,
such as cholera spread.
 Very high level of sewage contains large numbers of bacteria which use up the oxygen in the water
for their own respiration. This does not leave enough oxygen for any their water life, so many
organisms die.
 Smaller quantities of sewage also release ions, which encourage rapid growth of water plants
(eutrophication).
A
THE POLLUTION OF WATER BY INORGANIC WASTE
 House hold detergents, discharged into rivers along with sewage contain phosphate. This encourage
growth of algae, leading to possible eutrophication.
 Industrial wastes such as those which contain mercury and copper are highly toxic to all organisms.
It is expensive to remove these wastes in a completely safe way, so they, too, are often discharged
into rivers.
 Polluted rivers discharge into seas. Polluted seas lead to contamination of producers in the sea’s food
chain. One small fish eats many smaller contaminated food organisms. One large fish eats many
smaller fish. In this way, the amount of poison gradually increases in the organisms along the food
chain, if human eat contaminated fish, they may consume harmful levels of poison.
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AIR POLLUTION BY SULFUR DIOXIDE
Sulfur dioxide is a gas which is released whenever fossil fuels are burnt. In the air, sulfur dioxide dissolves in
rain and falls to earth as a dilute solution of sulfuric acid (ACID RAIN), and has these effects:
 Kills leaves of some species of plant
 It makes the water of lakes acidic. This acidic water dissolves toxic chemicals present in the mud of
the lake which are insoluble in neutral or alkaline solutions. Example. Aluminium salts may kills fish.
Sulfur dioxide is a gas linked with bronchitis and heart disease in human.
Acid rain can damage buildings, especially those made of limestone. This is calcium carbonate, and it is
dissolved by acid rain, causing the stone to crumble away.
POLLUTION DUE TO INSECTICIDES
 Useful insects, such as those re needed for pollination, may be killed as well
 If the livers of animals are unable to break down the insecticide, it may be passed from animal to
animal along the food chains.
 Agricultural pesticides can be washed into rivers, entering the food chains in the water as well as on
land.
Water pollution by nitrogen-containing fertilsers
There is a danger that the readily soluble nitrates will be washed into streams, rivers and lakes. These causes:
 Abundant growth of water plants (eutrophication)
 When the plants eventually die, they are decayed by bacteria which used up the oxygen in the water
resulting in the death of the water animals such as fish.
 If this water is used as drinking water by humans, the high levels of nitrate may lead to cancer of the
stomach
Greenhouse gasses
 The burning of fossil fuels releases CO2 into the air, and the way in which this can contribute to global
warming.
 Methane is another greenhouse gas. This gas produced by bacteria breaking down nutrients an
anaerobic conditions
Nitrogen oxides
The major cause of nitrogen oxides is exhaust fumes from vehicles such as cars and trucks. Nitrogen gas
also cause acid rain.
15.8 CONSERVATION
(m) discuss reasons for conservation of species with reference to maintenance of biodiversity,
management of fisheries and management of timber production;
(n) discuss reasons for recycling materials, with reference to named examples.
CONSERVING NATURAL RESOURCES
Human take and use a great many materials from the Earth. These are called RESOURCES. Fossil fuels
were produced millions of years ago. As we use them up, they are not being renewed they are NONRENEWABLE resources. Now several countries are turning to using more RENEWABLE energy sources,
such as the wind and solar power.
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THE THREAT OF EXTINCTION
The removal organisms from an environment at a faster rate than the organism can reproduce itself leads
to EXTINCTION of the species.
 Widespread deforestation can lead to extinction of plant species
- one hectare of tropical rainforest may contain 200 different species of trees
 Uncontrolled fishing can lead to the extinction of species of fish
- according to the international union for conservation of nature's (IUCN) red list of
endangered species, 1,414 species of fish
 Destruction of habitats lead to extinction of animal species
- Hawaii has suffered great loss of bird species
MAINTAINING SUPPLY OF COMMODITIES FROM TREES
Most trees that supply commodities grow very slowly: The product they supply may not be ready for harvest
until many years after planting.
VALUABLE PRODUCTS FROM PLANT
 Insecticide pyrethrum extract from daisy
 Quinine for treatment of malaria
 Rosy periwinkle, was recently discovered to contain a chemical that can help to cure some form of
cancer
 Aspirin for pain relief and treatment of circulatory disorders
 Many other drugs were first obtained from plants
 Deforestation could rob humans of the plant which might bring a cure for disease such as AIDS
 Timber, rubber and oils are commodities, or useful products, supplied by trees.
MAINTAINING FISHING SUPPLY
The oceans supply many communities with a large part of their food requirements. Overfishing can reduce
fish populations to a point where they are not able to maintain their numbers.
CONSERVATION OF OTHER SPECIES
 To maintain the wide variety (biodiversity) of living species on the planet, it is important to identify
threatened species so that their needs can be addressed before too late.
 This work is carried out by organisations such as the Worldwide Fund for Nature (WWF) and
convention on International Trade in Endangered Species(CITES).
 Countries throughout the world must also support these organisations with legislation.
RECYCLING
 Aluminium cans, tin cans and many car parts can be made of recycled metal.
 Reduces the need for mining activity
 Reduces the burning of fossil fuels
 Paper can be recycled. [Newspapers, magazines and cardboard etc.]
 Is suitable for making paper towels, paper bags, writing paper and packaging.
 So fewer trees need to cut
 Conserving water is to recycle it.
 Can be recycled to provide an effective fertilizer.
 Water can be purified even to the extent that it can be returned to drinking water
supplies.
 Bottles are made of recycled glass.
 Liter is also reduced by recycling, making our environment a more pleasant place in which to live.
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16. DEVELOPMENT OF ORGANISMS AND CONTINUITY OF LIFE
Reproduction is a characteristic of all living things. Because nothing lives forever, reproduction is necessary to
ensure that the species continues to survive.
There are two basic kinds of reproduction. Many plants and simple animals can reproduce asexually. Flowering
plants, that and most animals can reproduce sexually. There are many organisms, such as a flowering plants,
that can reproduce in both of these ways. Each method has its own advantages and disadvantages.
16.1 ASEXUAL REPRODUCTION
(b) define asexual reproduction as the process resulting in the production of genetically identical
offspring fromone parent and describe one named, commercially important application of asexual
reproduction in plants
‘Asexual’ means ‘not sexual’. In asexual reproduction, a single organism simply grows a new organism from
itself. Only one parent involved. The new organism is genetically identical to its parent. We can aseual
reproduction as:
Asexual reproduction is the production of genetically identical offspring from one parent
Example are:
Bacteria
Bacteria reproduce asexually by binary fission. Inside an individual
bacterium, the DNA replictates. Then the cell divides into two, with each
daughter cell containing a copy of the parental DNA. Once the daughter
cells have grown, they can also reproduce.
Fungi
Fungi can reproduce asexually by producing spores, which may be
formed inside a structure called a sporangium. When ripe, the
sporangium bursts open allowing the spores to be dispersed. In suitable
conditions the spores germinate and grow to form new individuals.
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Potatoes
Potatoes are stem tubers. The parent plant
photosynthesises and stores the food produced in
underground stems, which swell to form tubers. Each
tuber contains stored starch, and there are buds in
depressions in the surface known as eyes. In suitable
conditions the buds use the stored food to form shoots,
form which roots also develop. Each tuber can form a new
plant.
Tissue culture
A technique for keeping alive cells or tissues of living organisms after their removal from an organism. Plant
reproduced in this way include food plants and horticultural plants.
Method:
Some actively dividing cell are taken from the
parent plant. Placed on a sterilised culture
medium in many sterlilised dishes. The culture
medium is a jelly-like substance called agar. Agar
contains plant growing hormones an ions
necessary for healthy growth. The dishes are kept
at a suitable temperature, and are covered to
prevent the cells drying out.
Result:
The cell continue to divide, then some of them
become modified to produce small roots and
some become modified to produce small shoots
bearing a lateral buds
Advantages and disadvantages
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CELL DIVISION
(a) define mitosis as cell division giving rise to genetically identical cells in which the chromosome
number is maintained and state the role of mitosis in growth, repair of damaged tissues, replacement of
worn out cells and asexual reproduction
(c) define meiosis as a reduction division in which the chromosome number is halved from diploid to
haploid
(d) state that gametes are the result of meiosis (reduction division)
Mitosis
The kind of cell division that happens in asexual reproduction is mitosis.
Inside the nucleus of every cell, there are threads of DNA called
chromosomes. Each chromosome is made up of many genes.
Before a cell divides by mitosis, each of its chromosomes is copied. When
the cell divides, the chromosomes are shared equally between the two new
cells. So each cell gets a complete set of chromosomes exactly like its parent.
If the original cell had46 chromosomes, then the new ones also have 46. The
new cells are genetically identical to the parent cell and to each other. We
can define mitosis as:
Mitosis as cell division giving rise to genetically identical cells in which
the chromosome number is maintained by the exact duplication of
chromosomes.
Meiosis
A different kind of cell division is needed to produce gametes. It is called
meiosis. Before meiosis starts, the chromosomes are copied, exactly as
happened before mitosis. However, in meiosis something different happens
right at the start. The chromosomes then pair up with their partners.
Meiosis is called as a reduction cell division. It takes place in sex organs. As
a result of meiosis cell division 4 daughter cells are formed. All the daughter
cells have half the number of chromosomes from that of the parent cell. We
can define meiosis as:
Meiosis as a reduction division in which the chromosome number is
halved from diploid to haploid
Difference between Mitosis and Meiosis
mitosis
meiosis
Mitosis cell division takes place in the body cell
Meiosis cell division takes place in the reproductive
organs
As a result of mitosis 2 daughter cells are
formed
As a result of meiosis 4 daughter cells are formed
In mitosis, daughter cells will have the same
number of
In meiosis, daughter cells will have half the number
of chromosomes
Mitosis cell division helps body to grow
Meiosis cell division helps the body to reproduce
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SEXUAL REPRODUCTION
(e) define sexual reproduction as the process involving the fusion of haploid nuclei to form a diploid
zygote and the production of genetically dissimilar offspring
Sexual reproduction is more complicated than asexual reproduction. In sexual reproduction, an organism
produces sex cells called gametes.
In humans, the female gamete are ova and the male gamete are sperms.
In flowers, the female gametes are ovules and the male gametes are the nuclei inside the pollen grains.
The nuclei of two different gametes fuse together to form a new cell called zygote. This process is called
fertilization. The zygote then divides repeatedly by mitosis to form a new organism. Gametes cells contain
half number of chromosomes and are said to be haploid. The zygote contains full set of chromosomes and
are said to be diploid.
Gametes from different parents do not always contain the same genes. They are often genetically different
from each other, and from the cells in parents. So, the offspring produced by sexual reproduction are usually
genetically different from each other and from their parents. We can define sexual reproduction as:
Sexual reproduction as the process involving the fusion of haploid nuclei to form a diploid zygote
and the production of genetically dissimilar offspring.
Advantages and disadvantages
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16.2 SEXUAL REPRODUCTION IN PLANTS
STRUCTURE AND FUNCTIONS OF A FLOWER
(f) identify and draw, using a hand lens if necessary, the sepals, petals, stamens and carpels of one,
locally available, named, insect-pollinated, dicotyledonous flower, and examine the pollen grains under
a light microscope
(g) state the functions of the sepals, petals, anthers and carpels
(h) use a hands lens to identify and describe the anthers and stigmas of one, locally available, named,
wind-pollinated flower, and examine the pollen grains under a light microscope
Flowers are the most advanced and complex reproductive structures containing the reproductive organs in
the plant kingdom. Their function is sexual reproduction, as a result of which they form fruits and seeds that
give rise to the next generation. There is a great variety of shape and structure among the flowers, but all of
them have certain features in common.
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POLLINATION
(i) outline the process of pollination and distinguish between self-pollination and cross-pollination
The transfer of pollen grains from the anthers to the stigma of a flower is called pollination. The anthers when
mature split exposing the microscopic pollen grains. The pollen grains are then carried away on the bodies of
the insect or simply blown by wind and land on the stigma of a flower.
Self-pollination and cross-pollination
Self-pollination - this is the transfer of pollen grains from the anthers to the stigma of the same flower or to
another flower of the same plant.




↑ chance of successful pollination à smaller numbers of pollen
↑ chance of fertilisation and seed formation
↓variation in the offspring.
↓ ability to adapt to environmental change.
Cross-pollination - this is the transfer of pollen grains from the anther of one flower to the stigma in a
different flower of another plant of the same species.
o
o
o
o
↓ chance of successful pollination à large amounts of pollen
↓ chance of fertilisation
↑ variation
↑ ability to adapt to environmental change.
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(j) compare, using fresh specimens, an insect-pollinated and a wind-pollinated flower
AGENTS OF POLLINATION
The transfer of pollen grains is achieved in various ways. Insects and wind are the two main agents of
pollination.
INSECT POLLINATION
Nectar is produced by the nectary at the base of the filaments. When an insect visits a matured flower to collect
nectar, pollen grains present in the anthers stick to the tube like mouth parts of a butterfly or the hairy body of
an insect such as a bee. When this insect visits another flower to collect nectar, and it pushes its way into the
flower to reach the nectarines, its body brushes onto the sticky surface of the stigma which picks up the pollen
grains from its body. Pollination is complete when the pollen grain has landed on a stigma.
WIND POLLINATION
The pollination which takes place with the help of the wind is called as wind pollination. Wind pollinated flowers
do not have large scented petals, or nectar, because they do not need to attract the insects. They have
feathery stigmas which stick out from the flower to trap the pollen grains floating in the air. The anthers also
hang outside the flower, so that the pollen grains are easily carried away by the wind to distant places.
Adaptations of wind pollinating flowers:
o
o
o
Anthers hang outside the flower with long filaments.
Production of Large amount of light, small pollen grains
Spreading feathery stigmas to catch air-borne pollen grains.
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FEATURES OF INSECT AND WIND POLLINATED FLOWERS
Structure
Insect pollinated flowers
Wind pollinated flowers
Size of the flower
Insect pollinated flowers are
usually large
Stamens
Have short filament
Anthers tend to be small and
inside the flowers
They are brightly colored and
scented
Small inconspicuous flowers. Have
flower stalks well above the leaves to
increase flower exposure to air current.
Have large anthers which often have
long filaments so that they hang well
outside the flowers.
They have green leaf-like bracts (leaf-like
parts) rather than petals. They do not
have scent or sepals.
Feathery and a large surface area is
exposed to the outside of the flower to
collect pollen grains.
Smooth, light and small and are
produced in large quantities to
compensate the losses
Nectary absent
Petals (corolla)
Stigma
Are often short and enclosed
within the flower
Pollen grains
Sticky, rough and relatively large
Nectar
Nectaries are present at the base
of the stamen
(k) describe the growth of the pollen tube and its entry into the ovule followed by fertilisation (production
of endosperm and details of development are not required)
(l) investigate and describe the structure of a non-endospermic seed in terms of the embryo (radicle,
plumule and cotyledons) and testa, protected by the pericarp (fruit wall)
FERTILISATION
Pollination is completed when pollen from an anther lands on a stigma. If the flower is produce seed, pollination
has to be followed by a process called fertilisation. Fertilisation is the fusion of male and female gamete. The
resulting single is formed called zygote. In flowering plant male gamete is in the pollen grain and the female
gamete is in the ovule.
To meet the male and female nuclei the following process follows;
o
o
o
o
o
o
o
Once the pollen grains reach the stigma, the stigma starts to produces a sugary and sticky fluid. The
pollen grains absorb this fluid, produced by the stigma and
germinated.
Germination of the pollen grain involves the growth of a small
microscopic pollen tube
The tip of the pollen tube release enzymes which break down the
cells of the stigma and style.
This tube grows down the style and into the ovary. The growth of
the pollen tube is directed towards the ovules by chemicals
produced by the egg cell.
When the pollen tube arises at the ovary it enters the ovule through
a small hole called the micropyle. Inside the ovule is the female
gamete within which is the female nucleus. The male nucleus from
the pollen grain travels down the pollen tube to the ovule.
Once the pollen tube is inside the ovule, the tip of the tube is bursts
releasing the male nucleus into the ovule to fuse with the female
egg cell nucleus. Hence, fertilisation occurs
Each ovule in an ovary needs to be fertilised by a separated pollen grains.
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FRUIT & SEED FORMATION
Each ovule that has been fertilized begins to develop into a seed. Inside the seed, the zygote forms an embryo
plant. This contains an embryo shoot called plumule and an embryo root called the radicle. Food is brought to
the developing seed from the rest of the plant and is stored inside it, often a structure called cotyledons. The
outer wall of the ovule become thicker and harder forming the seed coat or testa of the seed. The tiny hole in
this outside wall, through which the pollen tube entered, is still there; it is called the micropyle
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Development of various parts of flower after fertilization
Parts of flower
After fertilisations
Function
Sepals, petals,
stamens, stigma
and style
Shrivels and falls off
Certain parts may persist or become
modified to help in fruit and seed formation
Ovary
Becomes the fruit
Ovary wall
Becomes the fruit wall (pericarp)
Ovules
Becomes the seed
Integuments
(ovule wall)
zygote
Becomes the seed coat (testa)
- As a source food for animal and man
- Protect and disperse the seed to colonise
new regions
Protects the seeds. It may be hard shell
(nuts), a fleshy edible layer (plum) or a
tough fibrous layer (coconut)
- For dispersal to new habitats
- A source of food for animals and man
- A means of survival in adverse conditions,
germinates in favorable ones into new
plants
Protective coat around the seed to protect it
from adverse conditions
Germinates to form the young shoot and
the young root
Endosperm
nucleus
Receptacle
Forms the embryo consisting of the
plumule, radicle and cotyledons in
the seed
Forming a endosperm surrounding A temporary storage of food for the growth
cotyledon in monocot seeds. In
of embryo
dicotyledonous seeds, endosperm
is absorbed by the cotyledon during
seed formation
Become the fruit in fruits like
apples, pears and strawberries
As a source of food for the animals and
man
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(m) state that seed and fruit dispersal by wind and by animals provides a means of colonising new
areas
(n) describe the external features of one, locally available, named example of a wind-dispersed fruit or
seed and of one named example of an animal-dispersed fruit or seed
SEED DISPERSAL
The flowers produce seeds which can be dispersed by the wind or other animals, providing a means
of colonising new areas. Scattering of seeds and fruits is known as dispersal.
Importance of dispersal
Reduces the competition for light, water and mineral salts between the members of the same species
Resulting plants growing in new place, which reduces the chances of the species being extinct
ANIMAL DISPERSAL
There are 2 main modification of fruits for animal dispersal: succulent fruits and hooked fruits.
Succulent fruits attract animals because they are brightly coloured, juicy and nutritious. When eaten, the
seed pass through animal’s faeces, which may be a long way from the parent plant. The faeces provides
nutrients when the seeds germinate.
Examples are: papaya, mango, straw berry, tomato apple
Hooked fruits catch on to an animal’s fur as it brushes past the parent plant. Eventually the seeds drops off,
or the animal grooms itself to remove them. This disperses the seeds away from the parent plant.
Examples are: burdock, sweet gum, birch
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WIND DISPERSAL
Small sized fruits or seeds. Fruits contain seeds, and usually have a parachute or a wing to help them be
carried away from the parent plant by the wind.
Examples: dandelion, sycamore
The dandelion fruit has a group of fine hairs called a pappus,
which catches the wind and acts like a parachute. The fruit
counterbalances the pappus. This allows the seed or fruit to
catch in the wind and be pulled clear of the parent. It also slows
the seed’s fall to the ground, allowing the wind to carry it some
considerable distance away.
The sycamore has a wing with a large surface area. When the
fruit drops off the tree it spins, slowing down in descent. If caught
by the wind the seed will be carried away from the parent plant,
reducing competition for nutrients, water and light.
SELF-DISPERSAL
Pericarp dries in the sun and shrinks. The tension generated splits the fruit longitudinally into two halves
suddenly and ejects the seeds out.
Examples are: pods of leguminous plant
(o) investigate and state the environmental conditions that affect germination of seeds: suitable
temperature, water and oxygen
(p) describe the uses of enzymes in the germination of seeds
GERMINATION OF A SEED
After embryo is formed the seed does not immediately grow in a seedling. It will remain in a resting stage for
a while. At this stage the seed is said to be dormant. It is important seed to remain dormant to:
o
o
Avoid unfavourable conditions
To be dispersed
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Germination of a seed occurs in the presence of water, warmth and oxygen. The seed absorbs water in large
quantities from the soil through micropyle and after some time from the testa too. The entry of water expands
the seed and causes the seed to split. Water softens the testa and makes it more permeable to oxygen. Water
entering the seed activates the secretion of enzymes in the cotyledon of the seed and digests insoluble foods;
o
o
o
amylase digests starch to maltose
maltase digests maltose to glucose
protease digests protein to amino acids
The soluble products are transported to the plumule and radicle. In the plumule and radicle the glucose is
used up for:
o Respiration to provide energy for cell division and growth
o To form new protoplasm
o To make cellulose for new cell wall
In the plumule and radicle the amino acids is used for the formation of new cell protein.
The radicle grows first and burst through testa. The radicle grows continuously and branches lateral roots.
Roots help to anchor it firmly in the soil and root hairs absorb water from the soil. The hypocotyl just above the
radicle starts elongate. Cotyledons are pulled out of the testa through the soil. The hypocotyl straightens up
and leaves of the plumule open out.
CONDITIONS NEEDED FOR GERMINATION
Water:o
o
o
o
Needed to activate the enzymes in the seed
Used in the hydrolysis of food stores
Transport the soluble products from the cotyledons to the growing region
Transport salts from the soil to the shoot
Temperature:o
o
o
Influences the rate of enzyme controlled reactions going on inside the seed
Speed up the rate of metabolic reaction until the optimum temperature is reached
Germination can occur temperature between 5oC to 40oC
Oxygen:o
Required for aerobic respiration. Respiration provides the energy for the metabolic reactions involved
inside the seed, which are necessary for growth.
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DRY MASS AND FRESH MASS
o
o
Dry mass is the actual amount of organic matter present in a seed (the stored food in the seed).
Fresh mass is the amount of water absorbed by the seed.
whole seed
plumule & radicle
dry mass/g
cotyledon
time
o
o
o
o
As seed germinates its dry mass decreases gradually as the stored food in its cotyledons are used in
respiration to produce energy for germination and for growth.
When first leaves are matured enough to do photosynthesis at a rate faster than the respiration of the
plant cell, the dry mass gradually increases.
The dry mass of plumule and radicle increases gradually as the food is always entering them.
The dry mass of the cotyledons constantly decrease as the food stored in it is constantly used up.
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16.3 SEXUAL REPRODUCTION IN HUMANS
Humans and some other mammals have the most advanced reproductive system in the
animal kingdom. Not only do they have internal fertilisation, they have internal
development as well. This means that the embryo develops inside the female’s body
where it lives and gets food and oxygen from mother’s blood.
The human reproductive system usually involves internal fertilization by sexual
intercourse. During this process, the male insert his erect penis into the female’s vagina
and ejaculates semen, which contains sperm. The sperm then travels through the
vagina and cervix into the uterus or fallopian tubes for fertilization and implantation.
Gestation of the fetus then occurs within the female’s uterus for approximately nine
months, this process is called pregnancy in humans. Gestation ends with birth, the process is called labor.
Labor consists of the muscles of the uterus contracting, the cervix dilating, and the baby pass out the vagina.
(q) identify on diagrams of the male reproductive system and state the functions of the testes, scrotum,
sperm ducts, prostate gland, urethra and penis
MALE REPRODUCTIVE SYSTEM
The male reproductive system is designed to manufacture sperms and to deliver them to the place where
one of them will be able to fuse with a female nucleus.
TESTIS
The testis is a male sex organ which produce sperms. Sperms are
the male sex cells or male gamete. To maintain proper temperature
testes are present inside the scrotum. Testes are otherwise called as
gonads. The testes are made of millions of tiny coiled tubes.
SPERM DUCTS
Sperm ducts are tubes which carry the sperms away from the testes
to the penis. They join with one another and with the tube bringing
urine, at a position just under the bladder. Each sperm duct bears a
SEMINAL VESICLE for sperm storage.
PROSTRATE GLAND
It is present just below the urinary bladder. Prostate gland is about
the size of a golf ball. It produces a nutrient fluid called seminal fluid
which mixes with sperm during ejaculation and helps to swim freely.
URETHRA
The urethra is a tube that carries both urine and semen along the
penis to be released from the body.
PENIS
Penis is the male muscular organ, which helps to introduce the
sperm into the female organ. During sexual excitement the penis
erect because of more blood flow in the tissue of the penis.
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(r) identify on diagrams of the female reproductive system and state the functions of the ovaries,
oviducts, uterus, cervix and vagina
FEMALE REPRODUCTIVE SYSTEM
The female nuclei which are involved in the process of sexual reproduction are located in the female
gametes called OVA (singular: ‘ovum’). The functions of the female reproductive system are:
o
o
To provide ova and ensure that they are fertilised by the male gametes.
To protect and nourish the embryo until it is born.
OVARIES
Ovaries are oval shaped structures. About 3 cm long in
human (smaller than a ping-pong ball), which are attached to
the back of the abdomen below the kidney. The ovaries are
the female gonads, making and releasing the female gamete
(ova). The female releases one ovum every four weeks from
alternate ovaries, that is, each ovary releases one ovum
every eight weeks.
OVIDUCTS
The oviducts are the tubes which carry the ova away from the
ovaries. They are lined with cilia which, together with a little
muscular assistance, help to move the ova gently along. If
fertilisation occurs, it usually does so about one-third of the
way along the oviduct.
UTERUS
The uterus is a pear-shaped organ lying behind and slightly
above the bladder. Its walls contain involuntary muscle. The
embryo develops in the uterus during pregnancy.
CERVIX
The cervix is the ‘neck’ of the uterus, where the uterus joins
the vagina. It supplies mucus to the vagina.
VAGINA
The vagina is the part of the female system which receives
the penis during copulation. It is muscular and stretchable and
connects the cervix with the slit-like vulva opening to the
outside
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(s) compare male and female gametes in terms of size, numbers and mobility
A COMPARISON OF MALE AND FEMALE GAMETES
Male gametes
Female gametes
Released in millions
Released one at a time
Able to move
Unable to move on their own
Very small in size (0.05 mm- 80% is tail)
Comparatively large (0.1 mm in diameter)
Very little cytoplasm
A lot of cytoplasm contains nourishment for
the zygote if the ovum is fertilised
Nucleus contains either an X or a Y chromosomes
Nucleus always contains an X chromosomes
PUBERTY
Although the ovaries of a young girl contain all the ova she ever produce, they do not start to be released until
she reaches an age of about 10-14 years. This stage in her life is known as puberty. At about the same time
as the first ovulation, the ovary also releases female sex hormones into the blood stream. These hormones
are called oestrogen and when they circulate round the body, they bring about the development of secondary
sexual characteristics
•
Increased growth of the breasts
•
A widening of the hips
•
The growth of hair in the pubic regions and in the armpits
•
Increase in the size of the uterus and vagina
Puberty in boys occurs at about the same age as in girls. The testes start to produce sperms for the first time
and also release a hormone, called testosterone, into the blood stream. Male secondary sexual characteristics
includes
•
enlargement of the testes and penis
•
deepening of the voice
•
growth of hair in the pubic regions, armpits, chest and, later on, the face.
•
Increased muscle and bone mass.
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(t) describe the menstrual cycle, with reference to the alternation of menstruation and ovulation, the
natural variation in its length and the fertile and infertile phases of the cycle
THE MENSTRUAL CYCLE
The menstrual cycle is a regular of changes to the female reproductive system in preparation for fertilisation
and pregnancy. It is controlled by hormones of the pituitary gland and the ovary.
Once a female reaches puberty, she will start to release ova from her ovaries. Ovulation is one stage in her
menstrual or monthly cycle.
Over a period of about 14 days, the walls of the female’s uterus develop a spongy lining, containing many
blood capillaries. When the spongy lining is ready, ovulation occurs. The ovum passes down the oviduct. If the
ovum is not fertilised by a sperm, it passes through the uterus and
vagina and out of the vulva. The spongy lining then peels away from
the uterus wall, damaging the blood capillaries. The lining is passed out
of the vagina and vulva, together with blood. This is menstruation or
monthly period. Menstruation lasts for about four days, and occurs
about two weeks after ovulation. Once the uterus wall has recovered,
it begins to rebuild its spongy lining under the influence of a hormones
from the ovary. At the time new ovum maturing in the ovary, under the
influence of hormone from the pituitary gland. When mature, the ovum
is released (ovulation), at around two weeks after menstruation. The
cycle continues in this way as long as the female remains healthy. If an
ovum is fertilised, and the woman becomes pregnant her menstrual cycle stops until after the baby is born.
When the female reaches the menopause, usually at around 50 years of age, she stops ovulating and can no
longer become pregnant.
Fertile and infertile phases of the menstrual cycle
When there is no ovum in the oviducts, fertilisation cannot occur. It is unlikely to occur if the ovum is not in the
correct position in the oviduct. A women most fertile period is from a few days before ovulation to a few days
after ovulation.
Factors effecting the menstrual cycle
Stress – at times of emotional stress the menstrual cycle may become irregular
Diet – an inadequate diet can lead to an irregular cycle, and starvation can suppress the cycle completely
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(u) explain the role of hormones in controlling the menstrual cycle (including FSH, LH, progesterone and
oestrogen)
THE MENSTRUAL CYCLE CONTROLLED BY HORMONES
Brain– receives information from other parts of the body, processes it and then ‘instructs’ pituitary gland.
PITUITARY GLAND produce two hormones
Follicle Stimulating Hormone [F.S.H] - Stimulates development of Graafian follicle in the ovary.
Luteinizing Hormone [L.H] - Stimulates release of mature ovum from ovary. Stimulates development
of corpus luteum from the remains of the follicle.
Ovary produce two hormones
Graafian follicle releases oestrogen - Repairs the lining of the uterus and stimulates development of
female sexual characteristics (breast development, fat distribution in the hips, legs, and breasts, and
the development of reproductive organs).
Corpus Luteum releases Progesterone - Keeps the lining of the uterus ready for implantation and
pregnancy. (If women pregnant, progesterone is secreted to prevent uterine contractions that may
disturb the growing embryo. The hormone also prepare the breast for lactation.)
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(v) describe fertilisation and early development of the zygote simply in terms of the formation of a ball of
cells that becomes implanted in the wall of the uterus
(w) state the function of the amniotic sac and the amniotic fluid
(x) describe the function of the placenta and umbilical cord in relation to exchange of dissolved
nutrients,gases and excretory products (no structural details are required)
(y) describe the special dietary needs of pregnant women
(z) describe the advantages of breast milk compared with bottle milk
FORMATION OF THE FETUS - FERTILISATION, IMPLANTATION
After sexual intercourse, sperms swim through the cervix and the uterus into the oviducts, where they meet an
egg. One sperm may fertilise the egg to produce a zygote. After
ovulation, the egg is caught in the funnel of the oviduct. Very slowly, the
egg travels towards the uterus. If the egg is not fertilised by a sperm
within 8-24 hours after ovulation, it will die. By this time, it has only
travelled a short way along the oviduct. So a sperm must reach an egg
while it is quite near the top of the oviduct if fertilization is to be
successful. Sperm can remain active in the oviduct for at least 2 days
and the ovum may take a day to pass from the ovary to the uterus, so
there is a fertile period of 3 to 4 days around ovulation when fertilization
can happen.

the sperm nucleus and the egg nucleus fuse to form a diploid zygote = fertilization
The fertilised ovum or zygote now starts to divide, first into two, then four and so on. It continues to move
towards the uterus. About six days after fertilisation the ball of cells now called an embryo, becomes embedded
in the thickened lining of the uterus. This implantation of the embryo in the uterus wall is called conception.
The embryo initially absorbs nourishment secreted by the cells of the uterus, but it soon embeds itself
(IMPLANTATION) in the spongy lining of the uterus. Further division of the cells turns the blastocyst into a
FETUS. The fetus is surrounded by a membrane (the AMNION) which forms the AMNIOTIC SAC enclosing
the fetus in a water bath (the AMNIOTIC FLUID).
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PLACENTA
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste
elimination, and gas exchange via the mother's blood supply. The stable environment needed for the
developing fetus is provided by the placenta.
Placenta is found in mammals. It forms early in
pregnancy partly from the lining of the uterus and
partly from outside cells of the developing embryo.
The fetus is attached to the placenta by the umbilical
cord. Umbilical cord contains blood vessels which
carry materials for exchange between mother and
uterus.
o
o
Umbilical artery: carry deoxygenated blood
Umbilical vein: carry oxygenated blood
The fetus is surrounded by amniotic sac which is
filled with amniotic fluid. Amniotic fluid protects the
fetus from knocks and bumps.
Functions of the placenta
o
o
Exchange of soluble materials (food, waste
and oxygen) between mother and fetus.
Physical attachment of the fetus to the uterus wall.
Functions of the amniotic fluid
o
o
o
To protect the embryo from physical damage, e.g. if mother falls over.
To support the embryo, keeping even pressure all around it, allowing organs to develop without
restriction.
To allow the fetus some restricted movement.
Diffusion of substance takes place between the two blood systems
Diffusing from mother to fetus
Diffusing from fetus to mother
Dissolved nutrients:
Nitrogenous waste:
Glucose
Urea
Amino acids
Ions
Vitamins
Water
Dissolved gas:
Dissolved gas:
oxygen
Carbon dioxide
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The dietary needs of a pregnant women
o
o
o
o
o
Protein for the manufacture of embryonic tissues
Carbohydrate for additional respiration in embryonic tissues
Vitamin C for making proteins in the embryo
Vitamin D and calcium for making bones of embryo
Iron for making embryo’s blood
The value of breast feeding
After the birth of the baby, milk from the mother’s mammary glands supplies the ideal food for the first
months of development. The milk:
o
o
o
o
o
Is cheap
Readily available
Contains all the necessary constituents, in the correct proportions
Is at the correct temperature
Contains some antibodies which protect the baby against disease
Breast feeding also helps to develop the bond between mother and baby. Some babies may suffer harmful
reactions to the substitute formula milk powders which are used in bottle feeding.
(aa) describe the following methods of birth control:
natural, chemical (spermicides), mechanical, hormonal and surgical
BIRTH CONTROL
As little as 4 weeks after giving birth, it is possible, though unlikely, that a women may conceive again. It would
be possible to have a children at about 1-year intervals. All human communities, therefore, practice some form
of birth control to space out births and limit the size of the family.
There are 5 main groups of birth control methods: natural, chemical, mechanical, hormonal
and surgical.
NATURAL METHOD (OR RHYTHM METHOD)
Mainly depend on menstrual cycle. If the sexual intercourse is avoided during fertile period of the menstrual
cycle fertilization can be avoided. But not 100% reliable.
CHEMICAL METHOD
Chemicals which kill sperms (‘spermicides’) are put into the vagina of the female before intercourse. This is
not very effective method of birth control when used on its own.
MECHANICAL METHOD
Condom - Condom is a rubber sheath placed over the penis before intercourse to avoid the fusion of the
sperm with fusion. They prevent pregnancy and reduce the risk of sexually transmitted diseases.
Condoms prevent pregnancy by collecting semen when a man ejaculates. This keeps sperm from entering
the vagina.
Like all birth control methods, condoms are more effective when you use them correctly.
o use spermicide with them
o pull out before ejaculation.
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Femidom - The female condom is a pouch that is used during intercourse to prevent pregnancy and reduce
the risk of sexually transmitted diseases.
Some women and men may not like the female condom because it may;
o cause irritation of the vagina, vulva, penis
o slip in to the vagina during intercourse
Diaphragm - It is a cup shaped structure which can be fit over the cervix of the uterus so that it can prevent
the entry of sperm into the uterus. Diaphragms prevent pregnancy by keeping sperm from joining with an
egg. In order to be as effective as possible, the diaphragm must be used with spermicide.
o
o
Some women who use diaphragms may develop frequent urinary tract infections
Some women who use diaphragms may develop vaginal irritation.
I U D (Intra-Uterine Device) - It is fitted inside the uterus. It does not stop fertilisation, but it prevents
implantation. This is an effective method of birth control. The IUD doesn't protect against sexually
transmitted infections.
HORMONAL METHOD
This method is otherwise known as the pill. Pill prevents ovulation, so that no ova are present to be fertilised.
Making cervical mucus thicker. This keeps sperm from getting to the eggs.These is an effective method of birth
control if the routine is followed.
SURGICAL METHOD
Vasectomy - Cutting the sperm ducts. Vasectomy does not change your hormones. An effective method but
rarely reversible.
Vasectomy may not be a good choice if the person;
o may want to have a child biologically in the future.
Tubectomy - Tying the oviducts to prevent the passage of ova- an effective method and usually reversible
Tubectomy may not be a good choice if the person;
o may want to have a child biologically in the future.
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16.4 Sexually transmitted diseases
(bb) explain that syphilis is caused by a bacterium that is transmitted during sexual intercourse
(cc) describe the symptoms, signs, effects and treatment of syphilis
(dd) discuss the spread of human immunodeficiency virus (HIV) and methods by which it may be
controlled.
SYPHILIS
Syphilis is a sexually transmitted disease which is commonly form in males. Normally syphilis has three stages.
1st stage of symptom;
o After 14 to 28 days of contact with an infected person.
o Appearance of sores around the sex organs, mouth and anus.
o Disappearance of sores without treatment.
nd
2 stage of symptom;
o appears after weeks or months after the contact with the infected person.
o rashes all over the body, no pain.
o Disappearance of sores without treatment.
3rd stage of symptom;
o 3rd stage of symptom is dangerous, because it effects the brain, heart or liver. Moreover it leads to
insanity.
Treatment - syphilis is caused by bacteria so, it can be treated by using proper antibiotics.
Prevention - syphilis can be prevented by avoiding sexual contact with an infected person, by limiting sexual
contact to one partner, and using a condom during intercourse.
AIDS
AIDS (Acquired Immune Deficiency Syndrome) is caused by the human immuno-deficiency virus (HIV). The
virus attacks the immune system and leaves the body vulnerable to a variety of life-threatening infections and
cancers. Common bacteria, yeast, parasites, and viruses that usually do not cause serious disease in people
with healthy immune systems can cause fatal illnesses in people with AIDS.
HIV has been found in saliva, tears, nervous system tissue and spinal fluid, blood, semen (including preseminal fluid), vaginal fluid, and breast milk. However, only blood, semen, vaginal secretions, and breast milk
have been shown to transmit infection to others.
TRANSMISSION
HIV may be transmitted in the following ways:
o From the host to host when intravenous drug users share unsterilised needles.
o In semen, from one partner to the blood of another, if there is any tearing of tissues during intercourse.
o From an infected mother’s blood to her baby’s blood during the birth process, or a nursing mother can
transmit it to her baby in her breast milk.
o An untreated blood during blood transfusion.
o unsterilised surgical instruments.
Other methods of spreading the virus are rare and include accidental needle injury, artificial insemination with
infected donated semen, and organ transplantation with infected organs.
HIV infection is NOT spread by:
o Casual contact such as hugging
o Mosquitoes
o Participation in sports
o Touching items that were touched by a person infected with the virus
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Common symptoms are:
o Fever
o Rash
o Sweats (particularly at night)
o Swollen lymph glands
o Weakness
o Weight loss
DISEASE CONTROL
o
o
o
o
o
o
o
Educating the public about how it is spread, and what precautions can be taken.
Never sharing needles.
Avoiding sex with prostitutes because they are often carriers of the disease.
Always using condom or other barrier method of contraception which prevents direct contact between
the body fluids of the two partners.
Treating all blood and blood products used in transfusion to destroy the AIDS virus.
use sterilised surgical instruments.
feed baby with bottled powdered milk (if mom has HIV).
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17. INHERITANCE
Inheritance is the transmission of genetic information from one generation to the next, leading to
continuity of the species and variation within it.
17.1 VARIATION
(a) describe the difference between continuous and discontinuous variation and give examples of each
Within a species there is usually a great deal of variation between individuals. Sexual reproduction leads to
variation in the offspring that is each individual has different characteristics.
Variation is all the differences which exist between members of the same species. It is caused by a
combination of genetic and environmental factors. Two type of variation are seen; Continuous variation and
Discontinuous variation.
Continuous Variation
Continuous variation describes the situation in which there are a great many intermediates between the
extremes. For example, there is every shade of hair colour between black and blond. People do not belong to
one or other of a small number of distinct categories. Variations such as these are under genetic control but
there are several pairs of genes involved.
Continuous variation also occurs when the characteristics are controlled by the genes and the environment.
Your height will depend on the genes you inherit and on the amount of food you eat during your growing period.
Discontinuous Variation
This is the result of inheritance only. Discontinuous variations are entirely genetically controlled. They cannot
be altered by external conditions.
Examples of discontinuous variation are:


You are either male or female, there are no intermediates
Your ABO blood group is either A, B, AB or O
Genetic defects such as colour blindness, albinism, dwarfism, sickle cell anaemia are all genetically controlled
and expressed in a discontinuous way. You either have these conditions or you do not. There are no
intermediate states.
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17.2 CHROMOSOMES and DNA
(b) state that a chromosome includes a long molecule of DNA
(c) state that DNA is divided up into sections called genes
(d) explain that genes may be copied and passed on to the next generation
(e) define a gene as a unit of inheritance and distinguish clearly between the terms gene and allele
(p) explain that DNA controls the production of proteins
(q) state that each gene controls the production of one protein
In the nucleus of every cell there are a number of long threads called chromosomes.
Chromosomes
Most of the time, the chromosomes are too thin to be seen except with an electron microscope. But
when a cell is dividing, they get shorter and fatter so they can be seen
with a light microscope. Chromosomes are thread-like molecules that
carry hereditary information for everything from height to eye color.
They are made of protein and one molecule of DNA, which contains
an organism’s genetic instructions, passed down from parents. In
humans, animals, and plants, most chromosomes are arranged in
pairs within the nucleus of a cell.
Human cells contain 46 chromosomes, which are in pairs. Sex cells (sperm and ova) contain only 23
chromosomes. The 23 chromosomes comprise one from each pair.
Inheritance of sex in humans
Of the 23 pairs of chromosomes present is each human cell, one
pair is the sex chromosomes. These determine the sex of the
individual. Male have XY, female have XX. So the presence of a
Y chromosome results in male features developing.
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DNA
Each chromosome contains one very long molecule of DNA. The DNA molecule carries a code that
instructs the cell about which kind of proteins it should make. Each chromosome carries instructions
for making many different proteins. The DNA molecule, looking rather like a very long, twisted rope
ladder, is made up of two strands (of alternating sugar and phosphate units) held together by pairs of
chemical units called bases.
There are four bases only:
A
C
G
T
(Adenine)
(Cytosine)
(Guanine)
(Thymine)
These bases link with one another in the following ways
A always with T
C always with G
Gene
A gene is defined as a unit of inheritance. Each chromosome is made up of a large number
of genes coding for the formation of different proteins which give us our characteristics. The gene
responsible for a particular characteristic is always on the same relative position on the
chromosome.
A part of a DNA molecule coding for one protein is called a gene.
Alleles
When the chromosomes are in pairs, there may be a different form (allele) of the gene on each
chromosome. Alleles are pair of matching genes.
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For the purpose of understanding the mechanism of simple inheritance, it is convenient to imagine a
chromosome as a string of beads, like that shown below, each bead represents one gene. During cell division,
genes are copied and these copies are passed on from parent to offspring via chromosomes in the nuclei of
the parent’s gametes.
Every member of the same species has the same number of chromosomes in each cell of their body. These
chromosomes exist in matching pairs. For e.g, human beings have 23 matching or homologous pairs of
chromosomes, a total number of 46. Each pair of matching chromosomes, one is inherited from a person’s
mother and one is inherited from their father. The genes of homologous chromosomes also match.
a pair of
alleles
Always match in shape, but do not always matching colors. This is the way of showing that one pair of alleles
controls one character, but each allele may exist in two forms: they may be dominant or recessive.
The alleles in position 1 are both dominant, in position 2 they are both recessive and in position 3, there is one
of each.
For a particular character, an offspring may be therefore inherited either:



Two dominant alleles, one from each parent. The offspring is described as HOMOZYGOUS
dominant.
Two recessive alleles, one from each parent. The offspring is described as HOMOZYGOUS
recessive.
One dominant and one recessive allele. The offspring is described as HETEROZYGOUS.
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17.3 MONOHYBRID INHERITANCE
(f) describe complete dominance using the terms dominant, recessive, phenotype and genotype
(i) predict the results of simple crosses with expected ratios of 3:1 and 1:1, using the terms
homozygous, heterozygous, F1 generation and F2 generation
(j) explain why observed ratios often differ from expected ratios, especially when there are small
numbers of progeny
(k) explain codominance by reference to the inheritance of the ABO blood group (phenotypes A, B, AB,
O, gene alleles IA, IB and IO)
(l) describe the determination of sex in humans (XX and XY chromosomes)
A monohybrid cross involves the crossing of individuals and the examination of one (mono) character
(flower colour, pod shape..) and different (hybrid) traits (red colour, white colour) in their offspring.
The Punnett square is a useful tool for predicting the genotypes and phenotypes of offspring in a genetic
cross involving Mendelian traits.
Mendel crossed true-breeding plants that differed for a given character. Pollen from true-breeding pea plants
with purple flowers (one trait) was placed on stigmas of true-breeding plants with white flowers (another trait).
The F1 seeds were all purple; the white flower trait failed to appear at all.
Because the purple flower trait completely masks the white flower trait when true-breeding plants are crossed,
the purple flower trait is called dominant, and the white flower trait is called recessive.
The F1 plants were allowed to self-pollinate. This step was the monohybrid cross (or the F1 cross). The
progeny, called F2, were examined: roughly 1/4 were white, and 3/4 were purple.
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There are two types of monohybrid inheritance.
A
B
with COMPLETE DOMINANCE, and
with CODOMINACE.
A
With COMPLETE DOINACE
All the genetic crosses shown below will involve examples using pea plants, which can be tall (T) of dwarf (t)
– tall is dominant to dwarf.
Punnett square
1. A cross between a pure-breeding tall pea plant and a pure-breeding dwarf pea plant.
As tall is dominant to dwarf, and both plants are pure-breeding, their genotypes must be TT and tt.
2. A cross between two heterozygous tall pea plant.
The genotype of both plants must be Tt.
tall
3. A cross between a heterozygous tall pea plant and a dwarf pea plant.
The hetetozygous tall pea plants must be Tt.
The dwarf pea plants must be tt.
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B
With CODOMINANCE
Sometimes, neither of a pair of alleles is completely dominant or completely recessive. Instead of one of them
completely hiding the effect of the other in a heterozygote, they both have an effect on the phenotype. This
is called codominance.
The result is that there can be three different phenotypes. When writing the genotypes of codominant alleles,
the common convention is to use a capital letter to represent the gene involved, and a small raised letter for
each phenotype.
Inheritance of A, B, AB and O blood group - an example of codominance



Blood type is controlled by 3 alleles: IA, IB, IO (the base letter = I stands for immunoglobulin)
IO is recessive, two IO alleles must be present for the person to have type O blood
IA and IB are codominant but both are dominant to IO. If a person receives an IA allele and
a IB allele, their blood type is type AB, in which characteristics of both A and B antigens are expressed.
Because IO is dominated by both IA and IB alleles, a person with blood group A could have the genotype IA IO
or IA IA. This has implication when having children because, if both parents carry the IO allele, a child could be
born with the genotype IOIO (blood group O), even though neither of the parents have this phonotype.
An example of the inheritance of blood groups in humans can be shown in the following genetic diagram:
Parents
Genotype:
Phenotype:
Alleles found in gametes
male
IAIO
Group A
IA
IO
Gametes
×
female
I BI O
Group B
IB
IO
Of the male
IA
IO
IB
IAIB
I BI O
IO
IAIO
IOIO
Of the female
offspring
Possible Genotype:
IAIA
IAIO
I BI O
IOIO
Phenotype:
-blood groups
Group AB
Group A
Group B
Group O
-probability
25%
25%
25%
25%
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THE INHERITANCE OF SEX
Whether a child is born male or female is determine at the moment of fertilization. Of the 23 pairs of
chromosomes in a human nucleus, one pair is known as the SEX CHROMOSOMES. In the female sex
chromosomes are identical and are called ‘X’ chromosomes. In the male, they are not identical and there is an
‘X’ chromosome and a ‘Y’ chromosome.
The SEX CHROMOSOMES are:
XX for a female
XY for a male
The gametes contain 23 single chromosomes, and therefore only one of the two sex chromosomes that exist
in normal body cells.
In females, all the gametes contain an ‘X’ chromosome.
In males, 50% of the gametes contain an ‘X’ chromosomes and 50% contain a ‘Y’ chromosome.
There is an exactly equal chance of the ‘X’ chromosomes in the ovum:


Fusing with an ‘X’-carrying sperm to produce a daughter, or
Fusing with a ‘Y’-carrying sperm to produce a son.
Parents
father
Sex chromosomes
in body cell:
XY
in gametes:
X
×
mother
XX
Y
X (only)
At fertilsation:
X
X
Y
XX
XY
offspring
chromosomes:
XX
XY
Phenotype:
female
male
-probability
50%
50%
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17.4 SELECTION
(g) describe mutation as a change in the structure of a gene (e.g. sickle cell anaemia) or in the
chromosome number (e.g. 47 in Down’s syndrome instead of 46)
(h) name radiation and chemicals as factors that may increase the rate of mutation
(n) assess the importance of natural selection as a possible mechanism for evolution
(o) describe the role of artificial selection in the production of economically important plants and animals
Genes and chromosomes are always subject to change (or mutation) as a result of environmental forces acting
upon them. These forces are known as mutagens, and
include; X-rays, atomic radiation, ultraviolet light
and
some chemicals.
Mutation
is
an
unpredictable
change
in
the genes or chromosome number, as a result of fault
copying when DNA is replicated, faulty separation of
chromosomes during cell division, or exposure to radiation
or some chemicals.
A mutation is a spontaneous change in the structure of a gene or chromosomes.
Gene Mutation
Sickle-cell anaemia
Sickle cell anaemia is caused by a mutation in the blood
pigment haemoglobin. Both parents pass on a mutated allele for
making haemoglobin in red blood cells. The homozygous recessive
offspring cannot make effective haemoglobin, and cannot carry
sufficient oxygen in their blood and more likely to become stuck in
a capillary, preventing blood flow. When the faulty haemoglobin is
present in a red blood cell, it causes the cell to deform and
become sickle-shaped, especially when oxygen levels in the blood
become low.
Chromosome Mutation
Down’s syndrome
Down’s syndrome is caused by a chromosome mutation. If, in the production of gametes by one of the
parents, one extra chromosomes enters one of the gametes, then
there will be 24 (instead of 23) chromosomes in that gamete. If this
gamete is involved in the process of fertilisation, there will be 47
(instead of 46) chromosomes in the zygote.
The presence of the extra chromosome causes unusual
characteristics in the baby. These usually include lowered life
expectancy, mental retardation (although some Down’s children
are very intelligent), early puberty, and a distinctive round face and
short neck.
MILANDHOO SCHOOL / SH.MILANDHOO / FIRST SEMESTER 2017 / BIOLOGY5090 / NOTES / INHERITANCE
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SELECTION
Natural Section
Natural selection is the process by which plants and animals that can adapt to changes in their environment
are able to survive and reproduce while those that cannot adapt do not survive. It gives the greater chance
of passing on of genes by the best adapted organisms.
Examples of the variation shown by members of a population in a given habitat include:



The shade of color of a leaf-eating insect - The leaf insect with better camouflage may escape the
notice of a hungry predator.
The sharpness of vision in a bird of prey - The bird of prey with sharper vision is more likely to find a
meal – particularly important when food is scarce.
The speed at which a gazelle can run - The faster the gazelle can run, the more chance it has of
escaping from a hungry lion
In all of these examples, the variation can have some effect on the success or even on the chances of survival
of that organism in its environment.
All organisms are therefore in competition with other members of their species in that particular environment.
The winners in that competition survive to reproduce. The winners in that competition survive to reproduce. It
is the environment which ‘decides’ which organisms survive. The process is called NATURAL SELECTION.
How natural selection may lead to EVOLUTION.
The evolution of present day life forms has occurred through a series of mutations and natural selection over
millions of years. New varieties of organisms may arise due to mutation. Mutation is an abrupt change in a
gene or chromosome or the chromosome number that is inheritable. It is brought about by a fault in the
replication of the gene or the chromosome. Completion occurs among the different varieties of organisms
produced and nature selects those varieties, which are more competitive, more resistant to diseases and better
adapted to changes in the environment to survive and reproduce their kind. The other varieties may perish.
The gradual change by natural selection is known as EVOLUTION. During the process, a population of
organisms may become separated and form two isolated branches. Each of the population will adapt to
different environmental changes, and new species may evolve.
Artificial Selection
Artificial selection is a method used by humans to produce varieties of animals and plants which have an
increased economic importance. People use selective breeding to produce new varieties of a species, so
that certain desirable traits are represented in successive generations.
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A variety is a type of a particular species that is different in some clear way from other varieties of that
species. The different breeds of domestic dogs and large ears of maize corn are products of artificial selection.
These common vegetables were cultivated from forms of wild mustard. This is evolution through artificial selection.
Some examples are;




Increased milk production in cows
Increased meat production in farm animals
Increased yield from cereals
Increased disease resistance in many crops
Selective breeding follows this procedure:
1.
2.
3.
4.
5.
The individuals showing the quality required are selected.
Those individuals are used as breeding stock.
Only those offspring showing the desired quality to the greatest extent are selected.
These selected individuals are used for breeding.
This process continued over many generations.
Selective breeding of cows
Suppose you wanted a variety of cow that produced a lot of milk. This is what you could do:





choose or select the cows in your herd that produce the most milk
let only these cows reproduce
select the offspring that produce the most milk
let only these offspring reproduce
keep repeating the process of selection and breeding until you achieve your goal.
As a result, greater profits are made from greater quantities of better quality produce.
Farmers have carried out artificial selection to improve the breeds of some animals. Some of the original breeds
have become very rare and are in danger of becoming extinct. This form of interbreeding’ will increase the
chances of two recessive alleles coming together. This may give rise to a genetically-controlled deformity (e.g.
a heart defect).
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PAGE 11 OF 13
17.5 GENETIC ENGINEERING
(r) explain that genes may be transferred between cells (reference should be made to transfer between
organisms of the same or different species)
(s) explain that the gene that controls the production of human insulin can be inserted into bacterial
DNA
(t) understand that such genetically engineered bacteria can be used to produce human insulin on a
commercial scale
(u) discuss potential advantages and dangers of genetic engineering.
Genetic engineering is a technology which is used to transfer a gene from one species to another, for this
purpose of producing any biochemical like enzyme or hormones. Since we are now able to identify specific
genes, that gene can then be isolated and inserted into another organism.
Examples:
The following examples are, gene transfer between organisms of the same species.


Genes for disease resistance existing in a crop plant with low yield can be introduced into a crop
plant with a high yield but low disease resistance.
Person inherits genetically-controlled condition (cystic fibrosis), it may be possible to improve their
condition by the introduction of genes from a healthy person.
Gene transfer between organisms of different species is commonly used in the production of the hormone
insulin. Human insulin can be manufactured in a large scale by using genetic engineering and biotechnology.







First an insulin gene is isolated from the pancreas cell of a healthy person.
Then from a bacterium, a plasmid is separated and spliced using a restriction enzyme.
The human insulin gene is inserted into the plasmid
The plasmid with the human insulin gene is called as ‘Recombinant DNA’.
The recombinant DNA is placed inside a bacterium and cultured in a fermentation tank with proper
nutrient solution.
The recombinant bacteria divides repeatedly and increases in population and synthesis the insulin.
The insulin can be extracted and purified from the nutrient medium and marketed.
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Using genetic engineering to produce bacteria that make human insulin.
The importance of this process




Diabetics need a source of insulin to control their blood sugar level. In the past cow insulin has been
used, but some people are allergic to it. Human insulin produced from genetically engineered bacteria
will not trigger an allergic reaction.
The insulin is acceptable to people with a range of religious belief who may not be allowed to use
insulin form animals such as cows or pigs.
The product is very pure.
Human insulin can be made on a commercial scale, reducing costs.
The ethics of genetic engineering
Benefits:


Cures for diseases, such as cystic fibrosis and cancer.
Food which is healthier, stays fresh for longer periods and tastes better.
Risks:



Unknown effects of moving genes from one organism to the other.
New dangerous disease being created.
Against nature.
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