GCSE
WJEC Eduqas GCSE in
BIOLOGY
ACCREDITED BY OFQUAL
GUIDANCE FOR TEACHING
Teaching from 2016
This Ofqual regulated qualification is not available for
candidates in maintained schools and colleges in Wales.
Contents
CELLS BIOLOGY
1.1 PROKARYOTIC AND EUKARYOTIC CELLS
3
1.2 GROWTH AND DEVELOPMENT OF CELLS
8
1.3 CELL METABOLISM
9
TRANSPORT SYSTEMS
2.1 TRANSPORT IN CELLS
17
2.2 TRANSPORT SYSTEMS IN HUMANS
22
2.3 TRANSPORT SYSTEMS IN PLANTS
26
HEALTH, DISEASE AND THE DEVELOPMENT OF MEDICINE
3.1 HEALTH AND DISEASE
28
3.2 COMMUNICABLE DISEASE
29
3.3 TREATING, CURING AND PREVENTING DISEASE
33
3.4 NON-COMMUNICABLE DISEASES IN HUMANS
40
COORDINATION AND CONTROL
4.1 NERVOUS COORDINATION AND CONTROL IN HUMANS
41
4.2 HORMONAL COORDINATION AND CONTROL IN HUMANS
47
4.3 HOMEOSTASIS IN HUMANS
49
4.4 PLANT HORMONES
54
PHOTOSYNTHESIS
55
ECOSYSTEMS
6.1 LEVELS OF ORGANISATION WITHIN AN ECOSYSTEM
60
6.2 THE PRINCIPLE OF MATERIAL CYCLING
62
6.3 BIODIVERSITY
66
6.4 SOME OF THE BIOLOGICAL CHALLENGES OF INCREASING FOOD YIELDS
USING FEWER RESOURCES
71
COMPONENT 7 – INHERITANCE, VARIATION AND EVOLUTION
7.1 THE GENOME AND GENE EXPRESSION
73
7.2 INHERITANCE
77
7.3 VARIATION AND EVOLUTION
78
7.4 SELECTIVE BREEDING AND GENE TECHNOLOGY
80
2
CELL BIOLOGY
1.1 PROKARYOTIC AND EUKARYOTIC CELLS
Spec Statement
Comment
(a)
draw and label animal and
plant cells
Including labels for nucleus, cytoplasm, cell
membrane, cell wall, chloroplast and vacuole.
(b)
describe the differences
between eukaryotic and
prokaryotic cells
Prokaryotic cells consist of a cell wall, cell
membrane and cytoplasm. There is no distinct
nucleus, no mitochondria and no chloroplasts.
Prokaryotic cells are much smaller than most
eukaryotic cells
(c)
explain how the following subcellular structures of eukaryotic
cells (plants and animals) and
prokaryotic cells (bacteria) are
related to their functions:
nucleus/DNA, plasmids,
mitochondria, chloroplasts, cell
membranes, cytoplasm,
vacuole, cell wall
Cell membrane: controls the entry and exit of
substances.
Cytoplasm: site of most cell reactions.
Nucleus: in plants and animal cells, contains
chromosomes which carry genetic information
consisting of DNA.
The genetic information in bacterial cells is carried
in a single loop of DNA.
Plasmids: small circular sections of DNA often
found in the cytoplasm of bacterial cells, separate
from the rest of the cell`s DNA, can transfer genetic
information between one cell and another.
Mitochondria: site of aerobic respiration.
Cell wall containing cellulose : structural support for
plant cells.
Chloroplast: site of photosynthesis in plant cells.
Vacuole: in plant cells, contains a watery sugar
solution (sap), a swollen vacuole pushes the rest of
the cell contents against the cell wall, making the
cell firm.
(d)
explain how the development of
the microscope (light, electron,
laser imaging) increased the
understanding of the sub
cellular structure of organisms
and the proposal that the cell is
the basic unit of life
A simple understanding of how the light and
electron microscopes and laser imaging work.
Cell theory was devised and refined as
microscopes have developed.
Calculation of total magnification is achieved by the
multiplication of the power of the eyepiece lens by
the power of the objective lenses.
• how a slide is prepared, including that
biological staining allows more detail of the
cell to be seen
• the limitations of light microscopy in
studying cell structure: restriction in
maximum magnification
• a simple comparison with the electron
microscope: greater magnification but can
only be used to view dead tissue
3
SPECIFIED PRACTICAL WORK
• SP1.1
Examination of plant and animal cells using a light microscope and production
of labelled scientific drawings from observation
Examination of animal and plant cells using a light microscope and production
of labelled scientific diagrams from observation
Introduction
Cheek cells are typical animal cells, they have a cell membrane, cytoplasm and a nucleus.
Onion cells are plant cells, they have a cell wall, cell membrane, cytoplasm, nucleus and
vacuole. This practical requires you to prepare cheek cell slides and onion cell slides. These
slides can then be observed using a microscope.
Apparatus
light microscope
2 × glass slides
2 × cover slips
cotton wool bud
mounted needle
forceps
freshly cut onion
0.1 % methylene blue solution
iodine solution
Access to:
beaker of disinfectant
Diagram of Apparatus
4
Method
Cheek Cells:
1.
2.
3.
4.
5.
6.
7.
8.
Put a drop of methylene blue on a glass slide.
Gently rub the inside of your cheek with a cotton bud.
Wipe the end of the cotton bud in the drop of methylene blue on the glass slide.
Place the cotton bud in the beaker of disinfectant.
Use the mounted needle to gently lower a coverslip onto the glass slide.
Using a light microscope, examine the slide using the ×10 objective lens.
Use the ×40 objective lens to identify some of the cell structures.
Draw a cell diagram. Identify and label: cell membrane, cytoplasm and nucleus.
Onion Cells:
1. Using forceps, peel a thin layer of epidermis from the inside of a freshly cut onion
piece.
2. Lay the epidermis onto a glass slide.
3. Add a drop of iodine solution to the onion epidermis on the glass slide.
4. Use the mounted needle to gently lower a coverslip onto the glass slide.
5. Using a light microscope, examine the slide using the ×10 objective lens.
6. Use the ×40 objective lens to identify some of the cell structures.
7. Draw a cell diagram. Identify and label: cell wall, cell membrane, cytoplasm and
nucleus.
Analysis
1. Calculate the total magnification of the image seen by multiplying the power of the
objective lens by the power of the eyepiece.
2. Your teacher will tell you the actual size of the cell, calculate the magnification of your
diagram.
5
Risk Assessment
Hazard
Risk
Control measure
Use the lowest concentration possible.
Methylene blue
is harmful
and/or irritant
Methylene blue can irritate the eyes
and lungs. Skin contamination
should be avoided.
Cheek cells are
a biohazard
There is a very small risk of virus
transmission.
Only handle samples from your own
body. After use, hygienically dispose of
cotton buds and slides in a disinfectant
such as Milton or Virkon.
Coverslips/
mounted
needles are
sharp
Can cut skin
Handle carefully
Wear eye protection when preparing
the cheek cell slide. Methylene blue is a
stain- avoid contact with skin.
Teacher/Technician notes
Methylene blue and iodine solution are stains. Avoid contact with the skin. Iodine is a low
hazard chemical as a dilute solution.
Suitable disinfectant would include Milton or Virkon which would need to be diluted to
suitable concentrations.
If the lamp is not an integral part of the microscope, a desk lamp will be needed for each
group.
Freshly cut onion is recommended. This should be prepared for student use in pieces
approximately 1 cm2.
Students will need to be briefed regarding safe and effective microscope use prior to this
practical activity. This practical activity is effective at developing microscope skills and
biological drawing skills.
Students can calculate the total magnification of the image as the power of the objective lens
multiplied by the power of the eyepiece. The actual size of the cells can be given to the
students to enable them to calculate the magnification of their diagrams.
6
Practical techniques covered
B3
Use of appropriate apparatus and techniques for the observation and measurement
of biological changes and or processes.
B4
Safe and ethical use of living organisms (plants or animals) to measure physiological
functions and responses to the environment.
B7
Use of appropriate apparatus, techniques and magnification, including microscopes,
to make observations of biological specimens and produce labelled scientific
drawings.
7
1.2 GROWTH AND DEVELOPMENT OF CELLS
Spec Statement
Comment
(a)
describe the process of mitosis
in growth, including the cell
cycle; cell division by mitosis
enables organisms to grow,
replace worn out cells and
repair damaged tissues
The chromosome number remains constant and
the genetic composition of the daughter cells is
identical to the mother cell. The exact spelling of
mitosis is required.
(b)
explain the importance of cell
differentiation to produce
specialised cells for greater
efficiency
Through differentiation in multicellular organisms,
many types of cells are produced which are
adapted to particular functions.
(c)
describe cancer as the result of
changes in cells that lead to
uncontrolled growth and
division
A simple understanding that cancer is a result of
uncontrolled mitosis.
(d)
describe the function of stem
cells in embryonic and adult
animals and meristems in
plants; some cells, both plant
and animal, do not lose the
ability to differentiate and are
called stem cells
The bodies of multicellular organisms consist of a
variety of different cells that are adapted for
particular functions. These different cells originate
from undifferentiated stem cells that have the
capacity to develop into specialised cells.
(e)
discuss the potential benefits,
risks and ethical issues
surrounding stem cell
technology in medicine
including the implications for
society e.g. the use of
embryonic stem cells
Stem cells are able to treat damaged or diseased
tissue, providing a potent medical tool. The benefits
of using your own stem cells include: no rejection,
no need to find a donor, no need for tissue typing.
However, the use of embryonic stem cells raises
particular ethical issues.
(f)
explain the role of meiotic cell
division in halving the
chromosome number to form
gametes; each meiotic division
produces four cells that are
genetically different because
genes separate and are
reshuffled during the process
of gamete formation
The exact spelling of meiosis is required.
8
1.3 CELL METABOLISM
Spec Statement
Comment
(a)
explain that chemical reactions
in cells are controlled by
enzymes. Enzymes are
proteins made by living cells.
Different proteins are
composed of different amino
acids linked together to form a
chain which is then folded to
form a specific shape held by
chemical bonds. The specific
shape of an enzymes active
site enables it to function. This
is called the 'lock and key'
hypothesis. Enzymes function
by the formation of the
enzyme-substrate complex at
the active site
Enzymes are involved in all metabolic reactions
building large molecules from small ones as well
breaking down large molecules into small ones.
Apply knowledge of ‘lock and key’ to the analysis of
simple, stylised diagrams of enzyme/substrate
interactions.
(b)
explain that enzymes speed
up/catalyse the rate of
chemical reactions. Each
enzyme has its own optimum
pH and temperature. Interpret
enzyme activity in terms of
molecular collisions. Boiling
denatures most enzymes by
altering their shape
Understand the term optimum as a particular
condition (such as temperature or pH) at which the
rate of enzyme action is greatest as increased
temperature results in increased collisions between
enzymes and substrates. In a denatured enzyme
the specific shape of the active site is destroyed
and can no longer bind with its substrate, so no
reaction occurs. Analyse data to show how enzyme
action is affected by temperature and pH.
(c)
describe cellular respiration as
an exothermic reaction which
is continuously occurring in all
living cells, enabling cells to
carry out cell processes.
Aerobic respiration occurs in
cells when oxygen is available.
It is a series of chemical
reactions within the cell,
controlled by enzymes.
Glucose and oxygen are used
and carbon dioxide, water and
energy are produced. The
energy released is in the form
of ATP. Recall the word
equation for aerobic respiration
Use germinating peas to show that energy is
released as heat during respiration. This should
include the role of Thermos flasks and disinfectant
in the experiment.
9
(d)
(e)
(f)
explain that in the absence of
oxygen, anaerobic respiration
may occur. This is less efficient
than aerobic respiration. In
humans energy is released
from glucose and lactic acid is
produced. An oxygen debt may
occur. In yeast, glucose is
broken down and ethanol and
carbon dioxide are produced.
Recall the word equation for
anaerobic respiration in human
cells and fermentation in yeast.
Explain that there is less ATP
released per molecule of
glucose in anaerobic
respiration than in aerobic
respiration because of the
incomplete breakdown of
glucose
compare the processes of
aerobic and anaerobic
respiration
Lactic acid is harmful to the body. It has to be
removed from cells and broken down following the
resumption of aerobic respiration (to repay the
oxygen debt).
explain that fats, made up of
fatty acids and glycerol,
proteins, made up of amino
acids, and starch (a
carbohydrate), made up of a
chain of glucose molecules, in
our food are insoluble. They
are broken down during
digestion into soluble
substances so that they can be
absorbed
The role of the following enzymes in digestion:
carbohydrase – breaks down starch into glucose;
protease – breaks down protein into amino acids;
lipase - breaks down fats into fatty acids and
glycerol. The products of these enzymes are
absorbed into the bloodstream.
Aerobic and anaerobic respiration compared in
terms of oxygen requirement, use of glucose and
release of ATP. Aerobic respiration is more
efficient.
SPECIFIED PRACTICAL WORK
•
•
SP1.3A Investigation into factors affecting enzyme action
SP1.3B Qualitative identification of starch (iodine), glucose (Benedict's) and protein
(biuret)
10
Investigation into factors affecting enzyme action
Introduction
Iodine is an indicator that turns blue/black when starch is present, but is otherwise brown.
In this investigation a blue/black solution of starch and iodine will change to brown as the
enzyme amylase digests/breaks down the starch into sugar.
The time taken for this reaction to occur is affected by temperature.
Apparatus
test tube rack and six test tubes
marker pen
stopwatch
25 cm3 measuring cylinder
10 cm3 measuring cylinder
beaker of 1 % starch solution
dropper bottle of iodine solution
beaker of 10 % amylase solution
spotting tile
dropping pipette
Access to:
water bath or alternative method of heating water
Method
Measure 10 cm3 of 1 % starch solution into a test tube.
Measure 2 cm3 of 10 % amylase solution into a second test tube.
Place both tubes into a water bath set at 20 ºC for 3 minutes.
Place a drop of iodine in six wells of a spotting tile.
Remove both test tubes from the water bath. Pour the amylase into the starch/iodine
solution and start the stopwatch.
6. Immediately, use the dropping pipette to place one drop of the mixture onto the first
drop of iodine. Record the colour of the solution.
7. Repeat step 6 every minute for five minutes.
8. Repeat steps 1-7 at 30 ºC, 40 ºC, 50 ºC, 60 ºC.
1.
2.
3.
4.
5.
Analysis
1. Use your observations to reach a conclusion regarding the effect of temperature on
enzyme action.
2. Evaluate your method and suggest possible improvements.
11
Risk Assessment
Hazard
Risk
Control measure
Amylase enzyme could get on to the
skin when pouring into the test tube
Wash hands immediately if amylase
gets on to them/ wear laboratory gloves
10 % amylase
enzyme solution
is irritant
Amylase enzyme could get
transferred to the eyes from the
hands
Wear eye protection.
Teacher/Technician notes
10 % bacterial amylase solution is a suggested concentration. Amylase varies in its
effectiveness with source and age so it will be necessary to try out the experiment before
presenting it to students to establish the optimum concentrations of starch and amylase to
use.
Iodine solution is a stain. It is a low hazard chemical as a dilute solution, however contact
with the skin should be avoided
The method as stated does not include repeats, but students should be encouraged to carry
out an appropriate number, if time allows.
Students should be encouraged to look at reproducibility by looking at the results of other
groups. Evaluation should include consideration of the end point of the reaction and possible
improvements.
Students should design their own table, but a suggested table format is shown below.
Colour of solution
Temperature of solution (ºC)
at
start
after 1 after 2
after 3
after 4
after 5
minute minutes minutes minutes minutes
20
30
40
50
60
12
Practical techniques covered
B1
Use of appropriate apparatus to make and record a range of measurements
accurately, including length, area, mass, time, temperature, volume of liquids and
gases, and pH.
B2
Safe use of appropriate heating devices and techniques including use of a Bunsen
burner and a water bath or electric heater.
B3
Use of appropriate apparatus and techniques for the observation and measurement
of biological changes and or processes.
B4
Safe and ethical use of living organisms (plants or animals) to measure physiological
functions and responses to the environment.
B5
Measurement of rates of reaction by a variety of methods including production of gas,
uptake of water and colour change of indicator.
B8
Use of appropriate techniques and qualitative reagents to identify biological
molecules and processes in more complex and problem solving context including
continuous sampling in an investigation.
13
Qualitative identification of starch (iodine), glucose (Benedict's) and protein
(biuret)
Introduction
The identification of the different food types can be carried out using different chemical tests.
A positive result for each food type is determined by a colour change. In this activity you will
carry out the chemical tests for starch, glucose and protein.
Apparatus
3 × test tubes
3 × dropping pipettes
3 × 5 cm3 syringe
iodine solution with dropping pipette
Benedict's reagent with dropping pipette
biuret reagent with dropping pipette
starch solution
glucose solution
albumen (protein) solution
Test for Starch
1. Add 2 cm3 of the starch solution to a test tube.
2. Add 2 drops of iodine solution and record the colour change.
Test for Glucose
1. Mix 2 cm3 of the glucose solution with 2 cm3 of the Benedict's reagent.
2. Heat the mixture in a water bath at a temperature of 60 oC.
3. Observe and record the colour changes.
Testing for Protein
1. Mix 2 cm3 of the protein solution with the 2 cm3 of biuret reagent.
2. Record the colour change.
Use these three tests to identify the contents of three unknown samples and some different
types of food.
14
Risk Assessment
Hazard
Risk
Control measure
Biuret is an
irritant
Could splash onto hands or into
eyes when transferring to a test tube
Wear gloves/eye protection
Hot water can
burn
Splashing water onto skin when
using water bath could burn
Care must be taken when removing
tubes from the water. Avoid splashing
hot water onto the skin
Benedict's and iodine solutions are classed as low hazard by CLEAPSS at these
concentrations.
Teacher / Technician notes
Iodine solution
Iodine is only sparingly soluble in water (0.3 g per litre); it is usual to dissolve it in potassium
iodide solution (KI) to make a 0.01 M solution (by tenfold dilution of a 0.1 M solution) to use
as a starch test reagent. Refer to CLEAPSS recipe card 33.
Benedict's reagent
Benedict's reagent can be purchased from a laboratory supplier or it can be made.
1 dm3 of Benedict's reagent contains:
100 g anhydrous sodium carbonate
173 g sodium citrate
17.3 g copper(II) sulfate pentahydrate.
Biuret reagent
Biuret reagent can be purchased from a laboratory supplier or potassium hydroxide and
dilute copper(II) sulfate could be used as an alternative.
Once students are familiar with the tests and positive results they could be asked to
investigate unknown samples or real foods for their chemical make-up by grinding small
portions of the food in water and carrying out the three tests.
The semi-quantitative nature of the Benedict's test could be discussed or further
investigated.
15
Concentration of Glucose (%)
0.5
1
1.5
2
Colour of precipitate
Green
Yellow
Orange
Brick Red
Standards of these precipitates could be useful for students investigating real foods to
estimate the amount of glucose in the foods tested rather than just its presence or absence.
Practical techniques covered
B2
Safe use of appropriate heating devices and techniques including use of a Bunsen
burner and a water bath or electric heater.
B3
Use of appropriate apparatus and techniques for the observation and measurement
of biological changes and or processes.
B8
Use of appropriate techniques and qualitative reagents to identify biological
molecules and processes in more complex and problem solving context including
continuous sampling in an investigation.
16
2 – TRANSPORT SYSTEMS
2.1 TRANSPORT IN CELLS
Comment
Spec Statement
(a)
explain that diffusion is a
passive process and that only
certain substances pass
through the cell membrane in
this way
(b)
explain that diffusion is the
movement of substances down
a concentration gradient
including the use of Visking
tubing as a model of living
material. Explain the role of the
cell membrane in diffusion
(c)
explain the process of osmosis
as the diffusion of water
through a selectively permeable
membrane, from a region of
high water (low solute)
concentration to a region of low
water (high solute)
concentration
(d)
explain that active transport
allows substances to enter cells
against a concentration
gradient and requires energy
Respiration provides the energy required in the
form of ATP. (No detail is required of the process
of ATP synthesis or how it is used to release
energy)
(e)
explain the need for exchange
surfaces and a transport
system in multicellular
organisms in terms of surface
area:volume ratio
Unlike single-celled organisms, larger multicellular
organisms cannot exchange substances simply by
diffusion through the body surface. This is because
the area is too small, in relation to the volume of
the body.
In a larger organism, such as an animal or plant,
specialised organs with large surface areas are
needed for the exchange of gases and other
substances. A transport system is necessary to
bring substances to and from these organs and to
distribute substances throughout the body.
17
(f)
describe how oxygen, carbon
dioxide, water, dissolved food
molecules, mineral ions and
urea maybe transported into
and out of humans, green
plants and single celled
organisms
Single-celled organisms – exchange of
substances occurs by diffusion through the cell
surface.
Humans – oxygen and carbon dioxide pass to and
from the air through the lungs and the respiratory
system. The blood carries oxygen and carbon
dioxide to and from all parts of the body.
Dissolved food molecules, water and minerals pass
into the blood, mainly though the intestines and are
distributed to all parts of the body.
Urea diffuses into the blood from cells throughout
the body. It is carried to the kidneys and then
excreted.
Plants – oxygen and carbon dioxide pass in and
out through the stomata of leaves. Water and
minerals are taken in through the roots.
SPECIFIED PRACTICAL WORK
•
SP2.1 Investigation into the effect of solute concentration on osmosis in potato chips
18
Investigation into the effect of solute concentration on osmosis in potato chips
Introduction
In this investigation, you will investigate osmosis in potato cells. You will prepare a range of
dilutions of blackcurrant squash and allow osmosis to occur. The concentration of the
blackcurrant squash will affect osmosis.
Apparatus
100 cm3 beaker containing approximately 95 cm3 of blackcurrant squash
50 cm3 measuring cylinders
6 × boiling tubes
white tile
scalpel
ruler
cork borers
distilled water
marker pen for labelling of boiling tubes
Access to:
blackcurrant squash
electronic balance ± 0.1 g
19
Method
1. Label boiling tubes with the concentrations of blackcurrant squash (0, 20, 40, 60, 80
and 100 %).
2. Using a measuring cylinder, transfer the relevant quantities of water and blackcurrant
squash into the boiling tubes to produce the solutions shown. Use the table below to
help you.
Concentration of
blackcurrant squash (%)
0
20
40
60
80
100
Volume of blackcurrant
squash needed to make
30 cm3 solution (cm3)
0
6
12
18
24
30
Volume of water needed
to make 30 cm3 solution
(cm3)
30
24
18
12
6
0
3. Place the boiling tubes in a test tube rack.
4. Cut six chips from a potato using a cork borer and cut into 5 cm lengths. Cut off any
potato skin.
5. Dry the chips on a paper towel.
6. Record the mass of each chip and place one chip in each of the boiling tubes. The
solutions should completely cover the chips.
8. Leave for 25 minutes.
9. Remove the chip from the 0 % solution boiling tube.
10. Dry the chip on a paper towel.
11. Record the final mass of the chip.
12. Repeat steps 9 -11 for the other solutions.
Analysis
1. Calculate the percentage change in mass for each chip.
2. Plot a graph of concentration against percentage change in mass.
3. Determine the concentration when there was no change in mass.
Risk Assessment
Hazard
Sharp scalpel
blade can cut
Risk
Control measure
Cuts to the skin while cutting potato
20
Always cut downwards and away from
the body
Teacher/ Technician notes
Blackcurrant squash (not sugar free) - 1 litre is enough for 9 working groups.
Large baking potatoes,1 per working group.
A potato chipper will quickly cut chips of uniform size. It saves time if the chips are cut (using
a chipper) just before or at the beginning of the lesson by a technician. Students will still
need to trim the chips to fit into the beaker/ boiling tube. If using a cork borer, each group
should use the same size borer for each of their potato cores.
No repeats are planned, but groups can compare results to discuss reproducibility.
The results should show that the chips gain mass in dilute concentrations of squash, but lose
mass in strong concentrations. The graph should be drawn with the x-axis across the centre
of the page, to show the increase and decrease in mass. Where the plotted line crosses the
x-axis shows the concentration where there is no gain or loss in mass. Students should
understand that this is the isotonic point and the concentration inside the potato cells is
equal to that in the external concentration.
Students should design their own table, but a suggested table format is shown below.
Concentration
(%)
Mass at
start (g)
Mass at end
(g)
Change in
mass (g)
Percentage
change in
mass (%)
Practical techniques covered
B1
Use of appropriate apparatus to make and record a range of measurements
accurately, including length, area, mass, time, temperature, volume of liquids and
gases, and pH.
B3
Use of appropriate apparatus and techniques for the observation and measurement
of biological changes and or processes.
B4
Safe and ethical use of living organisms (plants or animals) to measure physiological
functions and responses to the environment.
B5
Measurement of rates of reaction by a variety of methods including production of gas,
uptake of water and colour change of indicator
21
2.2 TRANSPORT SYSTEMS IN HUMANS
Spec Statement
Comment
(a)
describe the human circulatory
system as a double circulatory
system and its relationship with the
gaseous exchange system. The
blood passes through the heart twice
in every complete circulation. The
right side of the heart pumps the
blood to the lungs and the left hand
side pumps it around the rest of the
body
The human circulatory system is a double
circulatory system, as it involves one system for the
lungs – pulmonary and one for the other organs of
the body – systemic.
(b)
label on a given diagram of the heart:
the left and right atria and ventricles,
semi-lunar, bicuspid and tricuspid
valves, pulmonary artery, pulmonary
vein, aorta and vena cava
Observe a dissected/ model of the heart to include
coronary arteries and internal structure.
(c)
explain how the structure of the heart
is adapted to its function
The heart is made of cardiac muscle, which
contracts to pump blood around the body.
Understand the significance of the difference in
thickness of the muscle in the atria and ventricles
and between the right and left ventricles.
(d)
describe the passage of blood
through the heart including
explaining the functions of the valves
in preventing backflow of blood
Deoxygenated blood enters the right atrium from
the vena cava. It then goes through the tricuspid
valve to the right ventricle. From the right ventricle,
it goes through the semilunar valve into the
pulmonary artery to the lungs.
From the lungs, oxygenated blood is returned to left
atrium in the heart through the pulmonary veins.
The blood then flows through the bicuspid (mitral)
valve into the left ventricle.
From the left ventricle, it goes through the semilunar valve into the aorta. Blood is distributed to the
rest of the body (systemic circulation) from the
aorta.
(e)
describe and be able to compare the
structure of arteries and veins
In diagrams of arteries and veins, label: tough outer
coat, muscle layer, endothelium and lumen.
Compare the relative thickness of the blood vessel
walls and the size of the lumen in arteries and
veins. Veins contain valves.
(f)
explain how arteries and veins are
adapted to their functions
Arteries have thick muscular walls and a smaller
lumen to carry blood under pressure away from the
heart to all organs of the body. Veins carry blood
under lower pressure back to the heart and contain
valves which ensure flow of blood in one direction
only.
22
(g)
describe that in the organs
blood flows through very small
blood vessels called capillaries
which allow exchange of
substances. Explain that the
thin walls of the capillaries are
an advantage for diffusion and
that capillaries form extensive
networks so that every cell is
near to a capillary carrying
blood
Capillary walls are one cell thick - very short
diffusion pathway.
There are a large number of capillaries which
maintain the diffusion gradient between the tissue
and the blood.
(h)
describe the functions of the
four main parts of the blood:
plasma (transport of water,
nutrients, hormones, urea,
antibodies), red cells (carry
oxygen), white cells (defence)
and platelets (clotting). Explain
how red blood cells, white
blood cells, platelets and
plasma are adapted to their
functions in the blood
Red blood cells have no nucleus and contain
haemoglobin to carry oxygen. White blood cells
include lymphocytes and phagocytes.
Lymphocytes secrete antibodies and antitoxins and
phagocytes ingest and digest micro-organisms.
Platelets are fragments of larger cells which have
no nucleus. They stick to the walls of damaged
blood vessels forming a plug. This triggers a chain
of reactions which results in a mesh forming across
the damage (to form a scab).
SPECIFIED PRACTICAL WORK
•
SP2.2 Examination of artery and vein using a light microscope and production of
labelled scientific drawings of these from observation
23
Examination of artery and vein using a light microscope and production of
labelled scientific drawings of these from observation
Introduction
This practical requires you to observe and draw a prepared slide of an artery, and of a vein.
Apparatus
Light microscope
Slide of a Transverse Section (T.S.) of an artery
Slide of a Transverse Section (T.S.) of a vein
Method
1.
Use a light microscope to examine a T.S artery using the × 10 objective lens.
2.
Use the × 40 objective lens to identify the tough outer layer and the muscular and
elastic fibres.
3.
Draw a diagram to show the distribution of tissues in the correct proportion.
4.
Identify and label: tough outer layer; muscular and elastic fibres; lumen.
5.
Repeat steps 1 - 4 using a T.S. vein.
Analysis
1.
Compare the structure of the artery and vein and relate this to their function.
2.
Calculate the total magnification of the image seen under the microscope by
multiplying the power of the objective lens by the power of the eyepiece.
Risk Assessment
Hazard
Risk
Control measure
No significant risks are associated with this investigation.
24
Teacher/Technician notes
A lamp may be required, if not part of the microscope.
× 10 and × 40 objective lenses are suggested for viewing the slides. It will be necessary to
determine the optimum magnification before presenting the slides to students.
Students will need to be briefed regarding safe and effective microscope use prior to this
practical activity.
Students should produce low power plans of the blood vessels, no individual cells should be
drawn. This practical activity is effective at developing microscope skills and biological
drawing skills. Drawing skills should include using a pencil to draw smooth, continuous lines
with no overlapping or gaps. No shading or colour should be used.
Students can calculate the total magnification of the image as the power of the objective lens
multiplied by the power of the eyepiece. Students could also calculate the magnification of
their drawing if given the mean diameter of the blood vessel used.
A virtual microscope for demonstration purposes is available on the link below.
http://medsci.indiana.edu/a215/virtualscope/docs/chap7_3.htm
Practical techniques covered
B3
Use of appropriate apparatus and techniques for the observation and measurement
of biological changes and or processes.
B7
Use of appropriate apparatus, techniques and magnification, including microscopes,
to make observations of biological specimens and produce labelled scientific
drawings.
25
2.3 TRANSPORT SYSTEMS IN PLANTS
Spec Statement
Comment
(a)
explain that xylem tissue
contains tubes of dead cells
called xylem vessels and
explain how the vessels are
adapted to their role in the
transport of water and minerals
from the roots upwards within
plants
The tubes of dead cells in xylem have very strong
cell walls and are hollow. This means they do not
collapse under pressure and water passes through
easily.
The tubes pass up from the roots through the stem
and into the veins in every leaf.
(b)
explain how phloem is adapted
to carry sugar from the
photosynthetic areas to other
parts of the plant. Sugar is
moved to other parts of the
plant for use in respiration and
converted into starch for
storage. This is called
translocation
Phloem consists of long, narrow, living cells which
have large spaces inside for transporting sugar
solutions. These phloem cells carry sugars from the
veins in every leaf to all other part of the plant.
( No details of mechanisms are required)
(c)
explain the significance of root
hairs in increasing the area for
absorption, the role of osmosis
in the uptake and movement of
water through a plant and how
mineral salts are taken up by
root hairs by active transport
(d)
describe the structure of a leaf
and be able to label the
following structures on a
diagram of a T.S. leaf: cuticle,
epidermis, stomata, palisade
layer, spongy layer, xylem and
phloem
(e)
describe the structure of
stomata to include guard cells
and stoma and how stomata
can open and close to regulate
transpiration
When the guard cells surrounding a stoma change
shape the stoma becomes larger or smaller. This
opening and closing of stomata is important in
controlling how much water vapour passes out of
the leaves. Guard cells and stoma should be
identified on a given diagram.
( No details of mechanisms are required)
(f)
describe the process of
transpiration resulting in the
movement of water through a
plant
Transpiration occurs when water vapour, passing
out of the leaves of a plant, creates a negative
pressure on water in the xylem. Water then rises up
through the xylem from the roots.
Transpiration occurs even in conditions of water
shortage.
26
(g)
explain the environmental
factors that can affect
transpiration, including light
intensity, air movement and
temperature and that this can
be investigated with the use of
a simple potometer
Environmental factors affect the rate of loss of
water vapour from leaves and hence the rate of
transpiration.
Increased temperatures and increased air
movements tend to increase the rate of
transpiration. Light levels affect the opening and
closing of stomata.
27
3 – HEALTH, DISEASE AND THE DEVELOPMENT OF MEDICINE
3.1 HEALTH AND DISEASE
Comment
Spec Statement
(a)
describe the relationship
between health and disease
In the past, health was thought of simply as the
absence of disease. In modern times there is
greater emphasis on the promotion of health and
prevention of disease.
(b)
describe diseases as being
communicable and noncommunicable diseases as
exemplified by influenza and
cardiovascular disease
Communicable diseases – illnesses which result
from infections by micro-organisms (pathogens)
and are contagious among individuals.
e.g. Influenza- caused by a virus, can be caught
from an infected person by contact or droplet
infection..
Non-communicable disease – illnesses which are
often the result of unhealthy lifestyles and
sometimes inheritance.
e.g. cardiovascular disease (CVD)- linked to
obesity, lack of exercise, smoking
In former times most disease–related deaths were
caused by communicable diseases. Now, the
majority of serious illnesses are related to noncommunicable diseases.
(c)
describe the interactions
between different types of
disease, as exemplified by the
increased risk of developing
skin cancer when HIV positive
and the increased risk of
cardiovascular disease in
diabetes patients
HIV – The virus weakens the immune system and
reaches high levels in the blood. Skin cells, which
become infected by the virus, divide and grow
uncontrollably, leading to skin cancers such as
Koposi's Sarcoma.
Diabetes- In type II diabetes, blood sugar levels
can become very high (hyperglycaemia). This is
can damage the walls of blood vessels and lead to
CVD (high blood pressure, stroke , heart attack).
28
3.2 COMMUNICABLE DISEASE
Spec Statement
(a)
explain the means by which
communicable diseases
caused by viruses, bacteria,
protists and fungi can be
spread in animals and
plants. This should include
by contact, aerosol, body
fluids, water, insects,
contaminated food.
(b)
describe the following
diseases, this should include
the causative agent, the
effect on the infected
organism and how they can
be prevented from spreading
• HIV/AIDS
• Chlamydia
• Ash die back
• Malaria
Comment
AIDS (Acquired Immune Deficency Syndrome) is
caused by HIV (Human Immunodeficiency Virus). The
virus infects lymphocytes which are part of the body's
immune system. Without immunity, the body can
become infected with a variety of micro-organisms,
e.g. tuberculosis or pneumonia. The virus is spread by
blood to blood contact, especially during sexual
intercourse. Methods of prevention include the use of
condoms and disposable gloves should be used where
there is any danger of contact with contaminated
blood. Antiviral agents can be used, but they only
prevent the multiplication of the virus inside cells and
must be taken throughout life.
Chlamydia, this is the most common sexually
transmitted disease in Britain. It is caused by the
bacterium Chlamydia trachmatis and is spread during
sexual intercourse via the vagina and urethra. Its
spread can be prevented by the use of condoms. It can
be treated with antibiotics such as tetracycline or
erythromycin. However, if left untreated, it could cause
infertility in adults. It could also cause conjunctivitis in
babies during the process of birth if the mother is
infected. It can also spread to the babies lungs.
Malaria - This kills over a million people in the world
each year. It is caused by the single celled organism –
Plasmodium. Plasmodium is spread via female
mosquitoes of the genus Anopheles. Anopheles
mosquitoes bite humans and inject Plasmodium into
the blood stream. Plasmodium causes a fever when it
destroys red blood cells in humans. Treatment consists
of killing Plasmodium with anti-malarial drugs, such as
paludrine or daraprim. A vaccine against Plasmodium
has been developed. Prevention methods include:
killing mosquitoes with insecticide, releasing large
numbers of infertile male mosquitoes, biological control
of mosquitoes, use of mosquito nets and repellents.
29
(c)
describe the non-specific
defence systems of the human
body against pathogens,
including intact skin forming a
barrier against microorganisms
and blood clots sealing wounds
to seal the skin
(d)
explain the role of the immune
system of the human body in
defence against disease. This
should include the roles of
lymphocytes in secreting
antibodies and antitoxins and
phagocytes which ingest and
digest micro-organisms.
Explain the process by which
antigens from micro-organisms
trigger lymphocytes to release
antigen specific antibodies and
that antibodies activate
phagocytes
Lymphocytes are activated by the antigens on
micro-organisms and then multiply to form clones.
Each clone produces large quantities of identical
antibodies, specific to a particular antigen. These
antibodies attack and destroy the infecting microorganisms. After the infection is cleared, some of
the lymphocytes, called memory cells, remain in
the body.
The first time an infection occurs, the immune
system may respond rather slowly but if the
infection returns a second time the response is
much faster. This because memory cells produce
larger quantities of antibodies and in a much
shorter time than on the first infection.
(e)
describe how monoclonal
antibodies are produced from
activated lymphocytes which
are able to divide
continuously. Consequently
very large numbers of
identical antibodies, specific
to one antigen, are produced
continuously in very large
numbers
B-lymphocytes are fused with tumour cells
forming a hybridoma - this divides rapidly in
laboratory conditions to form a clone. The
hybridoma continuously produces specific
antibodies called monoclonal antibodies.
(f)
describe some of the ways in
which monoclonal antibodies
can be used including:
• diagnosis of diseases
including Chlamydia
and HIV
• tissue typing for
transplants
• monitoring the spread
of malaria
• supporting
chemotherapy for
cancers
Immunoassays are used in the diagnosis of
diseases caused by Chlamydia trachmatis, HIV,
and Plasmodium. Labelled (via radioactivity or
fluorescence) monoclonal antibodies are added
to test samples of infected body fluids and
attach to specific antigens. The extent of the
infection is related to the extent of the labelling.
Tissue typing for transplants - The
concentration of non-self-antigens in tissues is
assessed. Monoclonal antibodies can be used
against helper T-cells (T-lymphocytes) so Blymphocytes, normally causing rejection, are
prevented from functioning.
Monitoring the spread of malaria – blood is
taken from samples of people (even if they do
not show any malarial symptoms) and tested
with labelled monoclonal antibodies.
Monoclonal antibodies will detect the presence
30
of Plasmodium in the bloodstream (even if
they are dead - killed by anti-malarial drugs) as
they have specific antigens and will attach to
the labelled monoclonal antibodies. This
enables the success of anti-malarial drugs and
the potential spread of malaria to be monitored.
The destruction of cancer cells can be targeted
with the use of monoclonal antibodies. Some
types of cancer cells have specific antigens
called tumour markers. Monoclonal antibodies
can be produced that act against tumour
markers. If these are attached to anti-cancer
drugs, they will deliver the drug directly to the
cancer cells.
(g)
(h)
describe the following as
physical defence responses in
plants forming a barrier to
pathogens:
• cellulose cell walls,
which may be
strengthened by other
chemical substances
• leaf cuticle, which forms
a waxy layer on the
outside of the leaf
Physical defences to
herbivores include:
• specialised hardened
cells
• specialised structures
including stinging cells
and trichomes
describe chemical plant
defence responses, including
that many plants produce
enzymes or toxic chemicals
which attack insects and
disease-causing bacteria and
fungi
•
Pectins, added to cell walls, make them
stronger and prevent infections by mildew
fungi.
•
A thick waxy cuticle helps to prevent bacteria
and fungi from penetrating the surface of the
leaf.
•
Spines and thorns on stems and leaves of
plants prevent them from being eaten by
animals.
•
Stinging cells and trichomes ( specialised
hairs) inject irritating chemicals, such as
histamines, into animal skin and this deters
animals from eating them
Some plants produce terpenes in response to
attack by herbivores or invasion by microorganisms (pathogens). These toxic chemicals
destroy insects, fungi and bacteria.
Peroxidase enzymes are produced by many fruit
and vegetable plants as a defence response.
31
(i)
describe different ways plant
diseases can be detected and
identified, in the lab and in
the field. In the field,
diseased plants can be
identified by abnormal
growth or by signs of the
disease-causing organism,
such as bacterial slime or
eggs of insects. In the
laboratory, pathogens can be
grown on agar plates and
viruses can be cultured in
controlled conditions
Signs of abnormal growth include stunted
growth, excessive production of flowers or
altered colours of leaves.
Biochemical tests are used to identify bacteria
and viruses which have been cultured.
32
3.3 TREATING, CURING AND PREVENTING DISEASE
Spec Statement
Comment
(a)
explain that a vaccine contains
antigens derived from a
disease-causing organism. A
vaccine will protect against
infection by that organism by
stimulating the white blood
cells to produce antibodies to
that antigen. Vaccines may be
produced which protect
against bacteria and viruses
Vaccines generally use ‘non-active’ microorganisms,
antigens or parts of antigens to stimulate an immune
response (the details of individual vaccines and the
detail of vaccine production are not required).
(b)
discuss the factors influencing Candidates should consider the consequences for
parents in decisions about
individuals and society of when individuals decide
whether to have children
not to be vaccinated.
vaccinated or not, including the
need for sound scientific
evidence and the effect of the
media and public opinion.
Understand that science can
only provide a statistically
based ‘balance of probability’
answer to such issues
(c)
explain that antibiotics,
including penicillin, were
originally medicines produced
by living organisms, such as
fungi. Explain that antibiotics
help to cure bacterial disease
by killing the infecting bacteria
or preventing their growth
Antibiotics are now often chemically modified and so
are semi-synthetic or synthetic.
(d)
explain that antibiotics may kill
some bacteria but not viruses.
Some resistant bacteria, such
as MRSA, can result from the
over use of antibiotics. Explain
effective control measures for
MRSA
Some bacteria have become resistant to
antibiotics. The use of antibiotics in animal feed, in
some countries, could be discussed as well as
over-prescription for humans.
MRSA control measures could include:
• hand washing
• thorough cleaning of hospital wards
• use of alcohol gels
• MRSA screening
33
(e)
•
explain and understand the
safe use of basic aseptic
techniques involved in
inoculating, plating and
incubating microorganisms
•
•
•
•
•
•
(f)
describe the process of
discovery and development of
potential new medicines,
including preclinical and
clinical testing. New drug
treatments may have side
effects and extensive, large
scale, rigorous testing is
required including risk
management. Preclinical
stages involve testing on
human cells grown in the
laboratory, then on animals
and finally a group of healthy
volunteers. The new medicines
are then taken for clinical
testing using small groups of
patients
bacteria and fungi can be grown on
nutrient agar in a Petri dish, to produce
an agar plate.
Petri dishes and nutrient agar should
be sterilised before the agar is
poured.
an inoculating loop is used to transfer
bacteria and is sterilised before and
after use by heating it to red heat in a
Bunsen flame.
the Petri dish lid prevents microorganisms from the air contaminating
the culture and vice versa.
after inoculation the lid of the Petri dish
should be secured in place by strips of
adhesive tape for safety reasons
inoculated agar plates are incubated
at 250C in school laboratories, which
encourages growth of the culture
without growing pathogens
for safety reasons plates and
equipment should be sterilised after
use.
All drugs may have side effects. New drugs,
including medicinal drugs, may cause side effects
that do not show up until lots of people use them.
The use of the terms blind, double blind and
placebo in the context of drug development should
be understood.
SPECIFIED PRACTICAL WORK
•
SP3.3 Investigation into the effect of antibiotics on bacterial growth
34
Investigation of the effect of antibiotics on bacterial growth
Introduction
Antimicrobials are agents that are able to kill bacteria or halt their growth. They are widely
used in medicine to treat bacterial infections. In this experiment you will test different antimicrobial agents to assess how they affect bacterial growth.
Apparatus
Bunsen burner
1 × pre-prepared agar plate seeded with bacteria
4 × antimicrobial agents, labelled A, B, C and D
4-8 × paper discs (Whatman antibiotic assay paper discs/ or new filter/ chromatography
paper cut with a hole punch then sterilised by autoclaving)
sterile forceps
adhesive tape
marker pen
disinfectant solution and cloth
Diagram of Apparatus
35
Method
1. Wash your hands with the soap or handwash. Wipe down the working area thoroughly
with the disinfectant.
2. Work very close to a lit Bunsen burner. Flame the forceps and use them to pick up a
filter paper disc and dip the disc into antibiotic A.
3. Allow them to dry for 5 minutes on an open, sterile Petri dish, next to a lit Bunsen
burner.
4. Repeat step 3 for antibiotics B, C and D.
5. Use the agar plate that has already been prepared and seeded with bacteria.
6. Turn the dish upside down. Divide the base into four sections by drawing a cross with
the marker pen. Label the sections A, B, C, D.
7. Flame the forceps and then use them to pick up antibiotic disc A. Raise the lid of the
Petri dish at an angle and place the disc onto the agar in the centre of section A.
8. Repeat step 5 for the other 3 discs. Make sure the discs are placed in the centre of
each section.
9. Label the agar plate with your name and date. Tape the lid securely. Incubate inverted
for 2-3 days at 20-25 °C.
10. Observe the plates without opening them.
11. Record the width of the clear zone around each antimicrobial. A piece of squared
paper under the agar plate might be helpful here.
Analysis
1. Which antimicrobial agent was the most efficient in your investigation? Give reasons
for your answer.
36
Risk Assessment
Hazard
Risk
Bacteria can be
pathogenic
Touching bacteria when plate is
open
Bunsen burner
flame and
Forceps can
burn
Burning skin when placing discs on
plate
Control measure
Wash hands
Incubate plates at room temperature
Seal plate so that they are not opened
Care must be taken to keep hands a
safe distance away from the flame.
Do not touch tip of forceps after flaming
Teacher / Technician notes
Detailed instructions are given on the link below.
http://www.nuffieldfoundation.org/practical-biology/investigating-anti-microbial-action
Making agar and pouring plates
a
Calculate the quantity required and prepare just enough agar for the investigation –
around 15 cm3 for normal depth in a 90 mm Petri dish. Any surplus will keep for 6-12
months in tightly-sealed screw-top bottles if sterile.
b
Weigh out the agar medium powder containing the gel and chosen nutrients, add
water and sterilise the mixture for the time, and at the temperature, specified by the
manufacturer.
c
Heat agar and water at 95 °C to dissolve the agar. Always use a water bath to boil
agar, and never add agar to boiling water.
d
Stopper flasks with a well-fitting plug of non-absorbent cotton wool. Cover with
greaseproof paper or aluminium foil before sterilising by autoclaving.
e
After autoclaving, transfer to a water bath to equilibrate at 50 °C. Stack plates after
pouring to minimise condensation except in the top plate(s).
f
Warm the Petri dishes before pouring to minimise condensation.
g
Keep poured plates in a sealed plastic bag until needed to reduce dehydration of the
media.
37
Making a spread plate
1
Sterile spreaders are used to distribute inoculum of Bacillus subtilis over the surface
of prepared agar plates. You can sterilise a wrapped glass spreader in a hot air oven
or sterilise by flaming with alcohol.
2
To flame a spreader with alcohol:
a
Dip the lower end of the spreader into a small volume of alcohol (70% IDA)
contained in a vessel with a lid (either a screw cap or aluminium foil) or in a
glass (not plastic) Petri dish with a lid. Keep the alcohol container covered
and 1 metre away from the Bunsen burner flame.
b
Pass quickly through a Bunsen burner flame to ignite the alcohol. Ensure the
spreader is pointing downwards when and after igniting the alcohol to avoid
burning yourself.
c
Remove the spreader from the flame and allow the alcohol to burn off. The
burning alcohol will sterilise the glass.
d
Do not put the spreader down on the bench.
3
Cotton wool swabs can be used instead of glass spreaders. They may be preferable
as they avoid the need for using alcohol as a sterilising agent. Prepare them by
rolling small pieces of absorbent cotton wool around one end of a cocktail stick. Wrap
individually in aluminium foil or place inside a universal bottle to sterilise in an
autoclave or pressure cooker. These sterile swabs can then be dipped into the
solution or culture to be transferred, rubbed on the surface of the agar plate, and
immediately disposed of into disinfectant. (Note: Cotton buds from a pharmacist are
not sterile and may be impregnated with an antimicrobial agent.)
4
Use agar plates with a well-dried surface so that the inoculum dries quickly. Dry the
surface of agar plates by incubating for several hours (perhaps overnight) or put
them in a hot air oven (at 55-60 °C) for 30-60 minutes with the two halves separated
and the inner surfaces directed downwards.
The antibiotics can be bought as ready made discs or solutions can be made from everyday
ingredients. Many types of toothpaste contain low concentrations of anti-microbials, and
mouthwashes claim plaque-killing potential.
The ten spices with the most potent antibacterial effects are garlic, onion, allspice, oregano,
thyme, cinnamon, tarragon, cumin, cloves and lemon grass. Many spices with relatively
weak antibacterial effects become much more potent when combined; examples are in chili
powder (typically a mixture of red pepper, onion, paprika, garlic, cumin and oregano) and
five-spice powder (pepper, cinnamon, anise, fennel and cloves). Lemon and lime juice, while
weak inhibitors themselves, also have synergistic effects.
It is also possible to investigate different dilutions of a particular anti-microbial.
Students should be made aware of aseptic techniques before starting the practical activity. It
is possible that students can prepare their own pour plates and inoculate them if you wish.
38
Practical techniques covered
B1
Use of appropriate apparatus to make and record a range of measurements
accurately, including length, area, mass, time, temperature, volume of liquids and
gases, and pH.
B3
Use of appropriate apparatus and techniques for the observation and measurement
of biological changes and or processes.
B4
Safe and ethical use of living organisms (plants or animals) to measure physiological
functions and responses to the environment.
B5
Measurement of rates of reaction by a variety of methods including production of gas,
uptake of water and colour change of indicator.
39
3.4 NON-COMMUNICABLE DISEASES IN HUMANS
Comment
Spec Statement
(a)
recall that many noncommunicable human
diseases, including
cardiovascular disease, lung
cancer, skin cancer,
emphysema, type 2 diabetes
and cirrhosis can be caused by
the interaction of a number of
life style factors
(b)
explain the effect of the
following lifestyle factors on the
incidence of non-communicable
diseases at local, national and
global levels: exercise, diet,
alcohol, smoking and exposure
to UV radiation
(c)
evaluate the advantages and
disadvantages of the following
treatments for cardiovascular
disease
• statins
• angioplasty
• changes to lifestyle
diet/exercise
Candidates should understand the importance of
exercise and fitness to the individual combined
with the need for a healthy diet to control body
mass. This helps to prevent type 2 diabetes and
cardio vascular disease. Life style choices should
also take regard of the negative effects of smoking,
drinking alcohol and exposure to ultra violet light.
The links between these life style choices and
emphysema, cirrhosis and cancer should be
known.
Research the advantages and disadvantages of
the treatments for cardiovascular disease such as:
• Statins, a daily medication to control blood
cholesterol levels, but may cause side
effects.
•
Angioplasty, surgery to place a small
balloon in a blood vessel, which is inflated
to remove a blockage. This results in
improved blood flow e.g. in coronary
vessels, but sometimes is only a temporary
remedy.
•
Changes to diet/ lifestyle. These include
stopping smoking, taking up regular
exercise, eating more healthy food. These
can reduce risk and lower blood pressure.
However, a high level of self- discipline is
needed to maintain these long-term
changes.
40
4 – COORDINATION AND CONTROL
4.1 NERVOUS COORDINATION AND CONTROL IN HUMANS
Spec Statement
Comment
(a)
describe sense organs as
groups of receptor cells, which
respond to specific stimuli: light,
sound, touch, temperature,
chemicals, and then relay this
information as electrical
impulses along neurones to the
central nervous system
(b)
describe the structure of the
nervous system, including the
brain, spinal cord, sensory
neurones, motor neurones and
sensory receptors and the
central nervous system
consisting of the brain and
spinal cord
(c)
explain how the structure of the
nervous system (including
CNS, sensory and motor
neurones and sensory
receptors) is adapted to its
functions
(d)
describe the properties of reflex
actions. These reactions are
fast and automatic and some
are protective, as exemplified
by the withdrawal reflex,
blinking and pupil size
(e)
explain how the structure of a
Candidates need to be able to indicate, on a
reflex arc is related to its
diagram of a reflex arc, the direction of travel of the
function and be able to label a
impulse.
diagram to show: receptor,
sensory neurone, relay neurone
in spinal cord, motor neurone,
effector and synapses
Nerve impulses begin at receptors and pass along
sensory neurones to a coordinator. Motor neurones
pass on impulses to effectors. The function of
synapses should be known but knowledge of the
chemical nature of synaptic neuro transmitters is
not needed.
41
(f)
explain the functions of the
following parts of the eye:
sclera, cornea, pupil, iris, lens,
choroid, retina, blind spot and
optic nerve recognise and be
able to label these parts on a
diagram of a vertical section
through the eye
The functions include:
sclera – protective, tough white outer coat
cornea – clear part of sclera allows light to
enter and refracts light entering
pupil – hole in centre of iris which allows light to
enter
iris – muscles that alter size of pupil to control
amount of light entering
lens – changes shape to focus light onto
retina
choroid – a pigmented layer which absorbs
light to prevent reflection, also contains
blood vessels
retina – light sensitive layer , an image is formed
here, impulses sent to optic nerve
blind spot – where the optic nerve leaves the eye,
there are no light sensitive cells here
optic nerve – carries impulses from retina to brain
(g)
describe common defects of
the eye and explain how some
of these problems may be
overcome as exemplified by
long-sightedness, shortsightedness and cataracts
The ability of the lens to change its shape to focus
near and distant objects is called accommodation.
This becomes less efficient with age.
Cataracts can occur when changes in the lens of
the eye cause it to become less transparent. This
can lead to blurred vision and can be treated by
replacing affected lenses with new lens substitutes
within lens' capsules.
Long-sightedness, affects a person's ability to see
objects close to them. This occurs when the
eyeball is too short or the lens is not thick enough.
Convex lenses can be used to correct long
sightedness.
Short-sightedness, causes distant objects to
appear blurry. This occurs when the eyeball is too
long. Concave lenses can be used to correct short
sightedness.
(h)
describe the structure and
function of the following parts of
the brain: the cerebral
hemispheres, cerebellum and
medulla
Cerebral hemispheres control conscious activity
and act as centres for retaining past sensations
(memory).
The cerebellum controls balance and muscular
coordination.
The medulla controls automatic reactions taking
place in the body such as heart beat, peristalsis,
and breathing.
42
(i)
explain that brain function is
difficult to study and
involves the use of brain
scans, such as MRI and
electrical stimulation.
Discuss the ethical
implications of studying
patients with brain damage.
Magnetic resonance imaging (MRI) avoids surgery
in the diagnosis of brain damage. High frequency
radio waves are absorbed and transmitted in
tissues placed in a strong magnetic field. A
computer maps out the variation in signals to
produce a 3D image of the brain. Oxygenated
blood causes the image to become brighter. MRI
scans can therefore be used to follow the activities
of parts of the brain and can be used to analyse
function as well as structure.
(j)
explain some of the
limitations in treating
damage and disease in the
brain and other parts of the
nervous system as
exemplified by Parkinson's
disease and multiple
sclerosis
The major limitation in treating physical brain
damage is that brain cells do not regenerate when
they are lost. Degeneration of nervous tissue in
Parkinson's disease, multiple sclerosis and
dementia is permanent.
SPECIFIED PRACTICAL WORK
•
SP4.1 Investigation into factors affecting reaction times
43
Investigation into factors affecting reaction time
Introduction
If you notice a ball moving towards your head, the time it takes from when you first notice the
ball to when your arm reaches up to catch it is an example of reaction time. Even though
nervous impulses travel very quickly through your nervous system, your body doesn’t react
instantly. In this activity, you will conduct a simple, measurable experiment to study reaction
time and investigate the hypothesis that reaction time improves with practice.
Apparatus
30 cm ruler
Diagram of Apparatus
44
Method
1. Ask your first volunteer to sit in the chair with good upright posture and eyes looking
across the room.
2. Have the volunteer place their forearm (the part of the arm from elbow to hand) so it
extends over the edge of the table.
3. Ask the volunteer to place their thumb and index (pointer) finger on either side of the
bottom of the vertically placed ruler. The number “1” should be on the bottom, the “30”
near the top.
4. Let your volunteer practice holding the ruler with those two fingers.
5. Now, ask your volunteer to remove their fingers from the ruler while you continue to
hold it so that the bottom of the ruler is at a height of 2 cm above the fingers.
6. Tell your volunteer that you will release the ruler without warning. Their job will be to
catch it with their thumb and forefinger as soon as they sense it dropping.
7. Drop the ruler. When your volunteer catches it, record the number on the ruler
displayed just over the thumb. The lower the number, the faster the reaction time.
8. Conduct five trials with the same volunteer, dropping the ruler from 2 cm above their
fingers each time.
9. Repeat the experiment with at least five other volunteers and record your results in a
suitable table
Analysis
1. Use the conversion table below to convert the distance measured to a reaction time
for each volunteer
Catch distance
(cm)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Reaction time
(milliseconds)
50
60
701
80
90
100
120
130
140
140
150
160
160
170
170
Catch distance
(cm)
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
2. Discuss the extent to which your results support the hypothesis.
45
Reaction time
(milliseconds)
180
190
190
200
200
210
210
220
220
230
230
230
240
240
250
Risk Assessment
Hazard
Risk
Control measure
There are no significant risks associated with this procedure
Teacher / Technician notes
A possible alternative activity could be to compare the volunteer's dominant hand with their
non-dominant hand.
Students should design their own table, but a suggested table format is shown below.
Trial 1
Volunteer
Distance
(cm)
Reaction
time (ms)
Trial 2 etc
Distance
Reaction
(cm)
time (ms)
Practical techniques covered
B1
Use of appropriate apparatus to make and record a range of measurements
accurately, including length, area, mass, time, temperature, volume of liquids and
gases, and pH.
B3
Use of appropriate apparatus and techniques for the observation and measurement
of biological changes and or processes.
B4
Safe and ethical use of living organisms (plants or animals) to measure physiological
functions and responses to the environment.
B5
Measurement of rates of reaction by a variety of methods including production of gas,
uptake of water and colour change of indicator.
46
4.2 HORMONAL COORDINATION AND CONTROL IN HUMANS
Spec Statement
Comment
(a)
describe and be able to label
the positions of the following
glands on a diagram of the
human body: pituitary, adrenal,
thyroid, pancreas, ovaries and
testes
(b)
describe hormones as chemical
messengers, produced by
glands and carried by the
blood, which control many body
functions
(c)
describe the principles of
negative feedback mechanisms
in maintaining optimum
conditions inside the body
Any change from the balance in optimal internal
conditions results in the body's hormonal and
nervous systems compensating for the change and
restoring the balance.
(d)
explain the role of thyroxine
in the body as an example of
negative feedback.
Description should be
limited to effects of TRH and
TSH in the release of
thyroxine.
Thyrotropin-releasing hormone (TRH) is made
in the hypothalamus, an area at the base of the
brain. The nerve fibres that come out of it carry
TRH and release it into the blood surrounding
the pituitary gland. The TRH regulates the
formation and secretion of thyroid stimulating
hormone in the pituitary gland.
The pituitary gland secretes thyroid stimulating
hormone (TSH) which causes the thyroid to
secrete thyroxine. A decrease in thyroxine
levels stimulates TRH and therefore TSH
secretion, whereas an increase in thyroxine
slows down TRH secretion.
(e)
explain the action of
adrenaline in the body as an
example of positive
feedback. Description
should be limited to the
effects of adrenaline on the
heart, breathing and
muscles. Adrenaline is
converted into a less active
compound by the liver.
The positive feedback mechanism of adrenalin
production causes an increase in pulse rate and
volume of blood pumped by the heart with each
beat. It increases the depth of breathing and
dilates the blood vessels supplying muscles.
(f)
describe the roles of hormones
in human reproduction,
including the menstrual cycle
Testosterone regulates the development of male
secondary sexual characteristics.
Oestrogen stimulates the thickening of the uterine
wall during ovulation.
Progesterone prepares the uterus for pregnancy.
47
(g)
explain the interactions of
FSH, LH, oestrogen and
progesterone in the control
of the menstrual cycle
At the beginning of the menstrual cycle, two
hormones from the pituitary gland, follicle
stimulation hormone (FSH) and luteinizing
hormone (LH), stimulate the development of
egg-bearing follicles in the ovaries. As the
follicles mature, they secrete oestrogen.
(h)
explain the use of hormones in
contraception and evaluate
hormonal and non-hormonal
methods of contraception
Contraceptive pills or implants contain
combinations of synthetic oestrogen-like and
progesterone-like chemicals. These stop the
secretion of FSH and LH so neither follicle
development (an oestrogen effect) nor ovulation (a
progesterone effect) occurs. Non hormonal forms of
contraception such as condoms reduce the chance
of sexual transmission of diseases. Also some
hormonal forms of contraception may have a
variety of negative side effects such as nausea and
thrombosis.
(i)
explain the use of hormones
in modern reproductive
technologies to treat
infertility
Hormones are used to increase fertility.
Synthetic chemicals are used to stimulate
ovulation. They either act as FSH, which
stimulates the development of follicles or they
inhibit the production of oestrogen. Lack of
oestrogen (the normal FSH inhibitor) results in
more FSH being produced which stimulates
multiple follicle development.
48
4.3 HOMEOSTASIS IN HUMANS
Spec Statement
(a)
explain the importance to
animals of maintaining a
constant internal environment
in response to internal and
external change
(b)
explain why and how glucose
levels need to be kept within a
constant range. When the
blood glucose level rises, the
pancreas releases the
hormone insulin, a protein, into
the blood. This causes the liver
to reduce the glucose level by
converting glucose to insoluble
glycogen and then storing it
(c)
explain how glucagon
interacts with insulin to
control blood sugar levels in
the body
(d)
compare type 1 and type 2
diabetes and explain how they
can be treated. Diabetes is a
common disease in which a
person has a high blood sugar
(glucose) level. In Type 1
diabetes this is because the
body does not produce enough
insulin. In Type 2 diabetes the
body cells do not properly
respond to the insulin that is
produced
(e)
describe the function of the
skin in the control of body
temperature. Label a diagram
of a vertical section through the
skin to show: hair, erector
muscle, sweat gland, sweat
duct, sweat pore, blood
vessels. Explain the role of
these structures in temperature
regulation: change in diameter
of blood vessels, sweating,
erection of hairs; shivering as a
means of generating heat
Comment
Metabolism operates only within a narrow range of
temperature and pH and requires appropriate
nutrients and water.
The detection of glucose in urine is a symptom of
diabetes. Candidates should test artificially
prepared urine samples for the presence of glucose
using Benedict's solution.
The methods of treating diabetes include regularly
injecting insulin, a low sugar and low carbohydrate
diet and possible transplant of pancreatic tissue.
49
(f)
describe and be able to label a
diagram of the human
excretory system to show
kidneys, renal arteries, renal
veins, aorta, vena cava,
ureters, bladder, urethra and
be able to indicate the
direction of blood flow in the
blood vessels associated with
the kidney
(g)
describe the function of the
kidneys in maintaining the
water balance of the body and
remove waste products from
the blood and explain why this
is necessary. The waste, a
solution containing urea and
excess salts called urine,
passes from the kidneys in the
ureters to the bladder where it
is stored before being passed
out of the body. The presence
of blood or cells in the urine
indicates disease in the kidney
(h)
label a section through a
kidney to include: renal artery,
renal vein, cortex, medulla,
pelvis, ureter
(i)
label a diagram of a nephron
and its associated blood
supply to show: capillary knot,
Bowman's capsule, tubule,
collecting duct, capillary
network, arteriole to and from
capillary knot
(j)
explain the process of filtration
under pressure and that
selective reabsorption of
glucose, some salts, and much
of the water takes place in the
tubule
The position of nephrons within the kidney.
The significance of the difference in the diameter of
the blood vessels entering and leaving the capillary
knot in Bowman's capsule. Small molecules,
including urea, glucose, salts and water are forced
from capillary knot into the Bowman's capsule.
50
(k)
describe the effect of ADH
on the permeability of the
kidney tubules. The kidneys
regulate the water content of
the blood by producing
dilute urine if there is too
much water in the blood or
concentrated urine if there is
a shortage of water in the
blood. ADH increases the
permeability of the collecting
duct walls to water. More
ADH is produced if there is a
shortage of water in the
blood, more water is
reabsorbed and so a more
concentrated urine is
produced
(l)
explain the effect on cells of
osmotic changes in body fluids
(m)
Osmotic changes in body fluids will result in
changes in the concentration of chemicals in
cellular cytoplasm. Homeostasis aims to keep the
cytoplasm and body fluids isotonic. Dehydration of
cells will occur by osmosis if the water content of
body fluids is very low
explain the response of the
High external temperatures result in excess water
body to different temperature loss via sweating. In turn, this leads to body fluids
and osmotic challenges
becoming very concentrated compared to the
cellular cytoplasm. Osmosis then results in
dehydration if the water balance is not restored via
drinking.
SPECIFIED PRACTICAL WORK
•
SP4.3 Dissection of mammalian kidney
51
Dissection of mammalian kidney
Introduction
The kidney Is a vital component of the urinary system and is responsible for filtering the
blood and the production of urine. In this practical you will examine the external structure
and internal structure of the kidney following dissection.
Apparatus
kidney
scalpel
newspaper and dissection board
disposable gloves and goggles
Diagram of Apparatus
52
Method
1. Place dissection board on top of the newspaper and place the kidney on top of it.
2. BEFORE YOU DISSECT:
a. Examine the outside of the kidney. The ureter, renal artery and renal vein all enter
the kidney in the same area. It may be possible to observe these structures.
b. Draw a diagram of the kidney.
3. Slice longitudinally through the kidney as shown in the diagram.
4. Arrange the kidney with the cut surface facing upwards.
5. Locate the cortex, which is the outer dark red / brown layer; the medulla, which is the
lighter striped layer just below the cortex and the pelvis, which is the central white
mass that branches out into the medulla.
6. Draw a diagram of the kidney after dissection and label the following layers: cortex,
medulla and pelvis.
Risk Assessment
Hazard
Risk
Control measure
Sharp scalpel
blade could cut
Cuts to the skin whilst cutting kidney
Always cut downwards onto the
dissecting board
Use of animal
tissue is a
biohazard
Transfer of infection from animal
tissue to student
Ensure cuts are covered
Wear gloves
Teacher / Technician notes
Lamb or pig kidneys are widely available at a relatively low cost. Pig's kidneys are larger
and therefore easier to manipulate by the student. Some pre-packed kidneys that have
been freeze-thawed are often slippery to handle and difficult to dissect, therefore fresh
kidneys from a butcher would be preferable to use with students.
Practical techniques covered
B3
Use of appropriate apparatus and techniques for the observation and measurement
of biological changes and or processes.
B4
Safe and ethical use of living organisms (plants or animals) to measure physiological
functions and responses to the environment.
B7
Use of appropriate apparatus, techniques and magnification, including microscopes,
to make observations of biological specimens and produce labelled scientific
drawings.
53
4.4 PLANT HORMONES
Comment
Spec Statement
(a)
explain how auxins are
important in the control and
coordination of plant growth
and development, including the
positive response of plant
shoots to light, phototropism,
and plant roots to gravity,
gravitropism
Auxins are made in the tips of stems. They cause
cell elongation which enables stems to grow
towards light. The effect of auxin is inhibited by
light. If a stem is growing horizontally, the upper
side is exposed to more light than the upper side.
The lower side elongates more than the upper side
and therefore the tip of the stem grows up towards
light. Roots grow towards gravity because of auxin.
(b)
describe some of the effects of
plant hormones, relating to
auxins, gibberellins and
ethene
Gibberellins increase the stem length by
stimulating cell division and cell elongation.
They also break the dormancy of many types of
seeds. Ethene is a gas released from ripening
fruit. It speeds up the rate at which fruit ripens.
(c)
describe some of the
different ways in which
people use plant hormones
to control plant growth
Synthetic auxin is used in rooting powers to
encourage root growth in plant cuttings.
Ethene is used to control the ripening of fruit
when it is transported over long distances to be
sold out of season far from its site of
production.
54
5 – PHOTOSYNTHESIS
Comment
Spec Statement
(a)
describe the process of
photosynthesis and describe
photosynthesis as an
endothermic reaction, whereby
green plants and other
photosynthetic organisms use
chlorophyll and light to convert
carbon dioxide and water into
glucose, producing oxygen as a
by-product. Recall the word
equation for photosynthesis
(b)
explain the effect of
temperature, light intensity and
carbon dioxide concentration on
the rate of photosynthesis
(c)
explain the interaction of
these factors in limiting the
rate of photosynthesis
The chemical reactions of photosynthesis within
the cell are controlled by enzymes.
(Details of the enzymes involved in photosynthesis
are not required.).
The practical techniques used to investigate
photosynthesis: the use of sodium hydroxide to
absorb carbon dioxide; how to test a leaf for the
presence of starch; how oxygen and carbon
dioxide sensors and data loggers could be used.
The steps within the method for testing a leaf for
starch include: killing the leaf by placing in boiling
water, decolouration using ethanol, washing to
soften, testing with iodine. Understand the need for
de-starching the leaf prior to the procedure.
SPECIFIED PRACTICAL WORK
•
SP5 Investigation into factors affecting the rate of photosynthesis
55
Investigation of the factors affecting photosynthesis
Introduction
Light is one of the factors which affects the rate of photosynthesis.
In this investigation a green plant named Canadian pondweed (Elodea) will produce bubbles
of oxygen as a result of photosynthesis.
The number of bubbles of oxygen produced is affected by light intensity.
Apparatus
250 cm3 beaker
lamp
glass funnel
plasticine
test tube
8 cm length of pondweed (Elodea)
metre ruler ± 1 mm
sodium hydrogen carbonate powder
clamp stand, clamp and boss
spatula
Diagram of Apparatus
56
Method
1. Place the Elodea in a beaker containing 200 cm3 of water.
2. Add one spatula of sodium hydrogen carbonate to the water.
3. Stick 3 small pieces of plasticine to the rim of the funnel and place it upside down over
the plant.
4. Completely fill a test tube with water and carefully place over the end of the funnel with
the end under the water, clamp into place.
5. Place the lamp 5 cm away from the apparatus.
6. Start the stopwatch and record the number of bubbles of oxygen produced in
one minute.
7. Repeat the experiment with the lamp 10 cm, 15 cm, 20 cm, 25 cm and 30 cm from the
apparatus.
Analysis
1. Plot a graph of the distance against number of bubbles produced in 1 minute.
2. What conclusions can be reached from your results?
3. Evaluate your method and state how it could be improved.
Risk Assessment
Hazard
Lamps will
become hot
Risk
Control measure
Burning hand when moving lamp
57
Do not touch lamp until it has cooled
down.
Teacher/Technician notes
If the plant is not producing bubbles then the stem might have started to ‘heal’ up, cutting off
the end off may improve bubbling.
Begin the experiment with the lamp closer to the plant and move the plant further away as
this seems to give better results.
Cabomba caroliana (and Elodea crispa) are no longer available to buy. They have been
banned for culturing or sale under European regulations controlling invasive non-native
plants. CLEAPSS have worked with native plants (Hornwort and red Cabomba), and they
are OK for use. The CLEAPSS method (see the link below) overcomes the problems of the
native aquatic plants bubbling slowly.
http://science.cleapss.org.uk/Resource-Info/GL184-Using-video-recording-to-measure-therate-of-photosynthesis.aspx
If students have any difficulty in obtaining results, the link below can be used.
http://www.reading.ac.uk/virtualexperiments/ves/preloader-photosynthesis-full.html
The method as stated does not include repeats, but students should be encouraged to carry
out an appropriate number, if time allows.
This experiment is ideal for a discussion of the limiting factors of photosynthesis and how
they are controlled variables in this experiment. There is also a clear opportunity to discuss
the limitations of the investigation such as the difficulty in controlling temperature.
Students should design their own table, but a suggested table format is shown below.
Number of bubbles produced in one minute
Distance
from plant
to lamp (cm)
Trial 1
Trial 2
58
Trial 3
Mean
Practical techniques covered
B1
Use of appropriate apparatus to make and record a range of measurements
accurately, including length, area, mass, time, temperature, volume of liquids and
gases, and pH.
B2
Safe use of appropriate heating devices and techniques including use of a Bunsen
burner and a water bath or electric heater.
B3
Use of appropriate apparatus and techniques for the observation and measurement
of biological changes and or processes.
B4
Safe and ethical use of living organisms (plants or animals) to measure physiological
functions and responses to the environment.
B5
Measurement of rates of reaction by a variety of methods including production of gas,
uptake of water and colour change of indicator.
59
6 – ECOSYSTEMS
6.1 LEVELS OF ORGANISATION WITHIN AN ECOSYSTEM
Comment
Spec Statement
(a)
describe different levels of
organisation in an ecosystem
from individual organisms
through populations and
communities to the whole
ecosystem
The total number of organisms, of the same
species, in a given geographical area or location
make up a population. All the interacting
populations of different species within that location
form a community. The term ecosystem is used to
describe a community of organisms interacting with
each other and with their environment.
(b)
explain how some abiotic
factors affect communities as
exemplified by pH, light,
temperature and salinity
Abiotic (non-living) factors in a community are
constantly changing and these changes affect
living organisms. Plants in a community interact
with each other by competing for light, space and
mineral ions.
(c)
explain how some biotic factors
affect communities as
exemplified by predation,
disease and food availability
Biotic (living) factors in a community are constantly
changing. A change in a biotic factor might affect a
community e.g. by a change in the availability of
food or the presence of a new predator or
pathogen.
(d)
describe the importance of
interdependence and
competition in a community
(e)
describe photosynthetic
organisms as the main
producers of food and therefore
biomass for life on Earth. Green
plants, and other photosynthetic
organisms such as algae use
the light from the sun to
produce organic materials
Radiation from the sun is the source of energy for
living organisms. Green plants capture only a small
percentage of the solar energy which reaches
them.
(f)
describe the differences
between the trophic levels of
organisms within an ecosystem
including producers; first,
second and third stage
consumers; herbivores and
carnivores
Candidates should be aware that alternative terms
for the organisms in the trophic levels include:
primary consumers, secondary consumers and
tertiary consumers.
(g)
investigate data about food
chains and food webs and
explain that they show the
transfer of biomass between
organisms
Analyse data in terms of: efficiency of energy
transfer, numbers of organisms and biomass.
60
(h)
use data to construct and
interpret pyramids of numbers
(i)
describe pyramids of biomass
and explain, with examples,
how biomass is lost between
the different trophic levels. At
each stage in the food chain
biomass is used in repair and in
the maintenance and growth of
cells whilst biomass is lost in
waste materials and respiration
which is exothermic
(j)
calculate the efficiency of
biomass transfers between
trophic levels and explain how
this affects the number of
organisms at each trophic level
Draw and label pyramids of number and biomass
(to include names and values at each trophic
level).
61
6.2 THE PRINCIPLE OF MATERIAL CYCLING
Spec Statement
Comment
(a)
recall that many different
materials cycle through the
abiotic and biotic components
of an ecosystem. Nutrients are
released in decay, e.g. nitrates
and phosphates and these
nutrients are then taken up by
other organisms resulting in
nutrient cycles. In a stable
community the processes which
remove materials are balanced
by processes which return
materials
Only the general principle of the cycling of
elements is required here (no detail of nitrate or
phosphate cycles).
(b)
explain why it is important that
carbon is constantly cycled in
nature by the carbon cycle via
photosynthesis which
incorporates it and respiration
which releases it
Carbon is taken up by green plants in
photosynthesis and is passed to animals when they
eat the plants. Some of this carbon then becomes
part of carbohydrates, fats and proteins which
make up their bodies. Animals and plants release
carbon dioxide during respiration.
(c)
explain that microorganisms,
bacteria and fungi, feed on
waste materials from organisms
and that when plants and
animals die their bodies are
broken down by
microorganisms bringing about
decay. These micro-organisms
respire and release carbon
dioxide into the atmosphere.
Burning fossil fuels releases
carbon dioxide
Micro-organisms digest materials from their
environment for growth and other life processes.
These materials are returned to the environment
either in waste products or when living things die
and decay. When decay is prevented, fossil fuels
such as coal, oil and gas are formed and these
store energy in carbon compounds.
(d)
explain the importance the
water cycle to living organisms
Water evaporates from large bodies of water (seas
and oceans) and condenses to form clouds.
Precipitation provides fresh water for plants and
animals on land. Water from the land drains into
the seas and oceans.
62
(e)
explain the effects of factors
such as temperature and water
content on rate of
decomposition in aerobic and
anaerobic environments
If all other factors are equal then decomposition
occurs at a faster rate under aerobic conditions
than under anaerobic conditions. This is because
decomposers can metabolize more quickly in the
presence of oxygen. Generally an increase in
temperature increases the rate of decomposition up
to the point at which enzymes are denatured and/or
decomposers are killed. In waterlogged conditions
anaerobic decomposition may occur but it will be
very slow. In extremely dry conditions, such as
those found in hot deserts and the Dry Valleys of
Antarctica decomposition does not occur and the
mummification of animal remains is common.
(f)
evaluate the evidence for the
impact of environmental
changes on the distribution
of organisms, with reference
to water and atmospheric
gases
Interpret information and data providing evidence
for the possible changes in the distribution of
organisms as a result of increased desertification,
reported rise in sea levels, reported increases in
atmospheric carbon dioxide levels resulting in a
lowering of atmospheric pH and the acidification of
oceans.
SPECIFIED PRACTICAL WORK
•
SP6.2 Investigation into factors affecting decomposition
63
Investigation into factors affecting decomposition
Introduction
Decomposers secrete enzymes into the soil to break down waste. In this investigation the
enzyme urease catalyses the breakdown of urea into ammonia. The ammonia dissolves in
water to create an alkaline solution. The rate at which the solution becomes alkaline is
affected by the temperature. During this reaction the red acidic solution changes to an
alkaline blue.
Apparatus
10 × boiling tubes
test tube rack
labels
3 × syringes
dropping pipette
pH colour chart
1.5 % urease solution
1.25 % ethanoic acid
universal indicator in a dropper bottle
1 % urea solution
stopwatch
Method
1.
2.
3.
4.
5.
6.
7.
Label a test tube as 20 °C.
Use a syringe to add 2.5 cm3 of urea to the test tube.
Add 1 cm3 of ethanoic acid and 10 drops of universal indicator to the test tube.
Add 10 cm3 of urease to another test tube and place both tubes into a 20 °C water bath.
Pour the urease into the tube labelled 20 °C.
Start the stopwatch and record the time taken to turn from red to blue.
Repeat steps 1-6 for temperatures of 30, 40, 50 and 60 °C.
Analysis
1. Plot a graph of temperature against the time taken to change colour.
64
Risk Assessment
Hazard
Urea, urease
and
ethanoic acid
are all irritants.
Risk
Chemicals could get onto the skin
when adding to test tube
Control measure
Wash hands immediately if any
chemical gets onto them / wear
laboratory gloves.
Chemicals could get transferred from
Wear eye protection.
the hands to the eyes
Teacher/Technician notes
Thermostatically controlled water baths can be set up at specific temperatures and students
can fill beakers with water from these baths to use as water baths at their desks.
Thermometers could be provided and students asked to regularly check the temperature
allowing them to analyse the effectiveness of the method.
Urease enzyme has an optimum temperature of 60 °C, so it is possible that the denaturing of
the enzyme may not be seen in the range of temperatures given. Students could be asked to
predict what would happen to the time taken at higher temperatures.
Students should relate the results of their investigation to the enzymes involved in
decomposition and the effect of temperature on the rate of decomposition.
Students should design their own table, but a suggested table format is shown below.
Temperature
(ºC)
Time taken to change
from red to blue (s)
Practical techniques covered
B1
Use of appropriate apparatus to make and record a range of measurements
accurately, including length, area, mass, time, temperature, volume of liquids and
gases, and pH.
B2
Safe use of appropriate heating devices and techniques including use of a Bunsen
burner and a water bath or electric heater.
B3
Use of appropriate apparatus and techniques for the observation and measurement
of biological changes and or processes.
65
6.3 BIODIVERSITY
Spec Statement
(a)
describe how to use quadrats
to investigate the abundance of
species e.g. a comparison of
different sides of a hedge or
mown and unmown grassland
(b)
describe how transects can be
used to measure changes in
the abundance and distribution
of species e.g. seashore
(c)
describe the principles of
sampling, the need to collect
sufficient data and use of
appropriate statistical analysis.
(Details of statistical tests are
not required.) Describe the
principles of capture/recapture
techniques including simple
calculations on estimated
population size
Comment
Any suitable location could be used to show the
effect of different environmental factors. This
should include the use of line transects and random
quadrat distribution. An understanding that the
number/ distribution of quadrats used should be
enough to give valid results.
Candidates should know how to use the equation:
population size =
number in 1st sample x number in 2nd sample
number in 2nd sample previously marked
When using capture-recapture data, assumptions
made include: there is no death, immigration or
emigration and that the marking technique does not
affect chances of survival.
Candidates will not be expected to recall the
equation.
(d)
(e)
explain what is meant by
biodiversity, the variety and
number of different species in
an area, and why it is
important. Explain that indicator
species are an important set of
organisms whose numbers and
changing population can tell us
a lot about the changing state
of ecosystems
Biodiversity is important as it provides food,
potential foods, industrial materials, new medicines
and for human well-being.
describe both positive and
negative human interactions
within ecosystems and explain
their impact on biodiversity
An increase in the size of the human population
results in an increased demand for food, water and
other resources. These interactions, together with
urbanisation, industrialisation and globalisation, can
reduce biodiversity because ecosystems are
destroyed, reduced in area or damaged. The
extreme case is where populations die out or
organisms become extinct.
Indicator species and changes in pH and oxygen
levels may be used as signs of pollution in a stream
and lichens can be used as indicators of air
pollution.
If the resources in an ecosystem are used in a
sustainable way the human interaction within the
ecosystem can be considered as positive.
66
(f)
describe the ways in which
biodiversity and endangered
species can be protected
locally and globally, including
issues surrounding the use of
legislation. Explain the need
for and issues associated with
the collection of reliable data
and ongoing environmental
monitoring
Biodiversity and endangered species can be
conserved and protected by the following:
• Convention on International Trade in
Endangered Species
• Sites of Special Scientific Interest
• captive breeding programmes
• national parks
• seed/ sperm banks
• local biodiversity action plans
(g)
explain the use of biological
control agents and the
introduction of alien species
and their effects on local
wildlife. Explain the issues
surrounding the use of
biological control agents and
how the approach to using this
method of control has changed
as requirements for detailed
research and scientifically
based trials and analysis are
now more fully understood
Candidates should know that some animals and
plants have been introduced, deliberately and
accidentally, into areas where they do not naturally
occur and some have become invasive and caused
problems. Invasive species may grow faster than
native species and upset the natural eco-system.
Native species may not be able to compete with
them.
Research into the use of biological control agents
takes place, on a world-wide basis, in order to
understand how best to control alien species.
During the research, trials are needed to assess the
effects of biological control agents particularly on
non-targeted native species.
(h)
explain some of the benefits
and challenges of maintaining
local and global biodiversity
Maintaining biodiversity means that there is a
greater chance of the discovery of potential
treatments for many diseases and health problems.
It ensures the sustainable productivity of soils and
provides genetic resources for all crops, livestock
and marine species harvested for food.
Climate change, global warming and acidification of
the oceans all have a negative impact on
biodiversity. Controlling both climate change and
global warming is one of the greatest challenges
facing mankind at the present time.
SPECIFIED PRACTICAL WORK
•
SP6.3 Investigation into factors affecting the abundance and distribution of a species
67
Investigation into factors affecting the abundance and distribution of a species
Introduction
Daisies are a common plant species that can be found on a school field. Using quadrats for
random sampling allows you to estimate the numbers of daisy plants growing in this habitat.
This technique also reduces sampling bias. A simple calculation can then be used to
estimate the total number of daisy species in the entire school field habitat.
Apparatus
2 × 20 m tape measures
2 × 20 sided dice
1 m2 quadrat
Diagram of Apparatus
68
Method
1.
2.
3.
4.
5.
Lay two 20 m tape measures at right angles along two edges of the area to survey.
Roll two 20 sided dice to determine the coordinates.
Place the 1 m2 quadrat at the place where the coordinates meet.
Count the number of daisy plants within the quadrat. Record this result.
Repeat steps 2-4 for at least 25 quadrats.
Analysis
1. Use the following equation to estimate the total number of daisy plants in the field
habitat:
Total number of daisy plants in the habitat = total number in sample ×
Where:
total area = 400 m2
total sample area = number of 1 m2 quadrats used
total area �m2 �
total sample area (m2)
Risk Assessment
Hazard
Some plants have
thorns, sting or are
poisonous
Biting and stinging
insects
Tripping
Risk
Control measure
Adverse skin response
Cover skin at all times
Cover skin at all times.
Use insect repellent.
Care where walking
Adverse skin response
Strains and sprains
Teacher/Technician notes
Students could compare data for mown and unmown areas.
This practical activity is effective at developing practical fieldwork skills. Students can
discuss the need for a large sample of data in ensuring that there is confidence in a valid
conclusion. Also, students can describe the importance of random sampling techniques in
reducing/eliminating bias.
Alternative methods of generating coordinates can be used, such as using a random number
generator or random number tables.
69
Practical techniques covered
B1
Use of appropriate apparatus to make and record a range of measurements
accurately, including length, area, mass, time, temperature, volume of liquids and
gases, and pH.
B3
Use of appropriate apparatus and techniques for the observation and measurement
of biological changes and or processes.
B4
Safe and ethical use of living organisms (plants or animals) to measure physiological
functions and responses to the environment.
B6
Application of appropriate sampling techniques to investigate the distribution and
abundance of organisms in an ecosystem vis direct use in the field.
70
6.4 SOME OF THE BIOLOGICAL CHALLENGES OF INCREASING FOOD YIELDS USING
FEWER RESOURCES
Comment
Spec Statement
(a)
describe the issues
surrounding the need to
balance the human
requirements for food and
economic development with
the needs of wildlife. Discuss
how the collection of detailed,
reliable scientific information
and monitoring by biologists
could help to inform, manage
and reduce the impact of
development on the
environment e.g. the role of the
Environment Agency
The rising human population is causing increased
effects on the environment. This includes that more
space is needed for housing, industry and
agriculture. Where development is proposed, data
collected by biologists is used in an assessment of
environmental impact, including effects on
endangered species. The assessment is used to
decide whether the development should be allowed
to go ahead, be refused or modified to reduce the
effect on wildlife. Government agencies have an
important role in monitoring, protecting and
improving the environment.
(b)
describe some of the biological
factors affecting levels of food
security including increasing
human population, changing
diets in wealthier populations,
new pests and pathogens,
environmental change,
sustainability and cost of
agricultural inputs
Factors include:
•
•
•
•
An increasing human population has
threatened food security in some countries
– these countries cannot produce enough
food to feed their own population and often
these countries are financially too poor to
import food from other countries. Conflicts
have arisen in some parts of the World over
the availability or food.
Changing diets in wealthier countries has
resulted in ‘seasonal’ fruits and vegetables
being required all the year round. These
fruits and vegetables are often grown in
financially poor countries and transported all
around the World.
New pests and pathogens appear resulting
in an increased financial burden on
countries to find eradication solutions.
Environmental changes affect farming
practices throughout the World. Lack of
rainfall can result in crops failing causing
widespread famine. Conflicts have arisen in
some parts of the World over the availability
of water.
Attempts to increase crop yields throughout the
World have resulted in the increased cost of
agricultural inputs – fertilizers, pesticides,
herbicides, fungicides. Research must continue to
develop sustainable methods to feed the World’s
population.
71
(c)
describe and explain some
possible biotechnological and
agricultural solutions, including
genetic modification, to the
demands of the growing human
population
Alternative foods such as mycoproteins can be
grown on an industrial scale. Mycoprotein can be
produced from the fungus Fusarium and is protein
rich. The fungus is grown in large industrial vats on
a sugar syrup and under aerobic conditions.
Mycoprotein can be used to produce vegetarian
‘meat’ products such as ‘beefburgers’ or
veggieburgers.
Crop yields can be significantly increased by
genetic modification (GM).
Increased production of mycoprotein and the
further use of GM crops could provide more food
for the increasing world population.
72
7 – INHERITANCE, VARIATION AND EVOLUTION
7.1 THE GENOME AND GENE EXPRESSION
Spec Statement
(a)
describe chromosomes as
linear arrangements of genes.
Chromosomes that are found in
pairs in body cells are strands
of DNA
(b)
describe DNA as a polymer
made up of two strands forming
a double helix
(c)
describe DNA as a polymer
made from four different
nucleotides; each nucleotide
consisting of a common sugar
and phosphate group with one
of four different bases attached
to the sugar
(d)
recall a simple description of
protein synthesis. There are
four bases, A, T, C and G
within DNA and that it is the
order of these bases which
forms a code to produce
proteins
(e)
explain simply how the
structure of DNA affects the
proteins made in protein
synthesis. There is
complementary base pairing
between adenine and
thymine, cytosine and
guanine. The order of bases
determines the order in
which different amino acids
are linked together to form
different proteins. The bases
are read in groups of three,
this is called the triplet code
(f)
describe how the genes for a
particular protein may occur
in different forms (alleles or
variants) which have different
sequences of bases in their
DNA. These variants,
Comment
DNA has a ladder-like structure, the bases forming
the rungs. They should have an understanding of
complementary base pairing - A (adenine) pairs
with T (thymine) and that C (cytosine) pairs with
G (guanine).
Each triplet code identifies a particular amino
acid. In the cytoplasm, these triplet codes are
used to identify and link amino acids together
to form proteins.
Genes occur along chromosomes and different
forms of the same gene can occur. These different
forms of the same gene are known as alleles or
variants. These alleles would be found at the same
position on a pair of chromosomes. The alleles
would differ slightly in the arrangement of the base
73
therefore, will give rise to
differences in the order of
amino acids in the protein
and change its activity,
affecting a characteristic of
an organism
sequence in their DNA. The alleles of the same
gene deal with the same feature or characteristic in
an organism but each allele would make the
characteristic appear slightly differently in the
organism.
(g)
describe that a large amount
of DNA does not occur in
genes and the bases do not
form part of the genetic code
for producing proteins.
Instead, this non-coding DNA
coordinates and controls
how and when particular
genes become active and
produce proteins
Some of the DNA in a cell is responsible for coding
for the sequence of amino acids during protein
synthesis. This DNA is known as coding DNA or
genome DNA. Another type of DNA does not code
for amino acids during protein synthesis. This is
known as non-coding DNA. The ratio of coding to
non-coding DNA in a cell varies from organism to
organism. In humans it is about
80% non-coding : 20% coding.
The function of much of the non-coding DNA is not
known but some of it is important in switching on or
activating genes so that they can take place in
protein synthesis.
(h)
describe how an organism's
DNA can be analysed by
'genetic profiling' and how this
can be used to show the
similarity between two DNA
samples. The process involves
cutting the DNA into short
pieces which are then
separated into bands. The
pattern of the bands produced
can be compared to show the
similarity between two DNA
samples
The term genetic profiling should be used in place
of genetic fingerprinting to avoid confusion with
fingerprinting. No detail of the process is required.
(i)
describe the genome as the
entire genetic material of an
organism
All the genetic material of an organism is known as
its genome. It is the organism’s complete set of
DNA, including all of its genes. Each genome
contains all the information to build and maintain
that organism. In humans, a copy of the entire
genome – more than 3 billion DNA base pairs – is
contained in all cells that have a nucleus.
The entire genome of many organisms, including
humans, has now been studied. This will have
important medical significance in future.
(j)
discuss the potential
importance for medicine of our
increasing understanding of the
human genome
An understanding that the human genome is
important because it uses information from DNA to
develop new ways to treat, cure, or even prevent
disease.
SPECIFIED PRACTICAL WORK
• SP7.1 Simple extraction of DNA from living material
74
Simple extraction of DNA from living material
Introduction
DNA is the hereditary material found in all living things. In this practical you will extract the
DNA from strawberries. Strawberries can have up to 8 copies of each chromosome and so
contain a lot of DNA. When extracted from the strawberry this DNA is visible.
Apparatus
re-sealable plastic bag
strawberry
10 cm3 washing up liquid (detergent)
1 g sodium chloride
100 cm3 water
2 × 250 cm3 beakers (one beaker will be used for the filtering apparatus below)
filter funnel
coffee filter paper
ice-cold 90 % alcohol
ice lolly stick or plastic coffee stirrer
Method
1. Remove the green top from the strawberry.
2. Put the strawberry into the plastic bag, seal it and crush for about 2 minutes.
3. In a beaker mix together 10 cm3 of washing up liquid, 1 g of salt and 100 cm3 water. This
mixture is the DNA extraction liquid.
4. Add 10 cm3 of the extraction liquid to the bag with the strawberry.
5. Re-seal the bag and gently mix the extraction liquid with the strawberry for 1 minute.
6. Place the coffee filter inside the beaker and gently pour the strawberry mixture into it.
7. Pour 10 cm3 of ice-cold 90 % ethanol down the side of the beaker into the strawberry
mixture, do not mix or stir.
8. Within a few seconds you should see a white cloudy substance form in the clear layer
above the strawberry mixture. Use a lolly stick to pull strands of this out of the top
layer, this is the strawberry DNA.
75
Risk Assessment
Hazard
90% ethanol
could act as an
irritant
Risk
Inhalation could cause irritation of
the nose/throat
Ethanol could touch skin during the
experiment
Control measure
Use in well-ventilated area/wear safety
glasses.
Use gloves when pouring ethanol.
Teacher/ Technician notes
Chill the ethanol by keeping in the freezer for at least 2 hours or overnight. Keep on ice
during the experiment.
A variety of fruits can be used as an alternative to strawberries, such as kiwi or banana, but
check students have no allergies to the fruit used.
This experiment could be used as stimulus material to begin a piece of extended writing
describing what was observed in the experiment and linking it to what the student already
knows about the structure of DNA. It could also lead to a discussion of the ethical issues
surrounding DNA.
Practical techniques covered
B2
Safe use of appropriate heating devices and techniques including use of a Bunsen
burner and a water bath or electric heater.
B3
Use of appropriate apparatus and techniques for the observation and measurement
of biological changes and or processes.
B4
Safe and ethical use of living organisms (plants or animals) to measure physiological
functions and responses to the environment.
76
7.2 INHERITANCE
Spec Statement
Comment
(a)
explain the following terms:
gamete, chromosome, gene,
allele/variant, dominant,
recessive, homozygous,
heterozygous, genotype
phenotype
The terms gene and allele are not interchangeable.
(b)
describe genes as sections of
DNA molecules that determine
inherited characteristics and
that are in pairs. Genes have
different forms, called alleles
(c)
explain single gene inheritance
and be able to complete
Punnett squares to show this
(d)
predict the outcomes of
monohybrid crosses including
ratios
(e)
recall that most phenotypic
features are the result of
multiple genes rather than
single gene inheritance
(f)
describe sex determination in
humans. In human body cells,
one of the pairs of
chromosomes, XX or XY,
carries the genes which
determine sex. These separate
and combine randomly at
fertilisation
The use of Punnett squares to show the inheritance
of sex chromosomes.
(g)
describe the development of
our understanding of genetics
including the work of Gregor
Mendel. Discuss why the
significance of his work was
not recognised and validated
by scientists for many years
Gregor Mendel proposed the mechanism of
inheritance after a scientific process of meticulous
experimentation using large numbers of pea plants,
observation, further methodical experimentation,
statistical analysis and deduction. Mendel read his
paper at two meetings of The Natural History
Society of Brunn in Bohemia in 1865. It was
published in 1866 and circulated to many academic
institutions. However, the significance of Mendel’s
work was not recognised and validated until
scientists rediscovered his paper and replicated his
experiments in the early 1900s. The structure of
DNA and genes was unknown and not understood
until the 1950s.
An understanding of probability is also required.
77
7.3 VARIATION AND EVOLUTION
Spec Statement
(a)
explain some of the
advantages and disadvantages
of asexual and sexual
reproduction in a range of
organisms
Comment
Advantages of sexual reproduction:
• introduces variation into a population
• the species can adapt to new environments
• a disease is less likely to affect all the
individuals in a population
Disadvantages of sexual reproduction:
• time and energy are needed to find a mate
• not possible for an isolated individual
•
Advantages of asexual reproduction:
• population can increase rapidly
• can exploit a suitable habitat quickly
Disadvantages of sexual reproduction:
• does not lead to variation in a population
• the species may only be suited to one
habitat
• disease may affect all the individuals in a
population
(b)
describe simply how the
genome, and its interaction
with the environment, influence
the development of the
phenotype of an organism.
Variation may be due to
environmental or genetic
causes or a combination of the
two
(c)
state that there is usually
extensive genetic variation
within a population of a
species
(d)
recall that all variants result
from changes, mutations, in
existing genes and that
mutations occur at random.
Most mutations have no effect
on the phenotype but some
influence phenotype and very
few determine phenotype.
Mutation rates can be
increased by ionising radiation
The variation in height/length in organisms could be
used to show that individuals of the same species
are similar but they are never exactly the same.
Continuous and discontinuous variation should be
illustrated graphically – bell shaped curve for
continuous variation and discontinuous variation as
discrete groups.
The greater the dose/exposure to ionising radiation
the greater the chance of mutation.
(No reference to specific ionising radiation is
required.)
78
(e)
describe evolution as a change
in the inherited characteristics
of a population over time
through a process of natural
selection which may result in
the formation of new species.
Genes which enable better
adapted individuals to survive
are passed on to the next
generation. This may results in
new species being formed. The
process of natural selection is
sometimes too slow for
organisms to adapt to new
environmental conditions and
so organisms may become
extinct
The term natural selection should be understood.
The term ‘Survival of the fittest’ should be used with
care as it must be qualified in the context of
breeding i.e. survival of the fittest to breed.
(f)
explain how individuals with
characteristics adapted to their
environment are more likely to
survive and breed successfully.
This results in evolution
(g)
describe that evolution is
ongoing as shown by the
development of resistance to
antimicrobial chemicals by
bacteria or Warfarin resistance
in rats and that evolution can
also be evidenced by fossils
(h)
describe the impact of
developments in biology on
classification systems;
biological classification
systems continue to be
modified in the light of ongoing
research. Recently, the three
Domain system (based on
differences in RNA) proposes
two Domains of prokaryotes
and one further Domain
containing four main eukaryote
kingdoms – Protists, Fungi,
Plants and Animals
There is a need for a systematic scheme to divide
the variety of living organisms into groups in order
to make the understanding of the variety of living
things manageable and to understand trends and
relationships. The classification system maybe
based on morphological features or DNA analysis.
A simple understanding of possible groupings. The
five Kingdom classification using morphological
features: Bacteria, Single celled organisms, Plants,
Fungi, and Animals. The three Domain
classification based on analysis of DNA: Ancient
bacteria, Bacteria and All organisms with a nucleus.
No features of these groups required.
(i)
describe the work of Darwin
and Wallace in the
development of the theory of
evolution by natural selection
and explain the impact of these
ideas on modern biology
An understanding that Wallace and Darwin were
both working on the ideas of evolution and natural
selection at around the same time.
79
7.4 SELECTIVE BREEDING AND GENE TECHNOLOGY
Spec Statement
(a)
explain the impact of the selective
breeding of food plants and
domesticated animals
Comment
Humans have been carrying out selective breeding
of plants and animals for many thousands of years.
Parents, of the same species, with desirable
genetic features are bred together. Offspring, which
have inherited the desirable features, are selected
and also bred together. This continues over many
generations until all the offspring show the
desirable features.
Examples of these desirable features include:
• wheat plants with large seed grains
• sheep with fine wool
• cattle with high milk yields
• horses with fine features and a very fast
pace
However, selective breeding can result in the
inheritance of undesirable characteristics. This is
‘inbreeding’ and can lead to breeds becoming
particularly sensitive to disease or inherited defects
such as hip dysplasia in domestic dogs.
(b)
describe genetic engineering as a
process which involves modifying
the genome of an organism to
introduce desirable characteristics
The genome of an organism is modified by
introducing into it a gene from another organism.
The introduced gene would allow the required
desirable characteristic to be expressed in the
genetically engineered organism.
Crops that have had their genomes modified in this
way are known as genetically modified (GM) crops.
(c)
describe the main steps in the
process of genetic engineering
The steps include:
• the gene for the desirable feature is
identified in an host organism
• enzymes are used to cut out the required
gene from the DNA of the host organism
• the gene is inserted into a vector, either a
bacterial plasmid or a virus.
• the vector is used to insert the genes into
cells of animals, plants or microorganisms
at an early stage in their development
• organism develops the desirable features.
(d)
explain some of the possible
benefits and risks, including
practical and ethical considerations,
of using gene technology in modern
agriculture and medicine
Concerns include the risks of the spread of inserted
genes to other organisms and moral and ethical
concerns about modifying genomes.
Benefits include the possible use of genetic
engineering to treat or overcome inherited human
diseases.
80