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Biology Department
A Level
AQA Biology
GCSE TO A LEVEL BIOLOGY
SELF-STUDY BRIDGING UNIT
Name:………………………………………..………..
2
INTRODUCTION
Now that you’ve chosen to study biology in more depth, you may be feeling rather
unsure about starting your A-Level biology course. But don’t worry – this guide has
been designed to help you with the transition to the A-Level course! A-Level and GCSE
courses have recently changed, and some of these changes have made the GCSE
course a better preparation for the A-Level one, making the move to A-Level easier and
more logical. Consequently, you should already be familiar with most of the major topics
and important terms covered by the A-Level biology course, for example, cell structures
and the differences between plant and animal cells. You may need to refresh your
memory on some of these though!
Although there is much overlap in topics and terms, there is quite a lot of new material
that you won’t have met before. Also, you need to go into more detail regarding the
topics you are already familiar with and your level of thinking and explaining has to be
deeper.
In order to fully prepare yourself for the A-Level Biology course complete the following
tasks to the best of your ability using your GCSE Biology notes and the suggested
resources. This will then be used to fully support you in the first weeks and ensure that
you can plan your independent study accordingly.
Contents:
Topic 1 – Cells
Inside Cells Matching Cells to their Jobs Topic 2 – Enzymes Enzyme Action – Sort it Out! Enzymes Inside and Outside Cells Just Right for Enzymes Topic 3 – Biochemistry Respiration for Life Analysing the Rate of Photosynthesis Topic 4 – Gas Exchange
Diffusion in the Lungs Delving Deeper into Diffusion Topic 5 – DNA DNA Structure Protein Synthesis Topic 6 – The Heart
Heart Structure
3
Topic 1 – Cells
Inside Cells Below is a diagram showing an animal cell and a diagram showing a plant cell. 1) Label which is
which. 2) For each cell, add label lines and show the position of the following structures and
3) annotate the diagrams to show the functions of each structure:
nucleus;
mitochondria;
ribosomes;
chloroplast;
cell membrane;
cell wall;
vacuole.
You could use these resources if you are unsure of some of the features or functions.
http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/cells/cellsrev1.shtml
http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_gateway/living_growing/moleculesrev1.shtml
4) Use the cells alive website to add an additional structure to both cells.
http://www.cellsalive.com/cells/cell_model.htm
4
Matching Cells to their Jobs 1) Match up the diagrams in the table to the name and description of the cell type given on the
next sheet. Remember that the name of the cell is not important – you need to look at the
structure of each one and think about its function to work out which description matches.
2) Write the descriptions in the table.
Diagram of cell Cell type
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Taking it further
1 A skeletal muscle cell contains a lot of mitochondria. Why do you think this is?
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2 An intestinal epithelial cell has one edge with lots of folds, looking a bit like the teeth of a
comb. Why is the membrane folded like this and what advantage is it to the cell?
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3 Explain the difference between a sperm cell (head and long thin tail) and an egg cell (large
and round) in terms of their function.
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.................................................................................................................................................. This is a good video about cell structure and the difference between specialised cells https://www.youtube.com/watch?v=v2lHztS4sMU
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Topic 2 - Enzymes
Enzyme action – sort it out!
1 Match up the following words and definitions
Recap your knowledge of enzymes here first.
https://www.youtube.com/watch?v=smtCH5HX44o http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/proteins/proteinsrev2.shtml
A Catalyst
1 The enzyme and substrate bound together.
B Enzyme
2 The special site in the structure of an enzyme where the substrate binds.
C Enzyme-substrate complex
3 The way in which an enzyme works. The substrate fits into the enzyme’s active site like a key fits into a lock. They have complementary shapes.
D Activation energy
4 A substance which changes the rate of a chemical reaction without being changed itself.
E Active site
5 A biological catalyst.
F Lock and Key Theory 6 The energy needed for a chemical reaction to take place.
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Enzymes Inside and Outside Cells
1 Fill in the table below, using the boxed information above.
Activity Type of enzyme used:
intracellular or extracellular?
Respiration
Photosynthesis
Digestion of starch, in small intestine, by amylase
from pancreas
Decomposition of dead plants in a compost heap
by bacterial enzymes
Protein synthesis
Some enzymes work inside cells and some are secreted outside cells.
Those that do their job while inside cells are called intracellular enzymes.
Those that do their job while outside cells are called extracellular enzymes.
Enzymes that help with respiration are in found in the cytoplasm and in mitochondria.
Enzymes involved with photosynthesis are in found in the chloroplasts.
Enzymes for digesting food are usually secreted from cells in the gut wall into the space
(lumen) of the gut.
Bacteria and fungi have intracellular enzymes for jobs like making proteins and respiration.
They don’t have a gut, so to digest food they secrete enzymes outside their cells. When the
food is digested they can then absorb the products of digestion back into their cells.
8
2 Explain why all enzymes must be constructed inside the cell, but digestive enzymes must
carry out their function outside the cell membrane.
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3 Suggest why it is easier to obtain extracellular enzymes, rather than intracellular enzymes,
from bacteria.
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4 List four reasons why bacteria are good sources of enzymes for the food industry or for
washing powders.
i) ...............................................................................................................................................
ii) ..............................................................................................................................................
iii) .............................................................................................................................................
iv) .............................................................................................................................................
5 Kevin and Angela were having an argument. Angela said that bacteria excrete digestive
enzymes outside their cells. Kevin said that they secrete them. Who do you think was correct
and why?
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Many enzymes used in the food industry are obtained from bacteria or fungi. These organisms
produce a lot of enzyme molecules in relation to their size.
These organisms can easily be cultured in a lab and can therefore be grown anywhere and
meet the demand at the time. Some bacterial enzymes are very robust and can work at
temperatures up to 100 C. Bacteria can be genetically modified to produce enzymes that we
need.
9
Just Right for Enzymes Michael’s company is testing a new enzyme to be used in a biological washing powder. The
enzyme’s job is to remove stains such as blood. It is a protease enzyme and comes from
bacteria that live in soda lakes in a region of Africa. These soda lakes contain sodium
hydroxide and have quite a high temperature.
The development team is deciding what instructions to write on the packet, to help customers
get the best results from this washing powder.
They have done some experiments and are looking at the data.
Rate of reaction vs pH Rate of reaction vs temperature
Review the effect of pH and temperature on enzymes using these resources: https://www.youtube.com/watch?v=z1SzIGp4V00 https://www.youtube.com/watch?v=pno4MqC65M4
http://www.bbc.co.uk/schools/gcsebitesize/science/add_edexcel/cells/enzymesrev1.shtml
1 Why is this enzyme described as a protease enzyme?
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2 Why do you think they added this enzyme to the washing powder to remove blood stains?
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3 From the data, what is the optimum temperature for this enzyme?
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4 In what range of temperatures does this enzyme still work well?
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5 What is the best pH range for this enzyme to work well?
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10
6 What is the pH of tap water?
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7 Washing powder tends to be alkaline. Only a small amount of washing powder is added to a
large amount of water. Do you think this enzyme will work well when it is in the water along
with the washing powder? Explain how you have arrived at your answer.
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8 Why do you think this enzyme was obtained from bacteria that live in soda lakes in Africa?
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9 What instructions for customers using this washing powder would you write on the box?
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10 Wool is made from sheep’s hair and hair contains protein. Leather is made from animal skin
and skin contains protein. What might happen if you washed a woollen jumper and a pair of
jeans with leather trim using this washing powder?
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11 What might happen if you got some of this washing powder on your skin or in your eyes?
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12 What other information or warning signs would you put on the box for this washing powder?
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11
Topic 3 - Biochemistry
Respiration for Life Watch this video for a quick recap first. https://www.youtube.com/watch?v=Xp0o19gWX7E
1 Decide whether the following statements are true or false. Write T or F next to each one. a) Respiration releases energy from food. _______________ b) Respiration happens inside cells. _______________ c) Animals respire all the time. _______________ d) Plants respire only at night. _______________ e) Bacteria don’t respire. _______________ f) Aerobic respiration happens inside mitochondria. _______________ g) Aerobic respiration needs oxygen. _______________ h) Enzymes that catalyse stages of aerobic respiration are inside mitochondria. __________
2 Write a word equation for aerobic respiration.
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3 Write a word equation for photosynthesis.
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4 Complete the table to compare photosynthesis and respiration. Some have been done for you
already.
Feature Respiration Photosynthesis
Enzymes are involved
Needs light
Happens in plants
Happens inside cells
Happens in animals
Happens in mitochondria
Uses oxygen
Happens in chloroplasts
Uses carbon dioxide
Makes water
Uses water
12
Analysing the Rate of Photosynthesis Watch this video for a quick recap first.
https://www.youtube.com/watch?v=xEhvsXG8cNs
Alica measured the rate of photosynthesis of some pondweed.
She changed the light intensity and measured the volume of gas collected for 5 minutes at each
light intensity. She kept the temperature at 25 C.
1 Plot her results on the graph paper provided.
To recap graph drawing: https://www.youtube.com/watch?v=9BkbYeTC6Mo
1 What simple test could Alica carry out to show that the gas produced by the plant was
oxygen?
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2 Her friend, Hannah, said that the gas would also contain some carbon dioxide from the
respiration of the plant. Alica said it wouldn’t as plants don’t respire when it is light. Explain
who was correct.
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3 Describe the effect light intensity had on the rate of photosynthesis.
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Light Intensity /arbitrary units
Rate of photosynthesis
/mm3 min-1
40 1.1
60 2.4
120 3.7
150 4.6
200 5.5
250 6.2
330 7.9
420 7.8
500 7.9
600 7.9
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4 What factor limits photosynthesis in dim light?
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5 What do you think limits photosynthesis in bright light?
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6 Calculate the percentage increase in rate of photosynthesis as the light intensity increases
from 100 to 300 units. Write your answer to the nearest whole number.
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Taking it further
Alica repeated the experiment but this time she kept the temperature at 40 C.
Light intensity
in arbitrary
units
Volume of gas collected
in 5 minutes in mm3
Volume of gas collected
in 1 minute in mm3
30 8.5 1.7
60 15.0 3.0
125 25.0 5.0
150 29.0
200 36.0
240 40.0 8.0
325 50.0 10.0
420 51.0
500 50.0 10.0
600 50.5
7 Fill in the gaps in the table and then plot Alica’s second set of results on your graph.
8 Suggest why the rate of photosynthesis is higher at 40 C.
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In 1880 a scientist called Theodore Engelmann devised an experiment
to learn which wavelengths (colours) of light caused the highest rates of
photosynthesis. He placed a piece of a green alga under a microscope.
There were also bacteria present. The bacteria could move and
Engelmann knew that these bacteria always moved to areas where there
was lots of oxygen. He shone different colours of light onto the
chloroplasts in the alga and then counted the numbers of bacteria near
the chloroplasts.
Plot this
column
14
The results are shown in the table.
Colour of light Red Orange Yellow Green Blue Violet
Number of bacteria near
chloroplast
150 100 60 30 120 70
9 Which colour of light causes the greatest rate of photosynthesis? Explain how you arrived at
this conclusion.
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Photosynthesis questions Alica measured the rate of photosynthesis of some pondweed.
She changed the light intensity and measured the volume of gas collected for 5 minutes at each
intensity. The results were plotted on a graph, as shown below.
1 What is the gas produced by the plant?
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2 Look at the graph between points A and B. What happens to the rate of photosynthesis as
light intensity increases?
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3 What factor limits the rate of photosynthesis between points A and B on the graph?
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4 Is this still limiting the rate of photosynthesis between points B and C?
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The effect of light intensity on photosynthesis
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5 What other factor(s) could be limiting photosynthesis between points B and C on the graph?
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6 Alica did the experiment again but gave the plant more carbon dioxide.
On the graph, draw the line you would expect to show how the rate of photosynthesis
changed with increasing light intensity, at this new increased level of carbon dioxide.
7 In another experiment, pieces of pondweed of different sizes were placed in equal volumes of
an indicator solution and the tubes were placed near a lamp.
The indicator solution started as green. It became
yellow if carbon dioxide was added and blue if
carbon dioxide was removed. All tubes were placed
under a lamp and the time for the indicator to
become blue was noted.
Tube Length of
pondweed
/mm
Time for
indicator to
become blue,
/ min
Rate of
photosynthesis,
/ min-1
A No
pondweed
Does not
change
0
B 5 100
C 10 60
D 20 35
E 40 20
F 80 12
b) Suggest why the rate increased as the length of the plant increased. (Hint: what is it in the
plant that is needed for photosynthesis?)
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c) Why was tube A included in the experiment?
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d) What was the independent variable in this experiment?
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e) What was the dependent variable?
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f) State three things that would have been kept constant in the experiment.
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a) Complete the table to show the rates of
photosynthesis for the plants in tubes B–F.
Give each value to the nearest whole
number.
16
Topic 4 – Gas Exchange
Diffusion in the Lungs
http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/cells/cellsrev4.shtml
The diagram shows the following:
the position of the lungs in
the body;
a single alveolus in the
lungs;
how carbon dioxide and
oxygen diffuse across the
alveolus wall and blood
capillary wall.
The two lungs of an average
adult have about 300 million
alveoli. The average
diameter of each alveolus is
about 0.25 mm, and its walls
are extremely thin.
1 Describe what happens to the air in the lungs when we breathe. What happens to the
concentration of carbon dioxide and to the concentration of oxygen?
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2 When is the concentration of oxygen in the alveoli the greatest: when you have breathed in
fully or when you have breathed out fully?
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3 Which way does oxygen diffuse when the concentration of oxygen in the alveolus is higher
than in the blood capillary?
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17
4 What happens when the concentration of carbon dioxide in the blood of the capillary is higher
than in the air in the alveolus?
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5 Apart from gas concentration, what other factors are likely to affect diffusion of gases into and
out of the alveoli?
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6 Someone with cystic fibrosis produces a lot of mucus that builds up in the lungs. Why would
this affect oxygen intake into the blood?
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7 Draw diagrams of an alveolus and blood capillary to show how oxygen and carbon dioxide
diffuse. Use symbols to represent oxygen molecules and carbon dioxide molecules.
18
Delving Deeper into Diffusion The following graph shows data from a study carried out at the University of Glasgow. A team
there is investigating coatings that might be used on underwater sensors and cameras to
prevent the build-up of biofilms. A biofilm is a slime layer composed of algae, fungi and bacteria.
Biofilms form easily on lens surfaces used underwater and cloud the apparatus.
One coating being investigated
is an ammonium compound
that is resistant to
microorganisms. The
ammonium compound is
incorporated in thin,
transparent hydrogel sheets
placed over the camera lens.
It is important to see how long
the hydrogel would remain
functional under different
underwater conditions.
In one experiment, the rate at
which the ammonium
compound diffused out of the
hydrogel sheet in sea water
and fresh water at different
temperatures was assessed. Here are the results.
1 Under what conditions does diffusion occur the fastest?
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2 What two factors affect diffusion in this experiment?
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3 Where does this experiment suggest the hydrogel coating would be the most successful? Explain
your answer.
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4 Where does this experiment suggest the hydrogel coating would be the least successful? Explain
your answer.
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19
Topic 5 - DNA
DNA Structure http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_gateway/living_growing/moleculesr
ev3.shtml
1 Complete the diagram to show the structure of DNA. Include the following labels:
complementary bases, pentose sugar, nitrogenous base, phosphate group, hydrogen bonds
20
Topic 6 – The Heart
Heart Structure
http://www.bbc.co.uk/schools/gcsebitesize/science/triple_aqa/transport_systems/blood_system/r
evision/2/
1 Fill in the blanks using the terms below:
valves exchange arteries veins contracts capillaries
oxygen wastes nutrients
2 Label the diagram below showing the structure of the heart.
blood travels
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