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A-level
BIOLOGY
Paper 3
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Centre number Candidate number
Surname
Forename(s)
Candidate signature
I declare this is my own work.
A-level
BIOLOGY
Paper 3
2
*02*
IB/M/Jun22/7402/3
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ANSWER IN THE SPACES PROVIDED
3
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Section A box
Answer all questions in this section.
You are advised to spend no more than 1 hour and 15 minutes on this section.
0 1 Amino acids are used to make proteins. Table 1 shows the R groups of six different
amino acids.
Table 1
Amino acid R group
Alanine CH3
Asparagine CH2CONH2
Aspartic acid CH2COOH
Amino acid R group
Glutamic acid CH2CH2COOH
Glycine H
Serine CH2OH
0 1 . 1 Use Table 1 to identify the three different amino acids used to make the polypeptide
shown in Figure 1.
[2 marks]
Figure 1
Left amino acid
Middle amino acid
Right amino acid
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box 0 1 . 2 Table 2 shows three statements and names of four biological molecules.
Put a tick () in each box where the statement is true for the biological molecule.
[3 marks]
Table 2
Statement DNA ATP Reverse
transcriptase Phospholipid
Contains peptide
bonds
Is formed using a
condensation reaction
Is a polymer
Figure 2 represents the structure of adult human haemoglobin.
Figure 2
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box 0 1 . 3 The number of amino acids in the beta chains in Figure 2 is 3.546% greater than in
the alpha chains. Each alpha chain contains 141 amino acids.
Calculate how many amino acids there are in total in the haemoglobin molecule
shown in Figure 2. Give your answer to the nearest whole number.
[2 marks]
Answer amino acids
When a substance called BPG binds to haemoglobin, it reduces the affinity of
haemoglobin for oxygen.
0 1 . 4 Figure 3 shows an oxyhaemoglobin dissociation curve for haemoglobin in normal
conditions.
Sketch a curve on Figure 3 to show the oxyhaemoglobin dissociation curve for
haemoglobin when BPG binds to it.
[1 mark]
Figure 3
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box 0 1 . 5 Suggest and explain when it would be an advantage to a human for BPG to bind to
haemoglobin.
[2 marks]
10
7
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box 0 2 Figure 4 shows a diagram of a Pacinian corpuscle.
Figure 4
0 2 . 1 Name the structures labelled P, Q and R shown in Figure 4.
[2 marks]
P
Q
R
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box Two students (A and B) investigated reaction time in response to touch.
• Student A sat with her eyes shut and her forearm resting on a worktop so that her
hand was over the edge.
• Student B held a ruler vertically between student A’s thumb and first finger, with the
ruler at 0 mm lightly touching student A’s first finger.
• Student B released the ruler.
• As soon as student A felt the ruler fall, she closed her thumb and first finger to
catch the ruler as shown in Figure 5.
• Student B measured the distance the ruler had fallen to the nearest mm
Figure 5
The test was repeated three more times using the same hand to catch the ruler.
Table 3 shows student A’s results.
Table 3
Trial Distance the ruler has fallen / mm
1 79
2 97
3 10
4 94
The student was able to convert these distances into reaction times using Table 4.
Table 4
Distance the ruler fell / mm Reaction time / ms
10 45
20 64
30 78
40 90
50 101
60 111
70 120
80 128
90 136
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box 0 2 . 2 Calculate the percentage uncertainty in the measurement of Trial 1 in Table 3.
Put a tick () in the correct box below.
[1 mark]
0.633%
1.27%
2.53%
12.6%
0 2 . 3 In this investigation, it is not possible for a student to react in less than 45 ms
Suggest one explanation for the value recorded in Trial 3 in Table 3.
[1 mark]
0 2 . 4 Student A estimated that the length of the nerve pathway involved was 175 cm
Use Table 3 and Table 4 to calculate the mean speed of nerve impulse transmission.
Do not use the value for Trial 3 in your calculation.
[2 marks]
Answer m s–1
Question 2 continues on the next page
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box 0 2 . 5 In response to touch, nerve impulses can be transmitted at speeds of 76.2 m s–1
Suggest three reasons why, in this investigation, the estimated speed of student A’s
impulse transmission was less than 76.2 m s–1
[3 marks]
1
2
3
9
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box 0 3 A student prepared a stained squash of cells from the root tips of garlic to calculate a
mitotic index. He:
1. cut the end 5 mm from 10 garlic roots
2. placed the root tips into a Petri dish containing 5 cm3 of hydrochloric acid for
12 minutes
3. rinsed the root tips in distilled water
4. placed one of the root tips on a microscope slide and added toluidine blue stain
5. placed a coverslip onto the microscope slide, and gently pressed the coverslip
downwards on the root tip
6. observed the root tip using an optical microscope.
0 3 . 1 Suggest why the student soaked the root tips in hydrochloric acid in step 2.
[2 marks]
0 3 . 2 Pressing the coverslip downwards enabled the student to observe the stages of
mitosis clearly.
Explain why.
[2 marks]
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Figure 6 shows the student’s drawing of one field of view. box
Figure 6
0 3 . 3 Name the stage of mitosis shown in cell G. Explain the appearance of this cell.
[2 marks]
Stage of mitosis
Explanation
0 3 . 4 Use Figure 6 to calculate a mitotic index for the cells in this field of view.
[1 mark]
Mitotic index
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box 0 3 . 5 Other students in the class followed the same method, but calculated different mitotic
indices.
Apart from student errors, suggest two explanations why.
[2 marks]
1
2
Turn over for the next question
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box 0 4 . 1 Complete the following definitions.
[2 marks]
The genome is
The proteome is
Recombinant DNA technology can involve the transfer of fragments of human DNA
into bacteria. The bacteria are then used to produce human proteins.
0 4 . 2 Give two reasons why bacteria are able to use human DNA to produce human
proteins.
[2 marks]
1
2
0 4 . 3 Suggest and explain one reason why bacteria might not be able to produce every
human protein.
[1 mark]
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box Antithrombin is a protein. Antithrombin prevents blood from clotting too much.
Some people have a deficiency of antithrombin in their blood, so they need to inject
the protein.
Genetically modified goats are used to produce this protein. The human antithrombin
gene is transferred into goat embryos. The adult goats then make human
antithrombin protein.
Figure 7 shows an example of a DNA fragment that can be transferred into the cells
of goats.
Figure 7
0 4 . 4 The enhancer stimulates region M.
Name regions M and N shown in Figure 7.
[2 marks]
Region M
Region N
0 4 . 5 Explain the purpose of the marker gene.
[1 mark]
0 4 . 6 The enhancer only stimulates region M in the milk-producing glands of a goat.
Suggest two explanations for the importance of the enhancer being included in the
DNA fragment transferred.
[2 marks]
1
2
10
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box 0 5 Scientists investigated the effect of full sun and shade on the rate of photosynthesis in
a species of shade-tolerant tree.
To estimate the rate of photosynthesis, the scientists measured uptake of carbon
dioxide by trees in a forest. They measured uptake of carbon dioxide during two parts
of the day:
• 08.30 – 09.40 hours
• 11.40 – 13.15 hours.
Figure 8 shows the scientists’ results.
Figure 8
0 5 . 1 Calculate the total uptake of carbon dioxide between 11.40 and 13.15 hours in trees
exposed to full sun in a forest that is 12 000 m2 in area.
Give your answer in standard form. Show your working.
[3 marks]
Answer µmol
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box 0 5 . 2 Figure 8 shows there is a small difference in the mean uptake of carbon dioxide
between 08.30 and 09.40 hours by trees in full sun and by trees in the shade. When
the scientists performed a statistical test on these data, they calculated P > 0.5
State what this P value tells you about this difference.
Explain your answer using the words probability and chance.
[2 marks]
0 5 . 3 In this species of tree, very high light intensities can inhibit the release of electrons
from chlorophyll.
Suggest how this could explain the results shown in Figure 8 for 11.40 to 13.15 hours.
[4 marks]
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box Tomato plants grow best in high light intensities. To increase the yield of tomato
plants, a farmer uses LED lightbulbs to provide additional light.
The increase in dry mass (D) produced when using additional light can be calculated
using this equation.
L D =
0.4F
Where
L = light used in photosynthesis
F = GPP to NPP conversion factor for tomato plants
Table 5 shows some of these values for LED lightbulbs.
Table 5
L / MJ m–2 h–1 F / MJ kg–1
2.87 × 10–2 20
0 5 . 4 Use the equation and Table 5 to calculate the increase in dry mass produced when
using LED lightbulbs.
Give your answer in standard form and give the units.
[2 marks]
Answer Units
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Do not write
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box 0 5 . 5 Mature leaves from slow-growing, shade-tolerant plants produce poisonous chemicals
that are a defence against being eaten by herbivores.
Suggest how this benefits slow-growing, shade-tolerant plant
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