AQA A Level Biology Paper 3 June 2022 question paper 7402/3

Amino acids are used to make proteins. Table 1 shows the R groups of six different amino acids.

Use Table 1 to identify the three different amino acids used to make the polypeptide shown in Figure 1.

Middle amino acid

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.

Figure 2 represents the structure of adult human haemoglobin.

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.

When a substance called BPG binds to haemoglobin, it reduces the affinity of haemoglobin for oxygen.

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.

Suggest and explain when it would be an advantage to a human for BPG to bind to haemoglobin.

Figure 4 shows a diagram of a Pacinian corpuscle.

Name the structures labelled P, Q and R shown in Figure 4.

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

The test was repeated three more times using the same hand to catch the ruler. Table 3 shows student A ’s results.

The student was able to convert these distances into reaction times using Table 4.

Calculate the percentage uncertainty in the measurement of Trial 1 in Table 3.

Put a tick () in the correct box below.

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.

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.

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

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.

Suggest why the student soaked the root tips in hydrochloric acid in step 2.

Pressing the coverslip downwards enabled the student to observe the stages of mitosis clearly.

Explain why.

Figure 6 shows the student’s drawing of one field of view.

Name the stage of mitosis shown in cell G. Explain the appearance of this cell.

Use Figure 6 to calculate a mitotic index for the cells in this field of view.

Other students in the class followed the same method, but calculated different mitotic indices.

Apart from student errors, suggest two explanations why.

Complete the following definitions.

Recombinant DNA technology can involve the transfer of fragments of human DNA into bacteria. The bacteria are then used to produce human proteins.

Give two reasons why bacteria are able to use human DNA to produce human proteins.

Suggest and explain one reason why bacteria might not be able to produce every human protein.

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.

The enhancer stimulates region M. Name regions M and N shown in Figure 7.

Explain the purpose of the marker gene.

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.

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

Figure 8 not reproduced here due to third-party copyright restrictions

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.

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.

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.

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.

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.

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.

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 plants.

Scientists measured the concentration of poisonous chemicals produced by

shade-tolerant plant species in six taxa. They compared this with the mean concentration of poisonous chemicals produced by all plants and the phylogenetic relationships between the six taxa.

Figure 9 shows the scientists’ results.

A journalist published the following summary of these results.

‘The more recently a shade-tolerant plant species evolved, the greater the concentration of poisonous chemicals it produces.’

Do the data in Figure 9 support this summary? Justify your answer.

Write an essay on one of the topics below.

Either

The uses and importance of ATP in organisms.

Or

The importance of cycles in biology.