MERGED QUESTION PAPER AND MARK SCHEME BIOLOGY BIOLOGY PAPER 1-7402-1 FOR JUNE 2024, Exams of Biology

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For Examiner’s Use

Question Mark 1 2 3 4 5 6 7 8 9

10

TOTAL

Wednesday 5 June 2024 Afternoon Time allowed: 2 hours

A-level

BIOLOGY

Paper 1

Answer all questions in the spaces provided.

(^0 1). 1 Figure 1 shows the structure of a fatty acid molecule and the structure of a glycerol molecule.

Figure 1

On Figure 1 , draw a circle around the part of the fatty acid molecule and the part of the glycerol molecule that is removed to form a bond in a triglyceride molecule.

Name the bond formed between a fatty acid and glycerol in a triglyceride molecule.

Name the reaction involved in forming a bond between a fatty acid and glycerol in a triglyceride molecule. [3 marks]

Bond

Reaction

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Table 1 shows information about three fatty acids.

Table 1

0 1. 2 Name the fatty acid shown in Table 1 that is a saturated fatty acid. [1 mark]

(^0 1). 3 The melting point is the temperature at which a solid changes state to be a liquid.

Use Table 1 to describe the relationship between fatty acid structure and fatty acid melting point. [1 mark]

Question 1 continues on the next page

Do not write outside the (^0 1). 4 The ratio of saturated to unsaturated fatty acids in a cell-surface membrane^ box determines the extent of the membrane’s fluidity.

Scientists provided a cell culture of mouse phagocytes with liquid broth rich in unsaturated fatty acids.

The scientists observed:

• an increase in the proportion of phospholipids in the phagocytes containing unsaturated fatty acids
• more phagocytosis.

Suggest and explain why there was more phagocytosis. [3 marks]

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Do not write outside the (^0 2). 1 Describe the processes of facilitated diffusion and active transport.^ box [3 marks]

Facilitated diffusion

Active transport

(^0 2). 2 What are microvilli? [1 mark]

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Do not write outside the (^0 2). 3 Vitamin A is a fat-soluble substance.^ box

Micelles are involved in the process of vitamin A absorption.

Describe the process of vitamin A absorption into cells lining the ileum. [3 marks]

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Do not write outside the Turn over for the next question^ box

DO NOT WRITE ON THIS PAGE

ANSWER IN THE SPACES PROVIDED

Do not write outside the (^0 3). 1 Describe how we breathe in.^ box [3 marks]

(^0 3). 2 A scientist prepared alveolar tissue to view using an optical microscope. The scientist cut very thin slices of the alveolar tissue.

Explain why the scientist used very thin slices of alveolar tissue with the optical microscope. [2 marks]

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Do not write outside the (^0 3). 3 Figure 2 is an image of the lung tissue observed using an optical microscope.^ box

Figure 2

Identify the tube labelled A. [1 mark]

A

The scientist used a ruler to measure the diameter of some of the alveoli.

Table 2 shows the scientist’s results.

Table 2

Alveolus diameter / mm

Alveolus diameter / mm 4 2 5 1 2 3 5 2

0 3. 4 The magnification of the image in Figure 2 is × 40

Use this information and Table 2 to calculate the mean diameter, in μm, of the alveoli.

Show your working. [2 marks]

Answer μm

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Do not write outside the (^0 3). 5 Give the uncertainty associated with taking a measurement using a ruler with^ box 1 mm graduations.

Calculate the percentage error for a measurement using the ruler of 4 mm [2 marks]

Uncertainty ± mm

Percentage error

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Do not write outside the (^0 4). 1 Molasses is a solution obtained from sugar beet plants. The sugars present in^ box molasses are sucrose, glucose and fructose.

Give the number of different types of monosaccharides present in molasses. [1 mark]

(^0 4). 2 A student used the biochemical test for reducing sugars on a clear sample of molasses.

Describe the biochemical test for a reducing sugar.

Explain the result expected from the test on the sample of molasses. [3 marks]

Description of biochemical test

Explanation of expected result

(^0 4). 3 ‘Free sugar’ is the sugar in food and drinks released when food is crushed or when sugar is added to food at home or by manufacturers.

Scientists recommend that no more than 5% of the energy consumed per day should come from ‘free sugar’.

The mean daily energy requirement for a 10-year-old child is 8100 kJ

The ‘free sugar ’ in one tablespoon of molasses contains 250 kJ of energy.

Calculate the number of tablespoons of molasses required for a 10-year-old child to reach the recommendation for energy consumed in ‘free sugar’ per day. [1 mark]

Number of tablespoons per day

Do not write outside the (^0 4). 4 A scientist used the apparatus in Figure 3 to investigate osmosis.^ box

Figure 3

Use your understanding of osmosis to explain why the air pressure in the tube increased. [3 marks]

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Do not write outside the (^0 4). 5 The scientist repeated the investigation, but made one change to the molasses. The^ box scientist did not change the volume of molasses at the start of the investigation.

The scientist observed that the air pressure inside the tube increased by 160 kPa compared with 800 kPa in the first investigation.

Suggest the change the scientist made to the molasses to cause this smaller increase in air pressure.

Use the air pressure figures in a calculation to support your answer. [2 marks]

Suggested change

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Do not write outside the (^0 5). 1 Describe the appearance and behaviour of chromosomes during prophase and during^ box anaphase of mitosis. [4 marks]

Prophase

Anaphase

0 5. 2 A scientist used an optical microscope to determine the mitotic index in cells at different distances from the tip of onion roots.

Figure 4 shows the results.

Figure 4

Complete the word equation used to determine each mitotic index in Figure 4. [1 mark]

Mitotic Index =

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(^0 5). 3 The scientist used data from Figure 4 to calculate a correlation coefficient (r). The scientist then used a statistical test to determine the probability (P) associated with the value of r.

r = –0.98 (P < 0.05)

What can you conclude from this result? [2 marks]

0 5. 4 What can you conclude about the effect that distance from the root tip has on the proportion of cells in different stages of the cell cycle?

Use information in Figure 4. [3 marks]

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Do not write outside the (^0 6). 1 Give three structural differences between an mRNA molecule and a tRNA molecule.^ box [3 marks]

mRNA tRNA

0 6. 2 Table 3 shows mRNA codons and the amino acid coded by each codon.

Table 3

Figure 5 shows the mRNA base sequence produced when part of a gene coding for an enzyme is transcribed.

Figure 5

UUU CGG GCG

Use Table 3 to give the amino acids coded by the mRNA base sequence in Figure 5. [1 mark]

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Do not write outside the (^0 6). 3 A mutation occurred in the part of the gene transcribed in Question^ 06.2.^ box

Figure 6 shows the mRNA base sequence produced when the identical part in the mutated gene is transcribed.

Figure 6

UUU AGG GCG

The amino acids coded by this mRNA base sequence form part of the enzyme’s active site.

Use all the information in this question to:

• name the type of mutation that occurred to produce the mutated gene
• give the change in DNA caused by this mutation
• explain the effect this mutation will have on the function of the enzyme. [4 marks]

Type of mutation

Change in DNA

Explanation of effect on function of enzyme

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Do not write outside the (^0 7). 1 A student investigated the activity of the enzyme^ polyphenol oxidase^ (PPO) in^ box apple tissue.

When apple tissue is exposed to air, PPO catalyses a reaction between colourless phenol compounds in apple tissue and oxygen.

Figure 7 shows the reaction.

Figure 7

PPO phenol compounds + oxygen → brown pigment

The student measured the time taken for the brown pigment to appear in two apple varieties ( D and E ).

Method

1. Cut a 1 cm cube of apple tissue from variety D.
2. Put the cube on a plate and leave the plate at 30 °C
3. Measure the time for the brown pigment to appear.
4. Repeat steps 1 to 3 two more times.
5. Repeat steps 1 to 4 with apple tissue from variety E.

The student obtained the results shown below, but did not record the data in a results table.

Variety D = 15 min 50 s, 18 min, 14 min 30 s

Variety E = 6 min 30 s, 8 min, 7 min

In the box labelled Figure 8 , design a suitable results table.

• Enter the student’s results into the table.
• Calculate the mean results and include these in the table.
• Use 1 decimal place for both mean results. [3 marks]

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Do not write outside the Figure 8^ box

(^0 7). 2 Suggest and explain why the results for variety D are different from the results for variety E. [2 marks]

Question 7 continues on the next page

Do not write outside the (^0 7). 3 The student repeated the investigation but made one change to the method used to^ box prepare the apple tissue.

The student then observed shorter times for the brown pigment to appear in both apple varieties.

Suggest the change the student made to the method of preparing the apple tissue.

Explain why the brown pigment appeared in a shorter time.

Do not suggest using a different volume or mass of apple. [3 marks]

Change to method

Explanation

0 7. 4 The student wants to change the procedure to obtain a measure of PPO activity either in terms of how much substrate is used or how much product is produced.

Which change in procedure will provide a successful measure of PPO activity for the student?

Tick () one box. [1 mark] Measure the increase in oxygen concentration in the air around the cube of apple tissue on a plate. Measure the intensity of brown colour by comparing apple tissue with a colour chart showing a range of apple tissues of known pigment concentration. Measure the intensity of colour produced from brown apple tissue in a biuret test.

Measure the percentage of light transmitted through a cube of brown apple tissue using a colorimeter.^9

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Do not write outside the (^0 8). 1 Give two structural features of an aorta wall and explain how they are related to the^ box function of an aorta. [2 marks]

1

Question 8 continues on the next page

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Do not write outside the (^0 8). 2 Small tears may occur in the layers of tissue in an aorta wall. These tears weaken the^ box wall without bursting the aorta.

Scientists:

• measured the aorta diameter ( d ) in a large population of people over 60 years of age
• calculated the risk of an aorta wall developing a tear.

Table 4 shows their results.

Table 4

Aorta diameter d / cm Number of people inthe population^ Risk of an aorta walldeveloping a tear

d ≤ 3.5 2765 0.06

3.5 < d ≤ 4.0 630 0.33

4.0 < d ≤ 4.5 98 4.64

d > 4.5 7 380.00

Blood may push through the tears in the aorta wall. This produces a balloon-like swelling called an aneurysm and increases the aorta diameter. Aneurysms can cause the aorta to burst.

Using all the information, what can you conclude about aorta diameter and the risk of developing an aneurysm? [3 marks]

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Do not write outside the (^0 8). 3 A scientist investigated changes in a diseased heart and changes in a healthy heart^ box during cardiac cycles.

For each heart, the scientist obtained a value for:

• the mean blood volume in a full ventricle just before the ventricle contracts ( BVB )
• the mean ejection fraction ( EF ).

The EF is the proportion of blood pumped out of a full ventricle in one heartbeat.

The EF is calculated using this formula:

EF =

Blood volume pumped out of a full ventricle in one heartbeat (stroke volume) BVB

Table 5 shows the scientist’s results.

Table 5

Diseased heart Healthy heart

Mean BVB / cm 3 100 120

Mean EF 0.45 0.58

Using Table 5 , a student calculated that the percentage change in the stroke volume of the diseased heart compared with the stroke volume of a healthy heart is –30%.

The student’s answer is wrong because the final step of the calculation was performed incorrectly.

Using the equation and Table 5 , calculate the correct percentage change in the stroke volume of the diseased heart compared with the stroke volume of the healthy heart.

Identify the mathematical error in the final step of the student’s calculation. [3 marks]

Correct answer %

Mathematical error^8

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Do not write outside the (^0 9) Courtship behaviour in the frog species, Xenopus laevis , involves male frogs^ box calling to:

• attract sexually active females – these are advertisement calls
• start and continue mating – these are mating calls
• signal when a male is not sexually active – these are rasping calls.

Scientists investigated frog courtship behaviour by feeding a population of sexually active male frogs a diet containing the hormone EE2. The scientists also fed a separate control population of sexually active male frogs a diet without EE2.

They determined the percentage of males making advertisement calls or rasping calls in each population.

Table 6 shows their results.

Table 6

Population

Percentage of males making:

Advertisement calls Rasping calls

Males fed EE2 94.0 4.0

Males not fed EE2 (control) 97.0 0.5

(^0 9). 1 There were 800 males in the control population.

Each male made one type of call.

Use this information and Table 6 to calculate the number of males making mating calls in the control population. [1 mark]

Answer males

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Do not write outside the (^0 9). 2 Suggest one change the scientists could make to both frog populations to increase^ box the number of mating calls. [1 mark]

(^0 9). 3 The scientists also investigated the effect on female frog courtship behaviour of feeding EE2 to male frogs.

Table 7 shows their results.

Table 7

Population Median time females spent in courtship / s

Males fed EE2 8

Males not fed EE2 (control) 16

EE2 is contained in human contraceptive pills. Some EE2 is released in human urine and collects in sewage. Untreated sewage pollutes the water in frog habitats.

Suggest and explain the effect EE2 pollution in frog habitats will have on frog breeding.

Use information from Table 6 and Table 7 in your answer. [4 marks]

Effect on frog breeding

Explanation