Paper 3: Unified biology

1(a)3 marks

Figure 1 shows the rate of oxygen uptake by germinating peas at different temperatures. Describe the trend shown.

Figure 1

1(b)3 marks

Explain the shape of the curve.

1(c)2 marks

Use Figure 1 to calculate the temperature coefficient, Q₁₀, between 20 °C and 30 °C.

1(d)3 marks

Suggest three improvements to this investigation.

2(a)5 marks

Explain how the movement of water through a plant depends on water potential gradients.

2(b)4 marks

Compare the role of osmoregulation in mammals with water conservation in plants.

3(a)4 marks

Sickle cell anaemia is caused by a substitution mutation in the β-globin gene. Explain how this mutation leads to sickle-shaped red blood cells.

3(b)4 marks

Explain why the sickle cell allele is more common in parts of Africa where malaria is common.

3(c)3 marks

In one population, 1 in 25 babies is homozygous for the sickle cell allele. Calculate the frequency of heterozygotes.

4(a)4 marks

Explain how the structure of capillaries and the formation of tissue fluid allow cells in a muscle to receive glucose during exercise.

4(b)4 marks

Explain why muscles produce lactate during intense exercise and how this affects the body.

5(a)4 marks

A student used an eyepiece graticule. At ×400, 1 epu = 2.5 µm. A cell measured 18 epu long and 12 epu wide. Calculate the actual dimensions and the area of the cell, assuming it is rectangular.

5(b)3 marks

Give three rules for producing a scientific drawing from a microscope slide.

6*9 marks

Discuss how the structure of proteins is related to their functions in living organisms. Use examples from different areas of biology.

78 marks

A student compared the length of ivy leaves growing in sunlight and in shade.

	Sun	Shade
Mean length / mm	42	58
Standard deviation / mm	5.1	6.3
Number of leaves	15	15

(a) Suggest a null hypothesis. (b) The student calculated t = 7.64. The critical value for 28 degrees of freedom at p = 0.05 is 2.05. What can she conclude? (c) Explain why a large sample size is important. (d) Suggest a biological explanation for the difference.

8(a)4 marks

Using an example, explain how negative feedback maintains a stable internal environment.

8(b)3 marks

Explain why positive feedback is not usually used to maintain homeostasis, and give one example where it is useful.

Finished?

Answer every question to finish (17 left), or finish when the time’s up.

Score 0 / 70 · 0 of 17 marked

This paper is written by Plasmo in the style of the OCR A-Level Biology exam. It is not a past paper and is not produced or endorsed by the exam board.