Total marks: 100 · Duration: 105 minutes · Tier: Higher
Instructions to candidates
- Use black ink or black ball-point pen. Draw diagrams in pencil.
- Answer all questions in the spaces provided.
- In all calculations, show clearly how you work out your answer.
- You may use a calculator.
- Where a question describes apparatus, a graph or a diagram in words, you may find it helpful to sketch it.
Information
- The maximum mark for this paper is 100.
- The marks for questions are shown in brackets.
- You are expected to use good English and to organise information clearly, especially in questions marked with an asterisk (*).
- This paper covers AQA GCSE Biology topics 4.1 to 4.4: cell biology; organisation; infection and response; and bioenergetics.
Paper
Question 1 — Cells and microscopy (11 marks)
(a) Give two differences between the structure of a bacterial cell and the structure of an animal cell. [2 marks]
(b) A student views cheek cells with a light microscope. In a drawing, one cell is 6 mm across. The real width of the cell is 20 μm.
Calculate the magnification of the drawing. [2 marks]
(c) Describe how the student should prepare a slide of onion epidermis cells and bring the cells into focus under a light microscope. [4 marks]
(d) Explain why an electron microscope shows more detail of sub-cellular structures than a light microscope. [1 mark]
(e) A culture contains 4.0 × 10³ bacteria. The bacteria divide once every 20 minutes.
Calculate the number of bacteria after 3 hours. Give your answer in standard form to 2 significant figures. [2 marks]
Question 2 — Osmosis and active transport (12 marks)
A student cuts cylinders of potato, blots them dry and measures their masses. She places one cylinder in each of five sucrose solutions for 30 minutes, then blots and reweighs them.
| Sucrose concentration (mol/dm³) | 0.0 | 0.2 | 0.4 | 0.6 | 0.8 |
|---|---|---|---|---|---|
| Change in mass (%) | +12.0 | +5.5 | −1.0 | −7.0 | −12.5 |
(a) One cylinder had a mass of 2.50 g at the start and 2.38 g at the end. Calculate the percentage change in mass. [2 marks]
(b) Use the data to estimate the concentration of sucrose that would cause no change in mass. [1 mark]
(c) Explain why the cylinder in 0.0 mol/dm³ sucrose solution (pure water) gained mass. [3 marks]
(d) Explain why the student calculates the percentage change in mass instead of the change in mass. [1 mark]
(e) Explain why the student blots the cylinders dry before weighing them. [1 mark]
(f) Root hair cells absorb mineral ions from the soil by active transport. Explain why mineral ions must be absorbed by active transport rather than by diffusion. [3 marks]
(g) Give one way in which a root hair cell is adapted for absorbing water. [1 mark]
Question 3 — Cell division and stem cells (9 marks)
(a) Describe the three main stages of the cell cycle. [3 marks]
(b) Give one difference between embryonic stem cells and adult stem cells from bone marrow. [1 mark]
(c) Explain how therapeutic cloning could produce stem cells to treat a patient without the cells being rejected. [2 marks]
(d) Give one ethical objection to the use of embryonic stem cells. [1 mark]
(e) Explain why stem cells from plant meristems are used to clone rare species of plants. [2 marks]
Question 4 — Enzymes and digestion (12 marks)
A student investigates the effect of pH on the activity of amylase. She mixes amylase and starch solution with a buffer. Every 10 seconds she takes a drop of the mixture and adds it to iodine solution on a spotting tile. She records the time taken for all the starch to be digested.
| pH | 5 | 6 | 7 | 8 |
|---|---|---|---|---|
| Time taken for starch to be digested (s) | 140 | 60 | 90 | 200 |
(a) Describe how the student knows when all the starch has been digested. [2 marks]
(b) Calculate the rate of reaction at pH 6 using: rate = 1000 ÷ time. [1 mark]
(c) Explain why the rate of reaction is lower at pH 8 than at pH 6. [3 marks]
(d) Suggest how the student could find the optimum pH of amylase more precisely. [1 mark]
(e) Bile is released into the small intestine. State where bile is made and explain two ways in which bile helps the digestion of fats. [3 marks]
(f) Describe the test for protein, and give the positive result. [1 mark]
(g) Name the products of the digestion of lipids by lipase. [1 mark]
Question 5 — The heart, blood and gas exchange (12 marks)
(a) Humans have a double circulatory system. Explain one advantage of this. [2 marks]
(b) Describe how the resting heart rate is controlled. [1 mark]
(c) In 1.5 minutes, 7.2 dm³ of blood passes through the aorta. Calculate the mean rate of blood flow in cm³ per second. [2 marks]
(d)* Coronary heart disease can be treated with stents or with statins.
Evaluate the use of stents and statins to treat coronary heart disease. [6 marks]
(e) Give one way in which the alveoli are adapted for efficient gas exchange. [1 mark]
Question 6 — Plant tissues and transport (10 marks)
(a) Name the leaf tissue in which most photosynthesis takes place. [1 mark]
(b) A student uses a potometer to measure water uptake by a leafy shoot. An air bubble in the capillary tube moves 36 mm in 4.0 minutes. The radius of the capillary tube is 0.50 mm.
Calculate the rate of water uptake in mm³ per minute. Use: volume = π r² × distance moved. Give your answer to 2 significant figures. [3 marks]
(c) Explain why the rate of water uptake measured by a potometer is not exactly the same as the rate of transpiration. [1 mark]
(d) Explain why the rate of transpiration increases when air movement around the leaves increases. [2 marks]
(e) What is translocation? [1 mark]
(f) Explain how guard cells reduce water loss from a leaf when water is in short supply. [2 marks]
Question 7 — Communicable disease (12 marks)
(a)* Measles is a viral disease. Explain how vaccination protects a child from measles, and why vaccinating a large proportion of the population also protects people who have not been vaccinated. [6 marks]
(b) Explain why antibiotics cannot be used to treat measles. [1 mark]
(c) Malaria is a disease common in some tropical countries.
(i) Name the type of pathogen that causes malaria. [1 mark]
(ii) Name the vector that spreads malaria. [1 mark]
(iii) Give one way of reducing the spread of malaria. [1 mark]
(d) New drugs are tested in double-blind trials. Explain what a double-blind trial is and why it is used. [2 marks]
Question 8 — Photosynthesis (12 marks)
A student investigates the effect of light intensity on the rate of photosynthesis in pondweed. She places a lamp at different distances from the pondweed and counts the bubbles of oxygen released in one minute.
| Distance from lamp (cm) | 5 | 10 | 15 | 20 | 25 | 30 |
|---|---|---|---|---|---|---|
| Bubbles per minute | 60 | 60 | 52 | 31 | 20 | 14 |
(a) Light intensity is inversely proportional to the square of the distance from the light source. How many times greater is the light intensity at 10 cm than at 20 cm? [1 mark]
(b) Explain why the rate of photosynthesis decreases as the distance increases from 15 cm to 30 cm. [2 marks]
(c) The rate is the same at 5 cm and 10 cm. Explain why. [2 marks]
(d) The lamp gives out heat as well as light. Explain why this could affect the results, and suggest how the student could reduce the problem. [2 marks]
(e) Write the balanced symbol equation for photosynthesis. [2 marks]
(f) Give two ways in which a plant uses the glucose produced in photosynthesis. [2 marks]
(g) A greenhouse owner increases the carbon dioxide concentration, but only up to a certain level. Suggest why. [1 mark]
Question 9 — Respiration (10 marks)
(a) Write the word equation for aerobic respiration. [1 mark]
(b) Give two differences between aerobic respiration and anaerobic respiration in muscle cells. [2 marks]
(c) After a sprint, an athlete continues to breathe deeply for several minutes. Explain why. [3 marks]
(d) (i) Name the products of anaerobic respiration in yeast cells. [1 mark]
(ii) Give one use of this reaction. [1 mark]
(e) Metabolism is the sum of all the reactions in a cell or the body. Give two examples of metabolic reactions. [2 marks]