OxfordAQA International GCSE Biology: Digestion and enzymes (9201) – Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – examination boards hold copyright in their own papers. Use these alongside the official past papers from your board or school.

These questions cover section 3.2.4 (Digestion, parts a to c) of the OxfordAQA International GCSE Biology (9201) specification, Version 5.2, for exams May/June 2018 onwards.. Learn the content first from the study guide or the revision notes. Course pages: OxfordAQA IGCSE Biology and the checklist. The wider unit has Bioenergetics practice questions. Find weak areas with the free diagnostics.

Questions

1. Name the part of the digestive system that:

(a) makes bile [1] (b) stores bile [1] (c) absorbs most of the water from the food [1]

2. (a) Starch is insoluble. Explain why it has to be broken down before absorption. [2] (b) Name the products of protein digestion. [1]

3. A student boils a solution of amylase and then cools it. It no longer breaks down starch. Explain why. [3]

4. (a) Give two places in the body where lipase is made. [2] (b) Give two places where protease acts. [2]

5. Bile breaks a fat drop into smaller droplets. Model the drop as a cube of side 4 cm that breaks into 64 cubes of side 1 cm.

(a) Calculate the surface area of the large cube. [1] (b) Calculate the total surface area of the 64 small cubes. [1] (c) State how many times larger the surface area has become. [1] (d) Explain why this makes digestion of fat faster. [2]

6. Plan an investigation into how temperature changes the speed at which amylase breaks down starch. Include how you would make the results reliable. [6]

7. A protease from the small intestine is mixed with a milk-protein solution at five pH values. The time for the cloudiness to disappear is recorded.

pH	6	7	8	9	10
Time (s)	300	120	60	100	400

(a) Calculate the rate (1000 ÷ time) at pH 8. [1] (b) State the pH at which the enzyme works best, from these data. [1] (c) Calculate the percentage change in rate from pH 8 to pH 9. [2] (d) Explain the low rate at pH 10. [2] (e) Suggest why this enzyme works best at a different pH from a stomach protease. [1]

8. A drug stops the gall bladder releasing bile. Suggest and explain two effects on digestion. [4]

9. A student repeats an amylase and starch investigation three times at each of two temperatures. The time for the starch to disappear is in the table.

Temperature (°C)	Time 1 (s)	Time 2 (s)	Time 3 (s)
18	224	216	220
28	104	96	100

(a) Calculate the mean time at each temperature. [2] (b) Calculate the rate (1000 ÷ mean time) at each temperature. [2] (c) Calculate the percentage increase in rate when the temperature rises from 18 °C to 28 °C. [2]

10. A protease from a bacterium is tested for use in industry. Relative activity (100 is the highest) was measured.

Temperature (°C)	30	50	70	90
Relative activity	20	55	100	10

(a) Give one use of a microbial protease in the home. [1] (b) State the best temperature from these data. [1] (c) Calculate the percentage fall in activity from 70 °C to 90 °C. [2] (d) Explain the fall in activity at 90 °C. [2]

11. A meal contains bread, egg white and butter. Describe and explain how each food is digested in the digestive system. Include where enzymes are made, where they act and the roles of acid and bile. [9]

12. Lactase from a yeast is added to milk that contains 4.8 g of lactose in each 100 cm³. After 6 hours at constant temperature the milk contains 0.6 g of lactose in each 100 cm³.

(a) Calculate the percentage of the lactose that has been broken down. [2] (b) Calculate the mean rate of lactose breakdown in g per 100 cm³ per hour. [2] (c) Explain why the enzyme must be kept below a certain temperature in this process. [2] (d) Explain why enzymes released by microorganisms outside their cells are useful in industry. [1]

Answers

1. (a) Liver [1]; (b) gall bladder [1]; (c) large intestine [1] [3] Examiner insight: “Small intestine” is a common slip for (c). The water is mostly absorbed in the large intestine, so check the organ named matches the job described.

2. (a) Starch molecules are too large, or insoluble, to pass through the gut wall into the blood [1]; the small soluble sugars made by digestion can be absorbed [1] [2] (b) Amino acids [1] Examiner insight: Say that the molecules are large and insoluble, and that digestion gives soluble products. “So they can be used” alone is too vague to show understanding.

3. Boiling denatures the enzyme [1]; this changes the shape of the active site [1]; the starch cannot fit, and cooling does not restore the shape, so the enzyme cannot catalyse the reaction [1] [3] Examiner insight: “Killed” gains nothing because enzymes are not alive. Link the loss of activity to the changed shape of the active site.

4. (a) Pancreas [1]; small intestine [1] (b) Stomach [1]; small intestine [1] [4] Examiner insight: Read whether the question asks where an enzyme is made or where it acts. The pancreas makes lipase but does not act on food inside it.

5. (a) 6 × 4 × 4 = 96 cm² [1] (b) 64 × 6 × 1 × 1 = 384 cm² [1] (c) 384 ÷ 96 = 4 times [1] (d) The larger surface area gives lipase more fat surface to act on [1], so the fat is broken down faster [1] [5] Examiner insight: Show each product. A final “4” with no working gives no evidence of your method if one value is wrong.

6. Any six of (1 mark each, maximum 6): use equal volumes of amylase and starch; same enzyme and starch concentration; place the tubes in water baths at different temperatures, for example 20, 30, 40, 50, 60 °C; leave to reach temperature before mixing; mix and start the stopwatch; test drops with iodine every 30 seconds; record the time when blue-black no longer appears; repeat and calculate a mean [6] Examiner insight: A plan needs the variable you change, the one you measure and the ones you control. Writing “same amount” without saying what stays the same is weak.

7. (a) 1000 ÷ 60 = 16.7 [1] (b) pH 8 [1] (c) Rate at pH 9 = 1000 ÷ 100 = 10 [1]; (10 − 16.7) ÷ 16.7 × 100 = −40% [1] (d) pH 10 is far from the best pH [1]; the enzyme is denatured, because the shape of its active site has changed [1] (e) The small intestine is alkaline, but the stomach is acidic [1] [7] Examiner insight: Show the rate for the new pH before the percentage. A negative sign or the word “decrease” is needed to show the direction.

8. Bile neutralises the acid from the stomach [1]; so the small intestine would be too acidic and the enzymes would work less well [1]; bile emulsifies fat [1]; so the fat would have a smaller surface area and lipase would digest it more slowly [1] [4] Examiner insight: Each effect needs a function of bile plus its consequence. Writing “bile digests fat” is wrong because bile is not an enzyme.

9. (a) 18 °C: (224 + 216 + 220) ÷ 3 = 220 s [1]; 28 °C: (104 + 96 + 100) ÷ 3 = 100 s [1] (b) 1000 ÷ 220 = 4.55 [1]; 1000 ÷ 100 = 10.0 [1] (c) (10.0 − 4.55) ÷ 4.55 × 100 [1] = 120% [1] [6] Examiner insight: Use the same rounding throughout. Calculating from the mean times, not from one repeat, is what the question is testing.

10. (a) Biological washing powder [1] (b) 70 °C [1] (c) (10 − 100) ÷ 100 × 100 [1] = −90% [1] (d) The enzyme is denatured at high temperature [1]; the active site is a different shape, so the substrate cannot fit [1] [6] Examiner insight: “Best from these data” matters because only four temperatures were tested. The true best temperature could lie between them.

11. Any nine of (1 mark each, maximum 9): bread contains starch, digested by amylase; amylase made in the salivary glands, pancreas and small intestine; starch becomes sugars in the mouth and small intestine; egg white is protein, digested by protease; protease made in the stomach, pancreas and small intestine; proteins become amino acids in the stomach and small intestine; the stomach makes hydrochloric acid so its enzymes work in acid; butter is fat, digested by lipase made in the pancreas and small intestine; lipase acts in the small intestine to give fatty acids and glycerol; the liver makes bile and the gall bladder holds it until it is released; bile neutralises acid, so small intestine enzymes work in alkaline conditions; bile emulsifies fat, increasing the surface area for lipase; soluble products are absorbed into the blood in the small intestine [9] Examiner insight: Organise the answer food by food. A clear chain of food, enzyme, site and product is easier to credit than a general paragraph about the gut.

12. (a) 4.8 − 0.6 = 4.2 g [1]; 4.2 ÷ 4.8 × 100 = 87.5% [1] (b) 4.2 ÷ 6 [1] = 0.7 g per 100 cm³ per hour [1] (c) Too high a temperature denatures the enzyme [1]; the active site has a new shape, so lactose cannot bind [1] (d) The enzyme can be collected from the liquid around the microorganisms [1] [7] Examiner insight: Give units on a rate. “0.7” alone, without the quantity and time, would usually lose a mark.

Where marks are usually lost

• Writing “killed” instead of denatured.
• Saying the enzyme, rather than the active site, changes shape.
• Treating bile as an enzyme or saying that it chemically digests fat.
• Confusing where an enzyme is made with where it acts.
• Giving the small intestine as the main site of water absorption.
• Reading a longer time as a faster rate.
• Leaving out units, or the sign on a percentage change.
• Not stating the variables that must be controlled in a method.
• Stating the best temperature or pH as exact when only a few values were tested.

Next steps

• Revise with the revision notes and re-read the study guide.
• Go to the course hub and tick off the checklist.
• Try all the free 10-minute diagnostics.
• Book a free trial class.

Official syllabus

OxfordAQA International GCSE Biology (9201), Version 5.2, for exams May/June 2018 onwards, published by OxfordAQA. These questions cover section 3.2.4 Digestion, parts a to c.