Question bank › IGCSE Biology › Structure and functions in living organisms

Human diet, digestion and absorption

Answer on paper first, then reveal the mark scheme one mark at a time.

1Grade 4–54 marks

(a) Lipase digests lipids. Name the products of lipid digestion. [2]

(b) Bile is produced in the liver and stored in the gall bladder. Describe two roles of bile in digestion. [2]

(a) fatty acids(1)
(a) glycerol(1)
(b) neutralises (hydrochloric) acid from the stomach / makes conditions alkaline for (small intestine) enzymes(1)
(b) emulsifies fats / lipids, increasing surface area for lipase; reject 'digests fat' / 'breaks down fat' chemically(1)
Answer: (a) fatty acids and glycerol (b) neutralises stomach acid; emulsifies fats
Examiner tip: Bile is not an enzyme — it emulsifies fat, it does not digest it.

2Grade 6–7Triple only5 marks

A student burned a 0.50 g sample of a peanut under a boiling tube containing 20 cm³ of water. The temperature of the water rose from 21 °C to 47 °C.

Energy (J) = mass of water (g) × 4.2 × temperature rise (°C). 1 cm³ of water has a mass of 1 g.

(a) Calculate the energy released per gram of peanut. Give your answer in J per g. [3]

(b) The value on the food label is much higher. Give two reasons for the difference. [2]

(a) temperature rise = 26 (°C)(1)
(a) energy = 20 × 4.2 × 26 = 2184 (J)(1)
(a) 2184 ÷ 0.50 = 4368 (J per g); accept 4370 / 4400; correct answer with no working scores 3(1)
(b) any two from: heat lost to the air / surroundings; heat absorbed by the boiling tube (or thermometer); incomplete combustion / not all of the peanut burned; peanut not held directly below the tube / heat lost while moving it — first reason(1)
(b) second reason; ignore 'human error'(1)
Answer: (a) 4368 J per g (b) heat lost to surroundings; incomplete burning
Examiner tip: Students often forget the final step — 2184 J is for 0.50 g, so divide by 0.50 to get J per g.

Book a free introductory session and we'll find exactly which step is costing you.