IGCSE · Practice questions · Physical digestion

Cut, tear, grind, churn.

Six original Cambridge-style questions on physical digestion, the types and structure of teeth, the stomach and (Extended) bile, including a surface area calculation.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.

Keep these straight

Same molecules, smaller pieces.

Physical digestion: smaller pieces, no chemical change, larger surface area for enzymes.
Teeth: incisors cut, canines tear, premolars and molars chew and grind.
Tooth layers: enamel, dentine, pulp (nerves, blood vessels), cement; embedded in jaw bone and gum.
Extended: bile emulsifies fat; it is not an enzyme.

Recall

[2 marks]

Describe what is meant by physical digestion and state why it is important.

The breakdown of food into smaller pieces without chemical change to the food molecules. ✓
It increases the surface area of the food for the action of enzymes in chemical digestion. ✓

Recall

[4 marks]

Name the four types of human teeth and state the function of each.

Incisors: biting and cutting food. ✓
Canines: tearing and gripping food. ✓
Premolars: chewing and grinding food. ✓
Molars: chewing and grinding food into small pieces. ✓

Recall

[4 marks]

A diagram shows a vertical section through a molar. Describe the structure of the tooth from the outside of the crown to the centre, and state how the tooth is held in place.

The crown is covered by hard enamel. ✓
Under it is dentine, which forms most of the tooth. ✓
The centre is the pulp cavity, containing nerves and blood vessels. ✓
The root is covered by cement and embedded in a socket in the jaw bone, with the gum around the neck. ✓

Explain

[3 marks]

Describe the role of the stomach in physical digestion.

The muscular wall of the stomach contracts to churn the food. ✓
This breaks food into smaller pieces (without chemical change). ✓
And mixes it with gastric juice, increasing the surface area in contact with the enzymes. ✓

Calculation

[3 marks]

Extended. A drop of oil is a cube of side 2 mm. Bile emulsifies it into cubes of side 0.5 mm. (a) Calculate the surface area of the original drop. (b) Calculate the total surface area of the small droplets. (c) Use your answers to explain why emulsification speeds up fat digestion.

(a) 6 × 2 × 2 = 24 mm². ✓
(b) Number of droplets = (2 ÷ 0.5)³ = 64; each has area 6 × 0.5 × 0.5 = 1.5 mm²; total = 64 × 1.5 = 96 mm² (four times larger). ✓
(c) Lipase acts on the surface of the fat, so a larger surface area lets more lipase molecules act at once, and fat is digested faster. ✓

Explain

[2 marks]

Extended. A student says that bile digests fat. Explain why this is incorrect.

Bile contains no enzymes and does not change the fat molecules; it emulsifies fat into small droplets, which is physical digestion. ✓
The chemical digestion of fat into fatty acids and glycerol is done by the enzyme lipase. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.