Explain how peristalsis moves food along the alimentary canal.

Pearson Edexcel International GCSE Biology (4BI1) — 2.6 Nutrition: humans · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Food must travel from the mouth to the anus through the alimentary canal. This journey relies on muscular movements of the digestive tract rather than gravity alone.

Model answer (4 marks)

Peristalsis is a wave of rhythmic contraction of the smooth muscle in the wall of the alimentary canal. The contraction squeezes the lumen behind the bolus of food, narrowing it. Ahead of the bolus the muscle relaxes, widening the lumen. This alternating contraction and relaxation creates a travelling wave that pushes the bolus forward along the tract towards the anus.

Examiner tips

Use the terms "smooth muscle", "lumen", "bolus" and "wave" to show understanding.
Show the sequence: contraction behind, relaxation ahead, and the result of the wave pushing food.

Common mistakes

Confusing peristalsis with segmentation or omitting the relaxation phase.
Using vague language such as "pushes food" without explaining the muscle action.

Mark scheme (4 marks)

Peristalsis involves the contraction of muscles (in the wall of the alimentary canal / oesophagus / gut)
The contractions squeeze / narrow the lumen behind the bolus of food
Muscles relax ahead of the bolus (widening the lumen in front)
This wave of contraction and relaxation pushes the bolus of food along / towards the anus

Key terms in this question

peristalsis · alimentary canal

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