The Human Digestive System
Master The Human Digestive System for GCSE Biology with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. Know the job of each organ, and how bile emulsifies fats and neutralises stomach acid to speed up digestion in the small intestine.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
The digestive system breaks large insoluble food molecules into small soluble ones that can be absorbed into the bloodstream.
Food passes through the mouth, oesophagus, stomach, small intestine and large intestine. Along the way, glands including the salivary glands and the pancreas produce digestive enzymes, and the liver produces bile.
Absorption happens in the small intestine, which is adapted with villi. These give a very large surface area, have thin walls giving a short diffusion path, and have a good blood supply that maintains a steep concentration gradient — the same three adaptations that make any exchange surface efficient.
Revision notes
The organs and their roles
Mouth: chews food and begins starch digestion with amylase in saliva. Oesophagus: carries food to the stomach.
Stomach: churns food and produces hydrochloric acid and protease. Small intestine: digestion is completed and soluble products are absorbed. Large intestine: absorbs water.
Glands and secretions
Salivary glands produce amylase. The pancreas produces amylase, protease and lipase, releasing them into the small intestine.
The liver produces bile, which is stored in the gall bladder. Bile neutralises stomach acid and emulsifies fats.
Adaptations of the small intestine
Villi give a very large surface area for absorption. Their walls are one cell thick, giving a short diffusion path.
Each villus has a good blood supply which carries absorbed molecules away, maintaining a steep concentration gradient.
Key points
- Digestion breaks large insoluble molecules into small soluble ones.
- Amylase is produced by the salivary glands and pancreas.
- The stomach produces hydrochloric acid and protease.
- The liver produces bile, stored in the gall bladder.
- Absorption happens in the small intestine.
- Villi give a large surface area, thin walls and a good blood supply.
Worked examples
Example 1
Explain why food must be digested before it can be used by the body. [2 marks]
Model answer
Food molecules such as starch and protein are large and insoluble, so they cannot pass through the wall of the small intestine (1 mark). Digestion breaks them into small soluble molecules that can be absorbed into the bloodstream (1 mark).
Example 2
Describe three ways the small intestine is adapted for absorption. [3 marks]
Model answer
It is lined with villi which give a very large surface area (1 mark). The villi walls are one cell thick, giving a short diffusion path (1 mark). Each villus has a good blood supply which maintains a steep concentration gradient (1 mark).
Example 3
Name the organ that produces bile and state where bile is stored. [2 marks]
Model answer
Bile is produced by the liver (1 mark) and stored in the gall bladder (1 mark).
Common mistakes
Saying the gall bladder produces bile.
The liver produces it; the gall bladder only stores it.
Saying absorption happens in the stomach.
Most absorption of digested food occurs in the small intestine.
Listing villi adaptations without explaining them.
Link each to what it achieves — large surface area, short diffusion path, steep gradient.
Confusing digestion with absorption.
Digestion breaks molecules down; absorption moves them into the blood.
Exam tips
- Learn which gland produces which enzyme.
- Give the function alongside each organ you name.
- Use the three standard exchange-surface adaptations for villi.
- Keep digestion and absorption clearly distinct.
Key terms
- Digestion
- Breaking large insoluble molecules into small soluble ones.
- Villi
- Finger-like projections lining the small intestine.
- Bile
- A liquid produced by the liver that neutralises acid and emulsifies fats.
- Absorption
- The movement of digested food molecules into the blood.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.