Knowledge Organiser
Part of The Human Digestive System · GCSE GCSE Biology revision
This topic summary covers Knowledge Organiser within The Human Digestive System for GCSE Biology. Structure and function of digestive organs, mechanical and chemical digestion, enzymes, absorption, and practical investigations It is section 14 of 15 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 14 of 15
Practice
19 questions
Recall
24 flashcards
Knowledge Organiser
Key Terms
- Digestion: Breakdown of large insoluble molecules to small soluble ones
- Peristalsis: Wave-like muscle contractions that move food along
- Bile: Alkaline fluid that emulsifies fats (NOT an enzyme)
- Villi: Finger-like projections that increase absorption surface area
- Emulsification: Breaking large fat droplets into smaller ones
- Chyme: Acidic liquid mixture leaving the stomach
Must-Know Facts
- Small intestine surface area ~200 m² (tennis court) due to villi and microvilli
- Bile is produced by the liver, stored in the gall bladder
- Pancreas produces amylase, lipase, and protease enzymes
- Large intestine absorbs water only — no nutrients
- Fats are absorbed into lacteals (lymph vessels), not blood capillaries
- Stomach produces hydrochloric acid (pH 1.5–3.5) and pepsin
- Peristalsis allows food to travel upwards — gravity is not needed
- Hepatic portal vein carries absorbed nutrients from intestine to liver
Common Mistakes
- Saying bile is an enzyme: Bile is not an enzyme — it does not chemically break down fats. Bile emulsifies fats (breaks large droplets into smaller ones), increasing the surface area for lipase to work on.
- Confusing where enzymes are produced with where they act: The pancreas produces amylase, protease, and lipase, but these enzymes act in the small intestine. Salivary amylase is produced in the mouth and acts there.
- Stating the large intestine absorbs nutrients: The large intestine only absorbs water. All nutrients (sugars, amino acids, fatty acids) are absorbed in the small intestine through the villi.
- Forgetting to explain WHY villi increase absorption: Villi increase the surface area for absorption. For full marks also state that they have a rich blood supply (capillaries) and thin walls — both of which speed up diffusion into the blood.
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Practice Questions for The Human Digestive System
Which organ produces hydrochloric acid to kill bacteria in food?
Explain the role of bile in the digestive system.
Quick Recall Flashcards
19 questions on The Human Digestive System — practise free
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