The Human Digestive System
Trace food through the gut and explain mechanical and chemical digestion.
The digestive system breaks food into molecules small enough to absorb.
- Name the organs of digestion in order.
- Distinguish mechanical and chemical digestion.
- Explain the role of villi.
The Path of Food
Mouth → oesophagus → stomach → small intestine → large intestine → rectum → anus. The liver produces bile, stored in the gall bladder; the pancreas releases digestive enzymes.
Mechanical and Chemical
Mechanical digestion is physical breakdown by teeth and stomach churning. Chemical digestion uses enzymes: amylase for starch, protease for protein and lipase for fats.
Absorption
The small intestine has villi — finger-like projections that increase surface area and contain blood capillaries to absorb nutrients.
Bread (starch) → amylase in the mouth and small intestine → glucose.
Beans (protein) → protease in the stomach and small intestine → amino acids.
Butter (fat) → lipase in the small intestine → fatty acids and glycerol.
Practice
- List the organs food passes through, in order.
- Name the enzyme that digests starch and where it works.
- Explain how villi increase absorption.
Recap
Digestion breaks food down mechanically and chemically. Villi in the small intestine absorb the nutrients.
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Ecology and Human Biology
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