BIOLOGY WITH HAMZA · MDCAT REVISION
Digestion
Name: ____________________ Date: ______________
Recall first. Check second. Return to the ideas you missed.
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Learning targets
- Distinguish ingestion, digestion, absorption, assimilation and egestion.
- Match digestive enzymes with substrates, products and locations.
- Explain how villi absorb sugars, amino acids, fatty acids and glycerol.
Core notes
- Mechanical digestion increases surface area; chemical digestion hydrolyses molecules.
- Bile emulsifies fats but does not enzymatically digest them.
- Villi combine large area, thin barriers and good transport routes.
- Absorption enters the body; assimilation uses the absorbed material.
Read, cover and redraw
Chewing and the start of starch digestion.
Acid, mixing and protein digestion.
Most chemical digestion and absorption.
Water and ion recovery; faeces formation.
Written recall
1. Why does emulsification increase lipid-digestion rate without breaking triglyceride bonds?
2. Why do most lipid products enter lacteals rather than blood capillaries directly?
Apply the idea
1. A fat-digestion experiment uses identical lipase amounts. Adding bile salts increases digestion rate. Which explanation is best?
- Emulsification increases the lipid–water interface accessible to lipase
- Bile salts are protein-digesting enzymes
- Bile salts supply extra lipase molecules
- Bile converts all fat directly into glucose
My answer: _____ Reason: ____________________________________
2. Most long-chain dietary lipids packaged into chylomicrons first enter which structure after leaving intestinal epithelial cells?
- Hepatic portal capillaries directly
- Lacteals
- The stomach lumen
- Renal tubules
My answer: _____ Reason: ____________________________________
3. Which enzyme is most consistent with these results under otherwise controlled conditions?
| pH | Relative activity |
|---|---|
| 2 | 100 |
| 7 | 5 |
| 9 | 1 |
- Pancreatic lipase
- Salivary amylase
- Pepsin
- Maltase
My answer: _____ Reason: ____________________________________
Answer key
Cover this section while attempting the questions.
Written recall
1. It divides fat into smaller droplets, increasing the surface area available for lipase action.
2. They are reassembled and packaged into particles that are too large for ordinary capillary entry and therefore move through lymphatic lacteals.
Applied questions
1. A — Bile salts help disperse large fat globules into smaller droplets. More accessible surface assists lipase; emulsification itself does not hydrolyse the triglycerides.
2. B — Chylomicrons enter intestinal lymphatic lacteals before reaching the bloodstream. Many water-soluble nutrients instead enter blood capillaries and the hepatic portal circulation.
3. C — High proteolytic activity in strongly acidic conditions fits pepsin, a stomach protease. The other listed enzymes digest different substrate classes.