The human alimentary canal, teeth, mechanical and chemical digestion, how enzymes work, the effect of temperature and pH, and what happens after absorption.
Life Processes and DiseaseSO B 2.7SO B 2.8SO B 2.9SO B 2.10≈ 40 min🎮 4 games
Before you start
By the end of this lesson you can…
relate the structures of the human alimentary canal to their functions (SO B2.7)
explain the role and importance of enzymes (SO B2.8)
investigate the effect of temperature and pH on catalase or amylase (SO B2.9)
describe what happens to the products of digestion after absorption (SO B2.10)
7 narrated scenes. Press play, listen and read along — the points appear as they are explained. Use ‹ Prev / Next › or the scene bar to jump to any scene.
LESSON B5 · EXPLAINER
Digestion, Teeth and Enzymes
Why does a cracker start to taste sweet if you chew it for a minute?
Narration uses your device’s built-in voice. No sound? Switch to “Captions only” — the captions advance on their own.
Explore in 3D
Enzymes in 3D
Change the temperature and the pH and see why enzymes have an optimum.
Step 2 · Read
Key notes
Copy these into your notebook in your own words — that is how they stick.
Digestion
Breakdown of large insoluble food molecules into small soluble ones that can be absorbed.
Removal of undigested food (faeces) — NOT excretion.
EXAM TIPS & COMMON MISTAKES
An enzyme “increases the rate of a reaction and remains unchanged at the end” — include BOTH parts.
Starch–amylase practical: solutions kept in the water bath BEFORE mixing so both start at the test temperature.
Roti (not starch solution) would digest more slowly — larger particles/less surface area, contains other substances.
Pulp = the region with blood vessels and nerves (classic P1 tooth diagram).
Step 2 · Learn from examples
Worked examples & study resources
The kind of support a teacher gives after the lesson: worked examples to attempt first, a board illustration, key terms, common misconceptions and memory aids.
Worked example 1
Interpreting an amylase experiment
Starch and amylase were mixed at three temperatures. Every minute a drop was tested with iodine.
Temperature
Time for iodine to stay yellow-brown
20 °C
8 minutes
37 °C
3 minutes
60 °C
still blue-black after 15 minutes
Explain the results at each temperature.
Try it in your notebook first, then reveal the solution one step at a time.
Iodine stays yellow-brown when all the starch has been digested — so a shorter time means faster digestion.
At 20 °C digestion is slow: molecules have less kinetic energy, so enzyme and substrate collide less often.
At 37 °C digestion is fastest — close to the optimum temperature for human amylase, with frequent successful collisions.
At 60 °C the starch is never digested: the high temperature has denatured the amylase — its active site changed shape, so starch no longer fits.
Answer. 20 °C: slow (fewer collisions). 37 °C: fastest (near optimum). 60 °C: enzyme denatured — active site changed shape, so no digestion.
Examiner’s tip. Write “denatured”, not “killed” — enzymes are proteins, not living things. Link it to the active site: “the substrate no longer fits”.
Worked example 2
Tracing a meal through the gut
A student eats a cheese sandwich (bread = starch; cheese = protein and fat). Describe how each nutrient is digested and where the products go.
Try it in your notebook first, then reveal the solution one step at a time.
Mouth: teeth break the food into smaller pieces (mechanical digestion, larger surface area); salivary amylase begins digesting starch to maltose.
Stomach: hydrochloric acid provides an acidic pH and kills bacteria; pepsin begins digesting protein to polypeptides.
Duodenum: bile from the liver emulsifies fat into small droplets and neutralises the acid; pancreatic juice provides amylase, trypsin and lipase.
Ileum: digestion is completed — starch → glucose, proteins → amino acids, fats → fatty acids and glycerol.
The products are absorbed through the villi: glucose and amino acids into the blood capillaries, fatty acids and glycerol into the lacteals. They are then assimilated — used by body cells.
Answer. Starch → maltose (mouth) → glucose (ileum); protein → polypeptides (stomach) → amino acids (ileum); fat emulsified by bile, digested by lipase → fatty acids + glycerol. All absorbed through the villi of the ileum.
Examiner’s tip. Name the enzyme, the substrate, the product AND the place. Mark schemes award each of these separately.
On the board · The digestive enzymes
Enzyme
Made in
Acts in
Substrate → product
Best pH
Salivary amylase
Salivary glands
Mouth
Starch → maltose
About 7
Pepsin
Stomach wall
Stomach
Protein → polypeptides
About 2 (acid)
Pancreatic amylase
Pancreas
Duodenum
Starch → maltose
About 7–8
Trypsin
Pancreas
Duodenum
Protein → polypeptides
About 8
Lipase
Pancreas
Duodenum
Fat → fatty acids + glycerol
About 8
Maltase
Wall of ileum
Ileum
Maltose → glucose
About 8
Bile is not in this table — it has no enzymes. It emulsifies fats and neutralises stomach acid.
Key terms
Ingestion
Taking food into the mouth.
Digestion
Breaking large insoluble food molecules into small soluble ones.
Absorption
Digested food passing through the wall of the ileum into the blood or lymph.
Assimilation
Body cells using absorbed food molecules.
Egestion
Removing undigested food (faeces) through the anus.
Emulsification
Bile breaking fat into tiny droplets, giving lipase a larger surface area.
Villus (pl. villi)
Finger-like fold of the ileum wall that increases surface area for absorption.
Common misconceptions
✗ Bile is an enzyme.✓ Bile contains no enzymes. It emulsifies fats (physical change) and neutralises acid.
✗ High temperatures kill enzymes.✓ Enzymes are not alive. Heat denatures them — the active site changes shape permanently.
✗ Most digestion happens in the stomach.✓ The stomach starts protein digestion, but most chemical digestion and nearly all absorption happen in the small intestine.
Memory aid
The gut in order: Many Old Sailors Swim Laps Round Anchors — Mouth, Oesophagus, Stomach, Small intestine, Large intestine, Rectum, Anus.
Real-life link
Many adults, especially of African and Asian descent, make less lactase after childhood, so milk sugar (lactose) is not digested. Gut bacteria ferment it instead, causing bloating — this is lactose intolerance.
Try this
Chew a plain cracker for two minutes without swallowing. It starts to taste sweet — salivary amylase is turning starch into maltose.
Play & practise
Games
4 quick games on this lesson. Earn XP and badges as you play — your best score for each game is saved. Games are for practice and do not change your exam readiness.
Step 3 · Practise
Paper 1 practice — multiple choice
8 items modelled on real CSEC Paper 1 questions. Choose one answer for each, then check. Aim for 80% or better.
Step 4 · Apply
Paper 2 practice — structured questions
Write full answers, then reveal the mark scheme and tick the points you earned (18 marks in total). Your answers are saved on this device.
Based on CSEC P2 January 2024, Question 1(d)
Question 1 [11 marks]
Starch and amylase solutions were kept separately in a water bath for 15 minutes, then mixed. Every 2 minutes a drop of the mixture was added to iodine on a spotting tile. It was blue-black at 0–4 min, brown at 6–12 min, and light orange-brown from 14 min onward.
(a) Suggest ONE reason the mixture was kept in a water bath, and why solutions must be at the same temperature. [2]
MARK SCHEME — (a) (max 2)
(b) Suggest why the solutions were not mixed immediately, and a suitable aim. [2]
MARK SCHEME — (b) (max 2)
(c) How long did digestion take? Explain. [3]
MARK SCHEME — (c) (max 3)
(d) List THREE precautions and name a reagent to identify the product. [4]
MARK SCHEME — (d) (max 4)
Based on CSEC P2 May/June 2021 Q1(g) and May/June 2026 Q2(d)–(e)
Question 2 [7 marks]
Animals must ingest complex food and digest it mechanically and chemically.
(a) Explain TWO ways the human digestive system is adapted for MECHANICAL digestion. [4]
MARK SCHEME — (a) (max 4)
(b) Suggest THREE consequences of losing a tooth early. [3]
MARK SCHEME — (b) (max 3)
Your progress
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Sources
Where this topic appears in CSEC papers
Find these in your own past-paper booklets for extra timed practice. The practice above is adapted from them.