Question 1
Paper 4 short-answer style1 markName the enzyme that digests starch. (1 mark)
Model answer
Amylase.
Why this scores
One mark for 'amylase'.
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Detailed notes on Human Nutrition for Cambridge IGCSE Biology, covering key concepts, explanations, examples, and exam-focused revision points.
Three enzymes do most of the work: amylase (carbs), protease (proteins), lipase (fats). Cambridge wants the substrate, the product, and the right place to find them.
Mapped to the Cambridge IGCSE 0610 syllabus (2026-2028).
Starts in the mouth (saliva), pauses in stomach, finishes in small intestine (pancreas + intestinal wall).
Step 1 — mouth. Salivary glands secrete SALIVA containing AMYLASE. Saliva mixes with food during chewing.
starchamylasemaltose
Step 2 — stomach. Salivary amylase is DENATURED by stomach acid (pH 2). Starch digestion pauses.
Step 3 — small intestine. PANCREATIC AMYLASE (made in pancreas, released into duodenum) continues breaking starch into maltose.
Step 4 — intestinal wall. Maltase (in the small intestine WALL) splits maltose into two GLUCOSE molecules:
maltosemaltase2glucose
Glucose is small and soluble → ready to be absorbed.
Worked qualitative. Why does keeping bread in your mouth make it taste sweet?
Cambridge tip. "Starch is a polysaccharide; its monomer unit is glucose; amylase splits it into maltose; maltase splits maltose to glucose." Memorise this chain — full mark.
Two main proteases for two pH zones: pepsin (stomach, pH 2) and trypsin (SI, pH 8).
Stomach: pepsin.
proteinpepsinpolypeptides
Small intestine: trypsin and peptidases.
polypeptidestrypsin, peptidasesamino acids
Why two different enzymes?
Worked qualitative. Why don't the protein-digesting enzymes digest the gut wall (also made of protein)?
Cambridge tip. Memorise: pepsin lives in pH 2 (stomach), trypsin lives in pH 8 (small intestine). Mixing these up is a common deduction.
Made in pancreas, acts in small intestine. Bile emulsifies first to give lipase a fighting chance.
Where it's made. PANCREAS.
Where it acts. SMALL INTESTINE (duodenum).
The reaction.
fat (triglyceride)lipasefatty acids+glycerol
Why bile is essential.
Worked qualitative. Patients with cystic fibrosis can't release pancreatic enzymes properly. What digestive problem does this cause?
Cambridge tip. Don't forget GLYCEROL when listing products. "Lipase digests fat to fatty acids" alone misses a mark.
HCl gives optimum pH for pepsin AND kills bacteria.
Stomach lining cells secrete HYDROCHLORIC ACID (HCl). pH ~2 — very acidic.
Two functions:
1. Optimum pH for pepsin. Pepsin works fastest at pH 2. The acid creates the ideal environment for the stomach's protease.
2. Kills bacteria in food. Most pathogens can't survive pH 2 → first line of defence against food poisoning.
Why the stomach lining isn't digested by its own acid:
What can go wrong. Stomach ULCERS — when the mucus layer fails (often due to Helicobacter pylori bacteria) → acid + pepsin damage the lining → painful sore. Treated with antibiotics + acid-reducing drugs.
Worked qualitative. Why do antacid tablets relieve heartburn?
Cambridge tip. When asked "function of HCl", always give BOTH "optimum pH for pepsin" and "kills bacteria/pathogens". One alone misses a mark.
Made by liver, stored in gall bladder, released into duodenum. Two roles: emulsify fat + neutralise acid.
Path of bile:
Two roles:
1. Emulsification.
2. Neutralising stomach acid.
Worked qualitative. Why is bile yellow-green?
Cambridge tip. Bile is NOT an enzyme. Cambridge marks deduct for "bile digests fat".
Verbatim phrases and definitions Cambridge mark schemes credit.
Chemical digestion appears every Paper 4 (8-10 marks: enzyme + product + place; effect of pH/temperature; bile vs lipase). Examiner reports flag students forgetting glycerol, putting amylase in the stomach, and confusing bile with an enzyme.
Sources: Cambridge IGCSE Biology 0610 syllabus 2026-2028 (7.4); 0610/42 May/Jun 2024 — Q4 (chemical digestion); 0610 Examiner Reports 2022-2024. Last reviewed 2026-05-07.
Step-by-step solutions to past-paper-style questions on chemical digestion, written exactly the way a tutor would explain them at the board.
Question
For amylase, protease and lipase: state the substrate, the product and where the enzyme acts.
Step-by-step solution
Step 1
Amylase: digests STARCH → MALTOSE. Made in the salivary glands (mouth) and pancreas (acts in the small intestine).
Step 2
Protease (e.g. pepsin in the stomach, trypsin in the small intestine): digests PROTEIN → AMINO ACIDS.
Step 3
Lipase: digests FATS → FATTY ACIDS + GLYCEROL. Made in the pancreas; acts in the small intestine.
Answer
Amylase: starch → maltose. Protease: protein → amino acids. Lipase: fat → fatty acids + glycerol.
Question
List the enzymes found in the saliva, the stomach and the pancreatic juice.
Step-by-step solution
Step 1
Saliva (mouth): amylase — starts starch digestion.
Step 2
Stomach (gastric juice): protease (pepsin) plus hydrochloric acid. No carbohydrase or lipase here.
Step 3
Pancreatic juice (released into the small intestine): amylase, protease (trypsin) and lipase.
Step 4
Small intestine wall: maltase (and other enzymes) complete digestion.
Answer
Saliva: amylase. Stomach: protease (pepsin) + HCl. Pancreas: amylase, protease, lipase. Small intestine wall: maltase and others.
Question
Explain two functions of the hydrochloric acid in the stomach.
Step-by-step solution
Step 1
Function 1: it provides the acidic conditions (low pH) that are the optimum for the stomach protease (pepsin).
Step 2
Function 2: it kills many bacteria taken in with the food.
Step 3
(A third function sometimes credited: it begins to break down the food/denature proteins.)
Answer
The acid gives the low pH that pepsin needs to work, and it kills bacteria in the food.
Examiner tip
Cambridge marks 'optimum/low pH for the enzyme' and 'kills bacteria/pathogens'. 'Helps digestion' alone is too vague.
Question
Distinguish between the role of bile and the role of lipase in the digestion of fat.
Step-by-step solution
Step 1
Bile (from the liver, stored in the gall bladder) physically breaks large fat droplets into tiny droplets — emulsification.
Step 2
Bile is not an enzyme; it does not break chemical bonds.
Step 3
Lipase (from the pancreas) is the enzyme that breaks the chemical bonds in fat: fat → fatty acids + glycerol.
Step 4
Bile helps lipase by greatly increasing the surface area of fat for the enzyme to act on.
Answer
Bile = physical (emulsifies fat into small droplets). Lipase = chemical (digests the fat). Bile speeds up lipase by increasing the surface area.
Question
Describe how starch is completely digested into glucose as it passes through the gut.
Step-by-step solution
Step 1
In the mouth, salivary amylase begins digesting starch into maltose.
Step 2
In the stomach, starch digestion stops (the salivary amylase is denatured by the acid).
Step 3
In the small intestine, pancreatic amylase continues digesting the remaining starch into maltose.
Step 4
Maltase, an enzyme in the wall of the small intestine, then breaks maltose into glucose, which is small and soluble and can be absorbed.
Answer
Starch → maltose by amylase (salivary, then pancreatic), then maltose → glucose by maltase in the small intestine wall. The glucose is then absorbed.
Examiner tip
Two enzymes are needed: amylase (starch → maltose) and maltase (maltose → glucose). Forgetting maltase is a common slip.
Question
Starch mixed with amylase is sealed inside Visking (dialysis) tubing, which is placed in a tube of water at 37 °C. After 30 minutes the water outside is tested. Explain what results you would expect and what the experiment models.
Step-by-step solution
Step 1
The Visking tubing is partially permeable, like the wall of the small intestine: small molecules can pass through, large ones cannot.
Step 2
The amylase digests the starch into maltose (a small, soluble sugar) inside the tubing.
Step 3
The small sugar molecules diffuse out through the tubing into the water, but the large starch molecules cannot pass.
Step 4
So the water outside gives a positive Benedict's test (brick-red on heating) but a negative iodine test (stays orange-brown). This models how digestion produces small molecules that can then be absorbed through the gut wall.
Answer
Sugar (from digested starch) diffuses out and gives a positive Benedict's test; starch stays inside (negative iodine test outside). This models digestion making molecules small enough to be absorbed through the partially permeable gut wall.
Examiner tip
The tubing models the gut wall (partially permeable). The result links digestion (large → small) to absorption (only small molecules pass).
High-scoring sample answers for chemical digestion on the Cambridge IGCSE 0610 paper, with examiner-style notes mapping each response to the mark scheme and assessment objectives.
Name the enzyme that digests starch. (1 mark)
Model answer
Amylase.
Why this scores
One mark for 'amylase'.
State the products of the digestion of (a) protein and (b) fat. (2 marks)
Model answer
(a) Protein is digested into amino acids. (b) Fat is digested into fatty acids and glycerol.
Why this scores
One mark each. For fat, both 'fatty acids' AND 'glycerol' are needed.
Describe the functions of the hydrochloric acid in the stomach. (3 marks)
Model answer
The hydrochloric acid makes the stomach contents acidic (low pH), which provides the optimum pH for the protease (pepsin) to work. It also kills many of the bacteria (pathogens) taken in with the food. It can also begin to break down/denature the proteins in the food.
Why this scores
Three marks from: provides acidic/low pH; optimum pH for pepsin; kills bacteria; (denatures proteins). At least two distinct functions are needed.
Describe how starch is completely digested to glucose as it passes through the digestive system. (4 marks)
Model answer
In the mouth, salivary amylase begins to digest the starch into maltose. In the small intestine, pancreatic amylase continues to digest the remaining starch into maltose. The enzyme maltase, found in the wall of the small intestine, then breaks the maltose down into glucose. The glucose is small and soluble, so it can be absorbed through the wall of the small intestine into the blood.
Why this scores
Four marks: salivary amylase → maltose; pancreatic amylase → maltose; maltase → glucose; glucose is absorbed. Both enzymes (amylase and maltase) are required.
Explain the difference between the roles of bile and lipase in the digestion of fat. (5 marks)
Model answer
Bile is made in the liver and is not an enzyme. It emulsifies the fat — breaking large fat droplets into many tiny droplets — which increases the surface area of the fat. It is also alkaline, so it neutralises the acid from the stomach to provide a suitable pH for the enzymes in the small intestine. Lipase is the enzyme that actually digests the fat, breaking the chemical bonds to produce fatty acids and glycerol. Because the emulsified fat has a large surface area, lipase can act on it much faster, so bile and lipase work together.
Why this scores
Five marks from: bile is not an enzyme; bile emulsifies fat; increases surface area; bile neutralises stomach acid for the right pH; lipase digests fat to fatty acids + glycerol.
Describe the chemical digestion of a meal containing starch, protein and fat as it passes through the digestive system. (6 marks)
Model answer
In the mouth, salivary amylase starts to digest the starch into maltose. In the stomach, protease (pepsin), working in the acidic conditions produced by hydrochloric acid, begins to digest the protein into smaller pieces. When the food reaches the small intestine, bile from the liver emulsifies the fat into small droplets, and pancreatic juice adds more enzymes: amylase finishes digesting the starch to maltose, protease (trypsin) continues digesting protein, and lipase digests the fat into fatty acids and glycerol. Finally, enzymes in the wall of the small intestine, such as maltase, complete digestion — maltase breaks maltose into glucose and proteases break the remaining peptides into amino acids — producing small soluble molecules that can be absorbed.
Why this scores
Up to 6 marks: amylase on starch in mouth; protease + acid on protein in stomach; bile emulsifies fat; pancreatic amylase/protease/lipase in small intestine; maltase → glucose; final products (glucose, amino acids, fatty acids + glycerol) are absorbed.
Definitions to memorise and the exact keywords mark schemes credit for chemical digestion answers — sharpened from recent examiner reports for the 2026 0610 sitting.
Enzyme that digests STARCH into MALTOSE. Found in saliva and pancreatic juice.
Enzyme that digests PROTEINS into AMINO ACIDS. Examples: pepsin (stomach, low pH), trypsin (small intestine).
Enzyme that digests FATS into FATTY ACIDS + GLYCEROL. Made in the pancreas, acts in the small intestine.
Enzyme in the wall of the small intestine that breaks maltose into two glucose molecules.
Alkaline fluid from the liver. Emulsifies fat (physical) and neutralises stomach acid to give the right pH for enzymes (it is not an enzyme).
The stomach protease, which works in acidic conditions and begins protein digestion.
The traps other students keep falling into on chemical digestion questions — taken from recent Cambridge IGCSE 0610 examiner reports and mark schemes — and how to avoid them.
Why it happens
The stomach feels like 'where digestion happens'.
How to avoid it
Pepsin begins protein digestion; other proteases (trypsin and peptidases) complete it in the small intestine.
Why it happens
Saliva contains amylase, and food carries it in.
How to avoid it
Salivary amylase is DENATURED by stomach acid. Starch digestion pauses in the stomach and resumes in the small intestine via pancreatic amylase.
Why it happens
Both bile and lipase act on fat in the small intestine.
How to avoid it
Bile EMULSIFIES (physical). Lipase DIGESTS (chemical). Different processes.
The things students keep getting wrong in this sub-topic, answered.