Who this is for: Cambridge IGCSE Coordinated Science (0654) students who want digestion — physical and chemical breakdown of food into absorbable molecules — to become reliable marks instead of a vague “food is broken down in the stomach.”
What query it owns: how to understand and revise digestion in Cambridge IGCSE Coordinated Science.
Why this is safe: this page owns the digestion revision-guide angle, while Tutopiya’s Digestion subtopic page owns the learning resource and the free Digestion quiz owns the practice.

Digestion is the breakdown of large, insoluble food molecules into small, soluble molecules that can be absorbed into the blood. Cambridge IGCSE Coordinated Science (0654) tests whether you can distinguish physical from chemical digestion, match enzymes to substrates and products, and explain where each stage occurs in the alimentary canal. This guide covers the syllabus definitions, the enzyme table examiners expect, and the question types that appear every year.

Key takeaways

• Physical digestion breaks food into smaller pieces (teeth, churning) — no chemical change.
• Chemical digestion uses enzymes to break large molecules into small, soluble ones.
• Amylase digests starch → maltose; pepsin digests protein → peptides; lipase digests fats → fatty acids + glycerol.
• Chemical digestion produces molecules small enough for absorption in the ileum.
• Exam answers must state enzyme, substrate, product and location together.

What is digestion in Cambridge IGCSE Coordinated Science?

Digestion is the process by which food is broken down into molecules small enough to pass through the wall of the intestine into the blood. Physical digestion increases surface area for enzymes; chemical digestion uses hydrolysis to split starch, proteins and fats into soluble products. The main regions are the mouth, stomach and small intestine (duodenum and ileum).

You can read the full explanation, worked examples and notes on Tutopiya’s Digestion subtopic page before you attempt questions.

The core ideas you must master

Idea	What it means	How the exam uses it
Physical digestion	Mechanical breakdown into smaller pieces	”Distinguish physical and chemical digestion”
Chemical digestion	Enzyme-catalysed hydrolysis	”Name the enzyme that digests starch”
Substrate → product	What each enzyme breaks down	”State the products of fat digestion”
Optimum pH	Pepsin acidic; pancreatic enzymes alkaline	”Explain why pepsin stops in the duodenum”
Absorption	Soluble products enter blood via ileum	”Explain why digestion is necessary”

Main digestive enzymes you must know

Enzyme	Substrate	Products	Where	pH
Salivary amylase	Starch	Maltose	Mouth	Neutral ~7
Pepsin	Protein	Peptides	Stomach	Acidic ~2
Pancreatic amylase	Starch	Maltose	Duodenum	Alkaline
Trypsin	Protein / peptides	Smaller peptides	Duodenum	Alkaline
Lipase	Fats (emulsified)	Fatty acids + glycerol	Duodenum	Alkaline
Maltase	Maltose	Glucose	Ileum wall	Alkaline

Digestion in past-paper wording: command words that matter

Command word / phrase	What the question wants	Typical digestion stem
Define	Precise syllabus definition	”Define the term digestion.”
Name	Enzyme or product	”Name the enzyme that digests protein in the stomach.”
State	Short factual answer	”State the products of complete fat digestion.”
Explain	Cause and effect	”Explain the role of hydrochloric acid in the stomach.”
Distinguish	Clear differences	”Distinguish physical and chemical digestion.”

Worked exam-style stems (how to answer the wording)

1. “Name the enzyme that digests starch and state where it first acts.” Amylase (salivary amylase); mouth. Mark-scheme reward: correct enzyme + location.
2. “Explain the role of bile in fat digestion.” Bile emulsifies fats — breaks large fat globules into smaller droplets, increasing surface area for lipase. Reward: emulsification + surface area link.
3. “State the products of complete protein digestion.” Amino acids. Reward: amino acids (not just “peptides” for complete digestion).

When you can recognise the wording instantly, work the full set on the Digestion quiz to lock the enzyme table in.

How digestion connects to the rest of the syllabus

Digestion follows Diet and the Alimentary Canal in Animal Nutrition. Enzyme action links to the Enzymes topic. The Cambridge IGCSE Coordinated Science resource hub links every Animal Nutrition subtopic.

Common mistakes students make

• Saying pepsin produces amino acids directly (peptides first).
• Placing lipase in the stomach (it is pancreatic / duodenal).
• Confusing physical digestion with chemical digestion.
• Forgetting bile emulsifies fats before lipase acts.
• Ignoring pH when explaining why pepsin stops in the duodenum.

When you need more support

If digestion questions keep costing marks — especially enzyme tables — work through the Digestion quiz, then get focused help from a Cambridge IGCSE Coordinated Science tutor.

Frequently asked questions

Is digestion hard in Cambridge IGCSE Coordinated Science? The concepts are straightforward, but marks are lost when students mix up enzymes, substrates and products, or confuse physical with chemical digestion.

What is the difference between physical and chemical digestion? Physical digestion breaks food into smaller pieces mechanically; chemical digestion uses enzymes to break large molecules into small, soluble ones.

Why is hydrochloric acid needed in the stomach? It provides the acidic pH for pepsin to work and kills harmful bacteria.

How do I revise digestion effectively? Read the subtopic notes, learn the enzyme table from memory, then take the Digestion quiz.

Ready to master Cambridge IGCSE Coordinated Science digestion?

Start with the Digestion subtopic page, then book a free trial with a Cambridge IGCSE Coordinated Science specialist to turn digestion into guaranteed marks.

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