The digestive system — Cambridge IGCSE Biology
The organs of the alimentary canal and associated organs, the five processes of nutrition, teeth, and physical digestion in the mouth and stomach.
Revision notes
3 short notes, in the order of the specification. Each one in short:
The alimentary canal is the long tube that food passes through from mouth to anus, while the salivary glands, pancreas, liver and gall bladder are associated organs that make and store digestive juices. The five processes of nutrition are ingestion, digestion, absorption, assimilation and egestion, the removal of undigested food as faeces.
Physical digestion is the breakdown of food into smaller pieces without chemical change to the food molecules. It increases the surface area of the food for enzymes to act on. Incisors bite and cut food, canines tear and grip it, and premolars and molars crush and grind it. Teeth are embedded in the jawbone and gums.
The stomach churns food and mixes it with gastric juice containing protease and hydrochloric acid. The acid kills harmful microorganisms in food and provides the optimum pH for the stomach protease. Bile, made in the liver and stored in the gall bladder, emulsifies fats and neutralises the acidic mixture entering the duodenum.
Exam questions
7 exam-style questions (20 marks), each with its mark scheme.
Answer the questionsFlashcards
13 cards: flip them, mark what you knew, and practise the rest.
Practise the cardsMind map
The whole of human nutrition on one page, so you can see where this subtopic fits.
Open the mind mapPrint it
Free PDFs to print or save.
Quick check questions
Name the process: the removal of undigested food as faeces.
Show answer
Egestion.
Which type of tooth is used for tearing food?
Show answer
Canine.
What part of a tooth contains nerves and blood vessels?
Show answer
The pulp.
Give two functions of hydrochloric acid in the stomach.
Show answer
It kills harmful microorganisms in food and provides an acidic pH for optimum enzyme activity.
Supplement How does bile help the digestion of fats?
Show answer
It emulsifies them, which increases the surface area for lipase.
Frequently asked questions
What are the five processes of nutrition?
The five processes of nutrition are ingestion, digestion, absorption, assimilation and egestion. Ingestion is taking food and drink into the body, digestion is the breakdown of food, absorption is the movement of nutrients from the intestines into the blood, assimilation is the uptake and use of nutrients by cells, and egestion removes undigested food as faeces.
What is the difference between egestion and excretion?
Egestion is the removal of undigested food from the body as faeces, through the anus. Excretion is the removal of the waste products of metabolism, such as urea and carbon dioxide. Undigested food never entered the body's cells, so removing faeces is egestion, not excretion. Do not confuse egestion with absorption either.
What does each type of tooth do?
Incisors have a flat, chisel-shaped edge for biting and cutting food. Canines are pointed for tearing and gripping food. Premolars and molars are broad with ridged surfaces for crushing and grinding food. This physical digestion breaks food into smaller pieces, which increases its surface area for enzymes to act on.
Why is there hydrochloric acid in the stomach?
Hydrochloric acid in gastric juice has two functions. It kills harmful microorganisms in food, and it provides an acidic pH, which is the optimum pH for the protease enzyme in the stomach. The muscular stomach wall also churns food, mixing it with gastric juice and breaking it into smaller pieces.
What does bile do in digestion?
Supplement Bile emulsifies fats and oils, breaking large drops into many tiny droplets, which increases the surface area for lipase to act on. Bile is also alkaline, so it neutralises the acidic mixture entering the duodenum from the stomach, giving a suitable pH for enzymes in the small intestine. Bile is not an enzyme.
Written and checked against the Cambridge IGCSE Biology (0610) specification · Updated October 2026