Human nutrition — Edexcel International GCSE Science (Double Award)
A balanced diet, nutrient sources and functions, the alimentary canal and peristalsis, digestive enzymes, bile and absorption in the small intestine.
Revision notes
6 short notes, in the order of the specification. Each one in short:
A balanced diet contains the right proportions of carbohydrate, protein, lipid, vitamins, minerals, water and dietary fibre. Most energy comes from carbohydrate and lipid. Energy requirements vary with activity level, age and pregnancy: more active people respire more in their muscles, teenagers are growing quickly, and pregnant women need extra energy for the growth of the fetus.
Each nutrient has a source and a specific function. Carbohydrate provides energy, protein is needed for growth and repair, and lipid is an energy store and insulation. Vitamin A is needed for vision in dim light, vitamin C keeps skin and gums healthy, vitamin D helps absorb calcium, calcium builds bones and teeth, and iron is needed to make haemoglobin.
The alimentary canal is the tube from the mouth to the anus, made up of the mouth, oesophagus, stomach, small intestine (duodenum and ileum) and large intestine (colon and rectum). Food is moved along by peristalsis: waves of contraction of the circular and longitudinal muscles in the gut wall squeeze the food forward.
Digestive enzymes break large, insoluble food molecules into small, soluble molecules that can be absorbed into the blood. Amylase breaks starch into maltose, and maltase breaks maltose into glucose. Proteases break proteins into amino acids. Lipases break lipids into fatty acids and glycerol. Each type of enzyme breaks down one type of food molecule.
Bile is an alkaline liquid produced by the liver, stored in the gall bladder and released into the duodenum. It neutralises the acid from the stomach, giving the enzymes in the small intestine the alkaline conditions they work best in. It also emulsifies lipids into tiny droplets, increasing their surface area so lipase digests them faster.
The products of digestion are absorbed in the small intestine, mostly in the ileum. Its wall is covered in villi and microvilli, giving a very large surface area. Each villus has a wall one cell thick for a short diffusion distance, a capillary network that keeps a steep concentration gradient, and a lacteal that absorbs fatty acids and glycerol.
Exam questions
6 exam-style questions (21 marks), each with its mark scheme.
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23 cards: flip them, mark what you knew, and practise the rest.
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Quick check questions
Name the seven components of a balanced diet.
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Carbohydrate, protein, lipid, vitamins, minerals, water and dietary fibre.
What is peristalsis?
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Waves of muscle contraction that move food along the gut.
What are the products of digestion by amylase and then maltase?
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Amylase makes maltose from starch. Maltase makes glucose from maltose.
Give two roles of bile.
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It neutralises stomach acid and emulsifies lipids.
Where is bile made and where is it stored?
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Made in the liver and stored in the gall bladder.
Frequently asked questions
What enzymes digest carbohydrates?
Amylase and maltase digest carbohydrates. Amylase, made in the salivary glands and the pancreas, breaks starch down into the sugar maltose. Maltase, made in the small intestine, then breaks maltose down into glucose. Glucose is small and soluble, so it can be absorbed into the blood in the small intestine and used in respiration.
What enzymes break down proteins?
Proteases break down proteins into amino acids. Proteases are made in the stomach, the pancreas and the small intestine. Pepsin is a protease in the acidic stomach and works best at about pH 2. The amino acids are absorbed into the blood and used to make new proteins for growth and repair.
What enzymes does the pancreas produce?
The pancreas produces amylase, protease and lipase and releases them into the duodenum. Amylase breaks starch into maltose, protease breaks proteins into amino acids, and lipase breaks lipids into fatty acids and glycerol. The pancreas is not part of the alimentary canal itself, but it helps with digestion.
What does bile do in digestion?
Bile neutralises stomach acid and emulsifies lipids. It is made in the liver, stored in the gall bladder and released into the duodenum. Being alkaline, it gives small intestine enzymes the conditions they work best in. It breaks fat into tiny droplets, increasing the surface area so lipase works faster. Bile is not an enzyme.
How is the small intestine adapted for absorption?
The small intestine is adapted for absorption by being long, with a folded wall covered in villi and microvilli that give a very large surface area. Each villus has an epithelium one cell thick for a short diffusion distance, and a network of capillaries that carries food away, keeping a steep concentration gradient. A lacteal absorbs fatty acids and glycerol.
Written and checked against the Edexcel IGCSE Science Double Award (4SD0) specification · Updated October 2026