Cambridge IGCSE Biology 7 Human Nutrition Exam Questions

About Cambridge IGCSE Biology 7 Human Nutrition

Human nutrition follows the path of food through the body in Cambridge IGCSE Biology. It starts with diet: the nutrients in a balanced diet, their sources and the deficiency diseases scurvy and rickets. You then need the organs of the alimentary canal and associated organs, the difference between physical and chemical digestion, and which enzymes act where. Extended candidates also learn the role of hydrochloric acid, bile emulsifying fats and neutralising acid, the action of pepsin and trypsin, and the structure of villi and microvilli. Examiners often ask you to label the digestive system, link a structure to its function and explain how villi increase absorption.

What you need to know

• 7.1 Diet A balanced diet contains carbohydrates, fats, proteins, vitamins C and D, mineral ions calcium and iron, fibre and water. Vitamin C deficiency causes scurvy and vitamin D deficiency causes rickets. Fibre (roughage) helps peristalsis and prevents constipation.
• 7.2 Digestive system Mouth, oesophagus, stomach, small intestine (duodenum and ileum), large intestine (colon and rectum) and anus, plus the salivary glands, pancreas, liver and gall bladder. Ingestion, digestion, absorption, assimilation and egestion are the key processes.
• 7.3 Physical digestion Breaking down food into smaller pieces without chemical change, increasing surface area for enzymes. Teeth (incisors, canines, premolars, molars) and churning in the stomach do this. Extended: bile emulsifies fats into droplets to increase surface area for lipase.
• 7.4 Chemical digestion Breaking large insoluble molecules into small soluble molecules. Amylase breaks starch into simple reducing sugars (maltose, then maltase makes glucose in Extended); proteases break proteins into amino acids; lipase breaks fats into fatty acids and glycerol.
• 7.4 Acid and bile (Extended) Hydrochloric acid in the stomach kills harmful microorganisms and gives the optimum pH for pepsin. Bile is alkaline and neutralises acidic chyme entering the duodenum, giving a suitable pH for enzymes in the small intestine.
• 7.5 Absorption Most digested food is absorbed in the small intestine, and most water in the small intestine, with some in the colon. Villi and microvilli give a large surface area; Extended candidates add capillaries for absorbing glucose and amino acids, and lacteals for fatty acids and glycerol.

Common mistakes in 7 Human Nutrition

• Saying bile is an enzyme or that it digests fat. Bile emulsifies fat; lipase does the chemical digestion.
• Saying the large intestine absorbs most of the water. Most water is absorbed in the small intestine.
• Saying stomach acid digests protein. The acid kills microorganisms and provides the optimum pH for pepsin, which digests protein.
• Confusing egestion and excretion. Removing undigested food as faeces is egestion.
• Saying villi have thin walls 'so food can pass through'. Say the epithelium is one cell thick, giving a short diffusion distance.

Try three 7 Human Nutrition exam-style questions