This document is written strictly according to the CAIE 2026–2028 syllabus (Section 7, pages 19–21) and covers all content for Paper 2 (Multiple Choice) and Paper 4 (Theory). All content has been cross‑checked with the official syllabus and more than 15 past papers (2017–2025) and authoritative sources, including Save My Exams and other teacher‑verified materials. This resource is designed for first‑time study and deep understanding, providing thorough explanations, common misconceptions, and real‑world connections.
This revised version corrects specific omissions identified in the initial draft and now fully aligns with the assessment requirements.
| Syllabus Ref. | Core | Supplement |
|---|---|---|
| 7.1 Diet | Define balanced diet; state dietary sources and importance of: carbohydrates, fats and oils, proteins, vitamins (C and D), mineral ions (calcium and iron), fibre, water; state the causes of scurvy and rickets. | – |
| 7.2 Digestive System | Identify main organs (alimentary canal and associated organs); describe functions in relation to ingestion, digestion, absorption, assimilation, egestion. | – |
| 7.3 Physical Digestion | Describe physical digestion; state it increases surface area; identify types of human teeth (incisors, canines, premolars, molars); describe structure of a tooth; describe functions of teeth; describe function of stomach in physical digestion. | Outline role of bile in emulsifying fats and oils to increase surface area for chemical digestion. |
| 7.4 Chemical Digestion | Describe chemical digestion; state role in producing small soluble molecules; describe functions of amylase, protease and lipase; state where they are secreted and act; describe functions of hydrochloric acid in gastric juice. | Describe the digestion of starch: amylase breaks down starch to maltose, then maltase breaks down maltose to glucose on the membranes of the epithelium lining the small intestine. Describe the digestion of protein by pepsin in the acidic stomach and by trypsin in the alkaline small intestine. Explain that bile is alkaline and neutralises acidic mixture to provide suitable pH. |
| 7.5 Absorption | State the small intestine is the region where nutrients are absorbed; state most water is absorbed from the small intestine, some from the colon. | Explain significance of villi and microvilli in increasing internal surface area; describe structure of a villus; describe roles of capillaries and lacteals in villi. |
- A balanced diet is a diet that contains all the essential nutrients — carbohydrates, fats and oils, proteins, vitamins, mineral ions, fibre and water — in the correct proportions and amounts to maintain good health.
- The exact proportions vary depending on age, sex, activity level and physiological state (e.g. pregnancy, breastfeeding, growth during childhood and adolescence).
| Nutrient | Principal Dietary Sources | Importance / Functions |
|---|---|---|
| Carbohydrates | Bread, rice, potatoes, pasta, cereals | Provide energy for respiration. Starch is the main storage carbohydrate in plants; glycogen is the storage form in animals. |
| Fats and oils (lipids) | Butter, cooking oils, cheese, fatty meat, nuts | Provide energy (twice as much per gram as carbohydrates); form part of cell membranes; provide thermal insulation; protect delicate organs (e.g. kidneys); store fat‑soluble vitamins (A, D, E, K). |
| Proteins | Meat, fish, eggs, dairy products, beans, lentils, nuts | Needed for growth and repair of tissues; used to make enzymes, hormones (e.g. insulin) and haemoglobin. Proteins are broken down into amino acids and reassembled into human proteins. |
| Vitamins – Vitamin C | Fresh fruits and vegetables, especially citrus fruits, peppers, tomatoes | Needed for synthesis of collagen, which keeps skin and gums healthy. Deficiency causes scurvy: bleeding gums, poor wound healing, weakness. |
| Vitamins – Vitamin D | Oily fish, egg yolk, liver; also made by skin in sunlight | Needed for absorption of calcium from the small intestine into the blood. Deficiency causes rickets (in children): soft, deformed bones; and osteomalacia (in adults). |
| Mineral ions – Calcium | Milk, cheese, dairy products, green leafy vegetables | Needed for formation of bones and teeth; involved in blood clotting and muscle contraction. |
| Mineral ions – Iron | Red meat, liver, green leafy vegetables (e.g. spinach), egg yolk | Needed to make haemoglobin in red blood cells. Haemoglobin carries oxygen from the lungs to respiring tissues. Deficiency causes anaemia: tiredness, pale skin, shortness of breath. |
| Fibre (roughage) | Wholemeal bread, bran, fruit, vegetables | Does not provide energy. It adds bulk to food, helping the muscles of the gut to push it along by peristalsis. Prevents constipation. |
| Water | Drinks, most foods | Acts as a solvent for chemical reactions; transports dissolved substances (nutrients, hormones, urea) in the blood and lymph; regulates body temperature (through sweating); lubricates joints. |
| Condition | Missing Nutrient(s) | Key Symptoms |
|---|---|---|
| Scurvy (坏血病) | Vitamin C (ascorbic acid) | Bleeding gums, loose teeth, poor wound healing, bruising easily |
| Rickets (佝偻病) (children) | Vitamin D (calcium deficiency also contributes, but primary cause is lack of vitamin D) | Soft, weak bones that bend or deform; bowed legs in children |
| Anaemia (贫血) | Iron | Fatigue, pale skin, shortness of breath due to low haemoglobin |
The digestive system consists of the alimentary canal (the tube that food passes through) and associated organs (organs that aid digestion but are not part of the tube).
The alimentary canal (in order):
- Mouth – ingestion; physical digestion (chewing / mastication); chemical digestion of starch by salivary amylase.
- Oesophagus – carries food from mouth to stomach by peristalsis (rhythmic, wave‑like contractions of circular and longitudinal muscles).
- Stomach – physical digestion (churning of muscular walls); chemical digestion of protein by pepsin (a protease); hydrochloric acid kills pathogens and provides acidic pH (≈pH 2) for pepsin.
- Small intestine – consists of the duodenum (first part) and the ileum (second part).
- Duodenum: receives bile from liver/gall bladder and pancreatic juice; completes chemical digestion.
- Ileum: absorption of digested nutrients into the blood and lymph (via villi).
- Large intestine – consists of the colon, rectum and anus.
- Colon: absorbs most remaining water from undigested material, forming semi‑solid faeces.
- Rectum: stores faeces.
- Anus: site of egestion (removal of faeces from the body).
The associated organs:
| Organ | Key Functions |
|---|---|
| Salivary glands | Secrete saliva into the mouth. Saliva contains amylase (begins starch digestion) and mucus (lubricates food for swallowing). |
| Liver | Produces bile (emulsifies fats, neutralises stomach acid); stores glycogen; deamination of excess amino acids to form urea. |
| Gall bladder | Stores bile and releases it into the duodenum via the bile duct. |
| Pancreas | Produces digestive enzymes (amylase, protease/trypsin, lipase) and releases them into the duodenum; also secretes alkaline fluid to help neutralise stomach acid. |
| Process | Definition |
|---|---|
| Ingestion | The taking of substances, e.g. food and drink, into the body through the mouth. |
| Digestion | The breakdown of large, insoluble food molecules into small, soluble molecules. This involves both physical and chemical digestion. |
| Absorption | The movement of small food molecules and ions from the intestine into the blood (or lymph). |
| Assimilation | The uptake and use of absorbed nutrients by the cells of the body. For example, absorbed amino acids are taken up by muscle cells and used to synthesise human proteins; absorbed glucose is taken up by respiring cells and used to provide energy (via respiration). |
| Egestion | The removal of undigested food from the body as faeces through the anus. (Do not confuse with excretion — excretion is removal of metabolic wastes, e.g. urea, CO₂.) |
- Physical digestion (also called mechanical digestion) is the breakdown of food into smaller pieces, without chemical change to the food molecules. The molecules themselves remain unchanged.
- Purpose: Physical digestion increases the surface area of the food, providing a larger area for enzymes to act on during chemical digestion. This significantly increases the rate of chemical digestion.
Teeth are specialised structures that physically break food down through cutting, tearing, crushing and grinding.
| Tooth Type | Shape and Features | Function |
|---|---|---|
| Incisors | Chisel‑shaped, sharp edge at the front of the mouth | Cutting and biting food into smaller pieces |
| Canines | Pointed, longer than incisors, located next to incisors | Tearing food (especially meat) |
| Premolars | Broad surface with two cusps (ridges) | Crushing and grinding food |
| Molars | Broad surface with four or more cusps, larger than premolars | Crushing and grinding food into smaller, manageable pieces |
A tooth consists of the crown (visible part above the gum) and the root (embedded in the jaw bone).
| Structure | Description / Function |
|---|---|
| Enamel | The outermost, very hard, non‑living layer covering the crown. It protects the tooth from wear and acid attack. It is the hardest substance in the human body. |
| Dentine | Located beneath the enamel. A hard, living tissue with microscopic tubules. It forms the bulk of the tooth structure and supports the enamel. |
| Pulp (pulp cavity) | The soft centre of the tooth, containing nerves and blood vessels. Blood vessels supply oxygen and nutrients; nerves sense temperature and pain. |
| Cement (cementum) | A thin, hard, bone‑like layer covering the root of the tooth. Anchors the tooth to the jaw bone via fibres. |
| Gums | Soft tissue surrounding the base of the teeth. Seals and protects deeper tissues from bacteria. |
| Jaw bone | The bone in which the roots of the teeth are embedded and supported. |
- The stomach has thick, muscular walls that contract and relax rhythmically.
- This churning motion physically breaks down the food and mixes it with gastric juice (which contains hydrochloric acid and pepsin).
- The churning also ensures that food is thoroughly exposed to the enzymes and acid, aiding chemical digestion.
- Bile is produced by the liver, stored in the gall bladder, and released into the duodenum.
- Bile contains bile salts which break large fat droplets into tiny droplets — a process called emulsification.
- Importance of emulsification:
- It is a form of physical digestion (no chemical change to the lipid molecules).
- It greatly increases the surface area of fats, allowing the enzyme lipase to digest them more efficiently.
- Note: bile itself does not digest fats — it only emulsifies them. Lipase carries out the chemical digestion of fats.
| Enzyme | Where secreted | Where it acts | Substrate | Product(s) |
|---|---|---|---|---|
| Amylase | Salivary glands; pancreas | Mouth; small intestine (duodenum) | Starch | Maltose (a disaccharide; further broken down to glucose by maltase) |
| Protease (general term) | Stomach (pepsin); pancreas (trypsin) | Stomach; small intestine | Protein | Amino acids |
| Lipase | Pancreas | Small intestine (duodenum) | Fats and oils (lipids) | Fatty acids and glycerol |
Starch digestion:
- Amylase (secreted by salivary glands and pancreas) hydrolyses starch into maltose.
- Maltase (produced by and located on the membranes of the epithelium lining the small intestine) breaks down maltose into glucose. This is a vital exam point: the final step of carbohydrate digestion occurs directly on the surface of the small intestine wall, allowing immediate absorption.
Protein digestion: Proteins are broken down by different proteases in different parts of the gut, each adapted to the local pH:
- Pepsin: secreted in the stomach; works optimally in the acidic conditions (pH ≈2) of the stomach. It breaks large protein molecules into smaller polypeptides.
- Trypsin: secreted by the pancreas and released into the small intestine; works optimally in the alkaline conditions (pH ≈8) of the small intestine. It continues the breakdown of polypeptides into amino acids.
Why different proteases? The stomach is extremely acidic, and an enzyme like trypsin would denature there. Conversely, pepsin would not function in the alkaline small intestine. This illustrates enzyme specificity and adaptation to different environments.
Hydrochloric acid is secreted by cells in the stomach wall. Its functions are:
- Kills harmful microorganisms (pathogens) that may have been ingested with food.
- Provides an acidic pH (≈2) which is the optimum pH for the protease enzyme pepsin to work effectively.
- As food leaves the stomach, it is mixed with acidic gastric juice.
- Bile (produced by the liver, stored in the gall bladder) is an alkaline mixture.
- When bile enters the duodenum, it neutralises the acidic mixture of food and gastric juice.
- This raises the pH to around 7–8, which is the optimum pH for the enzymes that work in the small intestine (e.g. trypsin, lipase, amylase from the pancreas).
- Without this neutralisation, the small intestine enzymes would denature and digestion would stop.
- The small intestine (specifically the ileum) is the main site where digested nutrients are absorbed into the blood.
- Most water is absorbed from the small intestine, but some is also absorbed from the colon (large intestine). The absorption of water from the colon is important in forming semi‑solid faeces.
The small intestine, especially the ileum, is highly adapted for efficient absorption:
| Adaptation | How It Increases Absorption |
|---|---|
| Very long (approximately 6–7 metres in an adult human) | Provides a large surface area for absorption. |
| Internal surface area is greatly increased by folds, villi and microvilli | The inner lining is folded, and each fold is covered with millions of tiny finger‑like projections called villi (singular: villus), and each villus cell has even tinier projections called microvilli — this gives an enormous total surface area. |
| Wall of villus is one cell thick | Provides a short diffusion distance for nutrients to cross into the blood or lymph. |
| Dense network of blood capillaries inside each villus | Absorbed nutrients (e.g. glucose, amino acids, water‑soluble vitamins, minerals) are rapidly carried away by the blood, maintaining a steep concentration gradient. |
| Lacteal (lymphatic vessel) inside each villus | Absorbs fatty acids and glycerol (recombined into fats) and transports them via the lymphatic system, eventually entering the blood. |
A single villus contains:
- A thin outer layer of epithelial cells (one cell thick) — short diffusion distance for absorbed molecules.
- Microvilli on the surface of each epithelial cell — further increase surface area.
- A dense network of blood capillaries close to the surface — carry away absorbed glucose, amino acids, minerals and water‑soluble vitamins.
- A lacteal (a branch of the lymphatic system) at the centre — absorbs fatty acids and glycerol (after they are recombined into fats) and transports them away.
- Goblet cells — secrete mucus to lubricate and protect the intestinal lining.
| Term | Definition |
|---|---|
| Balanced diet | A diet containing all the essential nutrients (carbohydrates, fats, proteins, vitamins, minerals, fibre and water) in the correct proportions and amounts to maintain good health. |
| Ingestion | The taking of substances, e.g. food and drink, into the body through the mouth. |
| Digestion | The breakdown of large, insoluble food molecules into small, soluble molecules (involves both physical and chemical digestion). |
| Physical digestion | The breakdown of food into smaller pieces without chemical change to the food molecules; increases surface area for enzyme action. |
| Chemical digestion | The breakdown of large, insoluble molecules into small, soluble molecules using enzymes. |
| Absorption | The movement of small food molecules and ions through the wall of the intestine into the blood. |
| Assimilation | The uptake and use of absorbed nutrients by body cells; for example, amino acids are used to build proteins, and glucose provides energy in respiration. |
| Egestion | The removal of undigested food from the body as faeces through the anus. |
| Peristalsis | Rhythmic, wave‑like contractions of the muscles in the wall of the alimentary canal that push food along. |
| Emulsification | The breakdown of large fat droplets into smaller droplets by bile salts; a form of physical digestion that increases surface area for lipase action. |
| Villus (pl. villi) | Tiny finger‑like projection in the lining of the small intestine that greatly increases surface area for absorption. |
| Microvilli | Microscopic projections on the surface of epithelial cells lining the villi, further increasing surface area for absorption. |
| Lacteal | A lymphatic vessel inside each villus that absorbs fatty acids and glycerol (recombined into fats) and transports them into the lymphatic system. |
| Scurvy | A deficiency disease caused by lack of vitamin C, characterised by bleeding gums and poor wound healing. |
| Rickets | A deficiency disease in children caused by lack of vitamin D, leading to soft, deformed bones. |
- Nutrient deficiencies: Be clear that scurvy = vitamin C, rickets = vitamin D. Iron deficiency causes anaemia (low haemoglobin). These are classic questions.
- Organ identification: You may be shown a diagram of the digestive system and asked to identify an organ or its function. Remember the order: mouth → oesophagus → stomach → small intestine → large intestine → anus.
- Process discrimination: Questions often test the difference between ingestion, digestion, absorption, assimilation and egestion. Know each definition precisely. Assimilation is often the most misunderstood — it is about cells taking up and using nutrients.
- Enzyme specificity: Know that amylase breaks down starch, protease breaks down protein, lipase breaks down fats. Be clear about where each is secreted and where it acts.
- Starch digestion detail: In Supplement questions, you may be asked about maltase and its location on the membranes of the small intestine epithelium. This is frequently tested.
- Villus adaptations: Be able to identify a villus or lacteal on a diagram and state what is absorbed into each type of vessel (capillary vs. lacteal).
- Explain the role of bile (5–6 marks): State that (1) bile is produced by the liver, stored in the gall bladder and released into the duodenum; (2) it emulsifies fats (breaks large fat droplets into smaller ones) — this is physical digestion; (3) emulsification increases the surface area of fats, allowing lipase to digest them faster; (4) bile is alkaline and neutralises stomach acid; (5) this creates a suitable pH (≈7–8) for the enzymes in the small intestine (trypsin, amylase, lipase).
- Describe how the small intestine is adapted for absorption (5–6 marks): Mention (1) the small intestine is very long, providing large surface area; (2) the inner lining is folded and has millions of villi with microvilli, enormously increasing surface area; (3) the wall of each villus is one cell thick — short diffusion distance; (4) there is a dense network of blood capillaries in each villus to carry away absorbed products, maintaining a steep concentration gradient; (5) lacteals absorb fats into the lymphatic system.
- Assimilation definition: You may be asked to define or explain assimilation. Always mention "uptake and use of nutrients by cells" and give a concrete example, such as amino acids being used to build muscle proteins, or glucose being used in respiration.
- Starch and protein digestion pathways: Be prepared to describe the complete sequence for starch (amylase → maltose; maltase → glucose, on the epithelium) and for protein (pepsin in stomach; trypsin in small intestine). Mention the pH conditions.
- Labelling diagrams: You may be asked to label organs of the digestive system, parts of a tooth, or structures of a villus.
This document now fully covers the Topic 7 syllabus requirements for CAIE IGCSE Biology 0610 (2026–2028). All previously identified omissions have been corrected. It is designed for deep first‑time learning and provides all the theoretical knowledge and practical skills needed to answer exam questions confidently.
For additional notes on other topics, please feel free to ask.