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Detailed notes on Animal Nutrition for Cambridge IGCSE Coordinated Science, covering key concepts, explanations, examples, and exam-focused revision points.
A balanced diet contains the right amounts of all seven dietary components. Malnutrition (too little or too much of any component) causes specific, testable health problems. Students frequently confuse the function of different nutrients.
Mapped to the Cambridge IGCSE 0654 syllabus (2025-2027).
Each component has specific roles. Know at least one function and one deficiency per component.
| Component | Main Function(s) | Deficiency Consequences |
|---|---|---|
| Carbohydrates | Primary energy source; dietary fibre (from complex carbs) | Fatigue; weight loss; ketosis (extreme deficiency) |
| Proteins | Growth, repair, enzyme synthesis, hormones, antibodies | Kwashiorkor (protein-energy malnutrition) — muscle wasting, oedema, stunted growth |
| Lipids (fats/oils) | Energy storage; cell membranes; insulation; fat-soluble vitamins (A, D, E, K) | Deficiency of fat-soluble vitamins; energy shortage |
| Vitamin C | Synthesis of collagen (connective tissue); wound healing; antioxidant | Scurvy — bleeding gums, skin haemorrhages, poor wound healing |
| Vitamin D | Absorption of calcium and phosphorus; bone mineralisation | Rickets (children — bones don't harden) / Osteomalacia (adults) |
| Iron | Component of haemoglobin (carries O₂ in red blood cells) | Anaemia — fatigue, pale skin, breathlessness |
| Calcium | Bone and teeth mineralisation; muscle contraction; nerve impulse | Weak bones, osteoporosis, poor teeth |
| Water | Solvent for reactions; transport; temperature regulation; excretion | Dehydration — affects all cellular processes |
| Dietary fibre | Provides bulk to food — stimulates peristalsis (gut movement) | Constipation; increased risk of bowel cancer |
Malnutrition = unbalanced diet (too much OR too little of any component):
Verbatim phrases and definitions Cambridge mark schemes credit.
Paper 2: multiple choice on nutrient functions or deficiency symptoms. Paper 4: 'State the role of iron in the diet and describe the effect of iron deficiency' (2–3 marks). Table-completion on dietary components. Expect the exam to link iron → haemoglobin → oxygen transport → anaemia in a chain.
Sources: Cambridge IGCSE Coordinated Sciences 0654 syllabus 2025-2027 (B7). Last reviewed 2026-05-14.
Step-by-step solutions to past-paper-style questions on diet, written exactly the way a tutor would explain them at the board.
Question
State the role of iron in the body.
Step-by-step solution
Step 1
Iron is a component of haemoglobin, the protein in red blood cells.
Step 2
Haemoglobin binds oxygen in the lungs and transports it to body tissues.
Answer
Iron is a component of haemoglobin in red blood cells; haemoglobin transports oxygen around the body. Deficiency causes anaemia (reduced oxygen-carrying capacity).
Question
Explain why a pregnant woman requires more protein in her diet than a non-pregnant woman of similar age.
Step-by-step solution
Step 1
Protein is required for growth and repair of cells. During pregnancy, the fetus is growing rapidly and needs protein for new cell formation.
Step 2
Protein is also needed for the growth and maintenance of the placenta, for the increased blood volume and for the developing uterus muscle.
Step 3
Therefore total protein demand is significantly higher during pregnancy to support both maternal and fetal needs.
Answer
A pregnant woman needs more protein because protein is required for: growth of the fetus, development of the placenta, and increased maternal blood volume and uterine muscle. All involve new cell synthesis requiring protein.
Question
A teenager's diet is high in saturated fat. Explain ONE health risk associated with this diet.
Step-by-step solution
Step 1
Saturated fats raise the level of LDL cholesterol in the blood.
Step 2
Cholesterol can be deposited in artery walls, forming atherosclerotic plaques (atherosclerosis). This narrows the artery lumen and reduces blood flow.
Step 3
If a coronary artery is affected, blood supply to the heart muscle is reduced, increasing the risk of a heart attack (coronary heart disease). High blood pressure can also result.
Answer
A diet high in saturated fat raises blood cholesterol, leading to fatty deposits (atherosclerosis) in artery walls. This narrows arteries and increases the risk of coronary heart disease (heart attack) or stroke.
Question
State the symptoms of scurvy and identify its dietary cause.
Step-by-step solution
Step 1
Scurvy is caused by a deficiency of vitamin C (ascorbic acid) in the diet.
Step 2
Vitamin C is needed for the synthesis of collagen, a structural protein in connective tissue. Without sufficient collagen, blood vessels become fragile.
Step 3
Symptoms: bleeding gums, loose teeth, poor wound healing, bruising, joint pain.
Answer
Scurvy is caused by a lack of vitamin C in the diet. Symptoms include bleeding gums, poor wound healing, and bruising (due to weakened blood vessels from impaired collagen synthesis).
Question
Explain why an athlete needs more carbohydrate in their diet than an office worker.
Step-by-step solution
Step 1
Muscles contract during exercise, requiring energy released by aerobic respiration (and anaerobic at high intensity).
Step 2
Carbohydrates (glucose) are the primary and most efficiently used substrate for respiration. More exercise = more respiration = more glucose needed.
Step 3
An office worker has a lower activity level → lower energy expenditure → requires less carbohydrate.
Answer
Athletes have higher energy demands due to increased muscle activity; carbohydrates are the primary fuel for aerobic respiration. Greater physical activity requires more carbohydrate to supply glucose for respiration.
Definitions to memorise and the exact keywords mark schemes credit for diet answers — sharpened from recent examiner reports for the 2026 0654 sitting.
A diet that contains the correct amounts and proportions of all the necessary nutrients (carbohydrates, proteins, lipids, vitamins, minerals, water, and fibre) for health.
A condition resulting from an unbalanced diet — either over-nutrition (excess intake, e.g. obesity) or under-nutrition (insufficient intake, e.g. kwashiorkor, marasmus).
A water-soluble vitamin required for collagen synthesis. Deficiency causes scurvy (bleeding gums, poor wound healing).
Indigestible plant material (mainly cellulose) that adds bulk to food in the gut, stimulates peristalsis and helps prevent constipation.
A condition in which excess body fat has accumulated to a level that may impair health; caused by energy intake consistently exceeding energy expenditure.
A condition in which blood has a reduced oxygen-carrying capacity, often due to iron deficiency causing insufficient haemoglobin production.
The traps other students keep falling into on diet questions — taken from recent Cambridge IGCSE 0654 examiner reports and mark schemes — and how to avoid them.
Why it happens
Students associate food with energy and apply this to all macronutrients.
How to avoid it
Proteins are primarily used for growth and repair of cells. They are an energy source only when other sources are depleted.
Why it happens
Students lump vitamins in with energy-providing nutrients.
How to avoid it
Vitamins do NOT provide energy. They are needed in small amounts for specific metabolic functions (e.g. vitamin C for collagen synthesis, vitamin D for calcium absorption).
Why it happens
Media messages about diet oversimplify the role of lipids.
How to avoid it
Lipids are essential for energy storage, cell membrane structure, hormone production, and fat-soluble vitamins (A, D, E, K). Only excessive saturated fats are linked to health risks.
Why it happens
Students list fibre alongside carbohydrates and assume it is digested.
How to avoid it
Dietary fibre (cellulose) cannot be digested by humans — we lack cellulase. Its role is to add bulk and stimulate peristalsis.
The things students keep getting wrong in this sub-topic, answered.