Diet
Building on the concept of nutrition, a balanced diet must include:
- Energy-providing nutrients: Carbohydrates, fats, and proteins.
- Regulatory nutrients: Vitamins, mineral ions, and water.
- Non-nutrient components: Fibre (roughage), which aids digestion.
| Nutrient | Principal Dietary Sources | Importance / Function |
|---|---|---|
| Carbohydrates | Bread, rice, pasta, potatoes, sugar. | Main source of energy for respiration and physical activity. |
| Fats and Oils (Lipids) | Butter, margarine, oils, meat, nuts, avocados. | Long-term energy storage; insulation; protection of organs; component of cell membranes. |
| Proteins | Meat, fish, eggs, beans, nuts, dairy products. | Growth and repair of tissues; production of enzymes and hormones. |
| Vitamin C | Citrus fruits (oranges, lemons), strawberries, peppers, broccoli. | Prevents scurvy; essential for wound healing and immune function. |
| Vitamin D | Sunlight exposure (skin synthesis); oily fish, egg yolks, fortified milk/cereals. | Regulates calcium absorption; prevents rickets; maintains healthy bones and teeth. |
| Calcium | Dairy products (milk, cheese), leafy green vegetables, fortified foods. | Essential for strong bones and teeth; required for muscle contraction and blood clotting. |
| Iron | Red meat, liver, spinach, fortified cereals. | Component of haemoglobin in red blood cells; essential for oxygen transport. |
| Fibre (Roughage) | Whole grain products, fruits, vegetables, beans. | Promotes peristalsis; prevents constipation; adds bulk to faeces. |
| Water | Drinking water, fruits, vegetables, soups. | Solvent for chemical reactions; transport medium in blood; temperature regulation. |
Rickets is a disease affecting bone development in children, caused by a deficiency of Vitamin D OR Calcium. It results in soft, weak, or deformed bones.
Error: Students often confuse the causes of scurvy and rickets, or assume they are related to the same nutrient.
Correct Understanding:
- Scurvy is exclusively caused by a lack of Vitamin C. It affects gums and wound healing.
- Rickets is caused by a lack of Vitamin D OR Calcium. It affects bone strength and shape.
Do not mix these up. Vitamin C has no role in preventing rickets, and Vitamin D/Calcium does not prevent scurvy.
Why examiners accept this: Examiners look for two distinct ideas: the presence of all nutrients and the concept of correct proportions/amounts. Simply listing foods is insufficient.
Correct Usage Example: 'A balanced diet contains all the necessary nutrients (such as carbohydrates, proteins, vitamins, etc.) in the correct proportions to provide sufficient energy for the body's activities.'
Key Phrase: Use 'correct proportions' or 'appropriate amounts'. Avoid vague terms like 'healthy food' without specifying balance.
Why examiners accept this: The mark scheme is specific about the nutrient deficiency. For rickets, both Vitamin D and Calcium are valid causes because Vitamin D is required for calcium absorption.
Correct Usage Example:
- For Scurvy: 'Caused by a lack of Vitamin C.'
- For Rickets: 'Caused by a lack of Vitamin D' OR 'Caused by a lack of Calcium.'
Note: You may state either Vitamin D or Calcium for rickets. Both are accepted causes in Cambridge Biology.
- Contains all / 7 nutrients (or food groups) [1]
- In correct proportions / amounts / to supply sufficient energy [1]
Rickets: Lack of Vitamin D OR Calcium [1]