BIOLOGY · Stage 8 · Chapter 6: Nutrition, Health and Movement
Biology 6.1 The food we eat — Essential Nutrients and Food Tests
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Lesson summary
Biology 6.1 The food we eat — Essential Nutrients and Food Tests — Alhussan International Academy — Biology (Stages 7–9) notes: Name the main nutrients, give their sources and functions, explain how food is digested and describe tests for nutrients.Diet = the food a person eats e…
- Same nutrients
- Balanced diet
- Staple food
- Fibre and water
- Large insoluble molecules
- Small soluble molecules
Section 1 of 6Diet and the main nutrients
- Diet = the food a person eats each day, which must supply everything needed to stay healthy.
- Same nutrients
- different climates and cultures give different foods,
- but the body needs the same nutrients, for energy for the processes of life and for materials to build and repair cells.
- Balanced diet
- it includes carbohydrates, proteins, fats and oils, vitamins and minerals, with fibre and water also needed.
| Nutrient | Function | Sources |
|---|---|---|
| Carbohydrates | Store a lot of energy that the body uses easily | Rice, wheat, cassava, potatoes, bananas |
| Proteins | Build new tissues, replace old ones and repair damaged ones | Meat, fish, insects, eggs, peas, beans, nuts |
| Lipids (fats and oils) | A very important energy source, insulation under the skin and protection for organs | Butter, meat, cheese, olives, avocados, nuts |
| Vitamins | Needed in small amounts to help chemical reactions in cells | Fruit, vegetables and many other foods |
| Minerals | Needed in small amounts to build substances in the body | Red meat, green vegetables, dairy produce |
Section 2 of 6Carbohydrates and proteins
- Staple food
- carbohydrate-rich foods are eaten every day by many people.
- Proteins
- much of the body is built of protein, which contains 20 different building blocks called amino acids.
- The body breaks down the proteins eaten into amino acids and builds them into the proteins it needs.
Section 3 of 6Lipids, vitamins and minerals
- Lipids
- fats are solid lipids and oils are liquid lipids.
- Fat cells store energy, form an insulating layer under the skin and a protective layer around organs such as the kidneys.
- The membranes of all cells are made of fat molecules.
- Vitamins
- only very small amounts are needed.
- Vitamin C is found in citrus fruits and vitamin D in dairy produce and fish oils.
- Minerals
- only small amounts are needed.
- Iron is needed to make haemoglobin to carry oxygen in the blood.
- Calcium is needed for strong teeth and bones.
- Fibre and water
- fibre helps food move through the gut, and water is the solvent for all reactions.
Section 4 of 6Digestion
- Digestion
- whatever food is eaten, the body breaks it down in the digestive system.
- Large insoluble molecules
- most food is made of these, which the body cannot use.
- Small soluble molecules
- in the digestive system they are broken down into small soluble molecules that move from the gut into the blood by diffusion.
- Starch becomes glucose, proteins become amino acids, and fats become fatty acids and glycerol.
- Transport
- the dissolved nutrients are carried round the body in the blood to the cells that need them.
Section 5 of 6Testing foods for nutrients
| Nutrient | Reagent | Positive result |
|---|---|---|
| Starch | Iodine solution | Orange-brown to blue-black |
| Glucose (reducing sugar) | Benedict's solution, heated in a water bath | Blue to green, yellow, brick-red |
| Protein | Biuret reagent | Blue to purple |
| Lipid | Ethanol emulsion test | Cloudy white emulsion |
- Safety
- wear eye protection, and use a water bath and not a direct flame for Benedict's test.
- Recording
- record observations in a results table.
Section 6 of 6Proportions in the diet
- Needs vary
- they depend on age, activity and sex,
- such as a growing child needing more protein, an athlete more carbohydrate and a pregnant woman more iron and calcium.
- they depend on age, activity and sex,
- Balance
- too much of one nutrient and too little of another leads to poor health even when total energy is correct.
- Roles
- carbohydrates and lipids supply most of the energy, proteins supply amino acids for growth and repair,
- and vitamins and minerals regulate body processes.
- carbohydrates and lipids supply most of the energy, proteins supply amino acids for growth and repair,
- Labels
- food labels give the energy and nutrient content per 100 g to compare products.
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