Food

We need to eat a wide variety of foods to provide our bodies with all the substances that are needed. When we do this, we are said to have a balanced diet. Carbohydrates, proteins, fats, vitamins and minerals are nutrients, which means that they provide the raw materials for making other substances that the body needs.

Substances needed

• Carbohydrate: Starch, Sugars. We need it for energy. Good sources are pasta and bread
• Protein: We need it for growth and repair. Good sources are meat an beans
• Vitamins: Vitamin C. We need it for health. Good sources are fruit and veg.
• Minerals: Calcium. We need it for health. Good sources are fruit and veg.
• Fibre: We need it for health. Good sources are Wholemeal bread
• Water: We need it for health.

We can do tests to fi nd out which substances are in foods. For example, starch makes iodine solution go a blue-black colour.

Nutrition information labels on foods tell us what the food contains. The labels also tell us howmuch chemical energy is stored in the food. The amount of energy is measured in kilojoules (kJ). Food labels may also have health claims on them. Eating too much or too little can cause problems. Too much fat may cause heart disease and make you overweight. People who are very overweight are obese. People starve and become weak if they eat too little

Digestion turns large insoluble substances into small soluble ones. The organs of the digestive system help us digest food. Many of them produce enzymes (chemicals that break up food).

To help absorb the digested food, the wall of the small intestine is thin and covered with villi. These increase the surface area.

The digested food substances are carried around the body by the circulatory system. The blood travels through blood vessels. Arteries carry blood away from the heart. Veins carry blood towards the heart. The smallest blood vessels are capillaries. Cells in tissues get the substances they need from tissue fl uid, which leaks out of capillaries.

Use of digested food

Cells need food substances to:

• release energy
• make new substances.

Cells use a chemical reaction called respiration to release energy from a sugar called glucose.

Digestion turns large insoluble substances into small soluble ones. The organs of the digestive system help us digest food. Many of them produce enzymes (chemicals that break up food).

To help absorb the digested food, the wall of the small intestine is thin and covered with villi. These increase the surface area.

The digested food substances are carried around the body by the circulatory system. The blood travels through blood vessels. Arteries carry blood away from the heart. Veins carry blood towards the heart. The smallest blood vessels are capillaries. Cells in tissues get the substances they need from tissue fl uid, which leaks out of capillaries.

Use of digested food

Cells need food substances to:

• release energy
• make new substances.

Cells use a chemical reaction called respiration to release energy from a sugar called glucose.