Science 8th grade
UNIT 2: Food and digestion 2.1 Nutrients
Science 8th grade
UNIT 2: Food and digestion 2.1 Nutrients
Everyone enjoys eating tasty food. Food gives us pleasure. It also gives us the nutrients that we need to stay healthy.
Nutrients are substances in food that the body uses:
• to provide energy
• to provide materials for making the chemicals that are needed to make cells and other parts of the body.
Different kinds of food contain different nutrients.
Protein, carbohydrate and fat
The nutrients that we need to eat in the largest quantity are protein, carbohydrate and fat.
Protein is used for making new cells. Protein is also used for making many important chemicals in the body, such as enzymes (see pages 28-29) and antibodies (see page 37). Cells can use protein to supply energy.
Carbohydrate is used to provide energy. Starch and sugar are two kinds of carbohydrate.
Fat also provides energy. Fat can be stored in the body.
Fat stores underneath the skin provide insulation. Fat is needed to make new cell membranes.
Vitamins and minerals
Vitamins and minerals are nutrients that we need in only very small quantities. They do not provide energy. There are many different kinds of vitamins and minerals that we need to eat. Fruit and vegetables are a good source of some of them. There is more information about two vitamins and two minerals on page 20.
Fibre and water
Fibre (roughage) helps to keep food moving easily through the digestive system. We get fibre from fresh fruit and vegetables, and also from foods made from whole seeds such as brown rice or wholemeal bread.
Water is sometimes considered to be a nutrient.
Between $60\% $ and $70\% $ of the body is made up of water.
Questions
1) Explain the difference between food and nutrients.
2) The headings on the previous page contain the names of the seven kinds of nutrients. List them all.
3) Which three nutrients provide the body with energy?
Activity 2.1 (Testing foods for carbohydrates)
SE: Starch and sugar are two types of carbohydrate.
You can find out if a food contains starch using iodine solution.
You can find out if a food contains sugar using Benedict's solution.
1) First, test each food for starch.
• Put a small amount of the food onto a white tile.
• Add a drop or two of iodine solution. If the iodine turns blue-black, there is starch in the food.
2) Next, test each food for sugar.
• Chop or crush a small amount of the food, and put it into a boiling tube. Add a little water and stir or shake it well.
• Add enough Benedict's solution to make the mixture look blue.
• Put the boiling tube into a water bath at about ${80^ \circ }C$. Leave it for about 5 minutes.
• If there is sugar in the food, the colour will change as shown on the right.
3) Record your results in a results table like the one below. Add as many more rows as you need.
| ?Did it contain sugar | Colour with Benedict's solution | ?Did it contain starch | Colour with iodine solution | Food |