Nutrients

Question 1

Why do we need food?

Answer 1

1. Food provides energy for vital activities
2. Food provides raw materials to make new protoplasm
3. Food helps organisms to stay healthy
4. What are the nutrients in food?

Question 2

What are the functions of water?

Answer 2

1. As a solvent for chemical reactions
2. As a key component of tissues
3. Controlling body temperature
4. Water is a solvent which helps to transport dissolved substances

Question 3

How do we test for reducing sugars?

Answer 3

Carry out the Benedict’s test.
1. Place 2 cm^3 of food sample into a test tube.
2. Add 2 cm^3 of Benedict’s solution to the food sample.
3. Shake the mixture and place the tube in a boiling water bath for 2–3 minutes.
Solution remains blue: No sugar present.
Green precipitate formed: Traces of reducing sugar present.
Yellow/Orange Precipitate: Moderate amount of reducing sugars.
Brick-Red Precipitate: Large Amount of Reducing Sugar.

Question 4

How can we identify starch?

Answer 4

Iodine test,
Add a few drops of iodine solution to a piece of potato.
Obs: Blue-Black is positive.

Question 5

How can we identify fats?

Answer 5

Ethanol (alcohol) emulsion test
Add 2cm^3 of ethanol to 2cm^3 of sample. 
Add 2cm^3 of water and shake well.
If positive:
Cloudy white emulsion observed.

Question 6

What are the functions of carbohydrates?

Answer 6

1. Substrate for respiration, to provide energy for cell activities
2. Form supporting structures, for example, cell walls in plants
3. to be converted into other organic compounds such as amino acids and fats
4. for the formation of nucleic acids, for example, DNA
5. to synthesise lubricants, for example, mucus, which consists of
   a carbohydrate and a protein
6. to synthesise the nectar in some flowers to attract insects.

Question 7

What are the functions of fats?

Answer 7

1. A source and store of energy.
2. An insulating material that prevents excessive heat loss. For example, animals such as seals have a thick layer of fat (blubber) beneath the skin which helps to reduce loss of body heat.
3. A solvent for fat-soluble vitamins and many other vital substances such as hormones.
4. An essential par t of protoplasm, especially in cell membranes.

Question 8

How can we test for proteins?

Answer 8

Biuret test
1. Add 2cm^3 of biuret solution to 2cm^3 of sample and shake well.
If a purple/violet colour is observed proteins are present.

Question 9

What are the functions of proteins?

Answer 9

1. synthesis of new protoplasm, for growth and repair of worn-out body cells;
2. synthesis of enzymes and some hormones
3. formation of antibodies to combat diseases.