Nutrients

Question 1

What is the importance of food?

Answer 1

1. Food provides chemical potential energy for vital activities.
2. Foot provides raw materials to make new protoplasm.
3. Food helps organisms to stay healthy (vitamins)

Question 2

What is the importance of water?

Answer 2

1. Solvent for chemical reactions taking place in living things (i.e. photosynthesis).
2. Controlling body temperature.
3. Transporting dissolved substances,

Question 3

Carbohydrates

Answer 3

Components: hydrogen, carbon, oxygen.
Types: monosaccharides, disaccharides, polysaccharides.
Function:
1. A substrate for respiration to provide energy for cell activities.
2. To form supporting structures (i.e. cellulose cell wall)
3. To be converted into other compounds like amino acids and fats

Question 4

Monosaccharides

Answer 4

Examples: glucose, fructose, galactose

Question 5

Disaccharides

Answer 5

Examples: maltose, sucrose, lactose

A disaccharide molecule can be produced from 2 monosaccharide molecules in a condensation reaction.

A disaccharide can be split into 2 monosaccharide molecules by using an enzyme (maltase, sucrase, lactase) in a hydrolysis reaction. The equation is the direct opposite of the condensation reaction.

Question 6

Maltose

Answer 6

glucose + glucose = maltose + water

Question 7

Sucrose

Answer 7

glucose + fructose = sucrose + water

Question 8

Lactose

Answer 8

glucose + galactose = lactose + water

Question 9

Polysaccharides

Answer 9

Examples: starch, cellulose, glycogen

A polysaccharide molecule can be produced from thousands of monosaccharide molecules or disaccharide molecules in a condensation reaction.

A polysaccharide can be split into multiple disaccharide molecules by using amylase in a hydrolysis reaction and then into monosaccharides by using maltase to release individual glucose molecules.

Question 10

Starch

Answer 10

Structure: made up of several thousand glucose molecules joined together.
Function: Form of storage of carbohydrates in plants.

Question 11

Cellulose

Answer 11

Structure: made up of several thousand glucose molecules joined together. The bonds between glucose molecules are different from those in starch.
Function: Synthesis of cellulose cell wall, which protects the plant cell from damage and bursting.

Question 12

Fats

Answer 12

Components: hydrogen, carbon, oxygen.
Types: saturated, unsaturated
Function:
1. Source and store of energy
2. Insulating material that prevents excessive heat loss in animals.
3. A solvent for fat-soluble vitamins and other vital substances.

Fats can be broken down into fatty acids and glycerol in a hydrolysis reaction.
Fat molecule + 3 H2O = glycerol + 3 fatty acid molecules.

Question 13

Saturated Fats

Answer 13

Straight fatty acid chain
Examples: butter

Question 14

Unsaturated fats

Answer 14

Fatty acid chain may be bent or have a kink at a certain point. I
Examples: olive oil

Question 15

Proteins

Answer 15

Components: hydrogen, carbon, oxygen, nitrogen, sulfur (occasional)
Types: amino acids, polypeptide , protein
Function:
1. Synthesis of new protoplasm, for growth and repair of worn-out cells.
2. Synthesis of enzymes and some hormones.
3. Formation of antibodies to combat diseases.

Question 16

Amino Acids

Answer 16

Structure: made up of an amino group, acidic group and a side chain.

Question 17

Polypeptide

Answer 17

Structure: many amino acids joined in a linear manner via peptide bonds.

Question 18

Synthesis of Proteins

Answer 18

1. Polypeptides in turn may be linked up to form an even longer chain of amino acids.
2. A protein molecule is made up of one or more of such chains folded together.
3. In most proteins, the polypeptide chains are folded into more complex, 3D shapes.

Question 19

Breakdown of Proteins

Answer 19

Proteins are hydrolysed into short polypeptides, which are in turn hydrolysed into amino acids.

Question 20

Benedict’s Test for Reducing Sugars

Answer 20

Positive Result: formation of a brick-red precipitate.

Procedure:
1. Place food sample into test tube.
2. Add benedict’s solution to the food sample.
3. Shake the mixture and place the tube in a boiling water bath for 2-3 minutes.

Colour Change:
Blue -> Green -> Yellow / Orange -> Brick-Red

Question 21

Iodine Test for Starch

Answer 21

Positive Results: Iodine turns from yellowish-brown to blue-black

Procedure
Add a few drops of iodine solution to the food sample.

Question 22

Ethanol Emulsion Test for Fats

Answer 22

Positive Result: a cloudy white emulsion is formed.

Procedure:
1. Cut the food sample into small pieces and place the pieces in a test tube.
2. Add ethanol and shake thoroughly.
3. Allow the solid particles to settle. Carefully decant the ethanol into another test tube containing water.

Question 23

Biuret’s Test for Proteins

Answer 23

Positive Result: Biuret solution turns for blue to violet.

Procedure:
1. Add the sample to sodium hydroxide in a test tube and shake thoroughly.
2. Add copper (II) sulfate solution, drop by drop, shaking after every drop.

Note: biuret’s solution is the same as sodium hydroxide + copper (II) sulfate. To the food sample, add an equal volume of biuret’s solution for the same effect.