Biological molecules

Question 1

What do carbohydrates contain

Answer 1

They contain carbon, hydrogen, and oxygen

Question 2

What are the 3 types of carbohydrates

Answer 2

Monosaccharides, Disaccharides, Polysaccharides

Question 3

Example of monosaccharides

Answer 3

Glucose

Question 4

How to test for reducing sugars

Answer 4

Benedicts Test

Question 5

Steps for Benedicts Test

Answer 5

1. Add 2cm^3 of food sample into a test tube
2. Add 2cm^3 of Benedict’s solution into the same test tube
3. Place in boiling water for 2 minutes
4. If :
   - Brick red precipitate is observed, the food sample contains a large amount of reducing sugars
   - Orange precipitate is observed, the food sample contains a moderate amount of reducing sugars
   - Yellowish-green precipitate is formed, the food sample contains a small amount of reducing sugars
   - the solution remains blue, the food sample does not contain any reducing sugars

Question 6

Example of polysaccharides

Answer 6

Glycogen and Starch

Question 7

What are the stores of glucose

Answer 7

Glycogen and Starch

Question 8

Why are Glycogen and Starch suitable as storage materials

Answer 8

1. They are insoluble in water so they do not change the water potential of cells
2. They are large molecules that cannot diffuse through the cell membrane
3. Easily hydrolyzed to glucose if needed
4. They are made of molecules that have compact shapes so they occupy less space

Question 9

How to test for starch

Answer 9

Iodine test

Question 10

Steps for Iodine Test

Answer 10

1. Add a few drops of iodine solution to a food sample
2. If starch is present, the iodine turns from brown to blue-black

Question 11

Function of Carbohydrates

Answer 11

1. Substrate for respiration to provide energy for cellular activities
2. Form supporting structures such as cellulose in the cell wall
3. Converted to other organic compounds such as amino acids and fats

Question 12

What do fats contain

Answer 12

They contain carbon, hydrogen, and oxygen

Question 13

How to test for fats

Answer 13

Alcohol Emulsion Test

Question 14

Steps for Alcohol Emulsion Test in Liquid

Answer 14

For liquid:
1. Add 2cm^3 of ethanol to 2cm^3 of food sample in a test tube
2. Shake vigorously
3. Add 2cm^3 of water into the test tube and shake the mixture
4. If fats are present, cloudy white emulsion will form

Question 15

Steps for Alcohol Emulsion Test in Solid

Answer 15

For solids:
1. Cut the food sample into smaller pieces and place into a test tube
2. Add 2cm^3 of ethanol to 2cm^3 of food sample in the test tube
3. Shake vigorously and allow the solid particles to settle
4. Carefully decant the ethanol into another test tube containing 2cm^3 of water
5. If fats are present, a cloudy white emulsion will form

Question 16

Function of fats

Answer 16

1. They are a source and store of energy
2. A thermal insulator to prevent excessive heat loss
3. A solvent for fat-soluble vitamins and substances
4. Reduce water loss from the skin

Question 17

What do proteins contain

Answer 17

They contain carbon, hydrogen, oxygen and NITROGEN

Question 18

How to test for proteins

Answer 18

Biuret Test

Question 19

Steps for Biuret Test

Answer 19

1. Add 2cm^3 of biuret solution to 2cm^3 of food sample in a test tube
2. Shake well and allow the mixture to stand for 5 minutes
3. If proteins are present, the solution will turn violet

Question 20

Function of proteins

Answer 20

1. Synthesis of new protoplasm for growth and repair of cells
2. Synthesis of enzymes and hormones
3. Formation of antibodies to combat diseases