B3 Biological molecules

Question 1

list the chemical elements that make up protein

Answer 1

Hydrogen, Oxygen, Carbon, Nitrogen
HOCN

Question 2

list the chemical elements that make up fats

Answer 2

Hydrogen, Oxygen, Carbon
HOC

Question 3

list the chemical elements that make up carbohydrate

Answer 3

Hydrogen, Oxygen, Carbon
HOC

Question 4

glucose forms

Answer 4

glycogen and starch

Question 5

amino acids form

Answer 5

protein

Question 6

fatty acids and glycerol form

Answer 6

fat

Question 7

importance of carbohydrate

Answer 7

source of energy

Question 8

importance of fat

Answer 8

energy storage

Question 9

importance of protein

Answer 9

growth, repair of tissues, making enzymes

Question 10

test for starch

Answer 10

iodine solution test

1. Place one spatula of the food sample on a dish or 1 cm3 if the sample is liquid.
2. Using a dropper, place a few drops of iodine solution onto the food.
3. Record any change in the color of the solution.

negative - browny orange
positive - blue black

Question 11

test for reducing sugars

Answer 11

benedict’s solution test

1. Place two spatulas of the food sample into a test tube or 1 cm3 if the sample is liquid. Add about 1 cm3 depth of water to the tube and stir to mix.
2. Add an equal volume of Benedict’s solution and mix.
3. Place the tube in a water bath at about 95°C for a few minutes.
4. Record the colour of the solution.

negative - blue
positive - green (weak), yellow (low), orange (moderate), red (high)

Question 12

test for protein

Answer 12

biuret test

1. Place one-two spatulas of the food sample into a test tube or 1 cm3 if the sample is liquid. Add about 1 cm3 depth of water to the tube and stir to mix.
2. Add an equal volume of potassium hydroxide solution to the tube and stir.
3. Add two drops of copper sulfate solution and stir for two minutes.
4. Record the colour of the solution.

negative - blue
positive - purple

Question 13

test for fat (lipids)

Answer 13

ethanol emulsion test

1. Place two spatulas of the food sample into a test tube or 1 cm3 if the sample is liquid.
2. Add 2 cm3 of ethanol to the tube. Cover the end of the tube and shake the tube vigorously.
3. Allow the contents to settle.
4. Pour the liquid from the top of the mixture into a test tube half-filled with water.
5. Record the level of the food and whether the water is cloudy or clear.

negative - colorless
positive - cloudy emulsion

Question 14

uses of water as a solvent (4)

Answer 14

1. transport
2. digest
3. excrete
4. metabolic reactions