Nutrients

Question 1

How do you test for the presence of reducing sugars?

Answer 1

Benedicts test -
Place 2cm^3 of food sample, then 2cm^3 of Benedict’s solution into a test tube. Shake the mixture and place the tube in a hot water bath.

Blue -> green -> yellow/orange -> brick red ppt (in order of increasing reducing sugars)

Question 2

How do you test for the presence of starch??

Answer 2

Iodine test -
Add a few drops of iodine solution onto the sample.

Blue black -> present; yellowish brown -> absent

Question 3

Why is glycogen and starch suitable for storage in cells?

Answer 3

• Insoluble in water -> do not change water potential
• Large molecules -> cannot diffuse through cell membranes -> cannot be lost from cell
• Can easily be hydrolysed to glucose when needed
• Compact shapes -> occupy less space

Question 4

What are the functions of carbohydrates?

Answer 4

• Substrate for respiration
• Formation of supporting structures, as well as nucleic acids
• Conversion to other organic compounds
• Synthesis of lubricants, and nectar in some flowers

Question 5

How do you test for the presence of fats?

Answer 5

Ethanol emulsion test -
Add 2cm^3 of ethanol to a food sample in a test tube and shake.
For solid sample, decant the ethanol into another test tube containing 2cm^3 of water.
For liquid sample, add 2cm^3 of water to the mixture and shake.

White emulsion -> presents; clear -> absent

Question 6

What are the functions of fats?

Answer 6

• Source and storage of energy
• Insulation material
• Solvent for fat-soluble vitamins
• Essential part of protoplasm

Question 7

How do you test for presence of proteins?

Answer 7

Biuret test -
Add 2cm^3 of sodium hydroxide solution to 2cm^3 of food sample and shake thoroughly. Then add 1% copper (II) sulfate solution, drop by drop.

Violet -> present; blue -> absent

Question 8

What are the functions of proteins?

Answer 8

• Synthesis of new protoplasm, enzymes and some hormones

- Formation of antibodies