03. Biological Molecules (6093)

Proteins can contain the elements carbon, nitrogen, hydrogen, oxygen and sulfur.

• True

• False

Answer explanation

Proteins usually contain carbon, nitrogen, oxygen and hydrogen. However, there are amino acids that contain sulfur.

Carbohydrates and fats both contain carbon, oxygen and hydrogen only.

• True

• False

Answer explanation

Both carbohydrates and fats contain the same elements: carbon, oxygen and hydrogen.

However, they contain different proportions of each element.

Sucrose is the basic unit of carbohydrates.

• True

• False

Answer explanation

Glucose is the main basic unit of carbohydrates.

Fatty acids and glycogen make up fats.

• True

• False

Answer explanation

Fatty acids and glycerol make up fats.

Glycogen is a type of carbohydrate made by joining many glucose molecules.

Amino acids are the basic units of protein.

• True

• False

When Benedict's solution is added to sucrose solution, a yellow precipitate forms in the mixture.

• True

• False

Answer explanation

Sucrose is not a reducing sugar. Hence, when Benedict's solution is added, the mixture should remain blue.

A yellow precipitate forms when there is a moderate amount of reducing sugar present.

When biuret solution is added to a protein solution, it turns purple.

• True

• False

Answer explanation

The proper term to use when describing the colour change for the biuret test is 'violet'.

In the ethanol emulsion test, ethanol should be added to the food sample first. After which, water is added.

• True

• False

Answer explanation

The ethanol emulsion test tests for the presence of fats.

Fats cannot dissolve in water. Hence, ethanol is first added to dissolve any fat in the sample in the ethanol. After which, water is added and the mixture is shaken. As the fat and water do not mix, an emulsion forms.

When using solid food samples, the samples must first be crushed before conducting food tests on it.

• True

• False

Answer explanation

Crushing the solid food samples allows more nutrients in the food to dissolve in water. This allows the food test to be conducted easier as there is less debris to affect the observations, and increases the concentration of nutrients available which makes the colour changes more obvious.

Carbohydrates provide a long-term source of energy.

• True

• False

Answer explanation

Fats are the biological molecule that provide long-term storage for energy. Carbohydrates provide an immediate source of energy.