Page 35 - Biology Form Two

Biology for Secondary Schools

Activity 1.6 (b): Investigate the Test for lipids
solubility of starch in water Lipids are organic food substances
Materials consisting of carbon, hydrogen and

Maize or wheat flour, heat source, oxygen just like carbohydrates. A lipid
FOR ONLINE READING ONLY
water, stirring rod, measuring cylinder is composed of a glycerol molecule and
(10 ml), and a beaker fatty acids joined through condensation.
Procedure Unlike carbohydrates, lipids have much
less oxygen compared to carbon and
1. Take two full spatula of wheat flour hydrogen. For example, the formula
and put them in a 100 ml beaker. of beef fat is C H O . Lipids occur
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2. Add 50 ml of water and stir well naturally in the protoplasm of all living
to get a uniform mixture. cells and in adipose tissues of animals.
3. Leave it to settle for 3-4 minutes. An adipose tissue is a fatty tissue under
4. Observe and record the findings. the skin containing large deposits of
lipids.

Safety precautions Lipids can be either solid or liquid at
Ensure proper ventilation for heating room temperature. Some lipids remain
safely. Avoid flammable substances near in liquid form at 20°C while others
the heating source. Place your burner solidify at this temperature. Solid
on the bench, never hold in the hands. lipids are called fats, and liquid lipids
are called oils. Some plant oils dry

5. Take the mixture and boil it for and harden when exposed to air and
3-4 minutes. light at room temperature. Fats and
6. Observe and record the findings. oils are found in various foodstuffs
like groundnut, coconut, sunflower,
Questions margarine, and butter. Various types of

1. What happened when the unboiled oils are used for cooking.
mixture of flour and water was left Properties of lipids

to settle? (i) Fats are insoluble in water.

2. Was there any difference when the (ii) When oil is shaken in water, the oil
unboiled mixture was allowed to breaks down into droplets which
settle and when it was boiled? disperse in the water. The water
and oil separate into two layers
after a while.

Student’s Book - Form Two 29

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BIOLOGY FORM 2 NEW.indd 29