Page 33 - Biology Form Two

Biology for Secondary Schools

Disaccharides dissolve in water and form water, filter funnel, dropper, measuring
sweet solutions. Some disaccharides, for cylinder (10 ml), beakers, and test tube
example maltose and lactose can reduce brush

copper (II) ions (Cu ) to copper (I) ions Procedure
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FOR ONLINE READING ONLY
(Cu ) like monosaccharides. These 1. Peel the piece of sugarcane and
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are also called reducing sugars. Other cut it into smaller pieces using a
disaccharides such as sucrose cannot knife.
reduce copper (II) ions to copper (I) ions. 2. Grind the pieces of sugarcane using

These are called non-reducing sugars. mortar and pestle and add a small
amount of water to make a mixture.
Therefore, non-reducing sugars cannot 3. Decant and filter the mixture to

be tested directly by Benedict’s solution. obtain a solution.
Instead, it is first converted to reducing 4. Pour 2 ml of a sample solution into
sugar by using hydrochloric acid (HCl) the clean and dry test tube.
in the process called hydrolysis, as 5. Add 1ml of dilute hydrochloric

shown in the following example: acid.
Safety precautions
HCl
C H O + H O C H O + C H O Avoid flammable substances near the
12 22 11 2 6 12 6 6 12 6
Sucrose + Water Glucose + Fructose heating source. Burners should be
placed on the bench, never held in the
The acidic mixture is heated and hands. Use a test tube holder to hold the
left to cool. It is then neutralised by test tube. Heat the test tube at the top of
using sodium hydroxide (NaOH) or the solution, not at the bottom where gas
sodium bicarbonate (NaHCO ) for the
3 bubbles can cause an explosion. Ensure
Benedict’s solution to work properly. proper ventilation for heating safely.
Thereafter, steps for testing reducing
sugars is carried out. 6. Gently heat the mixture for 2-3
minutes.
Activity 1.5: Test for non-reducing 7. Cool the mixture. Then add 2 ml
sugars in sugarcane of sodium bicarbonate solution or

Materials sodium hydroxide solution.
Benedict’s solution, hydrochloric 8. Add 2 ml of Benedict’s solution to
acid, sodium hydroxide solution or the cooled mixture and heat gently.
sodium bicarbonate solution, a piece of 9. Record the series of colour change
sugarcane, a knife, mortar and pestle, occurring.
test tubes, test tube holder, heat source,

Student’s Book - Form Two 27

05/10/2024 15:36:20
BIOLOGY FORM 2 NEW.indd 27 05/10/2024 15:36:20
BIOLOGY FORM 2 NEW.indd 27