Page 32 - Biology Form Two

Biology for Secondary Schools

Activity 1.4: Test for the presence of 8. Tabulate your results showing
reducing sugars in an onion food sample tested, procedures,

Materials observation and inference
Benedict’s solution, an onion bulb, a Food
FOR ONLINE READING ONLY
knife, mortar and pestle, measuring sample Procedures Observation Inference
cylinder (10 ml), test tubes, test tube tested
holder, heat source, water, filter funnel,

dropper, test tube brushes and beakers
Questions
Procedure 1. What was the series of colour
1. Peel an onion and cut it into small change observed?
pieces using a knife.
2. Grind the pieces of onion using a 2. What was the final colour?
mortar and pestle. Then, add water
to make a mixture. Disaccharides
These are also known as double sugars.
3. Decant and filter the mixture into They are formed through condensation
a beaker to remove solid particles when two monosaccharide molecules
to get a solution. combine. For example, a glucose
4. Put 2 ml of the solution into a clean molecule and a fructose molecule
and dry test tube. combine to form sucrose, the sugar found
5. Add 2 ml of Benedict’s solution in sugarcane. The general formula for
into the test tube. this reaction is:

Safety precautions monosaccharide disaccharide

Make sure the knife is sharp. Burners + → +
monosaccharide water
should be placed on the bench. Never
hold them. Use a test tube holder to hold For example:

the test tube. Heat the test tube at the top C H O + C H O → C H O + H O
6
12
6
22
11
2
12
6
12
6
of the solution, not at the bottom where glucose + fructose sucrose + water
gas bubbles can cause an explosion Two glucose molecules combine to form
_
6. Gently heat the mixture for 2 3 maltose. Maltose is found in germinating
minutes. Observe colour changes seeds. A glucose molecule and a
while heating. galactose molecule also combine to form
7. Record the series of colour change lactose, a type of sugar found in milk.
occurring.
26 Student’s Book - Form Two

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