Grade 9 Biology Lab Worksheet
Chapter 4: Biological Molecules — Tests for Glucose & Starch
These two experiments help us identify simple sugar (glucose) and complex carbohydrate (starch)
in food samples.
Experiment 1: Test for Glucose (Benedict’s Test)
Aim: To test for the presence of glucose in a given sample.
Materials:
• Benedict’s solution
• Test tubes and rack
• Hot water bath (~90°C)
• Droppers
• Distilled water (control)
• Sample solution (e.g., fruit juice)
• Safety goggles
Procedure:
1. Label two test tubes: Control and Sample.
2. Add 2 mL of distilled water to the Control tube and 2 mL of the sample to the Sample tube.
3. Add 2 mL of Benedict’s solution to both tubes.
4. Place them in a hot water bath for 3–5 minutes.
5. Observe any colour change.
Interpretation: Blue → No sugar; Green/Yellow/Orange → Glucose present.
Observation Table:
Sample
Colour before heating
Colour after heating
Control (Distilled Water)
Sample (e.g., Fruit Juice)
Conclusion: ________________________________________________
Experiment 2: Test for Starch (Iodine Test)
Aim: To test for the presence of starch in a given sample.
Result (Positive/Negative)
Materials:
• Iodine solution
• White tile
• Distilled water (control)
• Sample (e.g., bread piece, rice water)
Procedure:
1. Place one drop of iodine on a white tile.
2. Add one drop of the sample next to it and mix.
3. Repeat with distilled water as a control.
4. Observe the colour change.
Interpretation: Brown/Yellow → No starch; Blue-black → Starch present.
Observation Table:
Sample
Colour with Iodine
Result (Positive/Negative)
Control (Distilled Water)
Sample (e.g., Bread Piece)
Conclusion: ________________________________________________
Think and Answer:
1. Why is the control needed in each test?
2. What colour indicates the presence of glucose?
3. What colour indicates the presence of starch?
4. Why is heating used in the glucose test but not in the starch test?