Describe the starch test on a leaf, explaining why a leaf in the dark turns pale brown and a leaf in light turns blue-black. Also identify hazard symbols A, B, C, D, and E.

3. Starch test in a leaf

a) Write out the procedure used by the student in each of the steps:

• I. The leaf is placed in boiling water for a few minutes.
• II. The leaf is then transferred to a test tube containing hot ethanol (alcohol) and heated in a water bath.
• III. The decolorized leaf is rinsed in hot water.
• IV. The softened leaf is spread out on a white tile or petri dish, and a few drops of iodine solution are added to its surface.

b) Give two (2) reasons why the leaf is dipped in boiling water:

• To kill the leaf cells and stop all enzyme activity.
• To break down the cell walls and membranes, making the leaf permeable to ethanol and iodine solution.

c) i) Why did the leaf in the dark turn pale brown?
The leaf kept in the dark did not undergo photosynthesis, so it did not produce or store starch. When iodine solution was added, it remained its original pale brown/yellow color, indicating the absence of starch.

c) ii) Why did the leaf in light turned blue-black?
The leaf kept in the light underwent photosynthesis and produced starch. When iodine solution was added, it turned blue-black, indicating the presence of starch.

4. Hazard symbols

a) Identify each of the symbols labelled A, B, C, D and E.

• A: Flammable (GHS symbol)
• B: Highly Flammable (Older symbol)
• C: Toxic
• D: Harmful / Irritant
• E: Corrosive

b) Name two (2) chemicals which can be associated with each symbol A, B, C, D and E.

• A (Flammable): Ethanol, Acetone
• B (Highly Flammable): Butane, Propane
• C (Toxic): Cyanide, Mercury compounds
• D (Harmful / Irritant): Dilute hydrochloric acid, Ammonia solution
• E (Corrosive): Concentrated sulfuric acid, Sodium hydroxide

c) Name two (2) places where symbol B can be used.

• Petrol stations
• Laboratories