Describe the experimental procedure to test for the presence of starch in a leaf and explain the results.

3a) 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), which is placed in a beaker of boiling water.
• III. The leaf is removed from the ethanol and rinsed with cold water.
• IV. The leaf is spread out on a white tile or petri dish, and a few drops of iodine solution are added to it.

3b) Give two (2) reasons why the leaf is dipped in boiling water:

• To kill the cells in the leaf, stopping all chemical reactions.
• To break down the cell walls and cell membranes, making it easier for the chlorophyll to be removed by ethanol.

3c) i) Why did the leaf in the dark turn pale brown?

• The leaf kept in the dark did not undergo photosynthesis and therefore did not produce or store starch. When iodine solution was added, it remained the characteristic pale brown color of the iodine.

3c) 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 reacted with the starch, resulting in a blue-black color change, indicating the presence of starch.

4a) Identify each of the symbols labelled A, B, C, D and E:

• A. Flammable (GHS pictogram)
• B. Flammable (Older European pictogram)
• C. Toxic or Poisonous
• D. Irritant or Harmful
• E. Oxidizing

4b) Name two (2) chemicals which can be associated with each symbol A, B, C, D and E:

• A. Ethanol, Acetone
• B. Petrol, Methanol
• C. Cyanide, Arsenic compounds
• D. Ammonia solution, Bleach (dilute sodium hypochlorite)
• E. Hydrogen peroxide, Potassium permanganate

4c) Name two (2) places where symbol B can be used:

• Petrol stations
• Chemical storage facilities (for flammable liquids like solvents)