Describe the process of testing a leaf for starch and explain the results observed in the presence and absence of light.

Here are the answers to your questions:

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

• Step I: The leaf is dipped in boiling water.
• Step II: The leaf is placed in a test tube containing hot ethanol, which is then heated in a water bath.
• Step III: The leaf is rinsed in hot water.
• Step IV: Iodine solution is added to the leaf.

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

• To kill the cells and stop all metabolic processes.
• To break down the cell walls and cell membranes, making it easier for ethanol to remove chlorophyll.

c) i) Why did the leaf in the dark turn pale brown?
The leaf in the dark did not undergo photosynthesis, so no starch was produced. Iodine solution remains pale brown in the absence of starch.

c) ii) Why did the leaf in light turn blue-black?
The leaf in the light underwent photosynthesis, producing starch. Iodine solution turns blue-black in the presence of starch.