Question

The experimental leaf (covered with black paper strips/ light screen) should be tested for the presence of

• A. Sugar in leaf
• B. Starch in leaf
• C. Water in leaf
• D. Carbon dioxide in leaf.

Answer 1

The correct option is B

Starch in leaf

The correct option is (B)

Explanation for the correct option:

1. Photosynthesis is the process by which green plant synthesizes carbohydrates in the presence of sunlight by utilizing carbon dioxide and water.
2. Starch is a carbohydrate formed in the plant's leaves due to photosynthesis.
3. The experiment conducted aimed at observing photosynthesis in the presence of starch, in the leaf.
4. The covered regions of the leaves receive no sunlight and therefore do not synthesize starch, unlike the uncovered leaf regions.
5. Adding iodine to the leaves changes the color to blue-black of the uncovered regions, indicating the presence of starch.
6. The covered regions show no coloration change, indicating the absence of starch.
7. Thus to conclude, the covered parts of the leaves did not perform photosynthesis in the absence of sunlight.

Explanation for incorrect options:

Option (A)

1. Photosynthesis forms starch in the plant’s leaves tested in the experiment.
2. Starch is a type of sugar which have a complex branched structure.
3. Not all sugars can be tested with this experiment.

Option (C)

1. Water is the essential component of living beings and is always present in the cells for various cellular processes.
2. Thus, an experiment is not required to test the presence of water.

Option (D)

1. To study the presence of carbon dioxide and its importance for a plant, a separate experiment is performed.
2. In that experiment, two plants are placed in two bell jars, one with potassium hydroxide (KOH) and another without KOH.
3. Thus, no black strips are required to test the presence of carbon dioxide.

Leaves are covered with black paper to check the presence of starch.