Question

Explain with an experiment how light is necessary for photosynthesis. [5 MARKS]

Answer 1

Experiment steps: 1 Mark each
Inference: 1 Mark

1) A plant is selected and destarched by keeping it in darkness for 3 days. Pick a leaf and test it with iodine to confirm that the plant is starch free. It won't turn blue-black, which means it did not perform photosynthesis in the darkness and all the starch is used up by the plant.
2) Cover one leaf with black paper.
3) Expose the plant to sunlight for a day.
4) After a day, test the leaf covered with black paper using iodine. It will not turn blue-black as it has not synthesised starch, while the other uncovered leaves will now turn black-blue on the addition of iodine.

Inference: Photosynthesis did not occur in the leaf covered with black paper confirming the essentiality of light for the synthesis of starch.