A potted plant with variegated leaves was kept in dark for 24 hours and then placed in bright sunlight. The diagram shows a leaf with a pale yellow portion and a green portion.
Why was the plant kept in dark for 24 hours?
Topic: Destarching
Answer
To DESTARCH the leaves. In darkness photosynthesis stops while respiration continues, so the starch already stored in the leaves is used up. Any starch found at the end of the experiment must therefore have been made DURING the test.
The word to use is DESTARCHING, and the reason matters as much as the term.
THE LOGIC: if the leaf already contained starch at the start, a positive iodine test at the end would prove nothing — the starch might be left over. Emptying the leaf first makes the result meaningful.
This step appears in EVERY photosynthesis experiment, whichever factor is being tested, and examiners ask about it repeatedly.