A potted plant with variegated leaves was taken in order to prove a factor necessary for photosynthesis. The potted plant was kept in the dark for 24 hours and then placed in bright sunlight for a few hours. Observe the diagram and answer the questions: A potted plant with variegated leaves was taken in order to prove a factor necessary for photosynthesis. The potted plant was kept in the dark for 24 hours and then placed in bright sunlight for a few hours. Observe the diagram and answer the questions:
Why was the plant kept in the dark before beginning the experiment?
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 must therefore have been made DURING the experiment.
The word to use is DESTARCHING, and the reason matters as much as the term.
THE LOGIC: if the leaves already contained starch at the start, a positive iodine test at the end would prove nothing — the starch might be left over. Emptying them first makes the result meaningful.
This step appears in EVERY photosynthesis experiment, whichever factor is being tested, and examiners ask about it repeatedly.