The diagram given below represents an experiment to demonstrate a particular aspect of photosynthesis. The letter ‘A’ indicates a certain condition inside the flask. Answer the questions: The diagram given below represents an experiment to demonstrate a particular aspect of photosynthesis. The letter ‘A’ indicates a certain condition inside the flask. Answer the questions:
In what manner do the leaves 1 and 2 differ at the end of the starch test?
Topic: Result of the starch test
Try it
Pick an option and check your answer. The full worked answer is below either way.
Answer
(a) Leaf 1 turns brown, Leaf 2 turns blue black..
LEAF 1 is inside the flask with KOH. Deprived of carbon dioxide, it could not photosynthesise, so it contains NO STARCH and iodine leaves it BROWN (the colour of iodine itself, meaning no change).
LEAF 2 is outside the flask in ordinary air. It had carbon dioxide, photosynthesised normally, made starch, and so turns BLUE-BLACK with iodine.
THE IODINE TEST: blue-black means starch is PRESENT; brown means it is ABSENT.
Option (b) is the same answer with the two leaves swapped, which is the trap — identify from the diagram WHICH leaf is inside the flask before choosing.
This result is the whole proof: two leaves on the SAME plant, treated identically except for carbon dioxide, and only the one that had it made starch.
Leaf 1 turns brown, Leaf 2 turns blue black..