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.
After the starch test what will be the colour of the yellow and green parts of the leaf? Give reasons to support your answer.
Topic: Result of the starch test
Answer
The GREEN portion turns BLUE-BLACK, because it contains chlorophyll, carried out photosynthesis and therefore made starch, which iodine stains blue-black.
The PALE YELLOW portion remains BROWN (the colour of iodine), because it has no chlorophyll, could not photosynthesise, and so contains no starch.
This proves that CHLOROPHYLL IS NECESSARY for photosynthesis.
The question says GIVE REASONS, so each colour must be explained, not merely stated.
Build each answer in three steps: presence or absence of chlorophyll → photosynthesis occurred or not → starch present or absent → colour with iodine.
IODINE TEST: blue-black means starch is PRESENT; brown (unchanged) means it is ABSENT.
THE CONCLUSION must be drawn explicitly. An answer that gives the two colours correctly but never states what the experiment PROVES has stopped one step short of what the question wants.