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.
Which aspect of photosynthesis is being tested in the above diagram?
Topic: Necessity of chlorophyll
Answer
That CHLOROPHYLL is NECESSARY for photosynthesis.
The clue is the word VARIEGATED. A variegated leaf has green parts (containing chlorophyll) and pale yellow or white parts (without it), growing on the SAME leaf under identical conditions of light, carbon dioxide and water.
That makes it a perfectly controlled experiment: only ONE factor differs between the two areas — the presence of chlorophyll — so whatever difference appears must be due to it.
Identify the variable in any experiment of this kind and you know at once what is being tested. A destarched plant in a flask of potassium hydroxide tests carbon dioxide; a leaf partly covered with black paper tests light; a variegated leaf tests chlorophyll.