Question

why was the plant kept in a dark room before conducting the experiment

Answer 1

so that plant not get sunlight and not able to do photosynthesis and not able to do light reaction as a reason plant become unable to make food this is a important step in detecting the starch in leaves and also in other experiment.

Answer 2

a plant is kept in a dark room for atleast 48hrs to eliminate the starch produced in the plant earlier through photosynthesis.this is known as destarching