Question

11. Will a leaf taken from a potted plant kept in a dark room for a few days turn blue black when tested for starch? Give reasons for your answer.​

Answer 1

No, a leaf taken from a potted plant kept in a dark room will not turn blue-black when it is tested for starch.

• A leaf turns blue-black when tested for starch when the iodine reacts with the starch present in the leaf.
• Starch is manufactured from the excess of glucose produced during photosynthesis.
• Here, since the plant is kept in the dark room, photosynthesis does not occur because of no sunlight present in the room. this resulted in no glucose production.

• Since no glucose is produced, no starch is manufactured as well.  

Therefore, the leaf does not turn blue-black during starch testing because there is no starch to react whit the iodine used for the test.