Question 3
After the starch test, what is seen on leaf A, the one covered with black polythene?
The right answer is the one marked above.
No colour change in the part that was covered. That part received no sunlight, so no photosynthesis took place there and no starch was made.
The rest of leaf A was uncovered and did receive light, so it turns dark. The iodine draws the shape of the polythene onto the leaf.