Question

A portion of destarched leaf of a potted plant was covered with a black strip of paper. The plant was then exposed to sunlight for six hours and then tested for starch. It was observed that:
(1) both covered and uncovered parts of leaf turned blue-black
(2) both covered and uncovered parts of leaf turned yellow-brown
(3) only the uncovered part of leaf turned blue-black
(4) only the covered part of leaf turned blue-black

Answer 1

In the above case, only the uncovered part of leaf turned blue black. Although the leaf had been destarched earlier, keeping it exposed to sunlight led to the synthesis of starch. But this process would not occur in parts which had been covered.

Hence, the correct answer is option 3.