Question

A destarched leaf on a potted plant was covered with Black (A) Transparent (B) strips of paper as shown in figure. After 6 hours of exposure to sunlight the leaf was removed from the plant and tested for starch. Which are the following will be the correct observation?

• A. Whole leaf turned blue black
• B. Only B portion turned blue black
• C. Only A & B portions remained colourless and the rest of the leaf turned blue black.
• D. Only A portion remained colourless and the rest of the leaf turned blue black.

Answer 1

Answer: (D)

Only A portion remained colourless and the rest of the leaf turned blue black.

The part of the destached leaf, when covered with black strip and exposed to sunlight it does not produce any starch because it cannot receive sunlight. The part of destarched lead covered with transparent strip produces starch because it can receive sunlight. when the test for starch is performed the leaf part which can produce starch turns to blue-black colour i.e transparent strip and uncovered part. When the starch test is performed, The part covered with the black strip (A portion )remain colorless because it cannot produce starch and the rest of the leaf turned blue-black because that portion receives sunlight and produce starch.

So, the correct answer is 'option D'.