CBSE Class 10 Answered

A potted plant is destarched by keeping it in dark for 2 days. One leaf of this plant is inserted in a bottle containing KOH through split cork in such a way that half of the leaf remains outside. The apparatus is kept in sunlight for few hours. The leaf is then removed from the plant. Its chlorophyll is then taken out by boiling it in alcohol. The decolourised leaf is then tested for starch with iodine solution. The part of the leaf which was within the bottle gives a negative test. Whereas the portion of the leaf which was outside the bottle gives positive test for starch. The part of the leaf which could not manufacture starch had all the requirements for photosynthesis except carbon dioxide, which was absorbed by KOH present in the bottle.