Question

The presence of starch in leaves can be tested with
A. Iodine solution
B. Copper sulphate solution
C. Lime water
D. Benedict’s solution

Answer 1

Photosynthesis is the mechanism by which green plants transform energy from the sun's light into chemical energy that can be used. Plants require energy to grow, reproduce, and defend themselves. Excess photosynthesis energy is retained in plant tissue as starch.
Starch is a powdery white material. It stores glucose, which plants use for energy.

Complete explanation:
Option A: The Iodine test can detect the presence of starch in leaves. When chlorophyll in the boiling of alcohol is removed from the leaf and two drops of iodine are added to it, its colours change to blue to indicate the presence of starch. This test is used to evaluate the photosynthesis process in plants.
So, option A is correct.
Option B: In the presence of proteins, copper sulphate in alkaline solution changes from blue to violet/blue. This is known as the Biuret reaction. The reaction of copper with tyrosine and/or tryptophan residues in proteins results in the formation of a cupric–peptide complex.
So, option B is incorrect.
Option C: Carbon dioxide reacts with calcium hydroxide solution to form a white calcium carbonate precipitate. Limewater is a calcium hydroxide solution. Limewater turns milky or cloudy white as carbon dioxide is bubbled into it.
So, option C is incorrect
Option D: Benedict's Test is used to determine the presence of simple carbohydrates. The Benedict's test distinguishes reducing sugars (mono- and disaccharides) with free ketone or aldehyde functional groups.
So, option D is incorrect.

So, option A is the correct answer.

Note:
Starch is a white, powdery material made up of glucose that plants use as food. The existence of starch in leaves is sufficient proof of photosynthesis occurring in leaves, as starch formation necessitates photosynthesis.
Starch molecules are made up of a large number of glucose units that are linked together by glycosidic bonds and are created by all vegetables and other plant sources through photosynthesis.
In plant cells, starch molecules serve as energy storage, which is needed for growth, development, and reproduction. A positive iodine test result (starch present) was a colour change ranging from violet to black; a negative result (no starch) was the iodine solution's yellow colour.