Question

Why we should not test for glucose instead of starch in the green leaves?
A. The glucose formed during photosynthesis gets polymerized into starch. So a stable product one can test is starch.
B. The glucose formed during photosynthesis gets polymerized into fructose. So starch gives a positive test.
C. Both A and B.
D. None of the above.

Answer 1

Hint: During photosynthesis glucose is produced in the chlorophyll in presence of sunlight. Oxygen is released as a byproduct. This glucose is then stored as starch. Starch can be identified by the iodine test which gives a purple-blue color when iodine reacts with starch. Glucose can be detected by Fehling’s test which is a difficult method.

Complete answer: Simple carbohydrate or sugar for example glucose is the main product of photosynthesis and from glucose other organic substances are formed.
Excess amount of glucose is stored as starch, which functions as an internal energy reserve that to be used when required.
So, we test starch instead of glucose in leaves as starch develops a purple-blue or blue-black color with iodine solution.
The glucose formed during photosynthesis gets polymerized into starch. So a stable product one can test is starch.

Therefore, the correct answer is option A.

Note: Sucrose and trehalose are the only non-reducing sugar.
1. All the other sugars are reducing. Seliwanoff's test is a test by which we can distinguish glucose and fructose. Basically, it helps to distinguish between aldose sugar and ketose sugar. 2. Ketose sugars are more rapidly dehydrated and reactive than aldoses.
3. The sugar solution is taken in a test tube and then resorcinol and concentrated HCl is added to the solution and heated.
4. The main mechanism of this test is acid hydrolysis.