Question

A potted plant was taken in order to prove a factor necessary for photosynthesis. The potted plant was kept in the dark for 24 hours. One of the leaves was covered with black paper in the centre. The potted plant was then placed in sunlight for a few hours.

(i) What aspect of photosynthesis was being tested?
(ii) Why was the plant placed in the dark before beginning the experiment?
(iii) During the starch test, why was the leaf 

      (1) boiled in water

      (2) boiled in methylated spirit

(iv) Write a balanced chemical equation to represent the process of photosynthesis.
(v) Draw a neat diagram of a chloroplast and label its parts.

Answer 1

(i) Light is required for photosynthesis.

(ii) Before beginning the experiment, the plant was kept in dark in order to destarch it, i.e. to remove the pre-existing starch from the storage organs.

(iii)

(1) The leaf was boiled in water to destroy enzymes so that further chemical changes do not take place in the leaf.
(2) The leaf was boiled in methylated spirit to dissolve chlorophyll.

(iv) Chemical equation for the process of photosynthesis:

     6CO₂+12H₂O`"Light"/"Chlorophyll"`C₆H₁₂O₆+6O₂+6H₂O

(v)Chloroplast: