Read the passage and answer any of the four questions from (a) to (e).
Some experiments were carried out using Croton sp. plants to understand the process of photosynthesis. It was observed that the leaves of the plant exposed to light for longer duration accumulated more starch. However, due to presence of preformed starch in the leaves, it was difficult to find the net productivity on a fixed exposure to light source. Therefore, it was necessary to obtain starch free leaves in the plant before starting the experiment.
(a) Which of the following would help obtain starch free leaves in the plant?
(i) Expose the leaves to blue light for 48 hours before starting the experiment.
(ii) Keep the plant in dark for about 48 hours before starting the experiment.
(iii) Remove starch from the leaves by exosmosis, 48 hours before starting the experiment.
(iv) Keep the leaves to the red light for 48 hours before starting the experiment.
Answer
Croton sp. Plants are plants with leaves that appear to be not green due to higher concentration of other colour pigments in the leaves. But since chlorophyll is also present , they carry out photosynthesis normal ly.
- The food prepared by the plants in the presence of sunlight by the process of photosynthesis is stored in the form of starch .
- Therefore, in order to obtain starch-free leaves , we can place the plant in the dark for 48hours
- Photosynthesis does not occur and no new starch is produced.
- The starch already present in the leaf will be utilized within these 48 hours to carry out various life processes of the plant.
So, the correct answer is (ii)
(b) After a period of illumination, the leaves were boiled in alcohol to make them colourless. Which of the following could be used to test the end product stored in the leaves?
(i) Cobalt chloride paper
(ii) Litmus paper
(iii) Iodine solution
(iv) Copper sulphate solution
Answer
When the leaves are boiled in alcohol, they lose chlorophyll, which is a green colored pigment, and become colorless.
- The end product after photosynthesis is starch.
- Starch is stored in the leaves
- It can be tested by adding iodine solution which gives a bluish black colour indicating the presence of starch in the leaf.
So, the correct option is (iii) Iodine solution
(c) Some of the starch free leaves were coated with wax on both the surfaces. The plant was maintained under normal environmental conditions. At the end of the experiment, the wax coated leaves are likely to show _____.
(i) Accumulation of more water.
(ii) Wilting of the wax coated leaves.
(iii) Increase in sucrose accumulation.
(iv) Decrease in number of chloroplasts
Answer
Due to the presence of wax, the stomata are blocked and therefore,
- the exchange of gases
- transpiration is inhibited .
This means, there is no exchange of gases or loss of water.
As a result, wilting of leaves takes place.
So, the correct option is (ii) Wilting of the wax coated leaves.
(d) During the morning hours, using a fine blade, an incision was made to the leaves such that the phloem tissue was cut open. Analysis of the liquid oozing out was found to contain high amount of:
(i) Xylose
(ii) Ribose
(iii) Sucrose
(iv) Galactose
Answer
The transport of glucose occurs in phloem in the form of sucrose , therefore, the cell sap that oozes out contains sucrose.
Thus, the correct answer is (iii)
(e) Why do plants coated with vaseline or wax do not remain healthy for a long time? Give any two reasons.
Answer
Covering a plant in vaseline/wax blocks the stomata in the leaves/stem of the plant.
These plants will not remain healthy for a long time because:
(i) They will not get oxygen for respiration.
(ii) They will not get carbon dioxide for photosynthesis.
(iii) Upward movement of water and minerals would be hampered due to lack of transpiration.
