Q2 of 70 Page 73

Photosynthesis in green plants is, directly and indirectly, dependent on so many plant structures. Explain briefly the role of the following structures in this process.

(a) Guard cells


(b) Cuticle


(c) Mesophyll cells


(d) Xylem tissue in the leaf veins


(e) Phloem tissue in Leaf Veins


(f) Stomata

(a) Guard cells: The guard cells aid the process of photosynthesis by regulating the opening and closing of the stomata in the leaves. This indirectly controls the movement of carbon dioxide through the stomata.


(b) Cuticle: The cuticle being transparent and waterproof, allows light to penetrate very easily.


(c) Mesophyll cells: Chloroplasts play a vital role in photosynthesis by trapping the light energy required for the process. These vital organelles are present in the mesophyll cells.


(d) Xylem tissue in the leaf veins: The xylem tissue controls the movement of water taken up by the root of the plant and directs it up to the leaves. Water is very essential for the process of photosynthesis.


(e) Phloem tissue in the leaf veins: The food prepared by photosynthesis is transported via the phloem tissue from the leaves, to the other parts of the plant.


(f) Stomata: The movement of carbon dioxide from the atmosphere into the cells is regulated by the stomata.


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17

Complete the following by filling the blanks 1 to 5 with appropriate words/terms/phrases:

To test the leaf for starch, the leaf is boiled in the wafer to ................... (1). It is next boiled in methylated spirit to ................... (2). The leaf is placed in warm water to soften it. It is then placed in a dish and ................... (3) solution is added. The region, which contains starch, turns ................... (4) and the region, which does not contain starch, turns……………. (5).

 1

A candidate studied the importance of certain factors in photosynthesis. He took a potted plant and kept it in the dark for over 24 hours. In the early hours of the next morning, he covered one of the leaves with dark paper in the centre only. Then he placed the plant in sunlight for a few hours and tested the leaf which was covered with black paper for starch.

(a) What aspect of photosynthesis was being investigated?


(b) Is there any control in this experiment? If so, state it.


(c) Why was the plant kept in the dark before the experiment?


(d) Describe step by step, how the candidate proceeded to test the leaf for the presence of starch.

 3

Given below is a schematic diagram to illustrate some aspects of photosynthesis.


(a) Fill up the gaps, in blank spaces (1-4), by writing the names of the correct items.


(b) What phenomenon do the think arrows A and B indicate respectively?

 4

Given below is the representation of a certain phenomenon in nature. With four organisms 1 – 4.


(a) Name the phenomenon represented.


(b) Name any one organism that could be shown at No.5.


(c) Name the biological process which was the starting point of the whole chain.


(d) Name one natural element which all the organisms 2-4 and even 5 are getting from No. 1 for their survival.