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9. Give comparison between the following:

             (c) Anatomy of leaf in C_{3} and C_{4} plants

  Anatomy of leaf in C3 plants Anatomy of leaf in C4 plants Bundle sheath cells are absent Bundle sheath cells are present around the vascular bundles RuBisCO is found in mesophyll cells RuBisCO is found in bundle sheath cells Plants do not possess 'Kranz' anatomy of leaves. Leaves show Kranz anatomy Chloroplasts are of a single type only                                           ...

9. Give comparison between the following:

             (b) Cyclic and non-cyclic photophosphorylation

Cyclic photophosphorylation Non-cyclic photophosphorylation Only photosystem I is involved in cyclic photophosphorylation  Both photosystems I and II are involved in non-cyclic photophosphorylation The active reaction centre is P700 The active reaction centre is P680 Electron transportation occurs in a cyclic manner Electron transport occurs in a non-cyclic manner Oxygen evolution...

9. Give comparison between the following:

             (a) C_{3} and C_{4} pathways

C3 Pathway  C4 Pathway There are plants in which the first stable product after the carbon assimilation is a 3-carbon molecule i.e. 3-phosphoglyceric acid. These plants are called C3 plants while the pathway for carbon assimilation in them is called the C3 pathway.  In the plants found in the tropical area, the first stable product after carbon assimilation is a 4 carbon molecule or...

Q. 8.     Figure 13.10 shows the effect of light on the rate of photosynthesis. Based on the graph, answer the following questions:


                (c) What do C and D represent on the curve?

C represents a stage beyond which light is not a limiting factor and D is the line beyond which the intensity of light does not affect the rate of photosynthesis.

8.     Figure 13.10 shows the effect of light on the rate of photosynthesis. Based on the graph, answer the following questions:


Figure 13.10  Graph of light intensity on the rate of photosynthesis


               (b) What could be the limiting factor/s in region A?

IN region A light is a limiting factor. The other limiting factors in this region can be temperature, CO2 and H2O.

8. Figure 13.10 shows the effect of light on the rate of photosynthesis. Based on the graph, answer the following questions:


            (a) At which point/s (A, B or C) in the curve is light a limiting factor?

At the A point, light is the limiting factor because the rate of photosynthesis is minimum here. 

7. Look at leaves of the same plant on the shady side and compare it with the leaves on the sunny side. Or, compare the potted plants kept in the sunlight with those in the shade. Which of them has leaves that are darker green? Why?

The leaves in shade are much greener than the ones exposed to sunlight because of the following reasons.  The chloroplasts of the mesophyll cells are irregularly arranged, and their orientation is in vertical files along the walls in strong light. Photooxidation of chloroplasts occurs in bright light and its non-oxidation occurs in shaded areas.

6. Why is the colour of a leaf kept in the dark frequently yellow, or pale green? Which pigment do you think is more stable?

A leaf kept in dark for long becomes yellow or pale green because of the disintegration of chlorophylls. Light is essential for the production of the chlorophyll pigment. In the absence of light, the production of chlorophyll-a molecules stops and they get broken slowly. It results in the change in colour of the leaf to light green. This causes, the xanthophyll and carotenoid pigments to become...

5. Suppose there were plants that had a high concentration of Chlorophyll  b, but lacked chlorophyll a, would it carry out photosynthesis? Then why do plants have chlorophyll b and other accessory pigments?

Chlorophyll-a molecules are essential for the process of photosynthesis as they act as antenna molecules. These molecules get excited by absorbing photons and emit electrons during cyclic and non-cyclic photophosphorylation. Chlorophyll a molecules form the reaction centres for both photosystems I and II. Due to these reasons, photosynthesis is absent in plants lacking chlorophyll a....

4.  RuBisCO  is an enzyme that acts both as a carboxylase and oxygenase. Why do you think RuBisCO carries out more carboxylation in C_{4}            plants?

RuBisCO functions as oxygenase only when there is a higher concentration of oxygen and a lower concentration of carbon dioxide. Both these conditions are not found in bundle sheath cells of C4 plants. These do not have a photolytic evolution of oxygen. They receive a regular supply of carbon dioxide even when the stomata are closed. Therefore, RuBisCO of C4 plants functions only as a...

3. Even though a very few cells in a  C_{4}  plant carry out the biosynthetic – Calvin pathway, yet they are highly productive. Can you discuss why?

The productivity of a plant is directly proportional to the rate of photosynthesis which in turn is dependent on the amount of carbon dioxide present in a plant. In C4 plants a mechanism for increasing the concentration of carbon dioxide is present. Here, the Calvin cycle occurs in the bundle-sheath cells. The C4 compound malic acid from the mesophyll cells is broken down inside the bundle-...

2. By looking at which internal structure of a plant can you tell whether a plant is C_{3} or C_{4} ? Explain.

By looking at the internal structure of the leaf, it can be revealed whether the plant is C3 or C4. In C4 plants, a leaf has Kranz anatomy wherein the undifferentiated mesophyll occurs in concentric layers around vascular bundles. Each vascular bundle is surrounded by a bundle sheath of large sized chloroplast containing cells. The chloroplasts of the bundle sheath cells are devoid of grana but...

1. By looking at a plant externally can you tell whether a plant is  C_{3} or C_{4} ? Why and how?

External morphology does not necessarily differentiates  plants from  plants. The  leaves are isobilateral but all isobilateral leaves are not  in nature. Anatomically,   plants can be differentiated from  plants as   plants possess leaves with Kranz anatomy