NCERT Solutions for Class 11 Biology Chapter 13
Photosynthesis in Higher Plants Class 11
Chapter 13 Photosynthesis in Higher Plants Exercise Solutions
Exercise : Solutions of Questions on Page Number : 224
By looking at a plant externally can you tell whether a plant is C3 or C4? Why and how?
By looking at which internal structure of a plant can you tell whether a plant is C3 or C4? Explain.
Even though a very few cells in a C4 plant carry out the biosynthetic - Calvin pathway, yet they are highly productive. Can you discuss why?
RuBisCo is an enzyme that acts both as a carboxylase and oxygenase. Why do you think RuBisCo carries out more carboxylation in C4 plants?
The enzyme RuBisCo is absent from the mesophyll cells of C4 plants. It is present in the bundle-sheath cells surrounding the vascular bundles. In C4 plants, the Calvin cycle occurs in the bundle-sheath cells. The primary
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 act as antenna molecules. They get excited by absorbing light and emit electrons during cyclic and non-cyclic photophosphorylations. They form the reaction centres for both photosystems I and II. Chlorophyll-b and other photosynthetic pigments such as carotenoids and xanthophylls act as accessory pigments. Their role is to absorb energy and transfer it to chlorophyll-a. Carotenoids and xanthophylls also protect the chlorophyll molecule from photo-oxidation. Therefore, chlorophyll-a is essential for photosynthesis.
Why is the colour of a leaf kept in the dark frequently yellow, or pale green? Which pigment do you think is more stable?
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?
Light is a limiting factor for photosynthesis. Leaves get lesser light for photosynthesis when they are in shade. Therefore, the leaves or plants in shade perform lesser photosynthesis as compared to the leaves or plants kept in sunlight.
Figure 13.10 shows the effect of light on the rate of photosynthesis. Based on the graph, answer the following questions:
(b) What could be the limiting factor/s in region A?
Answer :
(a) Generally, light is not a limiting factor. It becomes a limiting factor for plants growing in shade or under tree canopies. In the given graph, light is a limiting factor at the point where photosynthesis is the minimum. The least value for photosynthesis is in region A. Hence, light is a limiting factor in this region.
(b) Light is a limiting factor in region A. Water, temperature, and the concentration of carbon dioxide could also be limiting factors in this region.
(c)
Give comparison between the following:
(a) C3 and C4 pathways
(c) Anatomy of leaf in C3 and C4 plants
(a) C3 and C4 pathways
C3 pathways |
C4 pathways |
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1. |
The primary acceptor of CO2 is RUBP – a five-carbon compound. |
1. |
The primary acceptor of CO2 is phosphoenol pyruvate – a three-carbon compound. |
2. |
The first stable product is 3-phosphoglycerate. |
2. |
The first stable product is oxaloacetic acid. |
3. |
It occurs only in the mesophyll cells of the leaves. |
3. |
It occurs in the mesophyll and bundle-sheath cells of the leaves. |
4. |
It is a slower process of carbon fixation and photo-respiratory losses are high. |
4. |
It is a faster process of carbon fixation and photo-respiratory losses are low. |
(b) Cyclic and non-cyclic photophosphorylations
Cyclic photophosphorylation |
Non-cyclic photophosphorylation |
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1. |
It occurs only in photosystem I. |
1. |
It occurs in photosystems I and II. |
2. |
It involves only the synthesis of ATP. |
2. |
It involves the synthesis of ATP and NADPH2. |
3. |
In this process, photolysis of water does not occur. Therefore, oxygen is not produced. |
3. |
In this process, photolysis of water takes place and oxygen is liberated. |
4. |
In this process, electrons move in a closed circle. |
4. |
In this process, electrons do not move in a closed circle. |
(c) Anatomy of the leaves in C3 and C4 plants
C3 leaves |
C4 leaves |
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1. |
Bundle-sheath cells are absent |
1. |
Bundle-sheath cells are present |
2. |
RuBisCo is present in the mesophyll cells. |
2. |
RuBisCo is present in the bundle-sheath cells. |
3. |
The first stable compound produced is 3- phosphoglycerate –a three-carbon compound. |
3. |
The first stable compound produced is oxaloacetic acid – a four-carbon compound. |
4. |
Photorespiration occurs |
4. |
Photorespiration does not occur |