(a) C₃ and C₄ pathways C₃ pathways:- 1. The primary acceptor of CO₂ is RUBP – a six-carbon compound. 2. The first stable product is 3phosphoglycerate. 3. It occurs only in the mesophyll cells of the leaves. 4. It is a slower process of carbon fixation and photo-respiratory losses are high. C₄ pathwaRead more
(a) C₃ and C₄ pathways
C₃ pathways:-
1. The primary acceptor of CO₂ is RUBP – a six-carbon compound.
2. The first stable product is 3phosphoglycerate.
3. It occurs only in the mesophyll cells of the leaves.
4. It is a slower process of carbon fixation and photo-respiratory losses are high.
C₄ pathways:-
1. The primary acceptor of CO₂ is phosphoenol pyruvate – a threecarbon compound.
2. The first stable product is oxaloacetic acid.
3. It occurs in the mesophyll and bundle-sheath cells of the leaves.
4. It is a faster process of carbon fixation and photo-respiratory losses are low.
(b) Cyclic and non-cyclic photophosphorylations
Cyclic photophosphorylation:-
1. It occurs only in photosystem I.
2. It involves only the synthesis of ATP.
3. In this process, photolysis of water does not occur. Therefore, oxygen is not produced.
4. In this process, electrons move in a closed circle.
Non-cyclic photophosphorylation:-
1. It occurs in photosystems I and II.
2. It involves the synthesis of ATP and NADPH₂
3. In this process, photolysis of water takes place and oxygen is liberated.
4. In this process, electrons do not move in a closed circle.
(c) Anatomy of the leaves in C₃ and C₄ plants
C₃ leaves:-
1. Bundle-sheath cells are absent
2. RuBisCo is present in the mesophyll cells.
3. The first stable compound produced is 3-phosphoglycerate –a three-carbon compound.
4. Photorespiration occurs
C4 leaves:-
1. Bundle-sheath cells are present
2. RuBisCo is present in the bundlesheath cells.
3. The first stable compound produced is oxaloacetic acid – a four-carbon compound.
4. Photorespiration does not occur
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. In order to increase the rate of photosynthesis, the leaves pRead more
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.
In order to increase the rate of photosynthesis, the leaves present in shade have more chlorophyll pigments. This increase in chlorophyll content increases the amount of light absorbed by the leaves, which in turn increases the rate of photosynthesis. Therefore, the leaves or plants in shade are greener than the leaves or plants kept in the sun.
Since leaves require light to perform photosynthesis, the colour of a leaf kept in the dark changes from a darker to a lighter shade of green. Sometimes, it also turns yellow. The production of the chlorophyll pigment essential for photosynthesis is directly proportional to the amount of light availRead more
Since leaves require light to perform photosynthesis, the colour of a leaf kept in the dark changes from a darker to a lighter shade of green. Sometimes, it also turns yellow. The production of the chlorophyll pigment essential for photosynthesis is directly proportional to the amount of light available. In the absence of light, the production of chlorophyll-a molecules stops and they get broken slowly. This changes the colour of the leaf gradually to light green. During this process, the xanthophyll and carotenoid pigments become predominant, causing the leaf to become yellow. These pigments are more stable as light is not essential for their production. They are always present in plants.
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 xanthophRead more
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.
If any plant were to lack chlorophyll-a and contain a high concentration of chlorophyll-b, then this plant would not undergo photosynthesis.
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 CO2 acceptor in the mesophyll cells is phosphoenol pyruvate – a three-carbon coRead more
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 CO2 acceptor in the mesophyll cells is phosphoenol pyruvate – a three-carbon compound. It is converted into the four-carbon compound oxaloacetic acid (OAA). OAA is further converted into malic acid. Malic acid is transported to the bundle-sheath cells, where it undergoes decarboxylation and CO₂ fixation occurs by the Calvin cycle. This prevents the enzyme RuBisCo from acting as an oxygenase.
Give comparison between the following: (a) C₃ and C₄ pathways (b) Cyclic and non-cyclic photophosphorylation (c) Anatomy of leaf in C3 and C4 plants
(a) C₃ and C₄ pathways C₃ pathways:- 1. The primary acceptor of CO₂ is RUBP – a six-carbon compound. 2. The first stable product is 3phosphoglycerate. 3. It occurs only in the mesophyll cells of the leaves. 4. It is a slower process of carbon fixation and photo-respiratory losses are high. C₄ pathwaRead more
(a) C₃ and C₄ pathways
C₃ pathways:-
1. The primary acceptor of CO₂ is RUBP – a six-carbon compound.
2. The first stable product is 3phosphoglycerate.
3. It occurs only in the mesophyll cells of the leaves.
4. It is a slower process of carbon fixation and photo-respiratory losses are high.
C₄ pathways:-
1. The primary acceptor of CO₂ is phosphoenol pyruvate – a threecarbon compound.
2. The first stable product is oxaloacetic acid.
3. It occurs in the mesophyll and bundle-sheath cells of the leaves.
4. It is a faster process of carbon fixation and photo-respiratory losses are low.
(b) Cyclic and non-cyclic photophosphorylations
Cyclic photophosphorylation:-
1. It occurs only in photosystem I.
2. It involves only the synthesis of ATP.
3. In this process, photolysis of water does not occur. Therefore, oxygen is not produced.
4. In this process, electrons move in a closed circle.
Non-cyclic photophosphorylation:-
1. It occurs in photosystems I and II.
2. It involves the synthesis of ATP and NADPH₂
3. In this process, photolysis of water takes place and oxygen is liberated.
4. In this process, electrons do not move in a closed circle.
(c) Anatomy of the leaves in C₃ and C₄ plants
C₃ leaves:-
1. Bundle-sheath cells are absent
2. RuBisCo is present in the mesophyll cells.
3. The first stable compound produced is 3-phosphoglycerate –a three-carbon compound.
4. Photorespiration occurs
C4 leaves:-
1. Bundle-sheath cells are present
2. RuBisCo is present in the bundlesheath cells.
3. The first stable compound produced is oxaloacetic acid – a four-carbon compound.
4. Photorespiration does not occur
For more answers visit to website:
See lesshttps://www.tiwariacademy.com/ncert-solutions/class-11/biology/chapter-13/
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. In order to increase the rate of photosynthesis, the leaves pRead more
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.
In order to increase the rate of photosynthesis, the leaves present in shade have more chlorophyll pigments. This increase in chlorophyll content increases the amount of light absorbed by the leaves, which in turn increases the rate of photosynthesis. Therefore, the leaves or plants in shade are greener than the leaves or plants kept in the sun.
For more answers visit to website:
See lesshttps://www.tiwariacademy.com/ncert-solutions/class-11/biology/chapter-13/
Why is the colour of a leaf kept in the dark frequently yellow, or pale green? Which pigment do you think is more stable?
Since leaves require light to perform photosynthesis, the colour of a leaf kept in the dark changes from a darker to a lighter shade of green. Sometimes, it also turns yellow. The production of the chlorophyll pigment essential for photosynthesis is directly proportional to the amount of light availRead more
Since leaves require light to perform photosynthesis, the colour of a leaf kept in the dark changes from a darker to a lighter shade of green. Sometimes, it also turns yellow. The production of the chlorophyll pigment essential for photosynthesis is directly proportional to the amount of light available. In the absence of light, the production of chlorophyll-a molecules stops and they get broken slowly. This changes the colour of the leaf gradually to light green. During this process, the xanthophyll and carotenoid pigments become predominant, causing the leaf to become yellow. These pigments are more stable as light is not essential for their production. They are always present in plants.
For more answers visit to website:
See lesshttps://www.tiwariacademy.com/ncert-solutions/class-11/biology/chapter-13/
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 xanthophRead more
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.
If any plant were to lack chlorophyll-a and contain a high concentration of chlorophyll-b, then this plant would not undergo photosynthesis.
For more answers visit to website:
See lesshttps://www.tiwariacademy.com/ncert-solutions/class-11/biology/chapter-13/
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 CO2 acceptor in the mesophyll cells is phosphoenol pyruvate – a three-carbon coRead more
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 CO2 acceptor in the mesophyll cells is phosphoenol pyruvate – a three-carbon compound. It is converted into the four-carbon compound oxaloacetic acid (OAA). OAA is further converted into malic acid. Malic acid is transported to the bundle-sheath cells, where it undergoes decarboxylation and CO₂ fixation occurs by the Calvin cycle. This prevents the enzyme RuBisCo from acting as an oxygenase.
For more answers visit to website:
https://www.tiwariacademy.com/ncert-solutions/class-11/biology/chapter-13/
See less