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Photosynthesis in Higher Plants

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Biology

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Biology

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CBSE Gujarat Board Haryana Board

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Class 10 Class 12
Name the first stable compound formed in C3 cycle.

3-phosphoglyceric acid (PGA)
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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-and other accessory pigments?

The plant having high concentration of chlorophyll-b but lacking chlorophyll-a will not carry out photosynthesis.
Chlorophyll-a molecules forms the reaction centre and acts as the main pigment molecules. The other pigments like chlorophyll-b and other photosynthetic pigments such as carotenoids and xanthophylls act as accessory pigments. Their role is to absorb the different wavelength of light and make the process of photosynthesis efficient. Carotenoids and xanthophylls also protect the chlorophyll molecule from photo-oxidation. 

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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?

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

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

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?
(b) What could be the limiting factor/s in region A?
(c) What do C and D represent on the curve?



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?
(b) What could be the limiting factor/s in region A?
(c) What do C and D represent on the curve?

(a)  Since the rate of photosynthesis doe not increase with the increase in the incident light therefore light is a limiting factor in the region B.

(b) The other limiting factors may be water, temperature, and the concentration of carbon dioxide.

(c) Point D represents the optimum point and gives the light intensity at which the maximum photosynthesis is recorded.
Ponit c represents the region where the rate of photosynthesis remains constant even after incresing the incident light. 

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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?

The productivity of a plant is measured by the rate at which it photosynthesises. The amount of carbon dioxide present in a plant is directly proportional to the rate of photosynthesis. C4 plants have a mechanism for increasing the concentration of carbon dioxide. In C4 plants, the Calvin cycle occurs in the bundle-sheath cells. The C4 compound (malic acid) from the mesophyll cells is broken down in the bundle-sheath cells. As a result, COis released. The increase in COensures that the enzyme RuBisCo does not act as an oxygenase, but only as a carboxylase. This prevents photorespiration. Since there is no photorespiration, thus there is no waste of energy and rate of photosynthesis is increased which in turn increases the productivity. Thus, C4 plants are highly productive.
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Give comparison between the following :

(b) Cyclic and non-cyclic photophosphorylation

 


(b) Distinction between cyclic and non-cyclic photophosphorylation :

 

Cyclic photophosphorylation

Non-cyclic photophosphorylation

1.

It is performed by PS I independently.

It is performed by both PS I and PS II with the help of each other.

2.

An external source of electrons is not required because the same electrons get recycled.

The process requires an external electron donor, because the same electron is not recycled.

3.

It is not connected with photolysis of water, therefore, no oxygen is evolved.

It is connected with photolysis of water and liberation of oxygen.

4. 

It synthesizes only ATP.

ATP synthesis with the production of NADPH.

5

Electron flow is cyclic.

Electron flow is non-cyclic. 


 

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Give comparison between C3 and C4 pathways.


Cpathways

Cpathways

1.

The primary acceptor of CO2 is RUBP – a six-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.

5.

Occurs in all the plants

5. 

Occurs only in C4 plants

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