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Photosynthesis in Higher Plants

Short Answer Type

91. Name two green house crops. What is the type of these plants and why are they used in the green houses?

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Long Answer Type

92. Describe Priestley’s experiment.

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Short Answer Type

93. Why a plant cannot survive for long time at compensation point ?

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94. What does the chemiosmotic hypothesis state?

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95. Name the products of light reaction and where they are used ?

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96. By looking at a plant externally can you tell whether a plant is C₃ or C₄? Why and how?

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97. By looking at which internal structure of a plant can you tell whether a plant is C₃ or C₄? Explain.

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Long Answer Type

98. 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, CO₂is released. The increase in CO₂ensures 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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Short Answer Type

99. RuBisCo is an enzyme that acts both as a carboxylase and oxygenase. Why do you think RuBisCo carries out more carboxylation in C₄ plants?

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Long Answer Type

100. 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?

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