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  4. A plant in your garden avoids photorespiratory losses, has increased water using efficiency, shows high rates of photosynthesis at high temperatures and has improved efficiency of nitrogen utilisation. In which of the following physiological groups would you allot this plant?

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Q. A plant in your garden avoids photorespiratory losses, has increased water using efficiency, shows high rates of photosynthesis at high temperatures and has improved efficiency of nitrogen utilisation.
In which of the following physiological groups would you allot this plant?

NTA AbhyasNTA Abhyas 2020

Solution:

For the given information, we can clearly say that the plant is a C4 plant. C4 plants are better photosynthesizers. There is no photorespiration in these plants. In C4 plants, for the formation of one mole of hexose (glucose) $30$ ATP and $12$ NADPH2 are required. There is a difference in different C4 plants in the mechanism of the C4 model of photosynthesis. The main difference is in the way the 4C dicarboxylic acid is decarboxylated in the bundle sheath cells.
Characteristics of the C4 cycle
(1) C4 species have a greater rate of CO2 assimilation than C3 species. This is on account of the fact that
  • PEP carboxylase has a great affinity for CO2.
  • C4 plants show little photorespiration as compared to C3 plants or no photorespiration at all, resulting in higher production of dry matter.
  • C4 plants contain more chloroplasts.
(2) C4 plants are more adapted and evolved to environmental stresses in comparison of the C3 plants.
(3) CO2 fixation by C4 plants requires more ATP than that by C3 plants. This additional ATP is needed for the conversion of pyruvic acid to phosphoenol pyruvic acid and it's transport.
(4) CO2 acceptor molecule in C4 plants is a PEP.