ï»¿ What led to the evolution of C4Â plants or C4Â pathway of photosynthesis ? Describe in detail. from Biology Photosynthesis in Higher Plants Class 11 Assam Board

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What led to the evolution of C4Â plants or C4Â pathway of photosynthesis ? Describe in detail.

C4Â pathway is an adaptation to tolerate strong light, high temperature ; high quantity of oxygen etc. Evolution of C4Â plants from C3Â plants can be described as follows :

1.Â C3Â plants undergo photorespiration in strong light or at high temperature which is a wasteful process in which no energy is produced.

2.Â In C3Â plants RUBP carboxylase get denatured in strong light, but in C4Â plants it does not.

3.Â These C4Â plants have Kranz anatomy. In this case mesophyll cells have grana thylakoid and bundle sheath cells have agranal thylakoids present in stroma of chloroplast.

4.Â In C4Â plant, light reaction occurs in mesophyll cells and RuBisCo is found in bundle sheath cells in which CO2Â fixation occurs. Thus, in C4Â plants RuBisCo remains protected from sunlight and is also protected from oxygenation, because in bundle sheeth cells only dark reaction occurs.

Thus, to avoid photorespiration, oxygenation of RuBisCo etc. C4Â plants were evolved from C3plants. The C4Â plants are maize, sugar cane, grasses etc.

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What are grana ?

Grana are the stacks of thylakoids embedded in the stroma of a chloroplast. They are the sites of light reaction of photosynthesis.
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Name the first stable compound formed in C3Â cycle.

3-phosphoglyceric acid (PGA)
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What is stroma ?

Stroma is matrix or the cytoplasm of chloroplast where dark reaction of photosynthesis takes place.
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Why Rubisco is not affected by O2 in C4 plants ?

O2 is formed in mesophyll cells while Rubisco is present in bundle sheath cells. Therefore Rubisco does not come in contact with O2 and is thus not affected by it.
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Where CO2 assimilation occurs in CPlants ?

In bundle sheath cells.
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