Question

C4 photosynthesis has been described as "spatial separation" of the PS reactions. CAM has been described as "temporal separation". Why?

Answer 1

C4 cycle or Hatch and Slack pathway is present in C4 plants. C4 plants are those which live under dry climatic conditions including high light intensity and high temperature conditions. The first stable product of carbon fixation in these plants is a 4 carbon compound oxaloacetic acid. The enzyme involved is pepcase.

The C4 cycle is distributed in space because two types of cells are involved in carbon fixation. The C4 cycle occurs in mesophyll cells where are the C3 cycle occurs in bundle sheeth cells. Both the types of parrots have different types of chloroplast. The former has small granal chloroplast where as the latter has large agranal chloroplast.

Crassulacean acid metabolism is seen in the members of family crassulaceae. These plants are characterized by the absence of stem and leaves being thick succulent and store water and a large amount of parenchyma. This plant are found in very high temperature conditions like desert. Therefore to reduce the amount of water loss through transpiration by stomata, they have scotoactive stomata. Scotoactive stomata open during the daytime and uptakes carbon dioxide from the atmosphere. Carbon fixation occurs during the night time. The stomata remains closed during the daytime.

This is how C4 cycle is distributed in space and CAM cycle is distributed in time.

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