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C4 Cycle of Photosynthesis | Hatch and Slack Pathway

Hatch and slack (1967) discovered this alternative pathway for CO2 fixation hence also called as hatch and slack cycle<br>It is also called as C4 cycle because the first stable compound is 4C compound oxaloacetic acid in this cycle<br>C4 plants are special as they not only tolerate adverse conditions but also don't show a wasteful phenomena called photorespiration<br>Due to the lack photorespiration, productivity and yields are better in C4 plants. In addition these plants show tolerance to higher temperatures.<br><br>Reference<br>https://rajusbiology.com/photosynthesis-in-higher-plants-class-11-notes/

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C4 Cycle of Photosynthesis | Hatch and Slack Pathway

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  1. C4 PATHWAY

  2. DARK REACTION C4 PATHWAY • Hatch and slack (1967) discovered this alternative pathway for CO2 fixation hence also called as hatch and slack cycle • It is also called as C4 cycle because the first stable compound is 4C compound oxaloacetic acid in this cycle • C4 plants are special as they not only tolerate adverse conditions but also don't show a wasteful phenomena called photorespiration • Due to the lack photorespiration, productivity and yields are better in C4 plants. In addition these plants show tolerance to higher temperatures.

  3. DARK REACTION C4 PATHWAY C4 PLANTS ARE SPECIAL DUE TO FOLLOWING REASONS • In the C4 plants leaf show kranz anatomy • The large cells around the vascular bundles of the C4 plants are called bundle sheath cells. • They have large number of chloroplasts, thick walls impervious to gas exchange and no intercellular spaces. • Cells of mesophyll and bundle sheath are interconnected by plasmodesmata. • C4 plants are also characterised by Dimorphic chloroplast. • Chloroplasts of mesophyll cells are small in size and granal(with grana) • Chloroplasts of bundle sheath cells are large in size and agranal(without grana)

  4. DARK REACTION C4 PATHWAY IN MESOPHYLL CELLS • Primary CO2 acceptor is phosphoenol pyruvate (PEP). It is a 3-carbon molecule seen in mesophyll cells. The enzyme for this fixation is PEP carboxylase (PEPcase). • The mesophyll cells lack RuBisCO enzyme. • The C4 acid OAA is formed in mesophyll cells • It then forms other 4-carbon acids like malic acid or aspartic acid. • They are transported to bundle sheath cells.

  5. DARK REACTION C4 PATHWAY IN BUNDLE SHEETH CELLS • In the bundle sheath cells, C4 acids are broken down to release CO2 & a C3 molecule. • The C3 molecule (Pyruvic acid) is transported back to mesophyll where it is converted to PEP again. • The released CO2 enters the C3 pathway. • Bundle sheath cells are rich in RuBisCO, but lack PEPcase. Thus C3 pathway is common to C3 & C4 plants.

  6. DARK REACTION C4 PATHWAY Note (Per CO2) 3 ATP + 2 NADPH2 (C3 Cycle) + 2 ATP (Regeneration of PEP)

  7. DARK REACTION DIFFERENCES BETWEEN C3 & C4 PLANTS

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