With regard to special mechanisms of photosynthesis in hot or dry climates, photosynthesis separates carbon dioxide capture and the Calvin cycle physically, whereas photosynthesis separates carbon dioxide capture and the Calvin cycle in time.

C4, CAM

Explanation:

C4 photosynthesis separates carbon dioxide capture and the Calvin cycle physically and uses a special enzyme with a greater attraction for carbon dioxide.  C4 phtosynthesis is a CO2-concentrating mechanism that increases the carboxylation rate of Rubisco while simultaneously minimizing oxygenase activity and the inhibitory effects of photorespiratio

CAM(Crassulacean acid metabolism) keep their stomata closed during the day to prevent water loss. on CAM which  is a carbon fixation pathway that evolved in some plants as an adaptation to arid conditions. In a plant using full CAM, the stomata in the leaves remain shut during the day to reduce evapotranspiration, but open at night to collect carbon dioxide.

C4 and CAM

C4 -separated physically with the bundle sheath

CAM- with  day stomata closure

Explanation:

Theses two pathways were designed to ensure mximum C02 concentration,  to avoid competition of their Phosphoenolphytuvate(PEP) substrate with competitor oxygen and to conserve water(CAM).

To achieve this the  CAM plants e.g cacti.,orchids which thrive in extreme conditions, opens their Stomata at nights. therefore they take in enough Carbondioxide. This react with 3C PEP to from 4C- Oxaloaceteate. The reaction is catalyse  by enzyme PEP carboxylase.  The 4C oxaloacetate formed  is converted to Malate by NAD+ Malase dyhydrogenase. The Malate is stored as Mailic acid in the vacuole.

During the day, the Stomata are closed, to conserve water, to prevent entry of oxygen the  competitor with C02  for enzyme Rubisco.The ATP and NADPH, produced  during the day initiated the process of Calvin Cycle. The Malate is transferred to the chloroplast and the stored   C02  is  removed  by splitting Malate  to pyruvate and CO2 by Malic enzymes. The C02  is pick up by enzyme Rubisco. It  combines with Rubulose biphosphate for  the Calvin Cycle  to progress normally.

Thus C02 and Calvin cycle are separated in time

However the anatomy of C4 plants  ensures separation of C02 from the enzyme Rubisco,by bundle shealth cells so that the freely diffused oxygen with C02 will not compete with C02 for  enzymes Rubisco., for photorespiration to occurs, As mentioned above the C02 is conserved as 4C Malate,  and then splits to C02 and pyruvate as in CAM.

However instead of the C02   diffusion  into the chloroplast as in  CAM plants, it  is passed  through  into the air through group of air resistant bundle sheaths cells. Here  it combines with PEP , and catalysed by enzyme Rubisco, for the normal Calvin Cycle process to continue.

Thus C02  captures and Calvin cycle stages are separated by physical barriers the bundle sheath.

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