NEET BIOLOGY

Detailed explanation-1: -In C4 photosynthesis, where a four-carbon compound is produced, unique leaf anatomy allows carbon dioxide to concentrate in ‘bundle sheath’ cells around Rubisco. This structure delivers carbon dioxide straight to Rubisco, effectively removing its contact with oxygen and the need for photorespiration.

Detailed explanation-2: -What is the role of PEP carboxylase in C4 and CAM plants? PEP carboxylase is essential for carbon fixation in C4 and CAM plants. It is present in the mesophyll cells. It catalyses the initial carbon fixation where PEP acts as an acceptor for CO2, and produces OAA.

Detailed explanation-3: -In the C4 pathway, initial carbon fixation takes place in mesophyll cells and the Calvin cycle takes place in bundle-sheath cells. PEP carboxylase attaches an incoming carbon dioxide molecul to the three-carbon molecule PEP, producing oxaloacetate (a four-carbon molecule).

Detailed explanation-4: -Under high temperature, high light, and the current CO2 concentration in the atmosphere, the C4 pathway is more efficient than C3 photosynthesis because it increases the CO2 concentration around the major CO2 fixating enzyme Rubisco. The oxygenase reaction and, accordingly, photorespiration are largely suppressed.

Detailed explanation-5: -In C4 plants PEPC initiates carbon fixation in mesophyll cells but also plays an important role in providing malate as a counter ion and an osmoregulator in the guard cells to help counterbalance the large influx of potassium ions during stomatal opening (Vavasseur and Raghavendra, 2005).