Question

In which cell type the initial carboxylation reaction occurs in C₃ and C₄ plants?

Answer 1

Photosynthesis:

It is the process that plants use to utilize light, carbon dioxide, and water to make sugars that fuel plant growth using the enzyme rubisco through the Calvin cycle.

Restriction to photosynthesis:

1. Rubisco sometimes fixes oxygen molecules instead of carbon dioxide molecules. Some plants have generated a combat mechanism to fight this wasteful process. Based on combat mechanism plants are categorized as C₃ plants and C₄ plants.
2. C₃ plants have no special feature to prevent the loss by photorespiration whereas C₄ plants minimize photorespiration by separating initial carbon dioxide fixation and Calvin cycle in leaf space i.e. between mesophyll cells and bundle sheath cells.

C₃ plants :

1. These have no mechanism to fight photorespiration.
2. The first step of the Calvin cycle called carbon fixation takes place in mesophyll cells. The reaction produces a 3-PGA molecule.
3. These plants include rice, wheat, and soybeans.

C₄ plants :

1. These are adapted photosynthetically to fight photorespiration conditions.
2. In these plants, light-dependent reactions and the Calvin cycle are physically separated.
3. The light-dependent reaction occurs in mesophyll cells and the Calvin cycle occurs in special leaf cells called bundle sheath cells.
4. These plants include corn, sorghum, sugarcane, etc.

CAM plants :

1. Plants adapted to dry environments such as cacti and pineapples, use the crassulacean acid metabolism (CAM) pathway to reduce photorespiration.