Question

Explain the C4 pathway of photosynthesis.

Answer 1

Photosynthesis:

1. Photosynthesis is a biological process with the help of which the green plants, photosynthetic bacteria and the other autotrophs convert light energy into chemical energy.
2. In this process carbon dioxide and water combine in the presence of sunlight to form glucose.
3. Oxygen is the byproduct of photosynthesis.

The chemical equation is as follows-

6CO₂ + 6H₂O ———> C₆H₁₂O_{6 +} 6O₂

C4 Pathway:

1. The process of photosynthesis occurs in two phases.
2. One phase requires continuous presence of light and the reactions occurring in this phase are called light dependent reactions.
3. The other phase is the light independent phase also called as the dark reaction or the Calvin cycle.
4. Most of the photosynthetic plants follow the Calvin cycle and their first formed product is a 3 carbon compound that’s why they are said to follow the C3 pathway.
5. On the other hand there is a primary stage to the Calvin cycle known as the C4 pathway or the Hatch and Slack pathway in which the first formed product is a 4 carbon compound called Oxalo Acetic Acid (OAA).
6. This pathway is mainly seen in tropical desert plants, grasses, sugarcane, maize, sorghum and Amaranthus etc.
7. It is because these plants have a different type of leaf anatomy. Such kind of leaf anatomy is called Kranz anatomy.

Steps of C4 Pathway-

Step 1: C4 pathway starts with the formation of a three molecule compound called Phosphoenolpyruvate (PEP) which plays the role of primary carbon dioxide acceptor amd in the presence of enzyme PEP carboxylase the carboxylation takes place and the 4 molecule compound called Oxalo Acetic Acid(OAA) is formed.

Step 2: The compound containing four carbon is transferred from mesophyll cells to bundle sheath cells.

Step3- In bundle sheath cells decarboxylation occurs and a CO2 is released which enters the Calvin cycle and the C3 compound again goes back to the Mesophyll cell.

Step 4: The C3 compound undergoes regeneration to form for phosphoenolpyruvate.

Significance of C4 Pathway:

1. The C4 pathway increases the photosynthetic yield of plants by 2 to 3 times as compared to C3 plants.
2. The C4 plants can perform photosynthesis at a very high rate even when the stomata are nearly closed.
3. The C4 pathway increases the adaptability of C4 plants to survive in high temperature and high like intensity areas.
4. Plants following the C4 pathway can easily grow in saline soils because of the presence of C4 organic acid.