How do C3 and C4 plants differ in photosynthesis?

C3 and C4 plants differ in their photosynthetic pathways, particularly in how they fix carbon dioxide and minimize photorespiration.

In C3 plants, carbon fixation occurs directly through the Calvin cycle. The enzyme RuBisCO combines CO₂ with a 5-carbon compound (RuBP) to form a 3-carbon molecule, which is why they are called C3 plants. However, RuBisCO can also bind oxygen, leading to photorespiration, especially under high temperature and low CO₂ conditions. This reduces photosynthetic efficiency.

C4 plants have developed an additional mechanism to overcome this limitation. They initially fix CO₂ into a 4-carbon compound using the enzyme PEP carboxylase in mesophyll cells. This compound is then transported to bundle sheath cells, where CO₂ is released and enters the Calvin cycle. This spatial separation reduces photorespiration and increases efficiency under high light intensity and temperature.

Structurally, C4 plants exhibit Kranz anatomy, where bundle sheath cells are arranged around vascular bundles, supporting this specialized process. C3 plants lack this structure.

In terms of efficiency, C3 plants perform well in cooler, moderate conditions, while C4 plants are better adapted to hot, dry environments due to reduced water loss and minimized photorespiration.

Overall, the key difference lies in carbon fixation strategy, enzyme usage, and environmental adaptation.