Why do C4 plants need this adaptation?
* Photorespiration: In hot, dry climates, plants need to close their stomata (tiny pores on leaves) to prevent water loss. This limits CO2 intake, but also allows oxygen to build up inside the plant. This oxygen can then compete with CO2 in the process of photosynthesis, leading to a wasteful process called photorespiration.
* C4 solution: C4 plants have evolved a way to overcome this problem. They use a special enzyme called PEP carboxylase to capture CO2 in their mesophyll cells (the outer layer of the leaf). This enzyme has a higher affinity for CO2 than rubisco (the enzyme used in the Calvin cycle), so it can efficiently capture CO2 even when levels are low.
* Four-carbon acids: The CO2 is then incorporated into a four-carbon acid called malate. This malate is transported to the bundle sheath cells (inner layer of the leaf), where it is broken down, releasing CO2.
* Calvin cycle: The CO2 released from the malate is then used in the Calvin cycle, the main process of photosynthesis, to produce sugars.
In summary: C4 plants use a special mechanism to concentrate CO2 in their bundle sheath cells, allowing them to perform photosynthesis more efficiently in hot, dry conditions. This mechanism involves trapping CO2 in four-carbon acids.
