C4 plants have developed a specialized mechanism to minimize water loss during photosynthesis, particularly in hot and arid conditions. This unique method, referred to as C4 photosynthesis, employs a two-step process that effectively reduces photorespiration—a phenomenon that can result in significant water loss.

In the initial step of C4 photosynthesis, carbon dioxide is absorbed by mesophyll cells, which are situated between the upper and lower epidermis of the leaf. Within these cells, the enzyme phosphoenolpyruvate carboxylase catalyzes the reaction between carbon dioxide and phosphoenolpyruvate (PEP), resulting in the formation of a four-carbon compound known as oxaloacetate. This characteristic formation of a four-carbon compound is the reason for the name “C4 photosynthesis.” This process allows C4 plants to capture more carbon dioxide than their C3 counterparts, even in conditions of drought and elevated temperatures, thanks to its efficiency under low carbon dioxide concentrations.

In the subsequent step, the four-carbon compound is transported to the bundle-sheath cells, which are densely packed around the plant’s vascular tissue. Here, the compound is decarboxylated to release carbon dioxide, which is then utilized in the Calvin cycle to synthesize glucose. This reaction takes place in an environment with a high concentration of carbon dioxide, which significantly suppresses photorespiration.

Photorespiration occurs in C3 plants when the enzyme RuBisCO, responsible for fixing carbon dioxide in the Calvin cycle, inadvertently binds to oxygen instead of carbon dioxide. This unintended reaction not only results in energy loss but also leads to water loss through the stomata—tiny pores on the leaf surface. By minimizing photorespiration, C4 plants can afford to close their stomata, thereby reducing water loss without compromising their photosynthetic efficiency.

In conclusion, C4 plants possess a distinctive two-step photosynthetic pathway that enhances their ability to absorb carbon dioxide and reduce photorespiration, ultimately leading to decreased water loss. This remarkable adaptation enables C4 plants to thrive in hot and dry environments where water availability is limited.