The photosynthetic pathway that results in the least water loss for each molecule of CO2 fixed is CAM, which stands for Crassulacean Acid Metabolism. Here's why:
1. CAM plants, such as succulents and cacti, have a unique adaptation where they open their stomata (tiny pores on the leaves) only at night to take in carbon dioxide. By opening their stomata at night when it's cooler and less humid, CAM plants reduce water loss through transpiration during the day.
2. During the night, CAM plants store the carbon dioxide they've taken in as organic acids. These organic acids are then broken down during the day to release the carbon dioxide for use in photosynthesis. This allows CAM plants to fix carbon dioxide efficiently while minimizing water loss.
3. In contrast, C3 and C4 plants open their stomata during the day to take in carbon dioxide, which can lead to higher water loss through transpiration compared to CAM plants.
Therefore, CAM is the photosynthetic pathway that results in the least water loss for each molecule of CO2 fixed due to its unique nighttime carbon uptake and storage mechanism, which helps conserve water in arid environments.
