CAM plants open stomata at night to:

CAM (Crassulacean Acid Metabolism) is a specialized photosynthetic adaptation found in plants living in arid or desert environments, such as cacti and pineapples. 1. **The Challenge**: Plants must open their stomata (pores) to intake $CO_2$ for photosynthesis. However, when stomata are open, water vapor escapes through a process called **transpiration**. In hot, dry climates, opening stomata during the day would lead to lethal levels of water loss. 2. **The Adaptation**: CAM plants have evolved to separate gas exchange and carbon fixation by time. They open their stomata **at night** when the ambient temperature is significantly lower and the relative humidity is higher. This minimizes the water potential gradient between the leaf and the air, drastically reducing water loss. 3. **Carbon Storage**: During the night, $CO_2$ enters the leaf and is converted into organic acids (like malate) and stored in vacuoles. During the day, the stomata close completely to conserve water, and the stored organic acids are broken down to release $CO_2$ internally for the Calvin Cycle, powered by sunlight captured by chlorophyll.