Final answer:
Many plants adapted to arid environments utilize the CAM (Crassulacean Acid Metabolism) photosynthetic pathway to fix CO2 during the night to conserve water. This pathway involves closing stomata during the day and opening them at night to take up CO2. CAM plants store malic acid in vacuoles and use it during the day to carry out photosynthesis.
Step-by-step explanation:
This pathway allows plants to conserve water by closing their stomata during the day and opening them at night when temperatures are cooler and humidity is higher. CAM plants fix CO2 by combining it with PEP (phosphoenol pyruvate) to produce malic acid, which is stored in vacuoles. During the day, the stored malic acid is retrieved and split into pyruvate and CO2, which then enters the chloroplasts and joins the Calvin Cycle to make glucose and starches.