Many cacti and other succulent plants with CAM metabolism open their stomata at night and close them during the day. ... In contrast to C3 and C4 plants, CAM plants open their stomata and fix CO2 at night. The basic role of stomata is to regulate transpiration and photosynthesis.

It's correct ans is A. Stomata of CAM plants open during the night and close during the day.

Stomata of CAM Plants

CAM (Crassulacean Acid Metabolism) plants are a type of plants that have adapted to survive in arid or desert environments. They have a unique mode of photosynthesis that allows them to conserve water by keeping their stomata closed during the day and opening them at night. This helps them to minimize water loss while still being able to carry out photosynthesis.

Opening and Closing of Stomata
The stomata are small openings on the surface of leaves that allow for the exchange of gases, such as carbon dioxide and oxygen, with the surrounding environment. In most plants, stomata open during the day and close at night. This is because during the day, when the sunlight is available, plants can uptake carbon dioxide for photosynthesis. However, this process also leads to water loss through the stomata, which can be a significant issue for plants in arid environments.

Nocturnal Stomatal Opening
In CAM plants, the stomata have adapted to open at night and close during the day. This nocturnal stomatal opening allows the plants to take in carbon dioxide at a time when the temperatures are lower, and the moisture loss is minimized. During the night, CAM plants can fix carbon dioxide into organic acids, which are stored in the vacuoles of their cells.

Storing Carbon Dioxide
The organic acids produced during the night are stored in the vacuoles until the next day. When the day comes, the stomata close, and the stored organic acids are broken down to release carbon dioxide. This internal release of carbon dioxide allows the plants to carry out photosynthesis during the day without the need for stomatal opening. By keeping their stomata closed during the day, CAM plants can conserve water and reduce transpiration.

Adaptation to Arid Environments
The opening and closing of stomata in CAM plants is an adaptation to arid environments where water availability is limited. By opening their stomata at night, when the temperatures are lower and the humidity is higher, CAM plants can minimize water loss and still carry out photosynthesis. This unique mechanism allows them to survive in harsh conditions and thrive in arid habitats.

In conclusion, the stomata of CAM plants open during the night and close during the day. This adaptation helps them conserve water and carry out photosynthesis in arid environments.