Question

Stomata open at night and close during day time in
A. Succulent CAM plants
B. Hydrophytes
C. Halophytes
D. Mesophytes

Answer 1

Hint: Stomata are the specialized or well defined pores found at the epidermis of leaves in green plants. The function of stomata is to control the rate of exchange of gases during photosynthesis. Stomata help plants to take in carbon dioxide gas and release oxygen.

Complete step by step answer: Stomata is a tiny opening or pores present at the epidemic of the leaves, stem and other organ. These pores are surrounded by guard cells. Stomata have two types of cells- guard cells and subsidiary cells. The function of a guard cell is to regulate the size of the stomatal opening. While subsidiary cells or accessory cells provide support to guard cells. Opening and closing of stomata depend on the light, carbon dioxide level and change in environmental factors.
Mechanism of opening and closing of stomata: stomata function as turgor operated valves. When osmotic pressure of guard cells increases, water enters into it and makes stomata open. When osmotic pressure decreases, water moves out and makes the stomata close due to which stomata become more flaccid.
In most cases stomata open at day time and close at night. But there are some plants where reverse mechanisms occur for e.g. in xerophyte plants such as orchids, pineapple etc. because these plants live in dry conditions. Succulent plants are the plants that grow in dry conditions and follow CAM mechanism, also named as CAM plants.
So the correct option is (A) Succulent CAM plants. CAM is a Crassulaceae acid mechanism that occurs in succulent plants which perform fixation of carbon dioxide during night.

Note: In succulent plants stomata close at night and open in day time because there is no sunlight at night for photosynthesis. CAM plants change carbon dioxide into malic acid during night. They do so to avoid the loss of water as they are exposed under high temperature.