Why are a plant’s stomata generally open during the day and closed at night?
A. Stomata are generally open during the day because water pressure in the guard cells drops during the day and closed at night because the water pressure is high.
B. Stomata are generally open during the day to allow oxygen needed for cellular respiration to enter and closed at night because cellular respiration does not occur at night.
C. Stomata are generally open during the day to remove excess water from the plant and closed at night to keep oxygen from escaping.
D. Stomata are generally open during the day to allow carbon dioxide to enter the leaves when photosynthesis is possible and closed at night to prevent water loss.
The correct answer and explanation is:
The correct answer is D. Stomata are generally open during the day to allow carbon dioxide to enter the leaves when photosynthesis is possible and closed at night to prevent water loss.
Stomata are tiny pores found on the surface of plant leaves and stems. These pores play a crucial role in regulating gas exchange, which is vital for processes like photosynthesis and respiration. During the day, plants carry out photosynthesis, a process where carbon dioxide (CO2) is used to produce glucose in the presence of light. For this process to occur, plants need a constant supply of CO2, which enters through the stomata. In addition to CO2, oxygen (O2) is also produced as a byproduct of photosynthesis and exits through the stomata.
During the day, when light is available, the stomata remain open to allow for the intake of CO2. However, this process also leads to the loss of water through transpiration, which is the evaporation of water from plant surfaces. To minimize excessive water loss, plants need to regulate the opening and closing of their stomata.
At night, when there is no sunlight, photosynthesis does not occur, so there is no need for the plant to take in CO2. As a result, the stomata close to conserve water and prevent dehydration. Closing the stomata at night helps the plant retain moisture, which is essential for its survival, especially in environments where water availability is limited.
In summary, stomata are open during the day to facilitate gas exchange for photosynthesis, and they are closed at night to reduce water loss when photosynthesis is not actively occurring. This process helps maintain the plant’s water balance and overall health.