Final answer:
Plants close their stomata on hot, dry days to conserve water, which impacts photosynthesis as the intake of CO₂ is limited. Guard cells help balance the need for gas exchange with water conservation. Desert plants have adaptations such as nighttime carbon fixation to mitigate this issue.
Step-by-step explanation:
Plants close their stomata during hot, dry days to conserve water. However, this has an impact on photosynthesis because the stomata also control the exchange of gases necessary for this essential process. The closure of stomata limits the uptake of carbon dioxide (CO₂), which is a critical substrate for photosynthesis. Therefore, when stomata are closed, the photosynthetic rate will likely decrease because the plants are not taking in as much CO₂ as they require. However, this is a necessary trade-off for the plant to conserve water and prevent desiccation in harsh environmental conditions.
Stomata are flanked by guard cells that regulate their opening and closing. These guard cells react to various environmental factors and help maintain a balance between the need for CO₂ in photosynthesis and the prevention of excessive water loss through transpiration. In many cases, plants will sacrifice some potential photosynthetic activity to ensure they do not lose too much water, which is vital for their survival, especially in arid climates or during periods of drought.
Desert plants have evolved unique adaptations to these conditions. For instance, some plants like cacti perform a temporary carbon fixation process at night when temperatures are cooler and transpiration rates are lower. During the day, these plants can carry out photosynthesis using the stored CO₂ with their stomata shut, thus conserving water effectively.