Yes, stomata are generally closed at night.
Why Stomata Close at Night
The primary reason stomata close at night is to conserve water. Photosynthesis, the process plants use to create energy from sunlight, doesn't happen at night. With no need for carbon dioxide uptake for photosynthesis, the stomata close to prevent excessive water loss through transpiration. This water loss occurs when water vapor escapes through the open stomatal pores.
While gaseous exchange still occurs at night (though at a much lower rate), it's primarily done through diffusion across the plant's surface, rather than through the open stomata. This minimizes water loss while still allowing for some respiration.
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Key Point: The stomatal openings remain closed at night as photosynthesis is not conducted without sunlight.
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Water Conservation: Closing stomata at night is a crucial adaptation for plants, especially those in arid environments. It prevents them from losing significant amounts of water overnight, helping them to survive.
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Gaseous Exchange: Although minimal, some gas exchange is still required. This occurs via diffusion. Keeping stomata closed significantly reduces water loss while still allowing this exchange.
