If there isn’t enough water (or if the plant can’t move the water fast enough on a hot, windy day), osmosis moves the water out of the guard cells, which closes the stomata, conserving water inside the plant.
If there isn’t enough water (or if the plant can’t move the water fast enough on a hot, windy day), osmosis moves the water out of the guard cells, which closes the stomata, conserving water inside the plant.