Answer:
A pot plant kept on a sunny window sill will start to wilt because of excessive water loss through transpiration. The heat from the sun causes the moisture in the soil to evaporate, and the plant's leaves lose water through tiny pores called stomata. If the plant cannot keep up with the amount of water being lost through transpiration, it will begin to wilt as a way of conserving water. As the plant loses water, it becomes less rigid and unable to support itself, causing the stems and leaves to droop or collapse. In extreme cases, the plant may suffer permanent damage or die. To prevent this, it is important to ensure that the plant has adequate moisture and that the soil is not allowed to dry out completely, especially during hot, sunny periods. Additionally, plants that are sensitive to direct sunlight may benefit from being moved to a location with less intense light or filtered light.