The process through which plants expel excess water is called transpiration. Transpiration occurs primarily through small openings in leaves known as stomata, where water vapor is released into the atmosphere. This process not only helps in regulating the plant's temperature but also facilitates the uptake of nutrients and minerals from the soil. Transpiration plays a critical role in the water cycle, contributing to atmospheric moisture and influencing weather patterns. It is essential for maintaining plant health and overall ecosystem balance.