The water cycle is an important Biogeochemical Cycle involved in the flow or circulation of water through different levels of the ecosystem. The complete water cycle is carried into four stages which are as follows: Evaporation, Condensation, Precipitation and Collection. Plants absorb water from the soil. The water moves from the roots through the stems to the leaves. Once water reaches the leaves, some of it evaporates from the leaves, adding to the amount of water vapor in the air. This process of evaporation through plant leaves is called transpiration. The above given water cycle is in the plants. Hence, transpiration is the process in living plants is responsible for returning water vapour to the air at P.