Final answer:
The water cycle is essential for maintaining an unpolluted biosphere. It helps to filter out pollutants, remove impurities from water, and distribute clean water to different parts of the biosphere.
Step-by-step explanation:
The water cycle is essential to maintaining an unpolluted biosphere because it helps to regulate and purify water in the environment. As water moves through the water cycle, it undergoes processes such as evaporation, condensation, and precipitation, which help to filter out pollutants and remove impurities from the water. Additionally, the water cycle plays a crucial role in distributing clean water to different parts of the biosphere, ensuring that all living organisms have access to a freshwater supply.