The easiest way to think of the biosphere and the hydrosphere is to use the Greek roots for both of the words. Bio comes from the Greek and is translated as "life." Hydro also comes from the Greek and translates to "water." The biosphere refers the region of Earth where life can exist, while the hydrosphere refers to the water on and around Earth's surface. One of the basic needs of biological life is water. The primary interaction between the biosphere and hydrosphere is that the hydrosphere generates water (the first requirement for life) for life in the biosphere. The hydrosphere, observed through the water cycle, produces the water that makes life possible on Earth. The hydrosphere contains all of Earth’s water, whether in solid, liquid, or gaseous form.
Approximately 70% of the Earth’s surface is covered by water. That is a lot of space in which life can reproduce and survive! Biotic factors are living things. We can quickly determine there is a significant amount of biotic activity in oceans, rivers, streams, lakes, and other water environments. We can also observe the amount of plant life on Earth. Plants, which need water to survive, play an essential role as a food source and as producers of the oxygen (the second requirement for life) that animals breathe. It is the interaction between the biosphere and the hydrosphere that provides water for oxygen-producing plants and plant life for animals to eat.
These two spheres are interdependent. The biosphere produces the plants that produce oxygen. As photosynthesis occurs (bringing in the third requirement for life, light), plants transpire, releasing water back to the atmosphere. The water evaporates and returns to the hydrosphere in the form of precipitation in an endless cycle. Both spheres play a crucial role in Earth’s environment and climate.