The biosphere
Figure 15.2 shows the interactions between the living communities of a pond ecosystem and its non-living environment.
Figure to be added
The biosphere
The whole region of the Earth and the atmosphere in which living things are spread is the biosphere. It is made of three parts:
Lithosphere
The Earth's crust and the upper mantle.
Hydrosphere
The oceans and freshwater bodies; about 70% of the Earth's surface is covered by water.
Atmosphere
The layer of air spread round the Earth.
Why a pond is a small biosphere
Follow the arrows of figure 15.2. Sunlight reaches the water plants, which use it with carbon dioxide from the air and water to make food, as you studied in chapter 2. Fish and insects eat the plants, birds and frogs eat them, and when anything dies the soil at the bottom receives it and bacteria break it down, returning minerals to the water. Oxygen moves from the plants to the air and water; carbon dioxide moves back. The same exchanges, between the same three parts — rock and soil, water, air — happen on a planetary scale. The biosphere is simply every ecosystem on Earth taken together, the thin shell where land, water and air meet life.
Three spheres, one biosphere
The biosphere is every region of the Earth and air where life is found: parts of the lithosphere, the hydrosphere and the atmosphere.