Organization of natural systems

##Every natural system is a mix of biotic and abiotic factors

A biotic factor is a living organism, such as a plant, animal, fungus, or bacterium. Biotic factors can also include how an organism interacts with any living part of its environment. For example, bacteria inside an animal’s intestines are biotic factors that help with food digestion. A herd of bison feeding on grasses in a prairie is also a biotic factor.

An abiotic factor is a non-living part of the environment, such as sunlight, temperature, precipitation, or humidity. Other abiotic factors include water and wind currents as well as nutrients and minerals in soil.

##Earth is composed of many natural systems

Each natural system can be broken down into smaller and more specific parts. At the highest level, Earth is divided into four systems, called spheres:

1. The atmosphere is all the gases in the air that surround Earth.

2. The biosphere is all living organisms.

3. The geosphere is the interior and surface of the Earth, including rocks, continents, and the ocean floor.

4. The hydrosphere is all saltwater and freshwater (including precipitation, underground water, and ice).

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The biosphere contains all life on Earth

The biosphere is made up of all the living organisms on Earth. Living organisms can be found inside rocks deep underground to high in the atmosphere.

##The biosphere is made up of several biomes

Biomes are regions defined by specific abiotic factors to which plants, animals, and other organisms are well-adapted.

Terrestrial biomes are land-based biomes and are defined by their climate (temperature and precipitation). Aquatic biomes are water-based biomes and are defined by their water depth and salinity (saltiness of water).

Some biomes can be very small. A microbiome is a group of microbes (such as bacteria) that naturally live on or within another organism.

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##Each biome contains multiple ecosystems

An ecosystem includes all living organisms in a particular area along with the non-living parts of that environment.

Ecosystems can exist at different scales and within one another. Some ecosystems are very small and only occur under specific environmental conditions. These small, natural systems are called microecosystems and include soil, ponds and puddles, decaying logs, and tree cavities.

##Each ecosystem contains multiple communities made up of many populations

A community is a group of different species that interact with one another within a specific area.

A population is a group of individuals from the same species, living in the same general area.