Ecosystems Study Guide

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Updated on Feb 22, 2013


The study of living organisms and the ways in which they interact with their physical environment and each other is called ecology. All these relationships form an ecosystem. The physical environment includes the type of soils, the amount of sunshine and rainfall, the weather and climate, the topography (or shape) of the land, and many other factors. An organism's habitat provides for the needs of that organism. Large areas of the earth and its oceans share similar habitats and physical environment characteristics. These areas are called biomes, and because they include the relationships of many organisms and physical factors, they are also ecosystems.

Biosphere and Biome

Earth is a large planet, and much of its bulk is not suitable for living organisms, but three factors interact to make life possible. These three factors are air, water, and rock (or soil).We also refer to these factors as being the atmosphere (air), hydrosphere (water), and lithosphere (rocks and soil). An interaction takes place between these physical factors and the life of Earth to create an environment we call the biosphere. The biosphere contains all of Earth's living organisms. Large areas of the earth (both on land and in water) may contain several small living systems operating in a region with definable conditions. These large areas are called biomes. Each biome has organisms and physical environment characteristics that define it. Several biomes have been identified and defined.


We define an ecosystem as being all the relationships between organisms in a defined area and their interactions with their physical environment. An ecosystem can be very large, including the entire Earth (in which case, we refer to it as the biosphere) or the large regions we call biomes. However, ecosystems can also be very small; even a single tree can be the foundation of a whole ecosystem, and a terrarium or aquarium is a model of an ecosystem you can create yourself. No matter the size or form of an ecosystem, groups of organisms will affect and be affected by each other and their physical surroundings.

The living organisms in an ecosystem are collectively known as the biotic (biological) component, whereas the nonliving things such as water, minerals, and sunlight are collectively known as the abiotic (nonbiological) component. Studying the interactions between the biotic and abiotic components helps us understand an ecosystem.

The particular details of one ecosystem will differ when compared to another. They will have different organisms present or different abiotic factors available. But in all cases, ecosystems exhibit two primary features:

  1. a single direction to the flow of energy, in the form of chemical bonds, from photosynthetic organisms, like green plants or algae, to animals that eat the plants or other animals.
  2. the cycling of inorganic minerals, such as nitrogen, calcium, and phosphorous, through living organisms and then back to the environment. The return of these inorganic materials to the environment happens largely by the action of organisms known as decomposers (such as bacteria and fungi). Other organisms called detritivores (such as pillbugs, sowbugs, millipedes, and earthworms) help break down large pieces of organic matter into smaller pieces that the decomposers then work on.

A complete definition of an ecosystem could be stated as a combination of biotic and abiotic components through which energy flows and inorganic material recycles.

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