An ecosystem is a community of living organisms and their physical environment interacting together. It is a physically defined environment made up of two inseparable components: the biotope (abiotic) and the biocenosis (biotic) . The biotope is a particular physical environment with specific physical characteristics such as the climate, temperature, humidity, concentration of nutrients or pH, while the biocenosis includes all the living things (plants, animals, and organisms) in a given area, interacting with each other. Ecosystems can be of different sizes and can be marine, aquatic, or terrestrial. The organisms in an ecosystem are usually well balanced with each other and with their environment.

Ecosystems can be natural or artificial, land-based or water-based. Artificial systems may include a cropland, a garden, a park, or an aquarium. The introduction of new environmental factors or new species can have disastrous results, eventually leading to the collapse of an ecosystem and the death of many of its native species.

The fundamental source of energy in almost all ecosystems is radiant energy from the Sun. The energy of sunlight is used by the ecosystem’s autotrophic, or self-sustaining, organisms (that is, those that can make their own food) . These organisms are capable of photosynthesis, which means they can use the energy of sunlight to convert carbon dioxide and water into simple, energy-rich carbohydrates. The autotrophs use the energy stored within the simple carbohydrates to produce the more complex organic compounds, such as proteins, lipids, and starches, that maintain the organisms’ life processes. Organic matter generated by autotrophs directly or indirectly sustains heterotrophic organisms, which are the consumers of the ecosystem. They use, rearrange, and ultimately decompose the complex organic materials built up by the autotrophs.