Ecosystem: the organisms of a particular habitat together with the physical environment in which they live - for example, a tropical rainforest.  

Species: a group of individuals of common ancestry that closely resemble each other and are normally capable of interbreeding to produce fertile offspring. 

Population: a group of organisms of the same species that live in the same area at the same time.

Community: a group of populations of organisms living and interacting within a habitat. 

Abiotic factors: aspect of the environment that is not living - for example, humidity, temperature, salinity, wind, soil particles.
Biotic factors: the biological influences and factors on organisms in an ecosystem

Ecology: the study of the relationships between living organisms and their environment, including both the physical environment and the other organisms that live in it.

Autotrophs: organism able to make its own food from simple inorganic materials and an energy source.

Heterotrophs: an organism that feeds on organic molecules.

Consumers: an organism that feeds on another organism.

Detritivores: an organism that feeds on dead organic matter through ingestion.

Saprotrophs: organism that feeds on dead organic matter through absorption. 

Decomposers: organism that feeds on dead plant and animal matter so that it can be recycled; most decomposers are microorganisms. 

Mesocosm: A small-scale, self-sustaining natural system that can be used to study part of an ecosystem under controlled conditions. 

Symbiotic relationship: ‘living together’ - includes commensalism, mutualism and parasitism.