Ib Ess Definitions

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Abiotic Factor

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A non-living, physical factor that may influence an organism or ecosystem; for example, temperature, sunlight, pH, salinity, precipitation.

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Biochemical Oxygen Demand (BOD)

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A measure of the amount of dissolved oxygen required to break down the organic material in a given volume of water through aerobic biological activity.

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Biodegradable

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Capable of being broken down by natural biological processes; for example, the activities of decomposer organisms.

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Biodiversity

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The amount of biological or living diversity per unit area. It includes the concepts of species diversity, habitat diversity and genetic diversity.

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Biomass

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The mass of organic material in organisms or ecosystems, usually per unit area. Sometimes the term “dry weight biomass” is used where mass is measured after the removal of water. Water is not organic material and inorganic material is usually relatively insignificant in terms of mass.

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Biome

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A collection of ecosystems sharing similar climatic conditions; for example, tundra, tropical rainforest, desert.

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Biosphere

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That part of the Earth inhabited by organisms, that is, the narrow zone (a few kilometres in thickness) in which plants and animals exist. It extends from the upper part of the atmosphere (where birds, insects and wind- blown pollen may be found) down to the deepest part of the Earth’s crust to which living organisms venture.

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Biotic Factor

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A living, biological factor that may influence an organism or ecosystem; for example, predation, parasitism, disease, competition.

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Carrying Capacity

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The maximum number of a species or “load” that can be sustainably supported by a given environment.

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Climax Community

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A community of organisms that is more or less stable, and that is in equilibrium with natural environmental conditions such as climate; the end point of ecological succession.