A series of chemical reactions carried out by photoautotrophes. These organisms are the producers in ecosystems. The process transfers energy from sunlight and carbon from inorganic compounds such as carbon dioxide into food chains. The process results in biomass. The energy stored is termed the gross primary production and net primary production if respiration losses are taken into account.

Photosynthesis

An ecological unit including the community of living things and the abiotic factors that affect them.

ecosystem

A process carried out by bacteria which convert nitrogen gas into ammonium compounds. The bacteria can be found free living in the soil and associated with legume plants in their roots.

Nitrogen fixation

The mass of organisms at a particular trophic level in a food chain or web. It is also used to describe the growth (production) of organisms.

Biomass

Heterotrophic microorganism that secretes enzymes into its environment and absorbs the products of digestion.

Saprophyte

The removal of the amino group from amino acids to release ammonia and organic acids which can be used in respiration. The process is carried out by putrefying bacteria on excess amino acids.

Deamination

One of the steps in a food chain. It describes organisms that feed in a similar way such as producers or primary consumers.

Tropic level

The loss of nitrate from waterlogged soils due to anaerobic bacteria using the ion as an alternative electron final electron acceptor to oxygen in respiration.

Denitrification

The form of nutrition involving the digestion and absorption of complex organic molecules e.g. herbivore, carnivore and detritivore.

Heterotrophism

The total amount of energy stored in biomass by photosynthesis or other autotrophic nutrition.

Gross primary production

A method of nutrition where simple inorganic molecules are used to produce complex organic molecules e.g. photosynthesis in green plants and protoctistans.

Autotrophism

A type of heterotrophic nutrition where the organism takes organic molecules from another organism which causes it harm e.g. human tapeworm.

Parasitism

A series of processes converting ammonium ions first to nitrite ions and then nitrate ions, making nitrogen available to plants. The steps are carried out by bacteria releasing sufficient energy for them to fix carbon dioxide and produce organic molecules.

Nitrification

A relationship between two different species where both benefit in some way e.g. the alga in a lichen is protected from desiccation by a fungus which in turn uses some of the photosynthetic products made by the alga.

Mutualism

A relationship between two organisms in which one organism benefits while the other neither benefits nor is harmed.

Commensalism

The production of ammonia by putrefying microorganisms as they use excess proteins from decaying protein.

Ammonification

A sampling area of fixed size used to quickly and easily provide information about communities and populations. It is generally used together with a suitable randomising system to avoid bias but can therefore provide unreliable data when an organism’s distribution isn’t itself random.

quadrat

A systematic sampling method where samples (usually quadrats) are placed in a line. It is used to identify changes in space e.g. the frequency of weeds in relationship to the distance from a hedge.

transect

A factor caused by the physical environment such as temperature or pH.

abiotic

A diagram that describes the feeding relationships of organisms. The diagram shows the way that energy is passed between them.

Food chain

A factor caused by the biological environment such as competition and predation.

biotic

The number of an organism in a given area at a given time. It is affected by the impact of biotic and abiotic factors on birth rate, death rate and migration.

population

The loss of substrate such as soil from an ecosystem. This is one of the effects of loss of soil structure by poorly managed agriculture and the loss of protective vegetation such as hedges.

erosion

The place where an organism lives. The particular set of biotic and abiotic factors in that place will be matched with adaptations in the organism.

habitat

Competition for a resource between two organisms of the same species.

intra-specific competition

A chemical assessment of organic pollution in waterways. A sample is fully oxygenated and then incubated for a set time. The greater the loss of oxygen due to respiration of microorganisms, the higher the degree of organic pollution.

BOD

The amount of energy stored by autotrophs after respiration losses have been subtracted.

Net primary production

Changes to a community with time. The changes are due to changes to the abiotic environment by the organisms in the community which leads to competition between those organisms and invading organisms.

succession

The collection of living things present in an ecosystem. The living things provide the biotic factors of the ecosystem and are linked by nutrient cycling and food webs. Measurements of the number of different organisms is called diversity.

community

Plants with non-woody stems e.g. grasses. These plants form an early link in most successions, out competing pioneer species but are themselves out competed by woody species.

herbaceous

Where organisms of different species compete for the same resource e.g. light, food and nesting sites.

inter-specific competition

A chemical that is toxic to organisms that compete with humans for food. Some forms create a problem in ecosystems because they are non-biodegradable and are accumulate and magnify along food chains to concentrations that are toxic to non-pest species.

pesticide

A stable community resulting from a primary or secondary succession. The form of the community depends on the ecosystem’s climate e.g. in the UK it would be broad-leaved woodland but in the Arctic circle it would be tundra.

climatic climax

A measurement of the number of species present in an ecosystem. The value may change with time e.g. during a succession. It can be used as an indicator of the level of damage to an ecosystem by pollution.

diversity

A measurement of the number of a particular species in an ecosystem. The value can be given quantitatively e.g. as a population or qualitatively e.g. using terms such as rare or frequent giving a relative indication of number.

abundance

The number of samples in which an organism is found.

frequency

The increase in nutrient level in aquatic ecosystems. Such increases may be associated with a reduction in oxygen level and damage to communities as a result of organic or fertiliser pollution.

eutrophication

The build up of non-biodegradable chemicals in the environment. Such substances are often fat-soluble and their concentrations may increase along food chains until they reach toxic levels.

bioaccumulation

The collection of biotic and abiotic factors that affect a community of organisms in an ecosystem.

environment

When a substance can be broken down in the environment. This generally means that organisms possess enzymes capable of the breakdown.

biodegradable

Where an animal kills and feeds on another animal. The relationship between the animal and its prey often leads to a cyclical change in both populations.

predation

The utilisation of a resource can continue indefinitely without damage to the ecosystem that provides it.

sustainability

This describes the complete way of life of an organism. Two different organisms that share any aspect of their way of life will be in competition. If the overlap is significant, one organism will lose and its way of life will change by natural selection or it will become extinct.

niche