BRAINCAKEEcosystems
Revision notes for Ecosystems in OCR Biology A (H420). Read the start of any lesson here, then sign in free for the whole lesson, the R.E.C.I.P.E. recall steps and the quiz.
- EcosystemsAn ecosystem is all the living organisms in a particular area, interacting with each other and with the non-living (physical and chemical) parts of…
- Biotic FactorsBiotic factors are the living parts of an ecosystem that affect other organisms.
- Abiotic FactorsAbiotic factors are the non-living, physical and chemical, conditions of an ecosystem.
- Producers and ConsumersOrganisms in an ecosystem can be grouped by how they obtain their energy and nutrients.
- Trophic LevelsA trophic level is the position an organism occupies in a food chain, that is, its feeding level. • Trophic level 1: producers • Trophic level 2…
- Biomass TransferBiomass is the mass of living material in an organism or a trophic level.
- Ecological EfficiencyEcological efficiency is the efficiency with which biomass or energy is transferred from one trophic level to the next.
- Calculating Efficiency of Biomass TransferEcological efficiency can be calculated for any transfer, as long as both values are in the same units (biomass or energy, per unit area per year).…
- Human Activities and Biomass TransferFarming is about manipulating biomass transfer, so that as much of the energy captured by producers as possible ends up in food for humans.
- DecomposersDecomposers are organisms that break down dead organisms, faeces and other waste, releasing inorganic nutrients back into the environment.
- The Nitrogen CycleNitrogen is needed to make amino acids, proteins, nucleic acids (DNA and RNA) and ATP.
- Nitrogen-Fixing BacteriaNitrogen fixation is the conversion of nitrogen gas (N2) into ammonia (NH3), which dissolves in soil water to form ammonium ions (NH4+).
- Nitrification and DenitrificationNitrification Nitrification is the conversion of ammonium ions into nitrate ions.
- The Carbon CycleCarbon is found in all organic molecules: carbohydrates, lipids, proteins and nucleic acids.
- SuccessionSuccession is the progressive change in a community of organisms in an area over time.
- Primary SuccessionPrimary succession is succession that starts on newly formed or newly exposed land where there is no soil, for example bare rock after a volcanic…
- Secondary SuccessionSecondary succession is succession on land where a community has been removed or destroyed but the soil remains.
- Deflected SuccessionSuccession does not always reach its natural climax community.
- Sampling Distribution and AbundanceIt is almost never possible to count every organism in an area, so ecologists take samples and use them to estimate the whole population.
- Quadrats and TransectsQuadrats are used to sample plants and slow-moving or sessile animals.
- Measuring Abiotic Factors in the FieldThe distribution of organisms is strongly affected by abiotic factors (the non-living conditions of a habitat).