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This is based on the OCR A Gateway spec for A level biology, Chapter 23 from module 6.
Specification reference: 6.3.1
Key words for topic
Habitat |
Ecological / environmental area inhabited by particular species. |
Population |
Group of organisms of same species in area. |
Community |
Eco. unit composed of different populations. |
Niche |
Role of an organism in an ecosystem (competition occurs when 2 organisms share a niche). |
All affected by biotic + abiotic factors. |
Biomass transfer
Efficiency at producer level |
Photosynthesis ≠ 100% of sunlight. |
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Net production = gross prod. - respiratory losses |
Efficiency at consumer level |
Not all energy consumed (not all eaten or digested, metabolic heat...). |
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Ecological efficiency = (energy or biomass available after transfer / energy or biomass available before transfer) x 100 |
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Decomposition
Detritivors |
Feed on detritus (dead organic material). |
Saprotrophs |
Secrete enzymes in dead material to digest it. |
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Recycling nitrogen |
Nitrogen necessary for bio molecules, e.g. nucleic acids, amino acids... |
Nitrogen fixation - Nitrogen cannot be used 'raw', so needs to be bonded with other molecules (by Rhizobium and Azotobacter). |
Nitrification - Ammonium compounds converted into nitrogen-containing compounds.
Requires oxygen.
Carried out by Nitrosomonas and Nitrobacter. |
Denitrification - No oxygen --> denitrifying bacteria convert nitrates into N gas. |
Ammonification - Nitrogen into ammonium compounds. |
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Succession key terms
Succession |
Type of living organisms changes over time (in plants, from annual plants to hardwood trees).
Communities become increasingly complex, biodiversity increases. |
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Primary succession - Plants colonise barren land for the first time. |
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Secondary succession - Soil already present, plants grow for first time. |
Seral stages / seres |
Step in succession. |
Defected succession |
Succession halted before climax community.
If caused by human activity, then = plagioclimax. |
Plant succesion
Pioneer community |
Seeds, spores carried by wind, excrement...
Produce many seeds, germinates quickly, fix N2 from atmosphere. |
Intermediate community |
Erosion and decomp. of pioneer species form humus. Can support new species (secondary colonisers).
Tertiary colonisers - When conditions improve. Live with little water. |
Climax community |
Stable, little change over time. |
Distribution v. Abundance
Distribution |
Where organisms are found in an ecosystem. |
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Line or belt transect normally used. |
Abundance |
Number of individuals of a species found in an area. |
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Animals - Capture-recapture.
Plants - Individuals per area. |
Simpson's index of diversity
D = 1-∑(n/N)2 |
D = diversity index
N = total number of organisms in ecosystem
n = number of individuals in each species |
Value between 0-1. Higher value = higher biodiversity. |
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