S3 CfE Biology Summary Notes
Sampling an Ecosystem / Estimating Populations
for example
Quadrats
total area = 100m2
The sample has to be representative
sample area = 1m2
Take random samples (not to any set patterns or bias)
To get a reliable estimate repeat the sampling many times
Know how many times the total area is bigger than the
sample area
The total area is 100 times bigger
than the sample area - so multiply
the sample number by 100 to get a
population estimate.
Population estimate = total area ÷ sample area x average number of organisms in sample
Pitfall traps can be used for sampling small ground living invertebrates
Tullgren funnel - trap designed top trap tiny soil organisms by making them move away from hot dry bright
conditions
Biotic factors are connected to living organisms eg competition, disease, predation, grazing intensity, build
up of waste
Abiotic factors are non-living eg light, moisture, temperature, and pH
Species - organisms which can interbreed and produce fertile offspring
Population - the number of organisms of the same species in an area
Community - all the living organisms living in an area
Habitat - the area where organisms live
Ecosystem - the habitat and community - the area and organisms that live there
Biome - the world's major communities, determined by the vegetation and the adaptations of organisms to
that particular environment eg deserts, tundra, forests, grasslands, aquatic, marine
Be able to identify organisms using a branching key or a paired statement key
Feeding Relationships
The energy transfer in photosynthesis is Light energy  Chemical energy
Producer- an organism that can make it's own food by photosynthesis
Consumer - an organism that eats another organism
Trophic Level - level an organism occupies in a food chain
Food chain - shows the feeding relationship between different living things in a particular environment or
habitat
Food web - a series of interlinked food chains
Arrows in a food chain - show the direction of energy flow in a food chain
Niche describes how an organism or population fits into it's environment - where it lives, what it eats and
what it is eaten by
Biomass is the weight of a living organism (living material)
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S3 CfE Biology Summary Notes
Pyramids of numbers - a diagram to show the numbers of organisms at each level in a food chain
(not
all pyramids of numbers are pyramid shaped)
Pyramids of biomass - a diagram to show the biomass of organisms at each level in a food chain (all
pyramids of biomass are pyramid shaped)
Energy gets lost in a food chain by heat, movement or faeces - this is why pyramids of biomass are always
pyramid shaped
Indicator species are any type of organism (animal / plant) that can be used to show how 'healthy' the
habitat (environment) is.
The Nitrogen Cycle
Organisms need nitrogen for Protein and DNA
Nitrogen gas is very un-reactive
Plants take up nitrogen in the form of nitrate
Nitrogen fixing bacteria convert nitrogen gas into ammonia or nitrate
Nitrogen fixing bacteria can be free living in the soil or live in the root nodules of certain plants (legumes, eg
- peas, beans, clovers)
Nitrifying bacteria convert ammonia into nitrite then into nitrate
Dead organisms and plant and animal waste is decomposed into ammonia by fungi and bacteria
Ammonia or nitrates can also be added to the environment by lightening and by farmers adding fertilisers to
their fields.
Denitrifying bacteria convert nitrate into ammonia and back to nitrogen gas.
Pollution
Waste containing nitrogen compounds can pollute rivers and lakes eg chemical fertilisers, cattle slurry,
sewage
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S3 CfE Biology Summary Notes
Bacteria get their energy from the waste, they use it for growth.
When bacteria grow rapidly they use up the dissolved oxygen in the water. This is known as
eutrophication and as a result fish and other species may die or migrate.
The more organic waste in the river the higher the biological oxygen demand, ie more bacteria will be
growing and using up the available oxygen.
In a river the flow of the current will eventually dilute the organic waste and growing bacteria so the further
downstream from the waste outlet, the more likely the oxygen levels will be normal.
Some species of invertebrates will only live in non polluted water and some will only live in polluted water
(eg indicator species).
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