Ecosystems OCR A2 Biology F215

Keywords and quick revision of ecosystems has pictures :)

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Biology F215
Key Words
Key Term Definition
Abiotic factors The non-living components of an ecosystem.
Abundance The number of individuals of a species
Biotic factors The living components of an ecosystem.
Organism that makes its own complex organic molecules using simple inorganic
molecules, such as carbon dioxide and water, and chemical potential energy.
Climax community The final, stable stage in succession, typically woodland
All the populations of different species that live in the same place at the same time,
and who can interact with each other.
Consumers Living organisms that feed on other living organisms.
Organisms that feed on dead organic matter, releasing molecules, minerals and
energy that then become available to other living organisms in that ecosystem.
Distribution The presence or absence of a species from certain locations
All the living organisms and all the non-living components in a specific habitat, and
their interactions.
The ability to do work.
Rapid growth in algae, in water, that leads to oxygen depletion when algae are
Eutrophication decomposed by aerobic bacteria.
Habitat The place where an organism or population of organisms lives.
Plant of bean family which forms a mutualistic relationship with nitrogen-fixing
bacteria in root nodules.
Mutualism A relationship between two organisms from which both benefit.
Niche The role that a species plays in an ecosystem.

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Conversion of nitrogen gas into a form that is usable by plants, such as nitrate or
Nitrogen fixation
ammonium ions.
Organism that makes its own food using simple inorganic molecules, such as
carbon dioxide and water, and light energy.…read more

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What is an ecosystem?
An ecosystem is all the living organisms and non-living components of their environment occurring
together, and the interactions between them
o An ecosystem is a relatively self-contained, interacting community of living organisms (biotic
component) and their environment
(abiotic component)
E.g. all the community of
organisms living in the deciduous
woodland and all aspects of the
environment as well (e.g.…read more

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Topography (altitude/slope/aspect)
Catastrophes (flood/fire/frost)
Biotic factors
o Due to other organisms
Infection by pathogens or parasites
Competition between organisms for limited resources
(food, space, mates)
How is energy linked to ecosystems?
No ecosystem is entirely self-contained
o Energy flows though ecosystems
Enters ecosystems as light
energy used in
o Leaves as heat energy
Nutrients are recycled
within an ecosystem
Producers (e.g.…read more

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What are trophic levels?
The level at which an organism feeds is called its trophic
o Indicates its position in the food chain/web
Shows its main source of energy
What are food webs?
Consumers may be part of several food chains
o They may feed at different trophic levels in different
food chains
A food web shows all the trophic relationships
between organisms in a community
Contains many interconnecting food
How is energy lost in food chains?
Energy is lost at each stage…read more

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Light energy that is used in photosynthesis is stored as chemical energy in organic
Almost 50% is used by plants in respiration to generate ATP
o Only if the energy is used for the synthesis of plant tissues is the
chemical energy potentially available to the primary consumer
What is a pyramid of numbers?
The area of the bars represents the number of organisms at
each trophic level
o However there are limitations to this system
Organisms are different sizes
Pyramid of numbers does…read more

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Measured in kJm-2year-1
Secondary productivity is the transfer of energy from producers to consumers
Gross primary productivity (GPP) is the total energy converted by plants
o Some of the energy assimilated by plants will be lost as heat from respiration
Net primary productivity (NPP) is the energy which remains in tissues after the plant has
supplied its own needs in respiration (R)
NPP is the rate of production of new biomass available for consumption by
o NPP= GP- R
How can primary productivity be…read more

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They obtain nutrients from non-living organic matter by secreting enzymes on to the dead or
waste material
Extracellular digestion occurs and the soluble products are absorbed
They can then be used for growth, respired or stored
What is the nitrogen cycle and nitrogen fixation?
Air is 78% nitrogen (N2)
o It is uUnreactive and cannot be used by most organisms
It must first be converted into ammonium (NH4+) or nitrate (NO3-)
This process called nitrogen fixation
o Nitrogen fixation is done by Rhizobium
Bacteria may…read more

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Ammonium ions are then oxidised to nitrite ions (NO2-) by Nitrosomonas bacteria
Nitrites are oxidised to nitrate ions (NO3-) by Nitrobacter bacteria
These nitrifying bacteria are chemoautotrophs since they obtain energy from
oxidation reactions
o Nitrification only takes place under aerobic conditions in well aerated soil
What is denitrification?
Denitrification takes place under
anaerobic conditions e.g.…read more

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Nitrifying bacteria that convert ammonium ions into nitrate ions are aerobic and require well-aerated soil,
so will not survive in waterlogged soil
o Whereas denitrifying bacteria that remove nitrates from the soil, are anaerobic and can survive in
waterlogged soil
Why are very wet soils usually nitrogen-deficient and how the sundew is at a competitive advantage in such
Wet soils are under anaerobic conditions
o These conditions encourage denitrifying bacteria
Which can convert nitrate ions to (gaseous) nitrogen
This reduces available nitrogen ;
o…read more


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