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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…

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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.

The collection of species that is able to first colonise…

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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…

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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…

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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…

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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


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o 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…

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o 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)…

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o 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?…

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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…


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