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A series of chemical reactions carried out
by photoautotrophes. These organisms are
the producers in ecosystems. The process
transfers energy from sunlight and carbon
from inorganic compounds such as carbon
dioxide into food chains. The process
results in biomass. The energy stored is
termed the gross primary production and
net primary production if respiration losses
are taken into account.
Photosynthesis
An ecological unit including the community
of living things and the abiotic factors that
affect them.
ecosystem
A process carried out by bacteria which
convert nitrogen gas into ammonium
compounds. The bacteria can be found
free living in the soil and associated with
legume plants in their roots.
Nitrogen fixation
The mass of organisms at a particular
trophic level in a food chain or web. It is
also used to describe the growth
(production) of organisms.
Biomass
Heterotrophic microorganism that secretes
enzymes into its environment and absorbs
the products of digestion.
Saprophyte
The removal of the amino group from
amino acids to release ammonia and
organic acids which can be used in
respiration. The process is carried out by
putrefying bacteria on excess amino acids.
Deamination
One of the steps in a food chain. It
describes organisms that feed in a similar
way such as producers or primary
consumers.
Tropic level
The loss of nitrate from waterlogged soils
due to anaerobic bacteria using the ion as
an alternative electron final electron
acceptor to oxygen in respiration.
Denitrification
The form of nutrition involving the
digestion and absorption of complex
organic molecules e.g. herbivore, carnivore
and detritivore.
Heterotrophism
The total amount of energy stored in
biomass by photosynthesis or other
autotrophic nutrition.
Gross primary
production
A method of nutrition where simple
inorganic molecules are used to produce
complex organic molecules e.g.
photosynthesis in green plants and
protoctistans.
Autotrophism
A type of heterotrophic nutrition where the
organism takes organic molecules from
another organism which causes it harm
e.g. human tapeworm.
Parasitism
A series of processes converting
ammonium ions first to nitrite ions and
then nitrate ions, making nitrogen available
to plants. The steps are carried out by
bacteria releasing sufficient energy for
them to fix carbon dioxide and produce
organic molecules.
Nitrification
A relationship between two different
species where both benefit in some way
e.g. the alga in a lichen is protected from
desiccation by a fungus which in turn uses
some of the photosynthetic products made
by the alga.
Mutualism
A relationship between two organisms in
which one organism benefits while the
other neither benefits nor is harmed.
Commensalism
The production of ammonia by putrefying
microorganisms as they use excess
proteins from decaying protein.
Ammonification
A sampling area of fixed size used to
quickly and easily provide information
about communities and populations. It is
generally used together with a suitable
randomising system to avoid bias but can
therefore provide unreliable data when an
organism’s distribution isn’t itself random.
quadrat
A systematic sampling method where
samples (usually quadrats) are placed in a
line. It is used to identify changes in space
e.g. the frequency of weeds in relationship
to the distance from a hedge.
transect
A factor caused by the physical
environment such as temperature or pH.
abiotic
A diagram that describes the feeding
relationships of organisms. The diagram
shows the way that energy is passed
between them.
Food chain
A factor caused by the biological
environment such as competition and
predation.
biotic
The number of an organism in a given area
at a given time. It is affected by the impact
of biotic and abiotic factors on birth rate,
death rate and migration.
population
The loss of substrate such as soil from an
ecosystem. This is one of the effects of
loss of soil structure by poorly managed
agriculture and the loss of protective
vegetation such as hedges.
erosion
The place where an organism lives. The
particular set of biotic and abiotic factors in
that place will be matched with
adaptations in the organism.
habitat
Competition for a resource between two
organisms of the same species.
intra-specific
competition
A chemical assessment of organic pollution
in waterways. A sample is fully oxygenated
and then incubated for a set time. The
greater the loss of oxygen due to
respiration of microorganisms, the higher
the degree of organic pollution.
BOD
The amount of energy stored by
autotrophs after respiration losses have
been subtracted.
Net primary
production
Changes to a community with time. The
changes are due to changes to the abiotic
environment by the organisms in the
community which leads to competition
between those organisms and invading
organisms.
succession
The collection of living things present in an
ecosystem. The living things provide the
biotic factors of the ecosystem and are
linked by nutrient cycling and food webs.
Measurements of the number of different
organisms is called diversity.
community
Plants with non-woody stems e.g. grasses.
These plants form an early link in most
successions, out competing pioneer species
but are themselves out competed by
woody species.
herbaceous
Where organisms of different species
compete for the same resource e.g. light,
food and nesting sites.
inter-specific
competition
A chemical that is toxic to organisms that
compete with humans for food. Some
forms create a problem in ecosystems
because they are non-biodegradable and
are accumulate and magnify along food
chains to concentrations that are toxic to
non-pest species.
pesticide
A stable community resulting from a
primary or secondary succession. The form
of the community depends on the
ecosystem’s climate e.g. in the UK it would
be broad-leaved woodland but in the Arctic
circle it would be tundra.
climatic climax
A measurement of the number of species
present in an ecosystem. The value may
change with time e.g. during a succession.
It can be used as an indicator of the level
of damage to an ecosystem by pollution.
diversity
A measurement of the number of a
particular species in an ecosystem. The
value can be given quantitatively e.g. as a
population or qualitatively e.g. using terms
such as rare or frequent giving a relative
indication of number.
abundance
The number of samples in which an
organism is found.
frequency
The increase in nutrient level in aquatic
ecosystems. Such increases may be
associated with a reduction in oxygen level
and damage to communities as a result of
organic or fertiliser pollution.
eutrophication
The build up of non-biodegradable
chemicals in the environment. Such
substances are often fat-soluble and their
concentrations may increase along food
chains until they reach toxic levels.
bioaccumulation
The collection of biotic and abiotic factors
that affect a community of organisms in an
ecosystem.
environment
When a substance can be broken down in
the environment. This generally means
that organisms possess enzymes capable
of the breakdown.
biodegradable
Where an animal kills and feeds on another
animal. The relationship between the
animal and its prey often leads to a cyclical
change in both populations.
predation
The utilisation of a resource can continue
indefinitely without damage to the
ecosystem that provides it.
sustainability
This describes the complete way of life of
an organism. Two different organisms that
share any aspect of their way of life will be
in competition. If the overlap is significant,
one organism will lose and its way of life
will change by natural selection or it will
become extinct.
niche