Unit 1
Communication, Homeostasis and Energy
Module 3: Ecosystems and Sustainability
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Define the term ecosystem.
State that ecosystems are dynamic
systems.
Define the terms biotic factor and
abiotic factor, using named examples.
Define the terms producer, consumer,
decomposer and trophic level.
Describe how energy is transferred
though ecosystems.
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Ecology
 The study of how whole communities of living
organisms interact with each other and with their
environment.
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Ecosystem
 A relatively self-contained, interacting community
of organisms, and the environment in which they
live and with which they interact.
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Habitat
 The place where an organism lives
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Population
 The number of individuals of the same
species, living in the same place at the
same time.
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Community
 All the organisms, of all the different
species living in a habitat.
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Niche
 The role of an organism in the ecosystem.
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Flow of energy
 Energy flows
▪ into an ecosystem from outside
▪ through an organism in the ecosystem
▪ leaves the ecosystem
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Recycling of materials
 Matter cycles round an ecosystem, where
some atoms are reused over and over
again by different organisms.
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Biotic factors involve other living
organisms
 Feeding of herbivores on plants
 Predation
 Parasitism
 Mutualism
 competition
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Abiotic factors involve the non living
components of the environment
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Temperature
Light intensity
Oxygen concentration
Carbon dioxide concentration
Water supply
pH
Availability of inorganic ions
Edaphic features
Atmospheric humidity
Wind speed
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Living
organisms
need a
constant supply
of energy to
drive metabolic
reactions and
to stay alive.
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A food chain shows the way in which
energy flows from producer to
consumers
Arrows indicate the direction that the
energy flows
Oak tree caterpillar  great tit  sparrowhawk
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Each position along the food chain is
called a trophic level
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A food web
shows all the
different
interrelationships
between many
food chains.
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The role of decomposers in the
ecosystem is to feed on detritus
 Detritus is organic matter in dead
organisms and waste material
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Decomposers include
 Bacteria
 Fungi
 Detritivores
▪ Earthworms etc
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When energy is transferred from one form to
another, some energy is always lost as heat
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Less than 3% of
sunlight is
converted to
chemical energy
 Sunlight missing
leaves
 Reflection of light
 Transmission of light
 Not all the light
absorbed is used for
photosynthesis
1o = primary
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Productivity
 rate at which the plant converts light
energy into chemical potential energy
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Gross 1o Productivity (GPP)
 total quantity of energy converted by
plants in this way
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Net 1o Productivity (NPP)
 energy which remains as chemical energy
after plants have supplied their own needs
in respiration
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Only about 10% of the energy in plants
gets passed on to the animals that eat
them.
 half of the chemical energy in plants is
used by the plants themselves (respiration)
 not all the parts of the plants are eaten
 not all the parts eaten are digestible
 energy loss as heat from digestive system
as food is digested
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Classify each of these features as biotic or
abiotic
 The speed of water flow in a river
 The density of seaweed growing in a rock pool
 The oxygen availability on a high altitude
mountainside
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Energy losses from mammals and birds tend
to be significantly greater than from other
organisms. Suggest why this is.
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Outline how energy transfers between
trophic levels can be measured.
Discuss the efficiency of energy
transfers between trophic levels.
Explain how human activities can
manipulate the flow of energy through
ecosystems.
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Pyramid of biomass
 Area of the bars is proportional to the dry
mass of all the organisms at that trophic
level
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Pyramid of energy
 Bars represent energy available
 Organisms are burned in a calorimeter
and the amount of heat energy released
per gram is worked out.
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Net Primary productivity (NPP) is the
difference between primary
productivity and respiratory head (R)
NPP is the rate of production of
biomass available for heterotrophs
By manipulating environmental
factors, humans can increase NPP.
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Increasing light levels
Increase water availability
Maintain a constant temperature
Provide the correct nutrients required
for photosynthesis and growth
Pest control
Disease control
Remove competition
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Manipulating the energy from producer to
consumer
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Harvest animals before adulthood
Treat with steroids
Selective breeding
Treat with antibiotics
Maintain constant temperature
Limit movement
Supply food
A balance needs to lie between animal
welfare and efficient food production.
Gradual change in a
community over a period of
time
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Describe one example of primary
succession resulting in a climax
community.
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Succession
Pioneer community
Climax community
Seral stages
Sere
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Succession
 Gradual directional change in a
community of organisms over time
 its unidirectional
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Primary succession
 Original area has no soil or living organisms
present
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Secondary succession
 Following disturbance of the area, soil is
present.
New land is formed on the Earth’s surface at
river deltas, at sand dunes and from cooled
volcanic lava.
 When new land is exposed it is invaded and
colonised by plants, a sequence of
communities develops over time by Primary
succession
 Secondary succession is the colonisation of
an area that has been previously occupied
and become barren.
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The gradual replacement of one plant
community by another over a period
of time, through a series of seral
stages, starting with the pioneer
community and ending with a climax
community.
The first plants to colonise an area are
pioneer plants, which are adapted to
survive in difficult conditions.
 These are usually mosses or grass
 As they grow these plants change the
environmental conditions until they are no
longer the best suited.
 Better adapted plants start to colonise.
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Suggest and explain what happens to
each of the following during the
process of succession.
 The number of different species in the
community
 The quantity of biomass per unit area
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Plants colonise an area, they change
it in such a way that they are no
longer the best adapted to survive
there and are out competed, new
plants then colonise the area.
Pioneer
community
Climax
community
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In the early stages of succession,
abiotic factors are important in
determing what can survive.
 Availability of water
 Availability of nutrients in the soil
 Wind exposure
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Clearing of deciduous woodland for
 Agriculture
 Conifer forestry
 Human settlement
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Intensive grazing by sheep can deflect
succession from a forest climax
community to grassland.
A deflected climax community is
known as a plagioclimax
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Describe how the distribution and
abundance of organisms can be
measured, using line transects, belt
transects, quadrats and point
quadrats.
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We can use the distribution of the
communities in space on the ground
to show us what they look like at
different times during a succession
 Examples
▪ Retreating glacier (Glacier Bay, Alaska)
▪ Sand dunes
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Plant and animal communities can be
sampled using
 Point quadrats
 Quadrats
 Transects
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Transects are the best way showing
succession
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Line transect
 Record what is touching the tape
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Belt transect
 Quadrats are placed alongside the tape
 Continuous belt transect
▪ Record along the whole length of the tape
 Interrupted belt transect
▪ Record at intervals along the tape
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Distribution
 Presence or absence of each species
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Abundance
 Estimate or count the number of
individuals
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Percentage cover
Population size of
a species
=
Mean number of
individuals of the species
in each quadrat
Fraction of the total habitat
area covered by a quadrat
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Describe the role of decomposers in
the decomposition of organic
material.
Describe how micro-organisms recycle
nitrogen within ecosystems
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Nutrient cycling
 Provides elements for
▪ metabolic processes
▪ Constructing organic molecules
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Decomposition
 Provides mineral and nutrients for
metabolism
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Decomposers
 Bacteria and fungi
 Absorb organic nutrients from dead
organisms and waste from living
organisms, converting them into inorganic
molecules
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Detritivores
 Organisms living in or on the soil that feed
and gain nutrients from detritus.
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Breakdown of dead organic matter
with release of inorganic nutrients into
surrounding soil
Litter
decomposition
Humus
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Factors
 Type of organic matter present
 Number and types of decomposers and
detritivores
 Environmental conditions
▪ Temperature
▪ O2 content
▪ moisture
Nutrients in
environment
decomposition
decomposers
consumers
producers
The carbon cycle
Carbon dioxide
In the air (CO2)
photosynthesis
respiration
Combustion
(burning)
Fossil fuels
Coal, oil, gas, peat
feeding
Carbon compounds
in plants
Carbon
compounds
in animals
decay
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Most nutrient cycles have two components
 Geochemical
 Biological
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Cycling of Nitrogen
 Nitrogen fixation
 Assimilation
 Ammonification
 Nitrification
 denitrification
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Nitrogen gas converted to nitrogencontaining compounds.
Three ways – all require energy
 Lightning
▪ nitrogen + oxygen  oxides of nitrogen
 Industrial processes
▪ Haber process – combine hydrogen and
nitrogen to form ammonia
 Fixation by micro-organisms
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Free-living nitrogen fixers
 Bacteria reduce nitrogen to ammonia
 Used to manufacture amino acids
 Nitrogen rich compounds released when
die and decay.
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Mutualistic nitrogen fixers
 E.g. Rhizobium
 Live in root nodules of leguminous plants
 Nitrogenase converts N2 to NH4+ using H+
and ATP
 Requires anaerobic conditions
(leghaemoglobin)
 Plant uses ammonium ions to make amino
acids
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Nitrogen assimilated in the form of
ammonium ions
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Nitrate ions reduced to nitrite ions and then
ammonium ions.
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Animals assimilate nitrogen in the form of
protein
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Production of ammonium-containing
compounds
 E.g urea, protein, nucleic acids and
vitamins
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Decomposers feed on these releasing
ammonia
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Two stages
 Oxidation of ammonium ions to nitrites
▪ Nitrosomonas
 Oxidation of nitrites to nitrates
▪ Nitrobacter
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Anaerobic denitrifying bacteria
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Reduce soil nitrates into nitrogen gas
NO3-  NO2-  N2O 
N2
Nitrogen in atmosphere (N2)
Nitrogen-fixing
bacteria in root
nodules of
legumes
animals
Plants
assimilation
Decomposers
(aerobic and
anaerobic bacteria
and fungi)
ammonification
Nitrogen-fixing
soil bacteria
Ammonium
(NH4+)
Denitrifying
bacteria
Nitrates
(NO3-)
Nitrobacter
Nitrification
Nitrosomonas
Nitrites
(NO2-)