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Communities and
Ecosystems
Topic 5.1
Assessment Statements
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5.1.1 Define species, habitat, population, community, ecosystem and ecology.
5.1.2 Distinguish between autotroph and heterotroph.
5.1.3 Distinguish between consumers, detritivores and saprotrophs.
5.1.4 Describe what is meant by a food chain, giving three examples, each with at
least three linkages (four organisms).
5.1.5 Describe what is meant by a food web.
5.1.6 Define trophic level.
5.1.7 Deduce the trophic level of organisms in a food chain and a food web.
5.1.8 Construct a food web containing up to 10 organisms, using appropriate
information.
5.1.9 State that light is the initial energy source for almost all communities.
5.1.10 Explain the energy flow in a food chain.
5.1.11 State that energy transformations are never 100% efficient.
5.1.12 Explain reasons for the shape of pyramids of energy.
5.1.13 Explain that energy enters and leaves ecosystems, but nutrients must be
recycled.
5.1.14 State that saprotrophic bacteria and fungi (decomposers) recycle nutrients.
Species – a
group of
organisms
that can
interbreed
and produce
fertile
offspring
• Habitat – the
environment in
which a species
normally lives or the
location of a living
organism
• Population – a
group of organisms
of the same species
which live in the
same area at the
same time
• Community – a
group of populations
living and interacting
with each other in
an area
• Ecosystem – a
community and its
abiotic environment
• Ecology – the study
of relationships
between living
organisms and
between organisms
and their
environment
What is meant by
‘environment’?
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Hydrosphere
Atmosphere
Lithosphere
Biosphere
• What is the difference between abiotic
components of the environment and the biotic
components?
Distinguish between autotroph
and heterotroph.
• Autotrophs are capable of making their own
organic molecules from inorganic molecules
as a food source (a.k.a. producers);
Examples?
• Heterotrophs – cannot make their own food
and must obtain organic molecules from other
organisms (a.k.a. consumers); Examples?
Distinguish between
consumers, detritivores and
saprotrophs.
• Detritivores – eat non-living organic
matter; Examples?
• Saprophytes – live on or in non-living
organic matter secreting digestive
enzymes into it and absorbing the
products of digestion; Examples?
Describe what is meant by a food chain,
giving three examples, each with at least
three linkages (four organisms).
• A sequence showing the feeding relationships
and energy flow between species
• The direction of each arrow shows which way
the energy flows
• grass→grasshoppers→toad→snake→hawk
Describe what is meant by a
food web.
• An interconnecting series of food chains
Define trophic level.
• An organism’s position
in a food chain
• Classifies organisms’
feeding relationships
with each other within
the same ecosystem
• T5 – quaternary
consumer
• T4 – tertiary consumer
• T3 – secondary
consumer
• T2 – primary consumer
• T1 – producer
Which group would you
expect to have the most
number of organisms?
Deduce the trophic level of
organisms in a food chain and
a food web.
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4.
Find the producer
Determine what eats
the producer (primary
consumer)
Determine what eats
the primary consumer
(secondary
consumer)
Etc.
• Deduce the trophic level
of organisms from the
following list:
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Juvenile trout
Kingfisher
Algae
Mayfly larva
Construct a food web containing
up to 10 organisms, using
appropriate information.
• Put producer at bottom of diagram
(algae or plants)
• Above producers include all the primary
consumers
• Continue until you get to the top
predator
State that light is the initial
energy source for almost all
communities.
• Example:
– Milk gets its energy from the cow which
produced it
– The cow got its energy from grass, which
got its energy from sunlight
• Name a food chain that can start
without sunlight.
Explain the energy flow in a
food chain.
• Light energy absorbed by producers
• Chemical energy obtained by
photosynthesis is stored as
carbohydrates
• Energy is transferred from one
organism to the next when
carbohydrates, lipids, or proteins are
digested
• During cellular respiration energy is lost
as heat to the environment
State that energy
transformations are never
100% efficient.
• Only chemical energy can be used by the
next trophic level
• Only a small amount of the energy which an
organism absorbs is converted into chemical
energy
• No organism can use 100% of the energy
present in the organic molecules of the food it
eats
• Only 10-20% of the energy is used from the
previous step in the food chain
• Reasons for non-absorption
– Not all of the organism is consumed
– Not all the food can be absorbed
– Some organisms die before being eaten
– Considerable heat loss due to cellular
respiration at all levels
Explain reasons for the shape
of pyramids of energy.
• Energy pyramid used to
show how much and
how fast energy flows
from on trophic level to
the next in a community
• Units used are energy
per unit area per unit
time (kJm-2y-1)
• Because energy is lost
each level is always
smaller than the one
before it
• Organisms cannot
create energy
Explain that energy enters
and leaves ecosystems, but
nutrients must be recycled.
• Once energy has been radiated into the
environment, it cannot be collected back and
used as an energy source by the ecosystem
• Energy enters as light, exits as heat
• Nutrients, however, must be recycled
• Minerals and compounds are used to build
cells which are locked within the organism
until eaten or decomposed
State that saprotrophic
bacteria and fungi
(decomposers) recycle
nutrients.
• Decomposers unlock nutrients stored in
cells of plants and animals through
decay
• Digestive enzymes convert the organic
matter into a more usable form for
themselves and for other organisms