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V.C.E. Biology Unit 2
A Web of Interactions
Food Chains
• Food chains describe the feeding relationships within an
ecosystem, showing who eats whom and the direction of
energy flow (indicated by the arrow)
• Producers (autotrophs) – the important first link. These
organisms trap light and chemical energy and convert it
to simple sugars
• Consumers (heterotrophs) – they consume the
producers or each other to receive the energy they need:
• Herbivores – eat only plant material
• Omnivores – eat plant and animal material
• Carnivores – eat only animal material
Food Chains
• Parasites – specialised
consumers who live on and eat
other consumers
• Scavengers – consumers that
eat dead animals
• Detritivores – eat small particle
of dead plant and animal
material
• Decomposers – break down
dead and decaying matter by
secreting enzymes over them
and absorbing the nutrients.
Food Webs
• Food webs display all the different feeding
relationships within an ecosystem.
• Each of the organisms is ranked on a trophic
level. Producers are level 1, herbivores are level
2, first order consumers feeding on the
herbivores are level 3 etc.
• The food chains that make up a food web tend
to have no more than 5 links, as the system is
inefficient and there isn’t enough energy to
sustain more than 5 trophic levels.
Food Webs
Competition
• Organisms tend to compete for available
food, light, water, roosting sites, nesting
sites, mates etc.
• Some organisms are more successful at
competing with other organisms and are
said to limit the distribution of the other
species.
Interaction
• Symbiosis – is a term used to describe
different species living in a close
relationship.
• Mutualism – is a partnership between two
different kinds of organisms that benefits
both of the organisms.
• One example is the clown
fish and the sea anemone.
Interaction
• Commensalism is a relationship whereby
one organism benefits, but the other is
neither harmed nor does it benefit. One
example is that of epiphytic plants that use
other plants for support.
Interactions
• Parasitism is when organism benefits, but
the other is harmed in some way. One
example is the aphid which suck sugar
rich sap from the leaves and stems of
plants.
Interactions
• Pollination – many plants need animals to
help pollinate their flowers and mix up their
pollen and ovules ensuring successful
reproduction and variation of their gene
pool.