Food chains,energy and biomass

Revision on food chains, biomass, what plants and animals compete for.

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Food chains, energy and biomass.
Arrows show direction of energy flow.
Sun is where all energy comes from.
Biomass- The dry mass of an organism. The biomass in a particular step in a food chain is always less
than the biomass a step before it. In this food chain there are four steps.
Oak tree Caterpillar Blue tits Sparrow hawk
To draw a PYRAMID of biomass it is wide at the bottom and narrow at the top. The wider the bar the
more biomass there is.
The amount of energy decreases at every step in the food chain. Some energy goes into growth and
for mating, but most of it is used in other ways. Some energy is lost when sunlight is reflected on
leaves, instead of being used for photosynthesis. More energy is lost as respiration through heat and
through excretion.
Habitats have limited resources the organisms in them can only survive, if they compete successfully
with other organisms for these resources.
Animals compete for:
Plants compete for:
(They do not compete for food as they make their own through photosynthesis)
All living things in an ecosystem are interdependent. A change in size of one population will affect all
the other organisms living within that ecosystem. If the prey population in an ecosystem grows then

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Growing predator numbers will eventually reduce the food
supply, to the point where it can no longer sustain the predator population.
Predator-Prey Relationships (recap)
A predator is an organism that eats another organism. The prey is the organism which the predator
eats. Some examples of predator and prey are lion and zebra, bear and fish, and fox and rabbit.…read more


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