Ecosystems Chapter 14

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  • Created on: 22-10-14 17:13

Pyramids of numbers

Pyramids of numbers = relative numbers of each organism at each trophic level

Numbers usually decrease - 90% of energy is used for growth, movement, some is excreted


These are the trophic levels of a pyramid of numbers.    However some pyramids of numbers can be irregular.

There are usually no more than  five trophic levels in a food chain.

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Pyramids of biomass

Pyramids of biomass = quantity of biomass at each trophic level

Biomass is the total  dry quantity or weight of organisms.

Pyramids of biomass are always regular.


The pyramid of numbers is unbalanced and the pyramid of biomass is balanced.

Only around  10% of the energy is transferred to the next trophic level.

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Key terms

Key terms

Producers - plants which photosynthesise to produce food.

Consumers - Animals that eat plants and/or other animals.

Decomposers - Organsims that decay dead material and help to recycle nutrients.

Physical Environment - the sum total of non-biological components in an eco-system - e.g. water

Ecosystem - A distinct, self-supporting system of organisms interacting with each other and their physical environment

Population - All the organisms in a particular species living in an eco-system at any particular time

Community - All the populations of living organisms in an eco-system at any particular time

Habitat - A place where specific organisms live - their home

Quadrats - used to sample the distribution of organisms, or estimate the population size of an organism

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The Water Cycle

1. Heat from sun à evaporation (water) + transpiration (plants) à Water vapour in the air

2. Water vapour à  condensation (clouds) 

3. Clouds à precipitation (rain/snow) [when clouds go over high ground - air cools]

4. Water à run-off into streams + absorbed by plants

5. Run off à  lakes and seas

6. Starts again


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The Carbon Cycle


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The Nitrogen Cycle


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