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A2 Biology Revision Notes Ecosystems and sustainability

Ecosystems

Ecosystem ­ all the living organisms and all the non-living components in a specific habitat, and their
interactions

Ecosystems are dynamic

In most ecosystems, population sizes rise and fall, either very slightly or very noticeably. This is
because the community of living…

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A2 Biology Revision Notes Ecosystems and sustainability

Pyramids of biomass

Each bar within the pyramid is proportional to the dry mass of all organisms at that trophic level. An
ecologist must collect all the organisms within that trophic level and put them in an oven at 80 C until
all…

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A2 Biology Revision Notes Ecosystems and sustainability

Animals can be treated with antibiotics. This means that less energy is used in fighting off
pathogens and more energy is invested in growth.
Animals are often kept indoors in cages and not allowed to move. This means less energy is
used on…

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A2 Biology Revision Notes Ecosystems and sustainability

Randomly position the quadrats across the habitat, using random numbers to plot
coordinated for each one
Take samples at regular distances across the habitat, so you sample every part of the habitat
to the same extent.

Transects

A transect is a line taken…

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A2 Biology Revision Notes Ecosystems and sustainability

Nitrogen-fixing bacteria live freely in the soil and fix nitrogen gas, which is in the air in the
soil, using it to manufacture amino acids
Some of these bacteria also live in the root nodules of plants such as peas and beans. They…

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A2 Biology Revision Notes Ecosystems and sustainability

Competition

Carrying capacity

Carrying capacity ­ the maximum population size that can be maintained over a period of time in a
particular habitat

Predators and prey

A predator is an animal that hunts other animals for food. Predation can act as a limiting…

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A2 Biology Revision Notes Ecosystems and sustainability

more effectively than Paramecium caudatum. Over 20 days, Paramecium caudatum reduced and
died out.

Gause concluded that more overlap between two species' niches would result in more intense
competition. If two species have exactly the same niche, one would be out-competed by the…

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A2 Biology Revision Notes Ecosystems and sustainability

Managing large-scale timber

Large-scale production of wood for timber often involved clear-felling all the trees in one area. This
can destroy habitats on a large scale and is now rarely practised in the UK. Clear-felling the trees
reduces soil mineral levels and leave…

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A2 Biology Revision Notes Ecosystems and sustainability

Natural environments are a valuable source of potentially beneficial resources. Many of the
drugs we use today were discovered in wild plant species
Natural predators of pests can act as biological control agents. This has advantages over the
use of synthetic chemicals, although…

Page 10

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A2 Biology Revision Notes Ecosystems and sustainability

(lonesome George) now lives in the grounds of the Charles Darwin Research Station, which
has begun a captive breeding programme to supplement tortoise numbers
More recent fishing boom for exotic species in the 1990s has left populations seriously
depleted
Depletion of sea cucumber…

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