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Edexcel GCSE Biology Topic 1 - Key Concepts in Biology
Edexcel GCSE Biology Topic 2 - Cells and Control
Edexcel GCSE Biology Topic 3 - Genetics
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Ecosystems and Material Cycles CGP Topic 9
An ecosystem is a biological community of interacting organisms and their physical environment
Interdependence in Organisms
Habitat The place where an organism lives, e.g. a field.
Population All the organisms of one species living in a habitat.
Community All the organisms of different species living in a habitat.
Abiotic factors Non-living factors of the environment, e.g. temperature.
Biotic factors Living factors of the environment, e.g. food.
Ecosystem A community of organisms along with all the non-living (abiotic) parts of their
environment.
1. A fox is an individual organism.
2. It may belong to a population of foxes living in a woodland habitat.
3. The foxes are part of the community of other animals, birds, plants, trees and insects living in the
same habitat.
4. This community, along with abiotic factors such as the soil type, rainfall and light intensity in the
woodland make up the ecosystem.
Organisms depend on each other for things like food and
shelter in order to survive and reproduce. This is known as
interdependence. It means that a change in the population of
one species can have huge knock on effects for other species
in the same community.
e.g. If one organism is removed, others will be affected too.
Mutualism is an example of interdependence in ecosystems. It is a relationship between two organisms
where both organisms benefit.
E.g. Bees visit flowers to get nectar/pollen. And as they move from plant to plant they pollinate the
flowers. Bees get food and flowers get to have sex and produce varied offspring.
Parasitism is another example of interdependence. Parasites live very closely with a host species (e.g. in
or on them). The parasite takes what it needs to survive, but the host doesn't benefit and is often
harmed.
e.g. Fleas are parasites of mammals such as dogs. Fleas feed on their host's blood, but don't offer
anything in return. They can cause serious disease in cats and dogs too.
, Changes to the Ecosystem
Changes to the biotic (living) and abiotic (non-living) factors in an environment will affect everything living
there. For every change there will be winners and losers:
- Some populations will increase, whereas other populations will decrease
- And the distribution of populations may change too while some populations might not change
much at all
Light
Temperature Plants need light for photosynthesis – they
Organisms survive best at certain temperatures. If the are the producers in most ecosystems
temperature changes, some organisms might die but some
might move in from elsewhere. As trees grow and provide more shade,
grasses may be replaced by fungi (or mosses,
As temperatures rise, Britain might become more hospitable to etc.) which are better able to cope with the
species that couldn't survive here before. Certain birds or fish. lower light intensity. Pollution might reduce
While in Australia rising sea temperature might kill corals of the amount of light reaching a habitat.
the great barrier reef.
Pollutants
Pollution refers to the presence of harmful substances in the environment – substances which may have
harmful or poisonous affects
E.g. The number of fish in polluted rivers may decrease.
Lichens can’t survive if the concentration of sulphur dioxide (an air pollutant) is too high. An increase in SO2 from
cars is bad for lichen numbers. But some hardy species might thrive in conditions other organisms can’t tolerate
Predators Water
All organisms have their place in the food chain/food webs. In a All organisms need water to live so a
community containing prey and predators (as most of them do), change in the availability of water usually
the population of any species is usually limited by the amount of has a big effect on communities.
food available.
E.g. daisies grow best in soils that are
E.g. if the number of lions (predators) decreases then the number slightly damp. If the soil becomes
of gazelles (their prey) might increase because fewer of them will waterlogged or too dry, the population of
be eaten by the lions. daisies in that area will decrease.
Competition
There is only a finite amount of each resource (e.g. land, food, mates etc.). And organisms must compete with
each other for access to these resources. Organisms with characteristics enabling them to compete better are
more likely to survive and reproduce – driving evolution
E.g. Red and grey squirrels live in the same habitat and eat the same food. Competition with the grey squirrels for
these resources in some areas means there's not enough food for the reds - the population of red squirrels is
decreasing, partly as a result of this.
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