Biotic and Abiotic Factors

Edexcel Unit 4

Biotic and Abiotic Factors

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Biology Unit 4
Revision Notes
Topic 5: On the wild side
10. Explain that the numbers and distribution of
organisms in a habitat are controlled by biotic and
abiotic factors.
Abiotic factors
Abiotic factors are the non-living elements of the habitat of an organism. They include:
Light
The amount of light in a habitat (the solar energy input) has a direct effect on the number
of organisms found there
Plants depend on light for photosynthesis, so any plan populations which are going to
thrive in habitats with low light levels must be able to cope with this factor
Temperature
For any particular organism, there is a range of temperatures within which it can grow
and successfully reproduce.
Temperature of the environment particularly affects the rate of enzyme-controlled
reactions in plants and ectothermic animals
Wind and Water currents
Wind increases water and heat loss from the body and so adds to the environmental
stress an organism has to cope with
In water currents, organisms have to flow with the current, be strong swimmers or be
able to hang on tight and resist the force of the water
Water availability
Amount of water is affected by several factors: amount of precipitations, rate of
evaporation and edaphic factors
Water is vital for living organisms
An increase in the availability of water can lead to a huge change in a habitat and to a
massive increase in population size of some organisms
Oxygen availability
Oxygen can be in short supply in both water and in the soil
When water is cold, or fast flowing, sufficient oxygen dissolves in it to support life
If the temperature of the water rises, or it becomes still and stagnant, then the oxygen
content will drop, making it a much more difficult habitat
The space between the soil particles contains air so there is plenty of oxygen for the
respiration of plant roots. In waterlogged soil, the plant roots may be deprived of
oxygen
Edaphic factors: soil structure and mineral content
Sand has a loose, shifting structure that allows very little to grow on it. The soil is light,
easily worked and easily warmed, but also easily drained. Water passes through them
rapidly, leaching minerals from the soil which may be needed by plants
It is difficult for water to drain through soils that are made up of tiny clay particles. They
are heavy, take longer to warm up, are hard to work and are easily waterlogged
Loam is the ideal soil. It has particles of a wide range of sizes. Its heavier and less prone
to leaching than sandy soils, yet easier to warm and work than clay
Text Book: p. 18, 24 - 29

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Biology Unit 4
Revision Notes
Biotic factors
Biotic factors are the living elements of a habitat which affect the availability of a group of
organisms to survive there.…read more

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