B1.4 Interdependence and Adaptation

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Organisms are well advised to survive in their normal environments. Population size depends on variety of factors including competition, predation, disease and human influences. Changes in the environment may affect the distribution and behaviour of organisms.

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Survival and Competition


  • To survive, organisms require a supply of materials from their surroundings and from the other living organisms there
  • Organisms live, grow and reproduce in places where, and at times when , conditions are suitable


Animlas often compete with eachother for:

  • Food
  • Mates
  • Territory

Plants often compete with eachother for:

  • Light
  • Water from the soil
  • Nutrients from the soil
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  • Organisms have features (adaptations) which enable them to survive in the conditions in which they normally live
  • The organisms that are best adapted to make use of their resources in a habitat are more likely to survive and increase in numbers

For example:

  • To be able to obtain a certain food better
  • To make it more difficult for predators to catch them
  • To survive in extreme climates, e.g. the artic or deserts
    - Plants lose water vapour from the surface of their leaves
    - It is essential that they have adaptations which minimise this
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Extreme Adaptations

  • Extremophiles are organisms that live in extreme environments
  • Some may be tolerent to high levels of salt, high temperature or high pressures
  • Animals and Plants may be adapted to cope with specific features of their environments e.g. thorns, poisons and warning colours to deter predators

Extreme Animals

Animals may be adapted for survival in dry and artic environment by means of:

  • changes to surface area
  • thickness of insulating coat
  • amount of body fat
  • camouflage
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Extreme Animals

Example - Camel

  • The camel can go without food and water for 3 to 4 days
  • Fat stored in their humps provides long term food reserve, and a supply of metabolic water
  • The fat is not distributed around the body; this reduces insulation, allowing more heat loss
  • They are tall and thin, increasing their surface area to volume ratio, increasing heat loss by radiation

Example - Polar Bear

  • Polar bear has thick fur and fat beneath its skin to insulate it 
  • Their large, furry feet help them distribute their weight as they walk on thin ice
  • They are white which camouflages them against the snow. This helps them to hunt
  • They are compacted in shape, reducing their surface area to volume ratio; this reduces heat loss by radiation
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Extreme Plants

Plants may be adapted to survive in dry environments by means of:

  • changes to surface area, particlarly of the leaves
  • water-storage tissues
  • extensive root systems
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Extreme Plants

Example - Desert Plants

  • E.g. the cactus, require very little water to survive
  • Leaves are spines
  • Spines guard against most browsing herbivorous animals
  • Spines also reduce their surface area, reducing water loss by evaporation
  • A thick waxy coating surrounds the plant to reduce to reduce evaporation
  • Fewer 'stomata' to reduce water loss
  • Roots tend to spread sideways to catch rain

Example - Actic Plant

  • Many of the plants are small, growing close to the ground and very close together to avoid the wind and conserve heat
  • Some posses a light, fuzzy covering to insulate the buds so they can grow
  • Many are dark colours of blue and purple to absorb heat from the sunlight even during the winter months
  • Because of the cold and short growing seasons, artic plants grow very slowly
  • Some grow for ten years before they produce any buds for reproduction
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Microorganisms have adaptations that enable them to survive in different environments. Slime capsule(layer) around some bacterial cell wall sticks them to surfaces and prevents them drying out.

Some have the ability to form spores to survive when conditions are harsh. Some microorganisms have flagella which enable them to move around quickly. 

Bacteria undergo rapid reproduction which conditions are favourable. Some bacteria can survive extreme conditions:

  • Temperatures as little as -15°C to as high as 121°C
  • pH values of 0.0 to 12.8
  • High levels of pressure deep in the oceans
  • High salt concentrations
  • Very dry conditions
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Environmental Change

Changes in the environment affect the distribution of living organisms. For example, the changing distribution of some bird species and the disappearance of pollinating insects including bees. Animals and plants are subjected to environmental changes. Such changes may be caused by living and non-living factors.

Non-living (abiotic) factors:

  • Light
  • Oxygen
  • Water
  • Temperature

Living (biotic) factors:

  • Food
  • Predation
  • Grazing
  • Disease
  • Competition - for: food, light, water, space
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Living organisms can be used as indicators of poll

  • Lichens are symbiotic associations of algae and fungi species that attach to tree trunks and rock
  • They are sensetive to changes in air quality
  • They are very sensetive to sulphur dioxide (SO2) pollution in the air
  • This is released from industry and burning fossil fuels, especially coal
  • Lichens absorb sulphur dioxide dissolved in water
  • It destroys the chlorophyll in the algae preventing it from photosynthesising and killing the lichen
  • Some species only grow in non-polluted air
  • Some species grow in polluted air
  • These lichens can be used as air pollution indicators
  • Invertebrate animals are sensetive to change in the concentration of dissolved oxygen in water
  • Oxygen concentrations decrease when pollutants are released into rivers and lakes
  • some invertbrates survive in low-oxygen concentrations
  • Some invertebrates can only survive in higher oxygen concentrations
  • These invertebrate animals can be used as water polltion indicators
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Non-living indicators

  • Environmental changes can be measured using non-living indicators
  • For example, oxygen levels, temperature and rainfall
  • Scientists continually monitor these factors to show trends in environmental changes
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