B1.4 Interdependence and Adaptation

B1.4 Interdependence and Adaptation


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



  • 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.



Animals often compete with each other for:

  • Food
  • Mates
  • Territory


Plants often compete with each other for:

  • Light
  • Water from the soil
  • Nutrients from the soil



  • 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, eg arctic or deserts
      • Plants lose water vapour from the surface of their leaves.
      • It is essential that they have adaptations which minimise this.


Extreme adaptations:

  • Extremophiles are organisms that live in extreme environments.
  • Some may be tolerant to high levels of salt, high temperatures or high pressures.
  • Animals and plants may be adapted to cope with specific features of their environment eg thorns, poisons and warning colours to deter predators.


Extreme Animals

  • Animals may be adapted for survival in dry and arctic environments by means of:
    • changes to surface area
    • thickness of insulating coat
    • amount of body fat
  • Examples:
    • 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 ration, increasing heat loss by radiation.

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

Extreme Plants

  • Plants may be adapted to survive in dry environments by means of:
    • changes to surface area, particularly of the leaves
    • water-storage tissues
    • extensive root systems.


  • Desert plants
  • Eg 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 evaporation.
  • Fewer ‘stomata’, reducing water loss

Roots tend to spread sideways to catch rain water.

  • Arctic plants
  • Many of the plants are small, growing close to the ground and very close together to avoid the wind and conserve heat.
  • Some possess a light, fuzzy covering to insulate the buds so they can grow.
  • Many are dark colors of blue and purple to absorb the heat from the sunlight even during the winter months.
  • Because of the cold and short growing seasons, arctic plants grow very slowly.
  • Some grow for ten years before they produce any buds for reproduction.



  • Microorganisms have adaptations that enable them to survive in different environments.
  • Slime capsule 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 when conditions are favourable.
  • Some bacteria can survive extreme conditions:
    • Temperatures as little as -15°C to as high as 121°C
    • pH values 0.0 to 12.8
    • High levels of pressure deep in the oceans
    • High salt concentrations
    • Very dry conditions.


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 or non-living factors.


Non-living (abiotic) factors:

  • Light
  • Oxygen
  • Water
  • Temperature


Living (biotic) factors:

  • Food
  • Predation
  • Grazing
  • Disease
  • Competition – for:   food, light, water, space.


Living organisms can be used as indicators of pollution:

  • Lichens are symbiotic associations of algae and fungi species that attach to tree trunks and rock.
  • They are sensitive to changes in air quality.
  • They are very sensitive 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 sensitive to changes in the concentration of dissolved oxygen in water.
  • Oxygen concentrations decrease when pollutants are released into rivers and lakes.
  • Some invertebrates survive in low-oxygen concentrations.
  • Some invertebrates can only survive in higher oxygen concentrations.
  • These invertebrate animals can be used as water pollution indicators.


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