OCR 21st Century B3.1

Life on Earth- Interdependence of Species
Classification- look at the similarities and difference between two living organisms to cateogorise them
1. A species is a group of organisms that can breed together to produce fertile offspring
  1. living organisms are dependent on the environment and other species for their survival
    1. Light-needed for plants to make food
      1. Food for animals and minerals for plants
        Oxygen- for respiration and CO2 for plants photosynthesis
        there is competition for these resources between different species of animals or plants in the same habitat
    2. Water
2. adaptation of living organisms to their environment increases the species’ chance of survival by making it more likely that individuals will survive to reproduce
  1. e.g. Cactus- Store water in large stems. Large root systems to get water from deep into he soil. Hard spines instead of leaves
  2. Fish- absorb oxygen dissolved in water. Oxygen diffuses across the large Surface Area of the gills . Streamlined body and smooth surface move with little resistance. Swim bladder-buoyancy and depth change without energy wastage
a change in the environment may cause a species to become extinct, for example, if:
1. the environmental conditions change beyond its ability to adapt
2. a new species that is a competitor, predator or disease organism of that species is introduced
3. another species (animal, plant or microorganism) in its food web becomes extinct
  1. If the shrew was to become extinct, the woodmouse would be the sole source of food for the owl. Owl numbers would decrease, caterpillar numbers would increase and woodmouse numbers would decrease. If there are more caterpillars, that's less food for the squirrel and so there may be a decline in squirrel numbers. As the woodmouse numbers have severely decreased the fox is forced to eat more squirrels and so their numbers decrease
nearly all organisms are ultimately dependent on energy from the Sun
1. Plants, which are usually the producers use sunlight to build glucose from CO2 and water. Through photosynthesis, they trap 1-3% of the light energy that reaches their leaves
  1. A consumer e.g. greenfly eats the plants and the energy is transferred. Energy is transferred when detritivores feed on dead organisms and waste materials e.g. excrement and uneaten parts
    1. Energy is lost at each stage. In respiration and other life processes e.g. movement. Most is eventually lost to the surroundings as heat
      1. Energy available at the previous stage
        x100%
      2. It's not sustainable to have a food chain which is more than 5 stages. There isn't enough energy to support more organisms
        Efficiency= Energy available at the next stage/
carbon is recycled through the environment to include the processes of combustion, respiration, photosynthesis and decomposition
1. The combustion of fossil fuels release stored carbon into the atmosphere in the form of carbon doxide
2. Plants and animals respire producing carbon dioxide
3. Plants use light to convert Carbon dioxide and water into glucose to use for respiration and to make proteins, cellulose, enzymes and chlorophyll
4. The dead organisms are eaten by decomposers and the carbon in their bodies is returned to the atmosphere as carbon dioxide.
  1. In some conditions decomposition is blocked. The plant and animal material may then be available as fossil fuel in the future for combustion.
5. In the sea, marine animals may convert some of the carbon in their diet to calcium carbonate which is used to make their shells. Over time the shells of dead organisms collect on the seabed and form limestone. Due to Earth movements this limestone may eventually become exposed to the air where it's weathered and the carbon is released back into the atmosphere as carbon dioxide. Volcanic action may also release carbon dioxide.
6. The Carbon Cycle
The Nitrogen Cycle
1. Unreactive N2 is fixed by nitrogen fixing bacteria in the soil and roots of plants, to form nitrogen compounds including nitrates.
  1. Lightning- nitrogen is fixed as there is enough energy in a bolt of lightning to make nitrogen react with oxygen
    1. conversion of nitrogen compounds to protein in plants and animals
      1. transfer of nitrogen compounds through food chains- animals eat plants and receive their protein through the nitrates that they've eaten
        excretion, death and decay of plants and animals resulting in release of nitrates into the soil- urea is decomposed by microorganisms and turned into ammonia. This ammonia can be nitrified by nitrifying bacteria to produce useful nitrogen compounds
        denitrification- denitrifying bacteria turns nitrates back into nitrogen
        uptake of nitrates by plants
Living and Non-living Indicators
1. Non-living
  1. nitrate levels
    1. Used to measure changes in cleanliness of water. Increase in nitrate level caused by sewage or fertilisers= polluted water.
  2. temperature
    1. Measurements taken over long periods of time could indicate global warming
  3. carbon dioxide levels
    1. Used to measure the environmental change in the air/atmosphere. An increase in CO2 is an increase in global warming
  4. pH
2. Living
  1. Lichen
    1. Sensitive to sulfur dioxide levels in the atmosphere
      1. If present: clean
        Can give a good idea about the pollution from cars, power stations, etc.
  2. Mayfly larvae
    1. Sensitive to oxygen levels in water
      1. If present: clean
        If sewage is released, bacterial populations increase and use the oxygen so mayfly nymphs leave
  3. Phytoplankton
    1. Sensitive to Nitrate and Phosphate levels in water
      1. If present: polluted
        Adding fertilisers or sewage to water increases the amount of nitrates and phosphates causing algal blooms. Phytoplankton like nitrate/phosphate rich environments

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OCR 21st Century B3.1

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	Created by Pritesh Patel about 8 years ago