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ecology (ecosystem (populations (habitat (A habitat is the combination of…

- - - - Individual organisms are the smallest part of an ecosystem.
    - - Populations of individual organisms make up a single species.
    - - Communities are made up of populations of different species living in the same habitat (environment or area).
    - - A habitat is the combination of biotic and abiotic factors within the natural environment that an organism occupies.
      - Different species are adapted to different habitats.
    - - plants
        
        Plants often compete for water and mineral ions (minerals) from the soil, as well as for light and space.
      - animals
        
        Animals often compete for food, mates and territory.
    - - A species may depend on another to spread its seeds.
    - - A species may depend on another for food.
    - - A species may depend on another for shelter.
    - - A species may depend on another for pollination (transfer of pollen).
  - - - disease
      - food supply
      - preditation
  - - - light energy from the sun
      - chemical energy in plants
      - chemical energy in animals
      - energy in decomposed matter
    - - notes
        
        Food chains show the feeding relationships and transfers of energy within a community. Below are some important definitions of the types of organisms found in food chains:
        
        Producer.
        
        An organism that makes its own organic nutrients, usually using energy from sunlight.
        
        Consumer.
        
        An organism that gets its energy by feeding on other organisms.
        
        Depending on the position of the consumer in the food chain, it may be classed as primary, secondary or tertiary.
        
        Herbivore.
        
        Animals that get their energy from eating plants.
        
        Primary consumers.
        
        Carnivore.
        
        Animals that get their energy from eating other animals.
        
        Secondary and tertiary consumers.
        
        Food webs show networks of interconnected food chains.
    - - This is a food web. The arrows signify transfer of energy.
      - E.g. blue tits eat parasitic wasps, holly leaf miners and other insects.
  - - - biodiversity
        
        notes
        
        Biodiversity can be defined as the variety of different species and the numbers of individuals within those species in a habitat.
        
        Quadrats can be used to estimate the biodiversity of a habitat.
        
        The higher the number of different species in the quadrat samples, the higher the biodiversity.
        
        The more even the number of individuals of the different species, the higher the biodiversity.
      - population size
        
        The population size of a species in a habitat can be estimated by counting the number of individuals in various quadrat samples of the habitat.
        
        This can also give an indication of the distribution of a particular species and whether a species is more abundant in one habitat compared to another.
    - - quadrats
        
        Quadrats are normally 1m2 square frame divided into 100 squares.
        
        Each square represents 1% of the total area of the quadrat.
        
        If an individual covers more than half of a square, it is counted as representing 1% of the quadrat.
        
        Quadrats are used to count the population size within a large area.
      - sampling
        
        notes
        
        If you wanted to investigate the size of a population, it would take hours to count every individual.
        
        Taking samples (a small section of the total area) allows the population size to be estimated.
        
        It is important that the samples accurately represent the total population size.
        
        random sampling
        
        notes
        
        Random sampling can be applied by dividing the area of interest into a grid and labelling the grid with coordinates.
        
        A random number generator provides a set of random coordinates.
        
        The quadrats can be placed using the coordinates.
      - transects
        
        notes
        
        Quadrats could also be placed at regular intervals along a transect.
        
        A transect is a line across a habitat, usually placed using a tape measure.
        
        Transects are used when there is a change, or gradient, in abiotic conditions across the habitat.
        
        Transects are used when looking for changes in the abundance or distribution of a species across the environment (e.g. how abundance changes from open field to forest).
        
        line transects
        
        A line transect records the species that makes contact with the tape measure at regular intervals along the transect.
        
        belt transects
        
        notes
        
        A belt transect uses quadrats.
        
        Quadrats are placed at regular intervals along the transect.
        
        An abundance of different species in the quadrat can be measured by:
        
        Percentage cover – estimate how much of the quadrat is covered by a particular species
        
        Frequency – count how many individuals of a particular species are present in the quadrat.
      - Using Quadrats to Estimate a Population Size
        
        notes
        
        Divide the habitat up into a series of quadrat-sized cells.
        
        Randomly select a given number of cells, then go out into the habitat and place the quadrat in these positions.
        
        To evaluate the quadrat contents, either count the number of individual organisms of interest or record the percentage of the quadrat taken up by an organism (e.g. grass).
        
        The samples from the quadrat are used to estimate the total population in a given area:
        
        population = number counted x (total survey area / area sampled)
  - - - notes
        
        Biomass is the total dry mass of living material in an organism multiplied by the number of organisms.
        
        A pyramid of biomass can be constructed to represent the relative amount of biomass at each trophic level in a food chain.
        
        Pyramids of biomass are almost universally pyramid-shaped, whereas pyramids of numbers can take many different forms.
        
        The pyramid of numbers doesn't take into account the size of the organism and represents the amount of energy at each level less accurately.
        
        Pyramids of energy look similar to pyramids of biomass, but represent chemical energy rather than dry mass.
    - - notes
        
        Biomass is the total dry mass of living material in an organism multiplied by the number of organisms.
        
        A pyramid of biomass can be constructed to represent the relative amount of biomass at each trophic level in a food chain.
        
        Pyramids of biomass are almost universally pyramid-shaped, whereas pyramids of numbers can take many different forms.
        
        The pyramid of numbers doesn't take into account the size of the organism and represents the amount of energy at each level less accurately.
        
        Pyramids of energy look similar to pyramids of biomass, but represent chemical energy rather than dry mass.
    - - waste products
        
        Not all food is digested.
        
        Some food is removed from the body as the waste materials urine and faeces.
      - growth
        
        Energy is used to create new cells to allow organisms to grow.
      - Maintenance
        
        notes
        
        Organisms need constant maintenance and repair, which uses energy.
        
        Damaged cells need to be repaired or replaced.
        
        Warm-blooded animals need to expend energy to maintain a suitable body temperature.
      - respiration
        
        notes
        
        Large quantities of glucose are used in respiration to produce energy.
        
        Highly mobile animals require a lot of energy to sustain their movement.
        
        Respiration produces waste products that are removed from the body.
  - - - the carbon cycle
        
        notes
        
        Carbon is present in all living organisms.
        
        When organisms die, the carbon is recycled so that it can be used by future generations.
        
        When decomposers process decaying matter, they respire, releasing carbon dioxide back into the air.
  - - - Nitrogen is present in all living organisms.
      - It moves through food chains and is recycled when organisms die.
      - Decomposers are also responsible for recycling nutrients such as nitrates and phosphates back into the community from dead organisms.
    - - The nitrogen cycle is important for plants to absorb nitrates necessary for their growth.
      - Plants can absorb nitrates from the soil via their roots, and from the air, via root nodule bacteria.
      - Nitrates are passed to animals when they feed on plants.
      - Soil bacteria and other organisms decompose dead animals and urea, allowing nitrates to enter the soil.
      - The nitrates in the soil can also go back and forward to the air, due to the action of soil bacteria and lightning.
      - Farmers add nitrates to crops to increase their growth. They also do crop rotation, which means that different species are grown each year. This improves soil fertility because each type of plant removes different nutrients from the soil.
    - - nitrafication
        
        Nitrifying bacteria convert ammonium into nitrates.
      - Decomposition
        
        Microorganisms break down decaying matter and return nitrogenous compounds to the soil.
      - nitrogen fixation
        
        Bacteria in plants' root nodules 'fix' nitrogen into a useable form for plants.
      - denitrification
        
        Denitrifying bacteria remove nitrogenous compounds from the soil and release nitrogen back into the air.
- - - - air
        
        Smoke and gases are being added into the atmosphere constantly, particularly by power stations and cars.
        
        agriculture
        
        Many farming practices, such as rice paddies and cattle farms release huge amounts of methane into the atmosphere.
        
        Industrial processes linked to agriculture (such as producing fertiliser) emit nitrous oxides, which contribute to acid rain.
        
        burning fossil fuels
        
        Burning fossil fuels releases large amounts of greenhouse gases into the atmosphere that would otherwise have been locked away for millennia.
        
        Methane and carbon dioxide enhance the greenhouse effect, causing global warming and climate change.
        
        power station and cars
        
        notes
        
        Power stations and cars constantly pump gases into the atmosphere.
        
        Sulfur dioxide dissolves in atmospheric moisture to form acid rain, which has been shown to negatively impact forest, freshwater and soil ecosystems as well as human health.
        
        Most car exhausts pump out significant amounts of carbon monoxide, which is toxic to humans and other animals because it binds to haemoglobin, reducing the oxygen-carrying capacity of blood.
        
        cooling system
        
        CFCs are a group of gases released from aerosol cans, refrigerators and air conditioners.
        
        CFCs have been linked to creating a hole in the 'ozone layer'- a layer in the Earth's atmosphere that protects us from harmful radiation.
      - land
        
        Toxic herbicides and pesticides used in farming, buried nuclear waste and household waste in landfill sites are all land pollutants.
      - water
        
        Sewage and toxic chemicals, which are produced by industrial practices, as well as excess fertiliser from agriculture, all find their way into the Earth’s water sources.
    - - Increased growth of producers
        
        Very fast growth spurts, or 'blooms', of algae is common.
      - Increases the rate of decomposition
        
        notes
        
        Eutrophication increases the rate of respiration of decomposers.
        
        This means that producers decompose more quickly.
        
        This leads to a lower level of dissolved oxygen in the water (because decomposers use up the oxygen).
        
        Organisms that need oxygen can't then respire, so they die.