Biology U2: Ecology

• Define ‘Habitat’

  The environment in which an organism lives
• Define ‘Population’

  Total number of organisms of the same species living in the same geographical area
• Define ‘Community’

  Populations of all the different species that live in the same habitat
• What does ‘biotic’ refer to?

  The living factors of an ecosystem
• What does ’abiotic’ refer to?

  The non-living factors of an ecosystem
• What is an ‘ecosystem’?

  Both the biotic and abiotic parts of an environment and how they interact
• What resources do plants compete for?

  • Light
  • space
  • water
  • mineral ions
• What resources do animals compete for?

  • Food
  • water
  • territory
  • mating partners
• What is a stable community?


  The populations of all organisms are in balance with each other
• What is ‘interdependence’?

  Organisms depend on each other for survival
• What are some abiotic factors?

  • Light intensity
  • temperature
  • levels of moisture
• What are the two types of sampling?

  • Sampling along a transect
  • random sampling
• What is random sampling used for?

  Used to compare the numbers of organisms in different areas
• What can be counted using the random sampling method?

  Using the quadrat, this technique can be used to sample plants or slow-moving animals
• State the formula to find the estimated total population size

  Total population size = total area/area sampled x number of organisms of that species counted in sample
• Define ‘Biodiversity’

   the range and variety of different species of organisms on Earth, or within an ecosystem
• Food chains 


  Shows what eats what in a particular habitat
• Food webs


  A network of interconnected food chains in an ecosystem
• Trophic levels

  The different levels in a food chain
• State the order of trophic levels in a food chain

  Producer (1)—> Primary consumer(2) —> Secondary consumer (3) —> Tertiary consumer (4)
• What are Decomposers?


  Organisms (bacteria and fungi) that secrete a certain digestive enzyme to break down dead plant and animal matter
• What are detritivores?


  Organisms that feed on dead plant and animal matter
• What is the role of Decomposers and detritivores?


  To recycle nutrients from plants and animals back into the ground which can then be used by producers and in the food chain
• Biomass


  Measure of the total mass of living material in each trophic level
• How much of energy is transferred and lost in a food chain?

  10% energy transferred

  90% energy lost
• What are the four main reasons for energy/biomass loss in a food chain?

  1. Lost as heat mainly
  2. not all parts of the organism is consumed
  3. not all parts of food is absorbed by the consumer; resulting in it to be egested as faeces
  4. most of the nutrients that are absorbed are used to release energy through respiration
• What waste products can be released by biomass?

  Carbon dioxide, urea
• State the formula to calculate the efficiency of a biomass transfer:

  Efficiency = biomass transferred to the next level/ biomass available at the previous level x 100
• what is shown in pyramids of numbers?


  Shows the relative number of organisms at each stage in a food chain
• What is eutrophication?


  The process in which excessive growth of algae occurs in a water body due to excessive minerals and nutrients.
• Describe the process of eutrophication:

  1. excessive fertilizers in plants and soils are washed into water bodies due to rainfall
  2. increase in nitrate content in the water bodies encourages algal bloom over the water surface over time
  3. algae decomposes which uses up a lot of the dissolved oxygen in the water
  4. plants and organisms in the water body die due to lack of oxygen to breathe and carry out photosynthesis
• What are the stores in the nitrogen cycle?

  Atmosphere, plants, animals, soil
• What is the role of the nitrogen-fixing bacteria and where is it found?

  • found in the root nodules of legume plants
  • nitrogen gas(atmosphere)—> ammonia+ammonium(soil)
• What is the role of the nitrifying bacteria and where is it found?

  • Found in the soil
  • converts ammonia/ammonium(soil)—>nitrates+nitrites(soil and plants)
• What happens when plants and animals die and decompose?

  decomposers in the soil break down dead plant and animal matter and convert the nitrates and nitrites found in them into ammonia
• What is the role of the denitrifying bacteria and where is it found?

  • Found in the soil
  • converts nitrates/nitrites(soil and plants)—>nitrogen gas(atmosphere)
• what human activity increased carbon dioxide levels in the atmosphere?

  Burning of fossil fuels
• What human activity increased methane levels in the atmosphere?

  • Growing cattle population being fed (mainly cows) where methane is produced as a waste product of digestion
  • increasing decay in landfill which releases methane
  • Increasing rice production releases more methane due to bacteria that live there
• what human activity has increased levels of CFCs in the atmosphere?

  Man-made chemicals found in aerosols, fridges and industrialization
• What human activity has increased nitrous oxide levels in the atmosphere?

  • Car fumes contain nitrous oxide (catalytic converters reduce this)
  • use of fertilizers increase nitrous oxide as the nitrates are converted into nitrous oxide by denitrifying bacteria