ecology

• Ecosystem


  A self-sustained unit between all biotic and abiotic components
• Components of an ecosystem


  • Biotic
  • Abiotic
• Producers


  • Synthesise complex organic material from raw material using light energy
  • Always first in the food chain
  • Always plants
• Consumers


  • Depend on other living organisms for food
• Decomposers


  • Organisms that break down dead material and help recycle nutrients
• Habitat


  The place where an organism lives (food, water, shelter)
• Ecosystems have a variety of habitats
• Population


  A group of a particular species living in the same area at the same time
• Community


  The population of all species found in an ecosystem at a particular time
• Sampling experiment using quadrats


  1. Select the area of the field and add the quadrat

  2. Count the number of plants in each quadrant

  3. Repeat and take average

  4. Multiply by the total field
• Biodiversity


  The amount of variation shown by species in an ecosystem
• Measures of biodiversity


  • Species richness (number of species in an ecosystem)
  • Species abundance (distribution and number of organisms in the ecosystem)
• Having a higher biodiversity is important because the ecosystem will be more stable and less likely to be affected by ecological diseases
• Food chain


  A diagram that represents the flow of energy between different living organisms
• Food web


  Interacting food chains
• A food web is a more accurate representation than a food chain as it shows multiple predators and prey of a single organism
• Types of consumers


  • Herbivores (eat plants)
  • Carnivores (feed on other animals)
• Trophic level


  The position of a living organism in a food chain
• Plotting a food chain in a pyramid of numbers rather than a pyramid of biomass is a disadvantage because it doesn't consider the dry mass of an organism, so if the producer is large in dry mass the pyramid is inverted
• Energy is lost between different trophic levels in the food web


  • Some of the light energy doesn't fall on photosynthesis parts and not all light colours are absorbed
  • Some energy is lost as heat energy during respiration, not all parts are eaten, and not all eaten parts are digested (some energy lost in excretion)
• Carbon cycle


  1. Carbon dioxide in the atmosphere is used by plants in photosynthesis to produce carbohydrates and other biomolecules

  2. Carbon is returned to the atmosphere by respiration and combustion

  3. Carbon is stored in fossil fuels

  4. Carbon in dead decaying matter is broken down by decomposers
• Human activities are increasing atmospheric CO2 levels
• Nitrogen cycle


  1. Nitrogen fixation by lightning and nitrogen-fixing bacteria in soil

  2. Absorption of nitrates by plants to make proteins

  3. Animals get nitrogen from eating plants or animals

  4. Nitrogen is sent back into the soil as ammonium through urine and faeces

  5. Nitrifying bacteria convert ammonium back into nitrates

  6. Denitrifying bacteria can convert nitrates back into nitrogen gas
• Plants and animals cannot absorb nitrogen from air, so it must be converted
• Factors controlled in modern agriculture


  • Soil ions - adding fertilisers
  • Soil structure - drainage and ploughing
  • Soil pH - adding lime to acidic soils
• Reason for controlling factors in modern agriculture


  • Extra mineral ions can be taken up and used to make proteins
  • Good drainage allows better uptake of mineral ions by active transport
  • Unstable pH reduces uptake of mineral ions
• Biological control of pests


  Using natural predators, herbivores, parasites, or pathogens to control pests
• Chemical control of pests

  Spraying pesticides
• Biological control is better than chemical control because chemical control can cause death to harmless insects, pests may become resistant to pesticides, and there are issues with bioaccumulation and biomagnification
• Causes of deforestation


  • Removal of trees to build for agriculture or for timber
• Negative impacts of deforestation


  • Destruction of habitat
  • Loss of biodiversity
  • Some species may go extinct
  • Increase in CO2 resulting in global warming
• Greenhouse gases


  CO2, methane, CFCs trap infrared radiation and prevent their escape, resulting in an increase in the Earth's atmospheric temperature
• Negative impacts of global warming


  • Polar ice caps melt
  • Flooding and drought
  • Changes in global rainfall patterns
  • Loss of habitat
  • Migration of animals
  • Loss of biodiversity
• Effect of acid rain on ecosystems


  • Soil becomes slightly acidic, leaching some ions into lakes resulting in eutrophication
  • Kills microorganisms in soil
  • Root hairs lose their ability to absorb mineral ions
  • Kills aquatic organisms
  • Destroys lime-based buildings
• Negative impact of eutrophication on aquatic life


  • Mineral ions/fertilizers leach into the river, causing algal blooms
  • Death of algae leads to decomposition by aerobic bacteria
  • Bacteria use up oxygen, causing fish to suffocate
• Negative impact of dumping sewage in rivers


  Sewage contains microorganisms that consume oxygen, causing fish to suffocate
• Sustainable fish farming


  • Fish are kept in dense stacks of net enclosures in a river
  • Diet of fish is monitored
  • Oxygen for aerobic respiration is provided
  • Suitable temperature is maintained
  • Protection from predation
  • Selective breeding programs to sort fish by size and species
• Disadvantages of fish farming include the risk of disease spread and pollution problems due to the waste produced, as well as negative impacts on wild fish stocks