Organisms and their Environment

• Environment


  The total non biological living components in an ecosystem e.g. soil, water
• Habitat


  The space where a particular organism lives
• Population


  All organisms that belong to a particular species found in an ecosystem
• Community


  The population of all species found within an ecosystem
• Producer

  A plant which photosynthesises to produce food
• Consumer

  An animal which eats other animals or plants
• Decomposer

  An organism which breaks down dead material and recycles nutrients
• Parasite


  An organism which lives in another organism feeding and causing harm
• Predator


  An animal which kills and eats other animals
• Biodiversity


  The variety of plants and animals found within an ecosystem
• Biotic factors


  • Competition for food
  • Nesting sites
  • Disease
• Abiotic factors


  • Soil pH
  • Temperature
  • Carbon dioxide
  • Number of daylight hours
• Pyramid of numbers

  Shows the numbers of each organism at a specific trophic level
• Trophic levels

  Stages of a food chain or web
• Biomass

  The mass of living material
• Pyramids of numbers often end up looking really strange shape and not being pyramidal at all due to the producer being only a single large tree which is small compared to the amount of birds living
• Trophic levels

  • Tertiary consumers
  • Secondary consumers
  • Primary consumers
  • Producers
• Pyramid of biomass for grassland ecosystem: Dry weight (kgm-2) - Producers 585, Primary consumers 77, Secondary consumers 12, Tertiary consumers 11
• Energy originates from the Sun
• Vegetarian + Vegan

  Grass ->human (much better way of eating. You save energy.)
• Over harvesting of good species

  Deprives consumers of food
• Introducing foreign species

  Means more competition for food, less food available for others
• Carbon cycle

  1. Carbon dioxide is absorbed by green plants in photosynthesis

  2. Carbon used to make glucose and proteins

  3. Plants respire releasing carbon dioxide

  4. Plants eaten by animals and carbon becomes part of their bodies

  5. Animals respire releasing carbon dioxide

  6. Plants & animals die and are decomposed by microorganisms

  7. Microorganisms respire

  8. Combustion of fuels releases carbon dioxide
• Nitrogen cycle

  1. Nitrates in the soil are absorbed by root hairs cells by active transport

  2. Nitrates used to build plant proteins

  3. Plants die, decompose, and are converted to nitrates by nitrifying bacteria

  4. Denitrifying bacteria convert nitrates to nitrogen

  5. Nitrogen fixing bacteria are present on root nodules of beans and peas and convert nitrogen gas into nitrates which are added to the soil

  6. Lightning and the Haber Process are other sources of nitrogen
• Factors affecting population growth

  • Food supply
  • Predation
  • Disease
  • Temperature
  • Oxygen
  • Light
  • Toxins and pollutants
• Sigmoid population growth curve

  • Lag phase: Population growth begins slowly from a few individuals
  • Log phase: Exponential growth occurs, the conditions are ideal and maximum growth rate is reached
  • S-phase: Growth rate begins to slow down as factors such as food, water and space become limiting
  • Stable phase: Carrying capacity for the population has been reached and the population number becomes stable
  • Decline phase: If there is a sudden change in the environment meaning that the environment can no longer support the population, the population will crash and the whole process begins again
• Explain why only 10% of energy is transferred from one trophic level to the next

  1. Not all of the plant is eaten (in the case of producer primary consumer)

  2. Some parts are indigestible (in the case of producer primary consumer)

  3. Some form excretory products e.g. Sweat, urine

  4. Respiration leads to loss of carbon dioxide and water

  5. Maintenance of steady body temperature (e.g. In cows)