Topic 9 ~ Ecosystems and Material Cycles

• Levels of Organisation


  • Individual
  • Species
  • Habitat
  • Population
  • Community
  • Ecosystem
• Competition


  • Within a species
  • Between different species
  • Plants compete for light, space, water and mineral ions
  • Animals compete for space, food, water and mating partners
• Abiotic factors affecting communities

  • Light intensity
  • Temperature
  • Moisture levels
  • Soil pH and mineral content
  • Wind intensity and direction
  • Carbon dioxide levels
  • Oxygen levels for aquatic animals
• Abiotic factor


  Non-living factor
• Biotic factor


  Living factor
• Biotic factors affecting communities

  • Food availability
  • New predators
  • New pathogens
  • Competition
• Interdependence


  How organisms in a community depend on other organisms for vital services like food, shelter and reproduction
• Symbiotic relationship


  When two species live together
• Parasitism


  When a smaller species lives directly within or on a larger species and benefits at the expense of the other species
• Mutualistic relationship


  When a smaller species provides some benefit or resource to the other species
• Commensalism


  When there is no damage caused to either species, and there is often a mutual benefit
• Fieldwork techniques to count organisms

  1. Divide field into equal squares

  2. Randomly select square

  3. Use quadrat to count organisms in square

  4. Repeat in different squares

  5. Average results and multiply by total squares
• Pyramid of biomass


  Shows the relative biomass at each trophic level
• Producers (e.g. plants and algae) transfer about 1% of the incident energy from light for photosynthesis
• Only approximately 10% of the biomass of each trophic level is transferred to the next
• Not all biomass can be eaten by carnivores (e.g. bone, hooves, claws and teeth)
• Biomass consumed can be lost as faeces, especially in herbivores that don't have all the enzymes to digest all the material they eat
• Efficiency of biomass transfers

  (Biomass transferred to the next level / Biomass available at the previous level) x 100
• Positive human interactions with ecosystems

  • Maintaining rainforests
  • Raising public awareness
  • Reducing water pollution
  • Preserving areas of scientific interest
• Negative human interactions with ecosystems

  • Production of greenhouse gases
  • Introducing non-indigenous species
  • Producing sulfur dioxide
  • Chemicals from farming causing eutrophication
• Positive human interactions with ecosystems

  • Maintaining rainforests, ensuring habitats are not destroyed
  • Raising awareness among the public about how to protect ecosystems - e.g through large scale community projects
  • Reducing water pollution and monitoring the changes over time
  • Preserving areas of scientific interest by stopping humans from going there
  • Replanting hedgerows and woodlands to provide habitats which were previously destroyed
• Negative human interactions with ecosystems

  • Production of greenhouse gases leading to global warming
  • Introducing non-indigenous species into the environment, which prey on native species
  • Producing sulfur dioxide in factories which leads to acid rain – affects habitats
  • Chemicals used in farming leak into the environment - if they leak into a lake, this can cause eutrophication - excessive growth of plant life which can deplete the body of water of oxygen (making it less able to sustain other species such as fish)
  • Clearing land in order to build on, reducing the number of habitats
  • Overfishing which reduces biodiversity and can lead to endangerment of some species
• Programs to maintain biodiversity

  • Breeding programs: to stop endangered species from becoming extinct
  • Protection of rare habitats: to stop the species here from becoming extinct, if damaged they may even be regenerated to encourage populations to live here
  • Reintroduction of hedgerows and field margins around land where only one type of crop is grown: maintains biodiversity as the hedgerows provide a habitat for lots of organisms (because a field of one crop would not be able to support many organisms) and field margins provide areas where wild flowers and grasses can grow
  • Reduction of deforestation and carbon dioxide production: reduces the rate of global warming, slowing down the rate that habitats are destroyed
  • Recycling rather than dumping waste in landfill: reduce the amount of land taken up for landfills, and slows the rate we are using up natural resources
• Food security

  Having sufficient food to feed the population
• Factors affecting food security

  • Increasing birth rate and human population, meaning more food is required
  • Changing diets in developed countries (e.g an increase in meat and fish consumption) means food resources which are already in low amounts become even more scarce as the demand for them increases
  • New pests and pathogens can destroy crops
  • Climate change affects food production (such as no rain resulting in crops failing)
  • Conflicts in some countries can affect the availability of water and food
• To feed everyone on Earth, sustainable methods are needed
• Carbon cycle

  • CO2 is REMOVED from the air in photosynthesis by green plants and algae – they use the carbon to make carbohydrates, proteins and fats. They are eaten and the carbon moves up the food chain
  • CO2 is RETURNED to the air when plants, algae and animals respire. Decomposers (a group of microorganisms that break down dead organisms and waste) respire while they return mineral ions to the soil
  • CO2 is RETURNED to the air when wood and fossil fuels are burnt (called combustion) as they contain carbon from photosynthesis
• Compost

  • When biological material decays it produces this
  • It is used by gardeners and farmers as a natural fertiliser
  • To do this they have to provide optimum conditions for decay
  • If more oxygen is available they respire aerobically, producing heat
  • The increased temperature increases the rate of decay so the compost is made quicker
• Methane gas

  • Microorganisms decompose waste anaerobically to produce this
  • This can be burnt as a fuel
  • Biogas generators are used to produce methane
  • Require a constant temperature (30 degrees) so the microorganisms keep respiring
  • It cannot be stored as a liquid so needs to be used immediately
• Water cycle

  • The sun's energy causes water to evaporate from the sea and lakes, forming water vapour
  • Water vapour is also formed as a result of transpiration in plants
  • Water vapour rises and then condenses to form clouds
  • Water is returned to the land by precipitation (rain, snow or hail), and this runs into lakes to provide water for plants and animals
  • This then runs into seas and the cycle begins again
  • In areas of drought, we can harness the water cycle to produce potable (drinkable) water. For example, desalination is the process by which we remove salt and other minerals/impurities from seawater to make it drinkable. It is performed by a process called reverse osmosis and generally occurs on a large scale
• Nitrogen

  • Nitrogen gas in the atmosphere is too unreactive so cannot be used directly by plants
  • Nitrogen-fixing bacteria present in the root nodules of legume plants convert nitrogen gas into nitrates that can be used for growth
  • Lightning can convert nitrogen gas into nitrates
  • The Haber process converts the hydrogen gas into ammonia
  • Plants absorb nitrates through the roots by active transport
• Indicator species

  • Used to assess pollution levels in an area
  • Polluted water is often identified by the presence of bloodworms or sludgeworms (often called 'sewage worms' for this reason)
  • Clean water often harbours freshwater shrimps and stonefly. The presence of these species is indicative of clean, unpolluted water
  • Air quality can be indicated by a number of species of lichen. In areas where the air is heavily polluted with sulfur dioxide, lichen is less likely to be found. Clean air often provides an ideal environment for lichens, with a rich variety of species being found in clean air. The rose blackspot fungus is more likely to be found in less polluted areas, as sulfur dioxide protects plants from certain fungi
• Factors affecting rate of decomposition

  • Temperature: Chemical reactions generally work faster in warmer conditions, but if it is too hot the enzymes can denature and stop decomposition
  • Water: Microorganisms grow faster in conditions with water as it is needed for respiration. Water also makes food easier to digest
  • Availability of oxygen: Most decomposers respire aerobically
• Investigating effects of temperature on decay

  1. Make a solution of milk and phenolphthalein indicator

  2. Add sodium carbonate which will cause the solution to become alkaline and therefore appear pink

  3. Place the tube in a water bath at a specific temperature

  4. Add the lipase enzyme and begin stopwatch

  5. Time how long it takes for the pink colour to disappear (i.e. when the pH has decreased)

  6. Repeat this at different temperatures to see at which temperature the pink colour disappears the quickest, indicating the quickest decomposition