Ecosystems, nutrient cycles human impact on the environment

• Food chains


  Transfer of energy.

  Producers -> primary consumer -> secondary consumer -> tertiary consumer
• Energy transfers between herbivores, carnivores and decomposers

  Primary consumers are herbivores

  Secondary and tertiary are carnivores.

  Decomposers can obtain energy from dead organisms at any point in a food chain
• What is each stage in the food chain energy is used for

  For repair and in the maintenance and growth of cells whilst energy is lost in waste materials and respiration
• Pyramids of numbers


  Number of organisms per unit at each trophic level
• Pyramid of biomass


  Dry mass of living material per unit area each trophic level
• Efficiency


  Efficiency = biomass available after transfer ÷ biomass available before transfer × 100
• How does efficiency affect number of organisms each level

  The less efficient the energy transfers the fewer the trophic levels and the fewer the number of organisms at each trophic level
• Microorganisms 


  Microorganisms feed on waste materials from organisms, when plants and animals die their bodies are broken down by micro-organisms bringing about decay, micro-organisms respire and release carbon dioxide into the atmosphere
• Nutrients


  Released in decay

  These nutrients are then taken up by other organisms resulting in nutrient cycles and in a stable community the processes which remove materials are balanced by processes which return materials
• Carbon cycle


  . Photosynthesizing plants remove CO₂

  . Eating passes carbon compounds along food chains

  . Respiration in plants and animals return CO₂ to atmosphere

  . Organisms die and decompose. Decomposers break down dead materials and release CO₂ via respiration

  . Combustion of materials releases CO₂
• Nitrogen cycle


  . Organisms die and decompose. Decomposers break down proteins and urea into ammonia

  . Bacteria in soil converts ammonia into nitrates which are taken up by plants and used to build proteins

  . Nitrogen fixing bacteria also convert nitrogen gas into nitrates which are taken up by plants

  . Feeding passes nitrogen through food chains

  . Denitrifying bacteria converts nitrates in soil back to nitrogen gas. This occurs in anaerobic conditions
• Human impact on environment

  Need for human population sometimes conflicts with conservation of environment e.g. human population means we need more food however farmland distrups natural habitats and reduce biodiversity
• Advantages of intensive farming

  . Maximum crop yields - cheaper to produce

  . Maximises space - for crops and machinery

  . Enables more food - to need demand for growing population
• Disadvantages of intensive farming

  . Reduces biodiversity

  . Battery farming

  . Excess fertilizer can wash into water sources causing eutrophication and death of many species
• Indicator species


  Presence or absence in an environmental provides indication of environmental condition
• How can lichens be used to detect air pollution

  Different types of lichens grow in different levels of air pollution. The abundance and distribution of lichens indicate levels of pollution.
• What happens when metal enters food chains

  Heavy metals, present in industrial waste and pesticides, enter the food chain, accumulate in animal bodies and may reach a toxic level
• What happens to untreated sewage water and fertilizers

  May run into water and cause rapid growth of plants and algae; these then die and are decomposed; the microbes, which break them down, increase in number and use up the dissolved oxygen in the water; animals which live in the water may suffocate