n cycle

• why do plants and animals need Nitrogen?

  • Make proteins
  • Make nucleic acids (RNA and DNA)
• How can nitrogen enter an ecosystem

  • Nitrogen cycle
  • Lightning
  • Artificial fertilisers
• SAPROBIONTS= Decomposers that secrete enzymes and digest food externally then absorb only the nutrients they need.

  This breaks larger organic molecules into smaller inorganic molecules

  IN NITROGEN CYCLE

  1. Use enzymes to decompose proteins/DNA
  2. Releases ammonia/ammonium compounds
• NITROGEN CYCLE

  1. NITROGEN FIXATION= N gas in atmosphere turned into ammonia by bacteria eg. rhizobium
  2. AMMONIFICATION= N containing compounds eg DNA broken down by saprobionts to release ammonium ions into soil
  3. NITRIFICATION = ammonium ions oxidised into N compounds. First turned to nitrites and then to nitrates so that plants can use them
  4. DENITRIFICATION= Nitrates turned into nitrogen gas in anaerobic conditions
• Producers


  Green plants that can photosynthesize to use light energy to make their own organic compounds
• Food webs

  1. Begin with producers

  2. Energy is lost due to respiration and excretion between each trophic level

  3. Remaining energy used to form biomass
• Biomass

  Mass of carbon within the organism or the dry mass
• Productivity of an ecosystem

  • Depends on abiotic and biotic factors within that ecosystem
• Gross primary production (GPP)

  Chemical energy stored in the plant biomass in a given area or volume
• Net primary production (NPP)

  Difference between GPP and the energy that will be lost by respiration
• Net production in consumers

  N = I - F + R, where I is chemical energy stored in ingested food, F is chemical energy lost in the environment in feces and urine, and R is respiratory losses
• The rates of productivity are recorded using the units kilojoules per hectare per year
• Trophic level

  Level in a food chain
• Energy loss in photosynthesis

  1. Light energy hits non-photosynthetic parts of the plant

  2. Light energy hits photosynthetic pigments but is the wrong wavelength
• Chlorophyll pigments are unable to absorb green parts of the visible spectrum, which is why they appear green to us
• how can energy be lost in ecosystem?

  • not all light energy that hits plant will be absorbed
  • not all parts of organism will be eaten
  • consumers may not be able to completely digest organism
• increase energy efficiency transfer (respiration)

  • Animal movement is restricted by keeping in pens and cages.
  • Animals are kept indoors or in heated environments so that less energy is used to generate heat.
  • Antibiotics are given so less energy is used to generate an immune response.
• increase energy efficiency transfer (pests)

  • insecticides = kill insects which feed on crops. Less biomass is transferred to the insect and plants grow larger (higher NPP).
  • Herbicides kill weeds which compete with crops. More water, mineral ions and sunlight can be obtained, increasing GPP and NPP.
  • Biological agents are natural ways of getting rid of pests. Parasites that live off pest species can be used to reduce their numbers, or pathogenic bacteria/viruses that infect pests are two biological ways of reducing pest numbers.
• increasing efficiency of energy transfer?

  • reduce energy lost to other organisms eg pests
  • reduce respiratory loss
• Phosphorus Cycle

  1. Rocks erode away

  2. Phosphorus released into soil as phosphate ions

  3. Plants absorb phosphate ions

  4. Plants use ions to synthesise nucleic acids and cell membranes

  5. Animals eat plants

  6. Animals release ions in waste products

  7. Saprobionts decompose urine and faeces

  8. Animals die releasing phosphate ions

  9. Weathering of rocks releases phosphates into bodies of water

  10. Aquatic plants absorb phosphate ions

  11. Phosphate passed along aquatic food chain to sea birds

  12. Birds produce guano which returns phosphate to soil