energy transfer

• plants are the producers so produce their own carbohydrates via photosynthesis (CO2 + H2O)

  The glucose produced can be used:

  • respiration
  • stored as starch
  • beta glucose form cellulose
  • Nitrogen added to glucose to form amino acids and proteins
• Producer = photosynthesis absorbs light converting to chemical energy used for plant growth becoming biomass

  I

  Primary consumer = herbivore eats the plant so the biomass is transferred to the next trophic level

  I

  secondary consumer = carnivore eats animal receiving biomass

  I

  tertiary consumer/ apex predator = occupying the highest trophic level due to biomass decreasing as energy is lost at each step in the food chain
• between each trophic level majority of the energy is lost due to respiration and excretion (30%) - remaining energy is used to form BIOMASS (10%)
• rest of energy is lost:

  • not all the light energy that hits the plant will be absorbed, some is reflected or the wrong wavelength for the chloroplast pigment
  • not all parts of the organism is eaten (bones, roots) the energy is transferred to decomposers
  • consumers may not be able to completely digest the the organism - eg. cellulose in plants n humans unable to digest so excrete out faeces
• measuring trophic level energy transfer - CALORIMETER

  1. dehydrate in oven until their mass becomes constant to create dry biomass
  2. weigh them and calculate the difference in mass between organisms (same amount of biomass transfer)
  3. burn dry mass in a calorimeter
  4. measure the temperature of surrounding water
  5. use the values to calculate estimate of heat energy released from burnt biomass
• productivity depends on abiotic and biotic factors (more light, more warmth and more water = maximise rate of photosynthesis)
• Gross primary productivity = the chemical energy store in plant biomass in a given area or volume; total energy in plant entering food chain
• Net primary productivity = the chemical energy store in plant biomass taking into account the energy that will be lost due to respiration; energy left over available to create new biomass available to next trophic level

  • NPP = GPP - R
• net production of consumers = I - (F+R)

  I = chemical energy store in ingested food

  F = chemical energy lost to environment in faeces
• fertilisers are added to soil to replace the nitrates and phosphate ions lost when plants are harvested and removed from nutrient cycles as crops
• Natural fertilisers:

  • cheaper = often free if farmer owns animals (manure)
  • cant control proportions = harder to quantify
  • gradual release of nutrients = manure compost or crop residue gradually release nutrients as organic matter decomposers
• Artificial fertilisers:

  • expensive = powdered or pellet form
  • exact proportions = chemicals created for specific crops so have appropriate balance of minerals
  • more water soluble = inorganic substances likely to dissolve in water surrounding soil

  :) = easier for plant to absorb nitrates and phosphates

  :( = highly soluble mean larger quantity washed away with rainfall
• WHAT HAPPENS WHEN YOU APPLY FERTILISERS?

  • add more fertiliser = productivity and more crops grow
  • productivity decrease as ions lower soil water potential = water starts moving out of plant via osmosis = plant dehydrate and die!

  
• leeching is when water soluble compounds are washed away into rivers
• eutrophication is when nitrogen fertilisers leach into waterways

  1. stimulates excessive algae growth
  2. algae creates a blanket on surface of water blocking out light
  3. plants below cant photosynthesis + will die
  4. bacteria feed and respire on dead matter
  5. increase in bacteria use up oxygen (biological oxygen demand)
  6. fish DIE due to lack of dissolved oxygen in water
• bioaccumulation:

  1. toxic fertilisers even small amount run into the water source. Small marine creatures ingest it on the surface of sea floor
  2. larger predators eat large volume of small creatures therefore ingesting large amount of of toxins

  poisons will BUILD UP ALONG A FOOD CHAIN
• biological control = predators and pathogens used to control unwanted insects, weeds or disease
• extensive farming:

  • no fertilisers or chemicals
  • animals left to roam
  • low costs and low productivity

  intensive farming:

  • cheap and quick
  • artificial fertilisers
  • pesticides, fungicides
  • productive meat production
• RATES OF PRODUCITIVTY: KJ ha-1 year-1

  • KJ units for energy
  • per unit area = standardise results to enable environments to be compared as it takes into account different environments vary in size
  • per year = impact of seasons (on rain, light, heat) provides an annual average to allow fair comparison between environments