biomass transfer

• what is the main source of energy for almost all ecosystems on earth?

  the sun
• what is a producer?

  an organism that converts light energy into chemical energy through photosynthesis
• what is the role of decomposers in a food web?

  break down dead organisms and release nutrients back into the ecosystem
• where are producers found in a pyramid?

  at the bottom

  
• what is biomass?

  • the mass of living material present in a particular place or in particular organisms
  • equated to energy content
• how do you calculate biomass at each trophic level?

  • multiply the biomass present in each organism by the total number of organisms at that trophic level
  • represents the biomass present at a particular moment in time- doesn't take into account seasonal changes
• why can calculating the biomass of an organism by measuring the mass of fresh material be unreliable? how can this be dealt with?

  • water content must be discounted
  • varying volumes of water in different organisms makes the technique unreliable unless very large samples are used
  • scientists therefore calculate dry mass of organisms present
  • organisms killed, placed in oven at 80 degrees until all water has evaporates, this is indicated by two identical mass readings
  • to minimise the destruction of organisms, only a small sample is taken, but this may not be representative of the population
• what units are used to measure biomass?

  • g/m2 for land
  • g/m3 for water
• why is the biomass in each trophic level always less than the biomass in the trophic level below it?

  • biomass consists of all the cells and tissues of an organism
  • when animals eat, only a small proportion of food they ingest is converted into new tissue
  • only this part of the biomass is available for the next trophic level
• why is the energy at each trophic level measured in kJ/m2/yr?

  to allow for changes in photosynthetic production and consumer feeding patterns throughout the year
• what is the term given to the efficiency with which biomass/energy is transferred from one trophic level to the next?

  ecological efficiency
• why do producers only convert 1-3% of the sun's energy into chemical energy and subsequently biomass?

  • 90% solar energy is reflected, transmitted through the leaf, and some is of unusable wavelength
  • other factors can limit photosynthesis eg water availability
  • some of the energy is lost as it's used for photosynthetic reactions
• what is the total solar energy that plants convert to organic matter called?

  gross production
• what do plants use the energy produced from gross production for?

  respiration
• for plants, what is the remaining energy converted into biomass available for the next trophic level called?

  net production
• using net production and gross production, how can the energy to the next trophic level be calculated?

  net production= gross production - respiratory losses
• what kind of production occurs in produers?

  primary production
• what kind of production occurs in consumers?

  secondary production
• how much, of the biomass that consumers intake, is converted into organic tissue at each trophic level?

  very small amount
• why isn't all biomass consumed at each trophic level converted into organic tissue at CONSUMER level?

  • not all of the biomass of an organism is eaten eg plant roots/animal bones
  • some energy transferred to environment as heat because of respiration and movement
  • some parts of an organism are eaten but indigestible- these parts are egested as faeces
  • some energy lost in excretory materials like urine
• true or false? Biomass transfer is efficient

  FALSE- a lot of energy is lost at each trophic level
• what equation is used to calculate the efficiency of energy transfer between each trophic level?

  efficiency = biomass transferred (biomass available after the transfer/biomass intake (biomass available before the transfer) x 100
• how can human activities manipulate biomass in an ecosystem

  agriculture- environment manipulated to favour plant and animal species we eat

  • control of abiotic conditions for plant and animal survival eg- water, temp, by greenhouse use and stabling of animals
  • biotic factors controlled- competition removed (pesticides), predators removed by eg creating barriers
  • agriculture creates simpler food chains
  • only three trophic levels present - producers, primary, secondary consumers
  • so the minimum energy is lost as there are fewer trophic levels than in ecosystem, maximum energy consumed by humans
• what energy do consumers gain when they eat plants?

  chemical energy
• why do food chains rarely have more than 4 trophic levels?

  not sufficient biomass or stored energy left to support further organisms