3.3.4 Energy Transfer Through Ecosystems Flashcards Preview

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Flashcards in 3.3.4 Energy Transfer Through Ecosystems Deck (45)
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What is biomass?

Mass of living material


What can biomass be thought as?

Chemical energy stored in organisms


How is biomass measured in terms of? (2x)

  • Mass of carbon that organism contains
  • Dry mass of organism's tissue per unit area


What is dry mass?

Mass of organism with water removed


Describe how you would measure dry mass

  1. Sample of organism is dried in oven set at low temp (heat to evaporate water)
  2. Sample weighed at regular intervals (every day)
  3. Once mass becomes constant = all water is removed
  4. Weigh the dry mass
  5. (Result from sample can be scaled to give dry mass (biomass) of total population or area being investigated)


 Mass of carbon present is generally __% of dry mass



How you can estimate the amount of chemical energy stored in biomass?

By burning biomass in calorimeter

Heat given off = how much energy is in it


Describe how you can estimate the amount of chemical energy stored in biomass using calorimetery

  1. Sample of dry biomass is burnt and energy released is used to heat known volume of water
  2. Change in temperature of water is used to calculate the chemical energy of dry biomass


What's the unit for biomass?

kg m-2


Name reasons why most of the sun's energy isn't converted to
organic matter by photosynthesis

  1. Most of Sun's energy is reflected by into space
  2. Not all wavelengths of light can absorbed & used for photosynthesis
  3. Light may not fall on chlorophyll molecule
  4. Factor e.g. CO2 levels may limit rate of photosynthesis


State the equation to work out the efficiency of energy transfers

Energy transfer = energy available after transfer ÷ energy available before the transfer x 100


Name 2 cons of pyramids of numbers

  • No account of size is taken e.g. one giant tree = one tiny aphid
    • ∴ sometime pyramid is not a pyramid
  • Number of individuals can be so large that it's impossible represent them accurately on same scale as other species in food chain


Name a pro of pyramids of biomass

  • More reliable, quantitative descriptions of food chain


Name 2 cons of pyramids of biomass

  • Only represents the organisms present at the time
    • Doesn't account for seasonal differences
  • Organisms must be killed ∴ small sample = may not be representative


Name 2 pros of pyramids of energy 

  • Most accurate representation of energy flow through food chain
  • Results are more reliable than biomass
    • Two animals could have same dry mass but store different amounts of energy
      • e.g. organism with more stored fat = more energy than other organism will less fat


Name a con of pyramids of energy 

  • Collecting data is difficult + complicated
    • Data has to be collected in given area for set period of time


Define gross primary production (GPP)

Total amount of chemical energy converted from light energy by plants, in given area


50% of gross primary production is lost to environment as heat as _____ _____. What is this known as?

50% of gross primary production is lost to environment as heat plants respire

 Respiratory loss (R)


What is net primary production (NPP)?

  • Remaining chemical energy (after respiratory loss)
    • Energy available to plant for growth and reproduction (i.e. energy stored in its biomass)
    • Also energy available to organisms at next stage in food chain i.e. herbivores and decomposers


State the equation to work out net primary production (NPP)



What is primary productivity?

Rate at which plants convert light energy into chemical energy 

kJ ha-1 year-1


Name 3 reasons why not all chemical energy stored in consumers' food is transferred to next trophic level

  • Not all parts of food is eaten 
  • Parts that are ingested:
    • Some are indigestible ∴ egested as faeces
      • Chemical energy stored in these parts ∴ lost to environment
    • Some energy is lost environment though respiration or execration of urine


What is consumers' net production AKA secondary production?

Energy that's left i.e. stored in consumers' biomass & is available to next trophic level


State how net production of consumers can be calculated




Calculate net primary productivity


What do food chains + webs show?

How energy is transferred through ecosystem


What is each stage in a food chain called?

Trophic level


Name the 2 main ways farming practice increases the amount of energy available for human consumption

  1. Energy lost to other organisms (e.g. pests) can be reduced
  2. Energy lost through respiration can be reduced

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