13.2 Energy transfer and productivity

• What factors control the distribution and abundance of organisms in a habitat?

  Both biotic factors (living) and abiotic factors (non-living)
• What are examples of biotic factors?

  Predators and disease
• What are examples of abiotic factors?


  Light levels and temperature
• What is a niche in an ecosystem?


  A niche is the particular role of a species in its habitat, including its interactions with biotic and abiotic factors
• What is the source of all energy in ecosystems?

  The Sun
• What are autotrophs?


  Organisms that produce their own food using energy from the Sun
• What are heterotrophs?


  Organisms that cannot synthesize their own food
• What percentage of chemical food energy is passed on between organisms in the food chain?


  Approximately 10%
• What happens to the other 90% of chemical food energy in the food chain?


  • Lost as uneaten parts (e.g., bones)
  • Lost through decay of dead material (e.g., bacteria)
  • Lost in excretion (e.g., energy in faeces)
  • Lost in exothermic reactions (e.g., heat in respiration)
• How can biomass be measured?


  In terms of mass of carbon or dry mass of tissue per given area per given time
• Why is dry mass preferred over wet mass for measuring biomass?


  Because wet mass can vary too much
• How can the chemical energy stored in dry biomass be estimated?

  Using calorimetry
• What is a bomb calorimeter used for?


  To estimate the chemical energy in a biomass sample
• What happens to the bomb calorimeter during the calorimetry process?


  It is submerged in water to measure the change in water temperature
• What does net primary productivity (NPP) represent?


  The rate at which energy is transferred into organic molecules that make up new plant biomass
• How is NPP calculated?


  NPP = GPP - R
• What does gross primary productivity (GPP) measure?


  The rate at which energy is incorporated into organic molecules in plants during photosynthesis
• What is the significance of net primary production in an ecosystem?


  It is available for plant growth, reproduction, and other trophic levels like decomposers and herbivores
• How can the net production of consumers (N) be calculated?


  N = I - (F + R)
• What do the variables in the equation N = I - (F + R) represent?


  I is the chemical energy store in ingested food, F is the energy lost in faeces and urine, and R is the respiratory losses
• formula for efficiency of energy transfer


  percentage efficiency = energy available after the transfer divided by energy available before the transfer x 100