Energy and ecosystems

• What is biomass?

  the total mass of living material in a specific area at a given time, representing the chemical energy stored in organisms
• How to measure dry mass?

  • dry the sample e.g. heat in oven at 50 degrees
  • Weigh repeatedly until mass becomes constant
• How to estimate chemical energy stored in biomass?

  Calorimetry

  • burn sample in bomb calorimeter
  • Energy released heats a known variable of water
  • Temperature increased is used to calculate energy content of biomass in kJ g-1
• What is GPP

  Gross primary production

  total chemical energy stored in plant biomass, in a given area or volume, in given time
• What is NPP

  Net primary production

  Chemical energy store in plant biomass after respiration losses have been removed
• How to calculate NPP?

  NPP = GPP - R
• How to work out net production of consumers:

  N = I + ( F - R )

  I= energy ingested

  F= faeces

  R= respiratory loses
• What is productivity?

  the rate at which biomass is produced
• What is primary productivity?

  The rate at which producers convert light energy into chemical energy via photosynthesis
• What is secondary productivity?

  The rate at which consumers produce biomass by eating other organisms
• What are the unites for rate of productivity?

  KJ ha-1 year-1
• What is mycorrhizae?

  The association between plant roots and fungi
• How does mycorrhizae benefit plants?

  • it increases the root’s surface area for water and mineral uptake which increases the plant's chance of survival
  • Fungi act as sponges and hold onto water , especially helpful if there is drought
• What is the role of fertilisers?

  To replace nutrients like nitrate or phosphate ions
• What are the two types of fertilisers?

  Organic and inorganic
• What is leaching?

  Where excess nutrients are washed away into bodies of water
• What is eutrophication?

  When nitrogen fertilisers leach into bodies of water
• Process of eutrophication:

  • excess fertilisers leach into nearby bodies of water
  • this causes algae to grow rapidly at the surface of water. This is called algal bloom
  • The algae block sunlight meaning aquatic plants can’t photosynthesise and so die
  • As the algae run out of nutrients, they also die
  • Saprobionts feed on dead algae and plants and increase in number
  • They respire aerobically so use up all the oxygen
  • This triggers death of organisms in the water such as fish
• process of the phosphorus cycle:

  • rocks contain phosphorus. Some of the rock breaks away because of weathering and releases phosphate into the soil
  • Plants absorb the soil with the phosphate to make phosphate-containing compounds like ATP.
  • Animals eat the plants and make their own phosphate-containing compounds.
  • The plants and animals die, and animals excrete.
  • saprobionts break down the dead animal or plants or the excretion which releases phosphate back into the soil.
  • Some of this phosphate moves into nearby bodies of water and some is reabsorbed by plants.
• Process of nitrogen cycle:


  • free-living and mutualistic nitrogen-fixing bacteria converts nitrogen gas into ammonia. This ammonia is then converted into ammonium ions through water in the soIl. This is called nitrogen fixation.
  • Nitrifying bacteria converts ammonium ions into nitrites and then nitrates with the use of oxygen. this is called nitrification
  • Saprobionts break down nitrogen-contains compounds like DNA into ammonium which then reacts with water in the soil to form ammonium ions.
  • Denitrifying bacteria converted nitrate back into nitrogen gas while respiring anaerobically.