nitrogen cycle

• • N to make proteins
  • plants & animals cant absorb frm air as N gas very stable & bonds holding atoms tgt need lots of energy to break (N2 triple covalent bond)
  • 2 ways to take out of air n convert to smth easier to absorb:

  1. Nitrogen fixing bacteria: ‘free living’ in soil + root nodules of leguminous plants (eg peas, beans, clover, peanuts) (in exchange for carbohydrates etc) take N gas -> ammonia NH3 / nitrate NO3- in soil
  2. Lightning: high temperatures & pressures break N2 bonds -> N + O2 -> nitrous oxides eg N2O & NO2 -> dissolve in rainwater (HNO3), deposited on soil surface during rainfall
• • Plants absorb nitrates in soil, nitrogen to make proteins
  • Animals eat plants (or other animals) n get their nitrogen frm the proteins in the plant or animal
  • Waste (urine and faeces) frm animals -> nitrogen back into soil as ammonium (NH4+) compounds (the urea in urine contains nitrogen)
  • animals & plants die -> decay -> proteins inside r broken down into ammonium compounds n put back into soil by decomposers
• • plants cant absorb ammonium compounds -> NITRIFYING bacteria: ammonium -> NITRITES NO2- and then oxidised to NITRATES NO3- (plants absorb)
  • this is nitrification (in well aerated soils)
  • anaerobic unhelpful bacteria - denitrifying bacteria in poorly aerated soil
  • take nitrates out of the soil, convert back to N gas or nitrous oxide N2O
  • Farmers reduce them by ploughing & turning over soil (help to aerate the soil)
• bacteria summary

  good:

  1. Nitrogen Fixing: N2 gas -> nitrates NO3- (or ammonium NH4+), absorbed by plants. in root nodules of leguminous plants & free living
  2. Nitrifying: ammonium NH4+ -> nitrites NO2- then into nitrates NO3- (plants absorb)

  bad:

  1. Denitrifying: in anaerobic conditions, nitrates NO3- -> N2 gas / nitrous oxide N2O, reducing availability of nitrogen for plants
• label

  A) nitrates

  B) active transport

  C) amino acids

  D) proteins

  E) feeding

  F) deamination

  G) decomposition

  H) protein

  I) microorganisms

  J) ammonium

  K) nitrification

  L) nitrate

  M) nitrogen fixing

  N) soil

  O) legume

  P) root nodules

  Q) lightning

  R) atmospheric

  S) denitrifying

  T) nitrogen fixing

  U) nitrifying