Nitrogen Cycle

Question 1

nitrogen Cycle

Answer 1

the transfer of nitrogen as organic and inorganic compounds between the atmosphere, organisms and soil

Question 2

nitrogen Cycle processes

Answer 2

putrefaction
nitrogen fixation
nitrification
denitrification

Question 3

bacteria involved and their role

Answer 3

decomposers in putrefaction
azotobacter and rhizobium in nitrogen fixing
nitrobacter followed by nitrosomonas in nitrification
psuedomonas in denitrification

Question 4

putrefaction

Answer 4

decomposers use extracellular digestion to digest dead decaying organic material (dead plants and animals) via secretion of hydrolase enzymes (protease)
NH2 is removed from amino acids and released into the soi as NH4

Question 5

nitrification

Answer 5

NH4 - NO2 -NO3
nitrobacter oxidises ammonium to nitrite, then nitrosomonas oxides nitrite further to nitrate
aerobic condition
nitrates are added to soil

Question 6

assimilation

Answer 6

the NH4 and NO3 are actively transported across the root hair cell into the plant and are used to build organic compounds
-amino acids, nucleotides, chlorophyll

these are incorporated into the plants biomass
eventually they will be consumed by an animal and the process of putrefaction begins again

Question 7

denitrification

Answer 7

NO2- N2
psuedomonas reduces nitrogen from nitrate back into nitrogen gas and it is release back into the atmosphere from the soil
anaerobic conditions required

Question 8

nitrogen fixing

Answer 8

N2- NH4
nitrogenase enzyme catalyses the process

Rhizobium lives in root nodules of plants
-plant radicle and the bacteria both secrete chemoattractants to direct the bacteria to the plant root to form a mutualism relationship

azotobacter lives in the soil

both have leg haemoglobin which bind to molecular oxygen to prevent poisoning of the bacteria
require anaerobic conditions but need o2 to respire and for enzyme action

Question 9

improving nitrate circulation

Answer 9

crop rotation; so that different soil regions experience N2 fixing plants

aeration; puts more oxygen in soil to enhance nitrification bacteria and inhibit denitrification bacteria

soil drainage; prevents anaerobic conditions which encourage denitrification
artificial nitrogen fixing; haber process used to synthesise fertiliser

planting more nitrogen fixing plants

manure application; organic fertiliser

Question 10

human impact on nitrogen Cycle = Eutrophication

definition and process

Answer 10

eutrophication= the artificial and excessive enrichment of aquatic plant life due to leeching of fertilisers from crop into lakes and rivers

1. leeching
   rainwater washes excess fertiliser into rivers and lakes and creates high NH4 conc in water
2. algal Bloom
   algae use fertiliser as nourishment to grow on the surface of the water
   this blocks sunlight transmission through to photosynthetic life below
   the plants use the fertilisers to grow rapidly

((at this point the oxygen conc of water is still high due to high photosynthesis rate. as light intensity declines with increasing algal Bloom, the o2 content declines))

3. bacterial decomposition
   once all nitrates have run out, the algae die
   bacteria decompose the dead algae as nourishment
   bacteria population rapidly grows due to large amount of nourishment
4. anoxic condition
   o2 content too low to sustain life due to plants, bacteria, and organisms all demanding it

aquatic organisms die and this reduces biodiversity