Module 6: Nitrogen Cycle Flashcards
What are the 4 key processes involved in the nitrogen cycle?
-nitrogen fixation
-denitrification
-ammonification
-nitrification
The nitrogen cycle also involves 3 other processes:
1)decomposition by detritivores
2)decomposition by saprobionts
3)assimilation by producers like plants
Describe what each of these mean/entail
1)they feed on detritus which breaks it down into smaller pieces of organic material(speed up rate of decay)
2)convert nitrogen containing molecules in dead organisms/faeces/urine into ammonia
3)producers absorb useful substances and incorporate them into other compounds to aid their survival
Define nitrogen fixation
Nitrogen gas can be fixated by what 2 types of bacteria?
converts nitrogen gas into nitrogen containing compounds like ammonia
Rhizobium and Azotobacter
Where in leguminous plants are Rhizobium found , and describe what susbtances are exchanged between the plant and the bacteria
in the root nodules
the bacteria produce ammonia which is converted into amino acids for the plant , whilst the plant provides carbs to the bacteria
Name 3 abiotic processes that can also fix nitrogen gas
lightning
artificial fertilisers
the Haber process
Define ammonification
the process of converting organic nitrogen containing compounds in dead organisms/waste into ammonia or ammonium ions
Make 3 points about how ammonification makes ammonia and ammonium ions available to plants
1)death or excretion from living organisms releases nitrogen rich organic substances like urea/nucleic acids etc
2)saprobionts decompose these into simpler substances like ammonium ions
3)these can then be absorbed and assimilated by plants
In nitrification , NH3 and NH4+ are first oxidised into what … and then are further oxidised into …
what can then happen to these substances?
nitrites (NO2-) and then nitrates (NO3-)
they can be absorbed by the roots and assimilated
Name the bacteria responsible for oxidising NH3 and NH4+ into nitrites
Name the bacteria responsible for converting nitrites into nitrates
nitrosomonas bacteria
nitrobacter
Define denitrification
What can excessive denitrification result in?
the process of converting nitrates back into nitrogen gas
it can deplete soil nitrogen which will negatively impact plant growth
Make 2 points about how denitrification converts nitrates into nitrogen gas
-its carried out by denitrifying bacteria
-it occurs under anaerobic conditions (eg in water logged soil)
What would happen to ecosystems without the nitrogen cycle?
make 2 points
they would run out of usable nitrogen
-this would lead to a decline in vital biological molecules needed by organisms , such as proteins , DNA and RNA
