Nitrogen cycle Flashcards
What is a decomposer?
Organism that feed on + breaks down dead plant/animal matter.
–> Turns organic compounds into inorganic (nutrients) available to photosynthetic producers in ecosystem.
Primarily microscopic fungi + bacteria
Why are decomposers referred to as saprotrophs?
Obtain energy from dead/waste organic material (saprobiotic nutrition)
Digest food externally –> secrete enzymes onto dead organisms/organic waste matter.
Enzyme break down complex organic molecules into simpler soluble molecules
Decomposers then absorb molecules
.:Decomposers release stored inorganic compounds + elements back into environment
What are detritivores?
Help speed up decay process by feeding on detritus –> dead + decaying material
Increases SA for decomposers
e.g: woodlice (break down dead wood) , earthworms (break down dead leaves)
Perform internal digestion
Why is nitrogen in the atmosphere important?
Essential for making amino acids + nucleic acid.
N2 from environment can’t just be taken up –> needs to be combined with other elements like O2/H2
Bacteria plays role in converting nitrogen into a useable form for plants –> would become limiting factor w/o bacteria
What are the abiotic processes involved in nitrogen cycle?
Atmospheric fixation by lightning
Industrial fixation –> Haber process - application of fertilisers
Describe nitrogen fixation:
Nitrogen-fixing bacteria Azotobacter + Rhizobium –> contain enzyme nitrogenase
Combines atmospheric nitrogen (N2). + H2 –> NH3 (ammonia).
Can be absorbed by plants.
Where are azotobacter and rhizobium found?
Azotobacter= free-living soil bacteria
Rhizobium = live inside root nodules of legumes.
What does the phrase ‘symbiotic mutualistic relationship mean?
Both plant + bacteria benefit
~> Plant gains AA from rhizobium (from nitrogen fixation)
~> Bactria gains carbohydrates produced by plant during photosynthesis –> use as energy source.
What does nitrification mean?
Process by which ammonium compounds in soil are converted into nitrogen-containing molecules–> used by plants.
Oxidation reaction –> only occurs in well-aerated soil.
What are the nitrifying bacteria used in nitrification?
Nitrosomonas –> oxidise ammonium compounds into nitrites (NO2-)
Nitrobacter –> oxidises nitrites into nitrates (NO3-)
What is denitrification?
Absence of oxygen (waterlogged soil)
–> denitrifying bacteria convert nitrates in soil back to nitrogen gas.
Only happens in anaerobic conditions.
Pseudomonas reduce nitrates to nitrogen gas –> replenishes nitrogen gas in atmosphere
Bacteria use nitrates as source of energy fro respiration + N2 gas released
What is ammonification?
Process which decomposers convert nitrogen-containing molecules in dead organisms, faeces + urine into ammonium compounds.
How does nitrogen move up a food chain?
- Absorb fixed nitrogen from surroundings
- Reduce nitrate ions to ammonia
- Make AA (amination)
- Consumer feed on living organism
- Consumer digest proteins/nucleic acids –> broken down into monomer units
- AA assimilated into new protein/nucleic acids
- Excess AA deaminated in liver to form ammonia
- Mammals convert ammonia to urea –> excreted as urine.
