The Nitrogen Cycle Flashcards
what is Nitrogen a component of?
Nucleic acids and proteins.
What is meant by lack of availability of nitrogen?
Nitrogen is present in the air as N2 which is very inert, no nitrogen that is able to react with other chemicals is available.
How is most nitrogen fixed? and how much of it?
78% fixed by a few bacterial species.
Name the enzyme used in bioogical nitrogen fixation.
Nitrogenase enzyme.
What does the nitrogenase enzyme allow?
The fixation of nitrogen into ammonium.
What are the limitations of nitrogenase enzyme?
requires a lot of energy (16 ATP molecules per nitrogen atom fixed)
Is competitively inhibited by oxygen (requires anaerobic conditions)
What are the two main groups of nitrogen fixing bacteria?
Cyanobacteria and Rhizobia
Talk about cyanobacteria
Free-living bacteria in soil and water
live as chains of cells
some cells form cysts that are impervious to oxygen (creating anaerobic conditions for nitrogenase)
other cells respire aerobically (to cupply large amount of ATP needed)
Talk about Rhizobia
10% of nitrogen is fixed with this this type of bacteria
they form a mutualistic relationship with legume plants (peas, beans, clover)
Explain the mutualistic relationship between Rhizobia and legume plants
Rhizobia live in the root nodule that the plant fill with leghaemoglobin.
Leghaemoglobin binds to oxygen creating anaerobic conditions.
leghaemoglobin releases oxygen slowly=bacteria can produce ATP without O being inhibitor
Rhizobia converts ammonia to amino acids which are absorbed by the plant
what happens to the ammonia formed by cyanobacteria?
some of the ammonium diffuses into soil and is absorbed by plants, some converted into nitrate ions first.
How does nitrogen change once it is inside plants?
It is assimilated through metabolic reactions that form proteins and nucleic acids.
What happens to the nitrogen when plants are eaten?
It is transformed to make animal proteins.
What is ammonification?
a mineralisation process in which protein of dead animals and plants are decomposed by bacterium to release ammonium.
What happens to ammonium not absorbed directly by plant roots?
converted into nitrates through nitrification.
What are the two types of nitrifying bacteria required for nitrification? What do they do?
Nitrosomonas: convert ammonium to nitrite ions.
Nitrobacter: covnert nitrite ions to nitrate ions (which can be absorbed by plants)
Describe processes which lead to loss of nitrogen from the soil ecosystem
Leaching out in water (can lead to eutrophication)
Denitrification ( nitrate converted to nitrogen gas)
When does denitrification occur and by action of what bacteria?
In water logged soil and anaerobic conditions, free-living pseudomonas use ofygen from nitrate ions for respiration.
describe biological stages in the cycling of phosphorus
plants absorb phosphorus from soil
plants fix phosphorus during ATP productio, n.a., phospholipids
Animals get it from eating plants
decomposers mineralise
What is a major limiting factor of productivity in aquatic ecosystem and why?
phasphate deficiency, because phosphate ions combine with other chemicals to form insoluble compounds which cant be used by plants
Why do plants absorb phosphate quickly?
Usually in short supply so evolution has brought this about. Fertilisers added to soil to encourage plant growth.
What does the term chemeautotrophic mean?
organism which gains energy by oxidising inorganic ions.
