The Nitrogen Cycle - Stages Flashcards
What do living things need the element nitrogen to make?
4
Proteins
DNA
RNA
Other biomolecules
What is the chemical formula for nitrogen gas?
N2
What percentage of the air is made up of nitrogen gas?
79%
Why can’t the nitrogen gas in air be used by organisms?
Because it is inert or unreactive and cannot be used by plants and animals
Define nitrogen fixation.
Nitrogen fixation is the conversion of nitrogen gas into ammonia (NH3), ammonium (NH4+) or nitrate (NO3-)
What is the formula for ammonia?
NH3
What is the formula for ammonium?
NH4+
What is the formula for nitrate?
NO3-
What is nitrogen fixation carried out by?
4
Volcanic action
Lightning
Industrial processes
By nitrogen-fixing bacteria
Where can nitrogen-fixing bacteria be found?
2
They can be found free in the soil
They may be associated with the roots of certain plants
Some nitrogen-fixing bacteria may be associated with the roots of certain plants, where exactly are they found.
They live in nodules (swellings) on the roots of a group of plants called legumes,
Some nitrogen-fixing bacteria live in nodules on the roots of what group of plants?
Legumes
Where do nitrogen-fixing bacteria live in legumes?
In nodules on the roots
Give four examples of legumes which have nitrogen-fixing bacteria living in nodules on their roots.
Clover
Soya beans
Peas
Beans
Is nitrogen-fixation an aerobic or anaerobic process?
Nitrogen fixation is an anaerobic process
Nitrogen fixation is an anaerobic process, what does this mean?
This means it does not require oxygen
Nitrogen-fixation is an anaerobic process, how is it adapted for this process.
The nodules on roots allow the nitrogen-fixing bacteria to escape from oxygen
How can the relationship between the nitrogen-fixing bacteria and the legume be described?
It can be described as a form of symbiosis
Describe the symbiotic relationship between the nitrogen-fixing bacteria and the legume.
The bacteria get food and the plant gets nitrates (this is technically mutualism)
What are nitrates converted into?
They are converted into plant and animal protein, DNA and RNA
What organisms bring about decomposition?
Bacteria and fungi of decay
What do bacteria and fungi of decay cause the decomposition of?
The decomposition of dead organisms
Where are bacteria and fungi of decay mostly found?
They are mostly found in the soil
What is released when bacteria and fungi of decay decompose dead organisms?
These organisms release nitrogenous compounds such as ammonia (NH3) into the soil
Define nitrification.
Nitrification is the conversion of ammonia and ammonium (NH4+) compounds to nitrite and then to nitrate
What carries out nitrification?
Nitrifying bacteria
Where are nitrifying bacteria found?
They are found in the soil
How do nitrifying bacteria get their food?
They are chemosynthetic, i.e. they make their own food (normally in darkness in the soil) using energy from chemical reactions
What happens to some of the nitrate made by nitrifying bacteria?
Some of the nitrate formed in the soil is absorbed and used by plants
Define denitrification.
Denitrification is the conversion of nitrates to nitrogen gas
What carried out denitrification?
Denitrifying bacteria
Where are denitrifying bacteria found?
In the soil
Are denitrifying bacteria aerobic or anaerobic?
They are anaerobic
Where is the preferred place for denitrifying bacteria to live?
Swampy soil or deep down in the soil where water collects to produce anaerobic conditions
Why do denitrifying bacteria like living deep down in the soil?
As water collects here to produce anaerobic conditions
List the stages of the nitrogen cycle.
6
- Describe the need for the nitrogen cycle
- Nitrogen fixation
- Decomposition
- Nitrification
- Plants absorb nitrate
- Denitrification
