Nitrogen Cycle - Paper 2 Flashcards
(24 cards)
What is the nitrogen cycle?
The process by which nitrogen is recycled through an ecosystem
What is nitrogen fixation?
The process where atmospheric nitrogen in the air is converted to nitrates and ammonia in the soil
Name the five processes of the nitrogen cycle
In order
Nitrogen-fixation - atmospheric nitrogen to ammonia (or nitrates if lightning)
Nitrification - ammonia to nitrites to nitrates
Assimilation - nitrates to biological molecules
Decomposition - biological molecules (e.g. proteins and urea) to ammonia
Denitrification - nitrates to atmospheric nitrogen
Denitrification is the only one which doesn’t fit this as a complete cycle - it happens simultaneously with the other processes - it turns nitrates (not ammonia) into atmospheric nitrogen - it is not the direct opposite of either nitrogen fixing or nitrifying bacteria
Give the two methods of nitrogen fixation
Lightning
* converts atmospheric nitrogen directly into nitrates
Nitrogen-fixing bacteria
* found in soil and roots of some plants
* convert atmospheric nitrogen into ammonia
Describe lightning’s role in the nitrogen cycle
Nitrogen fixation
Converts atmospheric nitrogen directly to nitrates in the soil
Describe the role of nitrogen fixing bacteria in the nitrogen cycle
Nitrogen fixation
Converts atmospheric nitrogen to ammonia in the soil
Bacteria are found in soil and roots of some plants
What is nitrification?
The process where nitrifying bacteria in the soil converts ammonia in the soil into nitrites and then to nitrates
Name the organism which carries out nitrification
Nitrifying bacteria
What does nitrifying bacteria convert ammonia to before it is converted to nitrates?
Nitrites
Give the two steps of nitrification
Ammonia in soil converted to nitrites
Nitrites converted to nitrates
All done by nitrifying bacteria in the soil
Name the process by which nitrogen enters the food chain
Assimilation
What is assimilation in the nitrogen cycle?
The process where plants absorb nitrates and ammonium ions, and use them to create biological molecules such as proteins. These biological molecules form part of the plant’s tissues
when animals eat plants they assimilate these nitrogen containing compounds (e.g. proteins) into their own bodies.
What is decomposition in the nitrogen cycle?
When decomposers feed on dead organic matter and animal waste excretions, converting urea and proteins into ammonia.
Name the 3 types of bacteria involved in the nitrogen cycle in order
Starting from conversion of atmospheric nitrogen to ammonia in the soil
Nitrogen fixing bacteria
Nitrifying bacteria
Denitrifying bacteria
What is denitrification?
The process where denitrifying bacteria in the soil convert nitrates back into atmospheric nitrogen
Name the organism which is responsible for denirtification
Denitrifying bacteria
Where is denitrifying bacteria found?
In the soil
Why is denitrification bad for plants?
Because it means there are fewer nitrates in the soil
reducing the amount available for the plants to for absorption and assimilation.
Why is the nitrogen cycle necessary?
Both plants and animals need nitrogen ot survive and they can’t directly absorb atmospheric nitrogen so it needs to be converted to a form they can take in
How do plants recieve nitrogen?
From the soil, either as nitrates or ammonium ions
How do animals recieve nitrogen?
Animals get their nitrogen from digesting plants (or other animals)
Which nitrogen cycle process does lightning skip?
Nitrification
It converts atmospheric nitrogen directly to nitrates so nitrifying bacteria isn’t needed to turn the ammonia from nitrogen fixing bacteria to nitrites and then nitrates
Name two biological molecules which contain nitrogen
DNA
Proteins
Where can nitrogen fixing bacteria be found?
In the soil and the roots of some plants
