Plenty of nitrogen, little to use
Why nitrogen needs a cycle.
Surrounded by nitrogen
Most of the air around you is nitrogen gas. Yet plants cannot just take it in and use it.
Why might that be?
What this lesson covers
The idea
Nitrogen, essential for proteins and nucleic acids, is mostly atmospheric N2, which is non-reactive and must be converted to soluble compounds before organisms can use it; its movement between air, soil, water and organisms is the nitrogen cycle.
Surrounded by nitrogen
Most of the air around you is nitrogen gas. Yet plants cannot just take it in and use it.
Why might that be?
- The gas is very unreactive
- There is too little of it
- Plants do not need nitrogen
The nitrogen puzzle
Press Next step.
Plenty but not usable
Nitrogen is needed to make proteins, yet the nitrogen gas in the air cannot be used as it is. Nature has to turn it into other compounds first, and that is what the nitrogen cycle is about.
Nitrogen, essential for proteins and nucleic acids, is mostly atmospheric N₂, which is non-reactive and must be converted to soluble compounds before organisms can use it. Its movement between air, soil, water and organisms is the nitrogen cycle.
Notes
N₂ in the air is non-reactive, so it must be converted to soluble compounds for organisms to use. Nitrogen moving between air, soil, water and organisms is the nitrogen cycle.
Check yourself
Nitrogen is essential for making which molecules?
Where is the largest reservoir of nitrogen?
Why can plants and animals not use nitrogen gas directly?
What must happen to N₂ before living beings can absorb the nitrogen?
- Only water. Nitrogen is essential for proteins and nucleic acids.
- Proteins and nucleic acids — correct. Yes!
- Only sugar. The chapter names proteins and nucleic acids as the molecules that need nitrogen.
- In coal and oil. Fossil fuels are reservoirs of carbon. The largest reservoir of nitrogen is the atmosphere.
- In the oceans. The chapter names the atmosphere as the largest reservoir of nitrogen.
- In the atmosphere — correct. Yes!
- It is rather non-reactive — correct. Yes!
- It is not present in the air. Nitrogen gas, N₂, is the main gas of the air (78%).
- It is too hot. The chapter says nitrogen gas is rather non-reactive.
- It must be burnt as a fuel. The chapter says it must be converted to soluble compounds.
- It must be converted into soluble compounds — correct. Yes!
- It must be cooled. The chapter says N₂ must be converted to soluble compounds that living beings can absorb.