The nitrogen cycle

Question 1

How is N2 gas produced?

Answer 1

Denitrifying bacteria in anaerobic conditions

Question 2

How is NO3 ^- produced?

Answer 2

Fixation by lightning
The Haber process, then used as fertilisers
Nitrobacter oxidises ammonium ions NH4^+ to NO2^-

Question 3

How is NH4^+ produced?

Answer 3

• The Haber process, released as fertilisers
• Rhizobium bacteria fixes nitrogen in root nodules on leguminous plants which are then consumed by animals which release it again in death or in excretion as urea
• Azobacter fixes nitrogen
• NO3^- is absorbed by plants from the soil and is converted to ammonium ions by animals

Question 4

How is NO2^- produced?

Answer 4

Rhizobium oxidises NH4^+ to NO2^-

Question 5

What are saprotrophs and why are they important?

Answer 5

They are bacteria that feed on dead matter
by excreting enzymes which digest their food outside their bodies
this allows nitrogen and other nutrients to be released back into the soil

Question 6

How else can nitrates reach the soil?

Answer 6

Leeched from fertilisers

Question 7

What does Chemoautotrophic mean and how does it apply to the nitrogen cycle?

Answer 7

It applies to Nitrosomes and Nitrobacter as they both get their energy from the process of oxidising nitrogen

Question 8

What should you remember about wet soils?

Answer 8

It creates anaerobic conditions which are conducive only to denitrifying bacteria
these release N2 gas back into the atmosphere