Nitrogen Cycle

Question 1

How much nitrogen in atmosphere?

Answer 1

78%

Question 2

Why does the nitrogen cycle exist?

Answer 2

• The nitrogen in the atmosphere is inaccessible to most organisms
• Transforms nitrogen gas into various chemical forms organisms can use
• Facilitates continuous movement through ecosystems

Question 3

Nitrogen cycle: stages

Answer 3

1. Nitrogen fixation
2. Ammonification
3. Nitrification
4. Denitrification

Question 4

Also involves:

Answer 4

• Decomposition by detritivores
• Decomposition by saprobionts
• Assimilation by producers like plants

Question 5

Decomposition by detritivores

Answer 5

• They speed up decay by feeding on detritus, breaking it down into smaller pieces of organic material

Question 6

Decomposition by saprobionts

Answer 6

• They convert nitrogen-containing molecules in dead organisms, faeces and urine into substances like ammonia

Question 7

Assimilation by producers like plants:

Answer 7

• This is when producers absorb useful substances and incorporate them into other compounds that aid their survival

Question 8

Nitrogen fixation definition:

Answer 8

• Process converts atmospheric nitrogen gas (N2) into nitrogen-containing compounds like ammonia (NH3)

Question 9

How is atmospheric nitrogen gas fixed:

Answer 9

• Mutualistic bacteria (Rhizobium) in the root of leguminous plants
• Free-living bacteria (Azotobacter)
• Abiotic processes

Question 10

Mutualistic bacteria (Rhizobium)

Answer 10

• Fix N2 into NH3
• NH3 converted into amino acids for the plant
• Plant provides carbohydrates to the bacteria

Question 11

Free-living bacteria (Azotobacter)

Answer 11

• Fix H2 into NH3 and then amino acids
• When they die and are decomposed by saprobionts, nitrogen-rich compounds are released and converted into a form that can be assimilated by plants

Question 12

Abiotic processes:

Answer 12

• Lightning
• Artificial fertilisers
• Haber process

All fix N2

Question 13

Ammonification definition

Answer 13

• Converts organic nitrogen-containing compounds in dead organisms or waste into substances like NH3 or ammonium ions (NH4+)

Question 14

How does ammonification make NH3 / NH4+ available to plants?

Answer 14

1. Death or excretion by living organisms releases nitrogen-rich organic substances like urea, proteins, nucleic acids and vitamins
2. Saprobionts decompose these into simpler substances like NH4+
3. NH4+ can be absorbed and assimilated by plants

Question 15

Nitrification definition:

Answer 15

NH3 and NH4+ are first oxidised to nitrates (NO2^-) and then to nitrates (NO3^-)
Plants can absorb NO3^- through roots and assimilate them into plant

Question 16

Two stages of nitrification?

Answer 16

1. Nitrosomonas bacteria oxidise NH3 and NH4^+ into NO2^-
2. Nitrobacter bacteria further oxidise NO2^- into NO3^-

Question 17

Denitrification definition:

Answer 17

• Process converts NO3^- back into N2.
• Excessive denitrification can deplete soil nutrients, negatively impacting plant growth

Question 18

How denitrification converts nitrates into atmospheric nitrogen?

Answer 18

1. Carried out by denitrifying bacteria
2. It occurs under anaerobic conditions, such as waterlogged soils

Question 19

What would happen without nitrogen cycle?

Answer 19

• Run out of usable nitrogen
• Leading to decline in vital biological molecules needed by organisms

Question 20

What are the biological molecules that contain nitrogen?

Answer 20

• Proteins
• DNA
• RNA

Question 21

What human activities have altered the natural nitrogen cycle?

Answer 21

• Agriculture
• Combustion of fossil fuels

Question 22

What will balancing nitrogen cycle do?

Answer 22

• Maintain ecosystem health and sustainability

Question 23

Enzymes involved in ammonification?

Answer 23

Saprotrophic bacteria
(decomposers)

Question 24

Nitrification enzymes:

Answer 24

• Nitrosomonas
• Nitrobacter

Question 25

Nitrogen fixation enzymes:

Answer 25

- Rhizobium (mutualistic) - Azotobacter (free-living)

Question 26

Denitrification enzymes:

Answer 26

Denitrifying bacteria - Anaerobic conditions