The Nitrogen Cycle

Question 1

what is Nitrogen a component of?

Answer 1

Nucleic acids and proteins.

Question 2

What is meant by lack of availability of nitrogen?

Answer 2

Nitrogen is present in the air as N2 which is very inert, no nitrogen that is able to react with other chemicals is available.

Question 3

How is most nitrogen fixed? and how much of it?

Answer 3

78% fixed by a few bacterial species.

Question 4

Name the enzyme used in bioogical nitrogen fixation.

Answer 4

Nitrogenase enzyme.

Question 5

What does the nitrogenase enzyme allow?

Answer 5

The fixation of nitrogen into ammonium.

Question 6

What are the limitations of nitrogenase enzyme?

Answer 6

requires a lot of energy (16 ATP molecules per nitrogen atom fixed)
Is competitively inhibited by oxygen (requires anaerobic conditions)

Question 7

What are the two main groups of nitrogen fixing bacteria?

Answer 7

Cyanobacteria and Rhizobia

Question 8

Talk about cyanobacteria

Answer 8

Free-living bacteria in soil and water
live as chains of cells
some cells form cysts that are impervious to oxygen (creating anaerobic conditions for nitrogenase)
other cells respire aerobically (to cupply large amount of ATP needed)

Question 9

Talk about Rhizobia

Answer 9

10% of nitrogen is fixed with this this type of bacteria

they form a mutualistic relationship with legume plants (peas, beans, clover)

Question 10

Explain the mutualistic relationship between Rhizobia and legume plants

Answer 10

Rhizobia live in the root nodule that the plant fill with leghaemoglobin.
Leghaemoglobin binds to oxygen creating anaerobic conditions.
leghaemoglobin releases oxygen slowly=bacteria can produce ATP without O being inhibitor
Rhizobia converts ammonia to amino acids which are absorbed by the plant

Question 11

what happens to the ammonia formed by cyanobacteria?

Answer 11

some of the ammonium diffuses into soil and is absorbed by plants, some converted into nitrate ions first.

Question 12

How does nitrogen change once it is inside plants?

Answer 12

It is assimilated through metabolic reactions that form proteins and nucleic acids.

Question 13

What happens to the nitrogen when plants are eaten?

Answer 13

It is transformed to make animal proteins.

Question 14

What is ammonification?

Answer 14

a mineralisation process in which protein of dead animals and plants are decomposed by bacterium to release ammonium.

Question 15

What happens to ammonium not absorbed directly by plant roots?

Answer 15

converted into nitrates through nitrification.

Question 16

What are the two types of nitrifying bacteria required for nitrification? What do they do?

Answer 16

Nitrosomonas: convert ammonium to nitrite ions.
Nitrobacter: covnert nitrite ions to nitrate ions (which can be absorbed by plants)

Question 17

Describe processes which lead to loss of nitrogen from the soil ecosystem

Answer 17

Leaching out in water (can lead to eutrophication)

Denitrification ( nitrate converted to nitrogen gas)

Question 18

When does denitrification occur and by action of what bacteria?

Answer 18

In water logged soil and anaerobic conditions, free-living pseudomonas use ofygen from nitrate ions for respiration.

Question 19

describe biological stages in the cycling of phosphorus

Answer 19

plants absorb phosphorus from soil
plants fix phosphorus during ATP productio, n.a., phospholipids
Animals get it from eating plants
decomposers mineralise

Question 20

What is a major limiting factor of productivity in aquatic ecosystem and why?

Answer 20

phasphate deficiency, because phosphate ions combine with other chemicals to form insoluble compounds which cant be used by plants

Question 21

Why do plants absorb phosphate quickly?

Answer 21

Usually in short supply so evolution has brought this about. Fertilisers added to soil to encourage plant growth.

Question 22

What does the term chemeautotrophic mean?

Answer 22

organism which gains energy by oxidising inorganic ions.