Nitrogen Cycle

Question 1

Why is microbial involvement fundamental for nitrogen cycle?

Answer 1

• several key reactions are carried out exclusively in nature by microorganisms

Question 2

What is the most stable type of bond?

Answer 2

triple

Question 3

What would happen if there was no nitrogen cycle?

Answer 3

all nitrogen would be lost, give up free life

Question 4

What is an environmental example of a nitrogen fixing bacteria?

Answer 4

pseudomonas

Question 5

What happens when nitrates leach?

Answer 5

they grab nitrites and can enter atmosphere

Question 6

Why is nitrogen needed by organisms?

Answer 6

• synthesis of proteins
• nucleic acids

Question 7

What does a more valent nitrogen form mean?

Answer 7

more variety of transformation

Question 8

What is a highly stable form of nitrogen? what is it used by?

Answer 8

N2, used by restricted group

Question 9

Define nitrification

Answer 9

• conversion of ammonia to nitrate by nitrifying microorganisms (nitrate production)

Question 10

Where does nitrification occur? Why?

Answer 10

Well drained soils at neutral pH
- oxygen is able to penetrate soil matrix

Question 11

Define chemolithotroph

Answer 11

• chemo - energy source
• litho - inorganic forms of carbon
• gets energy from inorganic carbon

Question 12

Where do chemolithotrophs get their energy from?

Answer 12

• oxidation of ammonia or nitrite

Question 13

Why put manure in soil?

Answer 13

• fertilize it with organic material + encourage plant growth

Question 14

What do plants require for growth? what do they not want?

Answer 14

• want ammonia in biologically useable forms
• don’t want nitrification

Question 15

Why don’t plants want nitrification?

Answer 15

Deprives soil of ammonia needed

Question 16

What form of nitrogen is used by plants in soil?

Answer 16

• Nitrate (No3)

Question 17

What is the process that occurs with nitrate and ammonia in soil?

Answer 17

• NO3 and clay are neg charged and repel each other = nitrification and ends up in water to drive nitrogen out
• Ammonia charge is positive and attaches long enough for plants to use it

Question 18

What happens if there is excess ammonia?

Answer 18

• bacteria will transfer to nitrites and nitrates causing leaching

Question 19

Define denitrification

Answer 19

• conversion of nitrate to nitrous oxide or N2 by denitrifiers
• Nitrate consumption

Question 20

What are the conditions during denitrification?

Answer 20

Anoxic (anaerobic)

Question 21

What is used as the electron acceptor during denitrification?

Answer 21

NO3 rather than O2

Question 22

What kind of anaerobes are denitrifiers and where are they found? Give an example.

Answer 22

facultative, perform in waterlogged soil
- pseudomonas

Question 23

What kind of anaerobes are denitrifiers and where are they found? Give an example.

Answer 23

facultative, perform in waterlogged soil
- pseudomonas

Question 24

Define ammonification

Answer 24

decomposition of organic nitrogen compounds to produce ammonia

Question 25

What conditions is ammonia typically stable under?

Answer 25

- ANOXIC

Question 26

What is the conversion during nitrogen fixation

Answer 26

nitrogen gas --> ammonia

Question 27

What type of organism carries out nitrogen fixation

Answer 27

aerobic chemoorganotrophs

Question 28

What is the major reservoir of nitrogen?

Answer 28

atmosphere

Question 29

What does biological nitrogen fixation require?

Answer 29

nitrogenase

Question 30

Define nitrogenase

Answer 30

- enzyme composed of 2 proteins: dinitrogenase and dinitrogenase reductase

Question 31

What kind of protein is denitrogenase?

Answer 31

MoFe

Question 32

What kind of protein is dinitrogenase reductase?

Answer 32

Fe

Question 33

What is the electron flow in nitrogen fixation?

Answer 33

donor--> dinitrogenase reductase --> dinitrogenase --> N2 --> HN3

Question 34

What are nif regulators? give an example.

Answer 34

genetic regulators ex. kelbsiella pneumoniae

Question 35

What are the 2 types of nitrogen-fixing organisms?

Answer 35

- nonsymbiotic - symbiotic

Question 36

Where are nonsymbiotic nitrogen-fixing bacteria found? give an example

Answer 36

- rhizosphere (free living) - cyanobacteria

Question 37

Define Rhizosphere

Answer 37

soil impacted by plant root

Question 38

Define Rhizoplane

Answer 38

surface of root

Question 39

What is a specific structure cyanobacteria has that protects nitrogenase from O2?

Answer 39

heterocyst

Question 40

What is a specific structure cyanobacteria has that protects nitrogenase from O2?

Answer 40

heterocyst

Question 41

What is a symbiotic nitrogen-fixing bacteria and what is an example?

Answer 41

- have own ammonia generators attached to root matrix - ex. peanuts, soybean

Question 42

What is a root nodulator?

Answer 42

- N-fixing bacteria that are breedable with plants

Question 43

Define bacteroid

Answer 43

- bacteria like = no longer capable of free living life and becoming bacteria again - once you reach certain point you cannot return

Question 44

Steps in nodule formation

Answer 44

1. recognition/attachment 2. invasion of root hair 3. travel via infection thread to main root 4. formation of bacteroid 5. continued division to form nodule

Question 45

What is leghemoglobin and what does it do?

Answer 45

- O2 binding Fe protein - controls O2 levels in root nodule - found in healthy nodules - oxygen buffer

Question 46

What does leghemoglobin protect?

Answer 46

nitrogenase from O2

Question 47

What is the ratio of O2 bound --> leghemoglobin TO free O2 in nodule?

Answer 47

10 000:1

Question 48

What do bacteroids result from?

Answer 48

- rapid multiplication of bacteria in plant cells

Question 49

What do bacteroids cause physiologically?

Answer 49

swelling

Question 50

Define sybiosome

Answer 50

- bacteroid surrounded by portions of plant cell membrane

Question 51

Where is nitrogenase localized?

Answer 51

in bacteroid

Question 52

What happens to node and bacteroid when plant dies?

Answer 52

- released to surrounding soil: dormant cells can proliferate to initiate another infection

Question 53

Can bacteroid forms divide?

Answer 53

No

Question 54

what is symbiosome dependent on?

Answer 54

- plant for energy required for N2 fixation

Question 55

When does dissimilatory nitrate reduction occur?

Answer 55

- as substitute for aerobic respiration when O2 levels are low

Question 56

Why is N cycle naturally in balance?

Answer 56

N cycled between unusable N2 and usable NH3, NH4 ad NO3

Question 57

What is the main result of assimilatory nitrate reduction?

Answer 57

- reduce nitrate to ammonia - nitrate-->nitrite-->ammonia --> incorporated into organic carbon