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bi374 > Nitrogen Cycle > Flashcards

Nitrogen Cycle Flashcards

1
Q

Why is microbial involvement fundamental for nitrogen cycle?

A
  • several key reactions are carried out exclusively in nature by microorganisms
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2
Q

What is the most stable type of bond?

A

triple

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3
Q

What would happen if there was no nitrogen cycle?

A

all nitrogen would be lost, give up free life

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4
Q

What is an environmental example of a nitrogen fixing bacteria?

A

pseudomonas

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5
Q

What happens when nitrates leach?

A

they grab nitrites and can enter atmosphere

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6
Q

Why is nitrogen needed by organisms?

A
  • synthesis of proteins
  • nucleic acids
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7
Q

What does a more valent nitrogen form mean?

A

more variety of transformation

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8
Q

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

A

N2, used by restricted group

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9
Q

Define nitrification

A
  • conversion of ammonia to nitrate by nitrifying microorganisms (nitrate production)
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10
Q

Where does nitrification occur? Why?

A

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

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11
Q

Define chemolithotroph

A
  • chemo - energy source
  • litho - inorganic forms of carbon
  • gets energy from inorganic carbon
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12
Q

Where do chemolithotrophs get their energy from?

A
  • oxidation of ammonia or nitrite
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13
Q

Why put manure in soil?

A
  • fertilize it with organic material + encourage plant growth
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14
Q

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

A
  • want ammonia in biologically useable forms
  • don’t want nitrification
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15
Q

Why don’t plants want nitrification?

A

Deprives soil of ammonia needed

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16
Q

What form of nitrogen is used by plants in soil?

A
  • Nitrate (No3)
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17
Q

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

A
  • 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
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18
Q

What happens if there is excess ammonia?

A
  • bacteria will transfer to nitrites and nitrates causing leaching
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19
Q

Define denitrification

A
  • conversion of nitrate to nitrous oxide or N2 by denitrifiers
  • Nitrate consumption
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20
Q

What are the conditions during denitrification?

A

Anoxic (anaerobic)

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21
Q

What is used as the electron acceptor during denitrification?

A

NO3 rather than O2

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22
Q

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

A

facultative, perform in waterlogged soil
- pseudomonas

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23
Q

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

A

facultative, perform in waterlogged soil
- pseudomonas

24
Q

Define ammonification

A

decomposition of organic nitrogen compounds to produce ammonia

25
Q

What conditions is ammonia typically stable under?

A
  • ANOXIC
26
Q

What is the conversion during nitrogen fixation

A

nitrogen gas –> ammonia

27
Q

What type of organism carries out nitrogen fixation

A

aerobic chemoorganotrophs

28
Q

What is the major reservoir of nitrogen?

A

atmosphere

29
Q

What does biological nitrogen fixation require?

A

nitrogenase

30
Q

Define nitrogenase

A
  • enzyme composed of 2 proteins: dinitrogenase and dinitrogenase reductase
31
Q

What kind of protein is denitrogenase?

A

MoFe

32
Q

What kind of protein is dinitrogenase reductase?

A

Fe

33
Q

What is the electron flow in nitrogen fixation?

A

donor–> dinitrogenase reductase –> dinitrogenase –> N2 –> HN3

34
Q

What are nif regulators? give an example.

A

genetic regulators
ex. kelbsiella pneumoniae

35
Q

What are the 2 types of nitrogen-fixing organisms?

A
  • nonsymbiotic
  • symbiotic
36
Q

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

A
  • rhizosphere (free living)
  • cyanobacteria
37
Q

Define Rhizosphere

A

soil impacted by plant root

38
Q

Define Rhizoplane

A

surface of root

39
Q

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

A

heterocyst

40
Q

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

A

heterocyst

41
Q

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

A
  • have own ammonia generators attached to root matrix
  • ex. peanuts, soybean
42
Q

What is a root nodulator?

A
  • N-fixing bacteria that are breedable with plants
43
Q

Define bacteroid

A
  • bacteria like = no longer capable of free living life and becoming bacteria again
  • once you reach certain point you cannot return
44
Q

Steps in nodule formation

A
  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
45
Q

What is leghemoglobin and what does it do?

A
  • O2 binding Fe protein
  • controls O2 levels in root nodule
  • found in healthy nodules
  • oxygen buffer
46
Q

What does leghemoglobin protect?

A

nitrogenase from O2

47
Q

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

A

10 000:1

48
Q

What do bacteroids result from?

A
  • rapid multiplication of bacteria in plant cells
49
Q

What do bacteroids cause physiologically?

A

swelling

50
Q

Define sybiosome

A
  • bacteroid surrounded by portions of plant cell membrane
51
Q

Where is nitrogenase localized?

A

in bacteroid

52
Q

What happens to node and bacteroid when plant dies?

A
  • released to surrounding soil: dormant cells can proliferate to initiate another infection
53
Q

Can bacteroid forms divide?

A

No

54
Q

what is symbiosome dependent on?

A
  • plant for energy required for N2 fixation
55
Q

When does dissimilatory nitrate reduction occur?

A
  • as substitute for aerobic respiration when O2 levels are low
56
Q

Why is N cycle naturally in balance?

A

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

57
Q

What is the main result of assimilatory nitrate reduction?

A
  • reduce nitrate to ammonia
  • nitrate–>nitrite–>ammonia –> incorporated into organic carbon

bi374 (8 decks)

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