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Nutrition of Horticultural Crops > Nutrition of Horticultural Crops Exam 3 (Nitrogen) > Flashcards

Nutrition of Horticultural Crops Exam 3 (Nitrogen) Flashcards

1
Q

What is the plasma membrane?

A

phospholipid bilayer separating the outside of the cell from the inside of the cell

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2
Q

Which part of the phospholipid is hydrophobic? What is the consequence of this?

A

the tails are hydrophobic, hence they tuck themselves within the plasma membrane

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3
Q

What are the enzymes embedded in the plasma membrane which pump ions across the lipid bilayer?

A

H+-ATPases

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4
Q

In what direction do H+-ATPase enzymes move hydrogen ions?

A

H+-ATPase pumps the hydrogen ions from the inside of the cell to the outside of the plasma membrane

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5
Q

The cation nutrients are generally individual particles (K+, Mn2+, etc.). What is an exception to this tendency?

A

ammonium (NH4+)

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6
Q

The anion nutrients are generally polyatomic particles (NO3-, PO42-, etc.). What is an exception to this tendency?

A

chloride (Cl-)

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7
Q

The activity of H+-ATPase leads to what phenomenon, in which the lipid bilayer acquires a slightly negative charge while the intracellular space becomes very positiviely charged?

A

membrane polarization

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8
Q

What are the two kinds of passive diffusion of particles across the cell membrane?

A

(1) simple diffusion
(2) facilitated diffusion

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9
Q

What is the difference between simple diffusion and facilitated diffusion?

A

simple diffusion involves the movement of the cation across the lipid bilayer without a channel protein, while a channel protein is necessary with facilitated diffusion

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10
Q

What does it mean that channel proteins are “selective”?

A

channel proteins only allow certain ions based on the size or other factors the cations possess

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11
Q

What is an example of antagonism between two cation nutrients with a +1 charge?

A

potassium (K+; 39 amu) and ammonium (NH4+; 18 amu) are relatively small, so large concentrations of ammonium in the soil can reduce K+ concentrations in the leaves, leading to wilt

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12
Q

What is an example of antagonism between two cation nutrients with a +2 charge?

A

calcium (Ca2+; 40 amu) and magnesium (Mg2+; 24 amu)

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13
Q

What is an example of calcium-magnesium antagonism in agricultural operations?

A

crops in Florida often experience symptoms of magnesium deficiency due to the high calcium concentrations in the soil

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14
Q

The main way by which anions enter into plant cells is via what mechanism?

A

secondary active transport

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15
Q

What is “secondary” about the transport of anions into the cytoplasm of plant cells?

A

anion entry is powered by a “primary” event, which is the primary active transport of hydrogen ions by ATPase to the intracellular space

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16
Q

What is the most significant chemical change to the soil when plants take up anions through their roots?

A

the mediums in which the roots are situated becomes more alkaline

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17
Q

When nutrients are present at low concentrations in the soil relative to the demands of the plant, what do many activate to more easily scavenge the necessary nutrients?

A

high affinity transporters (HATs)

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18
Q

What are the counter-part enzymes and proteins to HATs known as?

A

low affinity transporters (LATs)

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19
Q

What are the four forms of nitrogen plants can acquire for their metabolism?

A

(1) nitrate
(2) ammonium
(3) urea
(4) amino acids

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20
Q

If plants acquire too great a concentration of nitrate anions in their cytoplasm, what can they do?

A

sequester the nitrate in their vacuole for later retrieval

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21
Q

Because nitrogen is a mobile nutrient, where can a higher concentration of nitrate be found than those in the leaves?

A

the plant sap often demonstrates significantly high concentrations of nitrates than the leaves

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22
Q

Once nitrate has entered the plant cytoplasm, what are the two enzymes which reduce the nitrogen within to turn it into ammonium nitrogen?

A

(1) nitrate reductase (NR)
(2) nitrite reductase (NiR)

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23
Q

Once the nitrogen has become part of an ammonium particle in the cytoplasm, what typically occurs?

A

ammonium is assimilated into glutamine (Gln) by glutamine synthetase (GS)

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24
Q

What does glutamine synthetase (GS) bond ammonium to in order to generate glutamine (Gln)?

A

glutamate (Glu)

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25
Q

Why do responsible horticulturalists only fertilize with ammonium-containing products when their crops have a high photosynthetic potential?

A

ammonium can only be assimilated into plant tissues if a proportional amount of glutamate (Glu) is present to be worked upon by glutamine synthetase

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26
Q

What are the two ways that urease enzymes (URs) reduce urea (NH2) to bond two hydrogen atoms to it to form ammonium (NH4+)?

A

(1) urea can be degraded in the soil into ammonium, which can then enter the cell through simple diffusion or via special channels
(2) urea can be acted upon once in the cytoplasm by urease

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27
Q

What is the assumption farmers make when they apply urea-based fertilizers to their soils?

A

the sum of urease enzymes in the soil and plant cell cytoplasm will be able to convert all of the urea into ammonium

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28
Q

There are (1)_____ different amino acids found in plants. These vary in both their (2)_______ as well as their (3)___________.

A

(1) 23
(2) size
(3) charges

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29
Q

In regards to the four kinds of molecules plants can acquire nitrogen from, which is still being studied to understand the fundamental dynamics of?

A

amino acids

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30
Q

The atmosphere is predominately divided between two gases (~99%). What are these gases?

A

(1) nitrogen (N2 ~ 78%)
(2) oxygen (O2 ~ 21%)

31
Q

What is the approximate global average atmospheric concentration of carbon dioxide (as of April 28, 2024)?

A

425 parts carbon dioxide per million atmospheric particles (0.0425% of the atmosphere)

32
Q

Expressed as parts per million, there are 780,000 parts nitrogen gas per 1,000,000 atmospheric molecules. This is about how many times larger than the 425 parts per million of carbon dioxide currently present as the global average (as of April 28, 2024)?

A

about 1830 times the quantity of N2 as there is CO2 in the global average concentration in the atmosphere

33
Q

What are the three molecular formulae which describe atmospheric nitrogen fixation, in which a bolt of lightning ruptures the triple-bond in a molecule of nitrogen gas?

A

(1) N2 + O2 –> 2NO
(2) 2NO + O2 –> 2NO2
(3) 2NO2 + H2O –> HNO2 + HNO3

34
Q

The formula “N2 + O2 –> 2NO” is a description of what process?

A

electrostatic discharge (lightning) and oxidation of a nitrogen gas particle into free nitrogen

35
Q

The formula “2NO + O2 –> 2NO2” is a description of what process?

A

oxidation of nitrogen monoxide into nitrogen dioxide

36
Q

The formula “2NO2 + 2H2O –> HNO2 + HNO3” is a description of what process?

A

aqueous dissolution of nitrogen dioxide into nitrous acid (less stable) and nitric acid (more stable)

37
Q

About what quantity of nitrogen in the global cycle is annually fixed by electrostatic discharges in the atmosphere?

A

about 5 teragrams of nitrogen
(5 Tg = 5 * 10^12 g)

38
Q

Which reservoir witnesses the fixation of more nitrogen in the global cycle, the land or the oceans?

A

marine biological nitrogen fixation > terrestrial biological nitrogen fixation

39
Q

About what quantity of nitrogen in the global cycle is annually fixed on solid land through biological processes?

A

about 120 teragrams of nitrogen
(120 Tg = 1.2 * 10^14 g)

40
Q

About what quantity of nitrogen in the global cycle is annually fixed in marine environments through biological processes?

A

about 140 teragrams of nitrogen
(140 Tg = 1.4 * 10^14 g)

41
Q

The industrial fixation of nitrogen occurs at an approximate annual rate of what?

A

about 120 teragrams of nitrogen are fixed annually by industrial processes (Haber-Bosch)

42
Q

The Haber-Bosch process is a (1)___________ reaction which is energetically expensive, requiring about (2)_________ of pressure and temperatures of about (3)____________.

A

(1) catalyzed
(2) 500 atm
(3) 600 *C

43
Q

About what percent of the world’s current population is reliant upon the Haber-Bosch process?

A

about 50% of people rely on the nitrogen fixed by the Haber-Bosch process

44
Q

About what percent of all the energy used globally may be for the production of ammonia in the Haber-Bosch process?

A

about 2% of all energy may be used to produce ammonia industrially

45
Q

When animals decompose, in what form does their nitrogen typically enter the soil as?

A

amino acids (R-NH2)

46
Q

Why are nitrates more prone to leach out of soils than ammonium?

A

negative charges on nitrates are repelled by aluminosilicates

47
Q

What kind of stress is denitrification (NO3- –> N2) associated with?

A

flooding

48
Q

During biological nitrogen fixation in (1)_______________, the enzyme (2)_____________ reduces the nitrogen atoms in N2, forming two molecules of (3)_________. This phenomenon is energetically intensive, requiring about (4)________ per molecule of gas.

A

(1) prokaryotes
(2) nitrogenase
(3) ammonia (NH3)
(4) 16 ATP

49
Q

What group of plants forms symbiotic relationships with nitrogen-fixing bacteria to reduce the energy costs associated with nitrogen fixation?

A

legumes

50
Q

What is the genetic material called in certain prokaryotes which allow them to fix nitrogen and have a history of being horizontally transferred from clade-to-clade?

A

nif genes

51
Q

Actinorhizal plants are like legumes in that they form symbiotic relationships with nitrogen-fixing microbes. What is the genus these bacteria hail from?

A

Frankium

52
Q

What are the two genera of nitrogen-fixing bacteria associated with legume crops?

A

Rhizobium and Bradyrhizobium

53
Q

In the absence of human intervention, the establishment of a relationship between the legumes and their beneficial bacteria begins when the plant secretes what?

A

flavonoids

54
Q

What do flavonoids bind to on Rhizobium or Bradyrhizobium cells?

A

membrane receptors

55
Q

Once nitrogen-fixing bacteria intercept flavonoids, what parts of their DNA do they begin to transcribe?

A

nod (short for “nodulation”) genes

56
Q

The binding of the legume’s root cells to proteins generated by the bacteria triggers an intake of what into the plant’s root hairs?

A

calcium ions (Ca2+)

57
Q

What occurs morphologically to plant root hairs following the intake of calcium ions therein?

A

root hairs curl and ensnare the bacteria, which then forms an infection thread

58
Q

What occurs once an infection thread by an ensnared Rhizobium or Bradyrhizobium bacterium reaches the cells of the root cortex of the host plant?

A

proteins called nodulins spur plant cortex cells to divide, producing uninhabited root nodules

59
Q

After previously mobile bacteria invade uninhabited root nodules, they become stationary and are referred to as what?

A

bacteroids

60
Q

What causes root nodules overtime to acquire a pink tint?

A

leghemoglobin (“legume hemoglobin”) secreted by the bacteroid

61
Q

First identified in 1939 in (1)____________, leghemoglobin is a (2)____________ which promotes the delivery of dissolved (3)__________ gas to organelles in the bacteroid which are (4)____________, while isolating the nitrogen-fixing enzyme (5)______________, which has an (6)______________ habit

A

(1) soybeans
(2) protein
(3) oxygen
(4) aerobic
(5) nitrogenase
(6) anaerobic

62
Q

What is the leguminous crop which forms root nodules with the nitrogen-fixer Ensifer (formerly Rhizobium) meliloti?

A

alfalfa (Medicago sativa)

63
Q

What legume forms root-nodule associations with the bacterial biovar vicae from the species Rhizobium leguminosarum?

A

garden peas (Pisum sativum)

64
Q

What legume nodulates with the biovar phaseoli of the species Rhizobium leguminosarum?

A

common beans (Phaseolus vulgaris)

65
Q

Why do horticulturalists distinguish the two biovars of Rhizobium leguminosarum (R. leguminosarum bv. vicae and R. leguminosarum bv. phaseoli) in particular?

A

the biovars of R. leguminosarum which modulate with their preferred host (peas for vicae, beans for phaseoli) cannot do so for the preferred host of the other biovar

66
Q

What are three factors which affect the nodulation rates Rhizobium bacteria already present in the soil demonstrate in the presence of legumes?

A

(1) nitrogen present in the soil
(2) soil pH
(3) availability of water

67
Q

Do applications of nitrogen to the soil at the time of a legume’s planting generally increase or decrease nodulation rates?

A

the more nitrogen applied to the soil when the legume is planted, the lower initial rates of nodulation will be

68
Q

What generally happens to the nodulation rates by Rhizobium as the soil becomes more alkaline?

A

as the soil pH increases, the rate of Rhizobium nodulation increases

69
Q

How does water availability in the soil affect nodulation rates by Rhizobium bacteria in legumes?

A

when there is too little or too much water, nodulation is low; when there is a moderate amount, it is highest (inverse parabola)

70
Q

What are three considerations which need to occur before soil is inoculated with Rhizobium bacteria?

A

(1) Were any leguminous crops planted within the past five years which nodulated of their own volition?
(2) Does the field under consideration for inoculation have a history of producing nitrogen-deficient plant?
(3) Was fumigation done beforehand?

71
Q

What is the relationship between artificial Rhizobium inoculation and pre-plant fumigation?

A

if fumigation occurs before planting, artificial Rhizobium inoculation may be necessary

72
Q

What two things need to be avoided when storing Rhizobium-inoculating products?

A

(1) extreme temperatures
(2) continued use pass the manufacturer’s expiration date

73
Q

What is the name of the landrace of Mexican maize whose adventitious roots produce a mucus which may contain microbes that can perform fixation of atmospheric nitrogen?

A

Sierra Mixe

Nutrition of Horticultural Crops (6 decks)

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