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Soils Exam #3 > humus > Flashcards

humus Flashcards

1
Q

what are the other three big categories that humans and earthworms can’t digest

A

cellulose, hemicellulose, and lignin

too large to dissolve in water

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2
Q

fungi and bacteria have soft or rigid cell walls

A

rigid

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3
Q

can fungi and bacteria fo phagocytosis

A

no- they have walls

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4
Q

what is depolymerization in terms of fungi and bacteria and such

A

digestion

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5
Q

if you chop up polymers and dissolve it in water what will happen

A

it will be digested

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6
Q

greater nitrogen content leads to faster or slower degredation

A

faster

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7
Q

which is degraded faster- proteins or carbohydrates

A

protiens

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8
Q

factors that increase the likelyhood that an enzyme digests a polymer into soluble oligomers

A

all monomers are the same

backbone within molecule made out of same monomers

linkages between monomers all the same

H bonding between polymers absent

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9
Q

oligopeptide

A

a little piece of a digested protien

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10
Q

what are the bonds between amino acid monomers that comprimise a protien

A

CO-NH

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11
Q

do bugs like oligopeptides

A

yes- they are easy to digest because a protease enzyme cuts the peptide bonds

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12
Q

xyloglucans

A

most abundant hemicellulose in primary cell wall of plants

backbone of glucose monomers linked by identical linkages

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13
Q

TF if an enzyme can cut through enough identical linkages, the xyloglucan should be soluble

A

T- breaking down the size due to identical bonds

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14
Q

cellulose properties

A

All monomers same- glucose

all linkages identical- B1,4

Occurs in bunches

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15
Q

can enzymes easily digest cellulose

A

no because it occurs in bunches

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16
Q

what keeps cellulose together

A

H Bonds

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17
Q

what do fungi and bacteria prefer, cellulose or lignin

A

cellulose

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18
Q

how is lignin polymerized

A

random linkages

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19
Q

is lignin easy to digest

A

no- random linkages, linkages can’t be hydrolyzed

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20
Q

how is lignin formed

A

plant has soup of lignin monomers

free radicals catalyze spontaneously at whatever position the linkage hits

New monomer now has free radical and will now go hunting to pair their unpaired electron, which will result in chain after chain after chain

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21
Q

how is polyethylene created

A

through ethylene monomers and spontaneous random linkages

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22
Q

how are humic substances created (polymer wise)q

A

random linkages like polyethylene and lignin

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23
Q

do proteins, starches, and lipids rot fast or slow

A

fast- worms can digest (people can too!)

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24
Q

do hemicellulose and cellulose decompose fast or slow

A

slow

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25
Q

who decomposes hemicellulose and cellulose

A

microbes

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26
Q

What substance is the most degradation resistant

A

lignin

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27
Q

what type pf enzymes can chop up lignin

A

peroxidases and white rot fungi

28
Q

TF how enzymes depolymerize the lignin creates a free radical

A

T

29
Q

TF the free radical that enzymes create during lignin depolymerization remain free radicals

A

F, this will catalyze the repolymerization of lignin monomers + almost anything else organic that happens to be how humic substances are formed

30
Q

is there more lignin in leafy plant tissue or woody plant tissue

A

woody

31
Q

what is typically with lignin in a plant cell (making it nearly undigestable)

A

cellulose and hemicellulose of woody tissue

32
Q

TF lignin if wrapped around tube of cellulose

A

T- defense mechanism

33
Q

TF humic substances and fresh plant residue is the same thing

A

F, humic substances are the digested versions of plant residue

34
Q

how do humic substances form

A

randomly assembled like lignin

35
Q

what type of rings are abundant in lignin

A

benzene rings

36
Q

two types of things to decompose

A

greens and browns

37
Q

greens- nitrogen cellulose lignin

A

high nitrogen
low cellulose
low lignin

38
Q

do greens rot fast

A

yes

39
Q

do greens leave a lot of humus

A

no

40
Q

browns- nitrogen lignin

A

High lignin
low nitrogen

41
Q

do browns rot fast

A

no

42
Q

As browns are depolymerized, part of their carbon skeletons become randomly assembled and turned into highly desireable humic substances TF

A

T

43
Q

If a plant residue has a high C:N ratio, is it a brown or green

A

brown- low N

44
Q

If a plant residue has a low C:N ratio, is it a brown or green

A

green- high N

45
Q

does humus have a high C:N ratio

A

no

46
Q

for annual crops, does the C:N ratio increase or decrease through the growing season

A

decrease- more lignin over time. More brown mass with more growing

47
Q

do residues of crops become more or less able to decompose with age

A

less

48
Q

if you add straw to your soil, the microebes will suck all of the __ out of the soil and incorporate it into their biomass

A

Nitrogen

49
Q

IF you add leafy greens to your soil, it will rot at high speeds and liberate ________– into the soil for the next crop

A

nitrogen

50
Q

green stuff will leave more or less humus

A

less, unless brown is added

51
Q

TF nematodes eat bacteria and fungi

A

T

52
Q

Do nematodes release nitrogen from the bacteria

A

yes

53
Q

polyphenols

A

compounds containing benzene rings with multiple -OH groups attached

54
Q

what are polyphenols good for for plants

A

defense against pathogenic fungi and insects

55
Q

do polyphenols make plants harder to decompose

A

yes if present at high levels

56
Q

mineralization*

A

conversion of any element from an organic to inorganic form

57
Q

If microbes convert nitrogen in soil to NH4+, is this immobilization

A

NO mineralization

organic -> inorganic

58
Q

immobilization

A

conversion of an element from an inorganic to an organic form

59
Q

What is the opposite of immobilization

A

mineralization

60
Q

immobilization or mineralization : plants take up N from soil and convert it into protiens

A

immobilization
inorg to org

61
Q

List some factors that would increase soil organic matter levels

A

more residues per year
cooler temp
moister soil
more clay
appropriate N fertilization
no till
cover crops
replacing inorganic N sources with organic N sources

62
Q

how do cooler temps lead to more organic matter

A

slows microbial destruction of humus

plants are less thirsty- same amt of water supports more biomass

63
Q

how does moister soil lead to more organic matter

A

soggy soil has more anerobic volume which means slower destruction of humus

64
Q

how does more clay lead to more organic matter

A

clay particles shield humus particles from microbes

65
Q

how does appropriate levels of N fertilizationa ffect the organic matter

A

excessive fert- microbes accelerate desctruction

too little- less plant biomass

66
Q
A

Soils Exam #3 (6 decks)

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