Deck 21: Nutrient Cycles

Question 1

Which iron species is produced primarily from iron smelting and rarely is produced by microbial-mediated processes?

A) ferric iron (Fe³⁺)
B) ferrous iron (Fe²⁺)
C) ferrulic iron (Fe¹⁺)
D) iron (Fe⁰)

Answer 1

D

Question 2

Which of the following is/are NOT a degradation product of organic material?

A) carbon dioxide
B) methane
C) oxygen
D) All of these answer choices are degradation products of organic material.

Answer 2

C

Question 3

Frozen methane molecules are called

A) anhydrous methane.
B) anoxic methane.
C) methane anhydrates.
D) methane hydrates.

Answer 3

D

Question 4

The primary energy source for termites comes from

A) acetogenic Archaea.
B) acetogenic Bacteria.
C) methanogenic Archaea.
D) methanogenic Bacteria.

Question 5

The burning of fossil fuels produces significant amounts of

A) sulfate.
B) sulfite.
C) sulfonate.
D) sulfur dioxide.

Question 6

The metabolic process of denitrification

A) oxidizes N₂.
B) oxidizes NO₃⁻.
C) reduces N₂.
D) reduces NO₃⁻.

Question 7

Which of the following is a sulfide?

A) H₂S
B) HS⁻
C) S²⁻
D) H₂S, HS⁻, and S²⁻ are all sulfides.

Question 8

________ is a term used to describe dead organic matter.

A) Humus
B) Loam
C) Pyrite
D) Xenocompost

Question 9

Which organisms form the foundation of the carbon cycle?

A) anaerobic chemolithotrophs
B) chemoheterotrophs
C) chemoorganotrophs
D) phototrophs

Question 10

The metabolic process of ammonification ________ ammonia.

A) oxidizes
B) produces
C) reduces
D) transforms

Question 11

A process where different microbial taxa work in cooperation to degrade a compound that neither can perform entirely on their own is called

A) allotrophy.
B) ammensalism.
C) commensalism.
D) syntrophy.

Question 12

Nitrate (NO₃⁻) reduced into ammonia (NH₃) to produce energy for the cell is called

A) ammonification.
B) dissimilative reduction of nitrate to ammonia (DRNA).
C) nitrification.
D) redox.

Question 13

Bacterial oxidation of Fe²⁺ is commonly studied in chemolithotrophs that thrive under which specific environmental condition?

A) cold temperature
B) high sunlight
C) low (acidic) pH
D) nutrient-replete

Question 14

The calcium cycle is tightly coupled to the

A) carbon cycle through calcium carbonate formation in ocean waters.
B) phosphorus cycle through calcium phosphate formation in sediments and rocks.
C) silica cycle through calcium silicate formation in coastal ocean sediments.
D) nitrogen cycle because nitrogenase requires calcium ions.

Question 15

Which compound in fertilizer do farmers use to inhibit the production of easily leached nitrogen compounds?

A) anhydrous ammonia
B) carbonate
C) nitrapyrin
D) nitrate

Question 16

What is a characteristic of a deep sea marine cold seep/vent?

A) acidic
B) luminous
C) low pressure
D) rich in methane

Question 17

Diatoms require silica due to their

A) Ca²⁺/Si⁴⁺ symporters.
B) DNA replication mechanism.
C) ornate frustules.
D) unique phototrophic physiology.

Question 18

When dimethylsulfoniopropionate (DMSP) is aerobically degraded in a marine environment, which product is most often used to support growth?

A) acrylate
B) dimethyl disulfide
C) dimethyl sulfoxide
D) methanethiol

Question 19

One important difference between the C, N, and S cycles and the P, Ca, and Si cycles is that

A) P, Ca, and Si are NOT cycled in terrestrial environments.
B) the P, Ca, and Si cycles do NOT involve redox changes or gaseous forms that can alter Earthʹs atmospheric chemistry.
C) the P, Ca, and Si cycles do NOT involve microbial activity.
D) the P, Ca, and Si cycles are NOT affected by global warming or other human activity.

Question 20

What would the result be when a soil is supplemented with S⁰?

A) dimethyl sulfide production due to mixotrophs
B) organic carbon production due to anaerobes
C) soil acidification due to chemolithotrophs
D) syntrophic utilization of sulfite

Question 21

The ocean has mitigated the impact of anthropogenic carbon dioxide production by

A) absorbing 500 billion tons of atmospheric carbon dioxide.
B) absorbing over 80% of the trapped heat energy.
C) storing 600 billion tons of organic carbon.
D) absorbing 500 billion tons of atmospheric carbon dioxide and over 80% of the trapped heat energy.

Question 22

Mercury is commonly found in

A) some electronics, but not in pesticides.
B) some compounds that are neurotoxins, but not in electronics.
C) some pesticides, but not in any neurotoxins.
D) some electronics, some pesticides, and some neurotoxic compounds.

Question 23

What is the major reservoir of stable nitrogen?

A) N₂
B) NO
C) NO₃⁻
D) NH₄

Question 24

The largest reservoir of methane is found

A) as methane hydrates trapped under permafrost and marine sediments.
B) in the rumen of cows and other ruminant animals.
C) in the atmosphere in gaseous form.
D) trapped in volcanic rocks in tropical environments around the world.

Question 25

What is the largest carbon reservoir on Earth?

A) terrestrial biosphere
B) rocks and sediments
C) aquatic biosphere
D) fossil fuels

Question 26

Agricultural application of nitrogen fertilizer

A) reduces global warming by increasing the storage of carbon dioxide in plant biomass.
B) increases global warming by increasing microbial respiration in agricultural soils.
C) increases global warming by increasing the production of nitrous oxide (N₂O) by denitrification in agricultural soils.
D) has little to no effect on the carbon cycle.

Question 27

Phosphonate comprises 25% of the ________ phosphorous pool in marine environments.

A) inorganic
B) organic
C) insoluble
D) biologically unavailable

Question 28

Which of the following processes does denitrification contribute to?

A) acid rain
B) ozone depletion
C) global warming
D) acid rain, ozone depletion, and global warming

Question 29

Sulfide is toxic to respiring organisms, because it can combine with metals present in ________ that serve a critical function in respiration.

A) glycolysis enzymes
B) oxidases
C) NADH
D) cytochromes

Question 30

Which statement exemplifies the biological pump concept?

A) Autotrophs bring in light photons to synthesize ATP.
B) Bacteria oxidize Fe²⁺ into Fe³⁺, and Archaea reduce Fe³⁺ back into Fe²⁺.
C) Calcium ions are brought into cells while toxic physiological by-products are released.
D) Primary producers sink to the deep ocean, which provides deep ocean organisms with nutrients when the primary producers die.

Question 31

Phosphorus reservoirs include

A) phosphate minerals in rocks, dissolved phosphates in aquatic environments, and the nucleic acids and phospholipids of living organisms.
B) mineral phosphonates and the nucleic acids and phospholipids of living organisms.
C) elemental phosphorus minerals and phosphonates.
D) elemental phosphorous, polyphosphate, and phosphonates.

Question 32

What reaction is catalyzed by mercuric reductase?

A) CH₃HgCH₃ to Hg²⁺
B) CH₃Hg⁺ to Hg²⁺
C) Hg⁴⁺ to Hg²⁺
D) Hg²⁺ to Hg⁰

Question 33

The Fe and Mn cycles include

A) reduced and oxidized forms that are very chemically reactive.
B) large reservoirs of solid mineral forms that are chemically inert.
C) incorporation of Fe and Mn into the exoskeletons of diatoms and other alga.
D) toxic forms that can poison aquatic ecosystems if the cycles are imbalanced.

Question 34

Coccolithophores and foraminiferans both use ________ to form their exoskeletons.

A) Si⁴⁺
B) Fe³⁺
C) Ca²⁺
D) HPO₄⁻

Question 35

Greenhouse gases

A) such as CO₂, CH₄, and N₂O trap infrared radiation, heating the Earth.
B) such as CO₂ increase plant and animal growth, resulting in more heat production on Earth.
C) such as CO₂ and O₃ (ozone) interact with UV light and heat the Earth.
D) such as CO₂, CH₄, and N₂O destroy O₃ (ozone) and allow more UV light to enter the atmosphere, thus increasing the temperature of the Earthʹs surface.

Question 36

Which is the most toxic form of mercury?

A) CH₃Hg⁺
B) Hg⁰
C) Hg²⁺
D) Hg⁴⁺

Question 37

Lignin is a complex polymer of methoxylated ________ compounds and is present in ________.

A) silica / aquatic environments
B) mineral / rocks
C) oil / fossil fuels
D) aromatic / vascular plant material

Question 38

The two major forms of carbon that remain following microbial degradation are

A) methane, organic matter, and fossil fuels.
B) methane and carbon dioxide.
C) lignin and fossil fuels.
D) organic matter and hydrocarbons.

Question 39

Lysis of marine algae and cyanobacteria releases the major osmoregulatory solute, dimethylsulfoniopropionate (DMSP), which is degraded into the most abundant organic S compound in nature, ________.

A) dimethyl sulfide (CH₃-S-CH₃)
B) hydrogen sulfide (H₂S)
C) gypsum (CaSO₄)
D) elemental sulfur (Sᵒ)

Question 40

In the oceans, sulfur exists primarily as

A) hydrogen sulfide (H₂S).
B) elemental sulfur (Sᵒ).
C) sulfate (SO₄²⁻).
D) gypsum (CaSO₄).

Question 41

When carbon is limiting in a system, sulfate reducers often predominate the system when sufficient sulfate ions are present for reduction.

Question 42

Increasing atmospheric carbon dioxide is

A) increasing sedimentation of C, Ca, and Si.
B) increasing the effect of the biological pump.
C) fueling increased primary production in ocean waters.
D) acidifying the ocean and decreasing the rate of formation of calcareous shells.

Question 43

The precipitation of soluble iron ions (Fe²⁺ and Fe³⁺) into solid iron occurs spontaneously in the presence of organic carbon compounds.

Question 44

Nitrous oxide (N₂O) is a

A) direct product of ammonification.
B) direct product ofnitrogen fixation.
C) potent greenhouse gas that is a product of nitrification.
D) potent greenhouse gas that is a product of denitrification.

Question 45

Humic acids are difficult to degrade, and therefore they usually remain in a system for several decades.

Question 46

Studying the redox cycling of Fe in the environment has led to the discovery

A) of bacteria that transfer electrons as a form of electricity.
B) of bacteria that destroy toxic metal ions.
C) of archaea that have Fe in their cell walls.
D) that Fe limits primary production in terrestrial ecosystems.

Question 47

Climate scientists are developing methane hydrates to decrease the effects of global warming.

Question 48

Nitrification and anammox both

A) create nitrogen gas, but nitrification is aerobic while anammox is anaerobic.
B) oxidize ammonia, but nitrification uses O₂ ₐs ₐn ₑlₑctᵣₒn ₐccₑptₒᵣ and anammox uses NO₂-.
C) are aerobic processes, but nitrification produces NO₃- and annamox produces N₂ gas.
D) occur in soils at neutral pH.

Question 49

The disposal of garbage or sewage in the ocean is known to cause the sudden growth of sulfate reducers.

Question 50

The oxidation of ________ occurs both biotically and abiotically, but biotic oxidation is more common at ________ pH values. pH

A) Si / low
B) ammonia / high
C) Fe²⁺ / low
D) Hgᵒ / low

Question 51

Most chemolithotrophic bacteria that oxidize sulfur are aerobes.

Question 52

More carbon is present in dead organic material on Earth than in living organisms.

Question 53

Acetogens can ferment glucose into acetate, but methanogens cannot.

Question 54

Nitrogen fixation results in the

A) loss of biologically available N from an ecosystem.
B) formation of nitrogen gas.
C) direct formation of nitrate.
D) addition of biologically available N to an ecosystem.

Question 55

In the natural carbon cycle, carbon dioxide is returned to the atmosphere by the respiration of animals and chemoorganotrophic microorganisms.

Question 56

Abiotic oxidation of Fe²⁺ requires oxygen and occurs rapidly when the pH is near 7.

Question 57

Methanogens, among other compounds, use alcohols and fatty acids to synthesize methane gas in anoxic environments.

Question 58

In a global sense, all nutrient cycles are coupled together.

Question 59

Human activities have disrupted the carbon cycle by

A) burning carbon stored as fossil fuels or biomass, thus increasing the amount of carbon dioxide in the atmosphere.
B) decreasing the primary productivity of the oceans, resulting in increased atmospheric carbon dioxide.
C) burning methane hydrates to produce electricity.
D) acidifying the ocean, resulting in the release of large amounts of dissolved carbon dioxide into the atmosphere.

Question 60

Syntrophic organisms cannot grow fermentatively without a hydrogen-consuming partner organism.

Question 61

Calcium is cycled most rapidly in terrestrial environments.

Question 62

Ocean acidification decreases the precipitation of calcium carbonate and thus will probably affect the cycling of Ca and other nutrients in the ocean.

Question 63

Microbial activity generates methylmercury, which is much less toxic than the mercuric ion.

Question 64

Why is the water solubility of different nitrogen species of importance to agriculturalists? What processes in the nitrogen cycle are LEAST beneficial to agricultural production of crops?

Question 65

The two main biological activities in the Ca and Si cycles are the biosynthesis of shells and exoskeletal material as well as the mineralization of these materials in sediments.

Question 66

Marine wetlands (salt marshes) are highly productive coastal ecosystems that produce a lot of organic carbon, similar to freshwater wetlands; however, salt marshes smell very different than freshwater wetlands. What nutrient cycle is different between the two ecosystems that causes this difference in smell?

Question 67

Silicoflagellates use silicon compounds in substrate-level phosphorylation.

Question 68

Using the sudden bloom of cyanobacteria in a lake due to anthropogenic fertilizer inputs as an example, explain the coupling of carbon, nitrogen, and oxygen cycling. Exclude discussion of all organisms other than microorganisms.

Question 69

Carbon dioxide is the only greenhouse gas produced by anthropogenic activities.

Question 70

How would Si depletion in the photic zone of the open ocean affect the biological pump and the C cycle?

Question 71

Most phosphorous, such as that found in inorganic phosphate (HPO₄⁻), exist in the +5 oxidation state in nature.

Question 72

Mercury has both organic and inorganic forms that are neurotoxic.

Question 73

Energy yields are high enough for Fe²⁺ oxidation that the bacteria that perform this reaction require only small quantities of Fe²⁺ to be available.

Question 74

Some bacteria have genes that confer resistance to mercury.

Question 75

Coal contains substantial amounts of mercury. When coal is burned to generate heat or electricity, the mercury is released into the atmosphere. Most of this mercury is eventually deposited in the ocean or other aquatic environments. What happens to the mercury once it is deposited in the ocean?

Question 76

Mercury-resistant bacteria detoxify mercury by producing Hg⁰.

Question 77

Denitrification of fertilizer can result in harmful algal blooms.

Question 78

The mercury in fish is normally in the form of elemental mercury (Hg⁰).

Question 79

Mercury can serve as a transcriptional activator in the regulation of certain genes.

Question 80

What are the similarities and differences between the Fe cycle and Ca cycle?