Deck 22: Decomposition and Nutrient Cycling

Question 1

Litter degrades into a dark brown or black homogeneous organic matter known as ________.

Answer 1

humus

Question 2

Given that mass loss is expressed as a negative exponential function (original mass remaining = e-kt),how much mass would be left after 20 weeks given a decomposition coefficient k = 0.0167 in units of proportion mass loss per week?

A)0)203
B)0)716
C)0)916
D)1)390

Answer 2

B

Question 3

The process of conversion of nutrients from an organic form into an inorganic form that plants can use is called

A)immobilization.
B)respiration.
C)transpiration.
D)mineralization.

Answer 3

D

Question 4

In a process known as the ________,the rise and fall of water depth with tidal cycles bring nutrients into coastal marshes from coastal ocean waters.

Question 5

Bacteria and fungi secrete ________ into plant and animal tissues to break down the complex organic compounds.

Question 6

The rate of decomposition is greatest in

A)cold and moist environments.
B)cold and dry environments.
C)warm and moist environments.
D)warm and dry environments.

Question 7

As decomposition proceeds,which molecule is lost to the atmosphere?

A)H2O
B)CH4
C)CO2
D)NH3

Question 8

In general,litter with a C:N ratio greater than 30 leads to immobilization,litter with a C:N ratio less than 20 leads to mineralization,and litter with a C:N ratio of 20-30 leads to a balance of immobilization and mineralization resulting in no net N production.If garlic mustard leaf litter collected on the forest floor had 43.2% C and 1.16% N,this tissue would lead to

A)immobilization.
B)mineralization.
C)a balance of immobilization and mineralization.

Question 9

The C:N ratio of litter is important because litter with a

A)high C:N ratio does not contain enough nitrogen for decomposers,resulting in immobilization.
B)low C:N ratio does not contain enough nitrogen for decomposers,resulting in immobilization.
C)high C:N ratio cannot be utilized by most organisms without extra carbon available.
D)low C:N ratio cannot be utilized by most organisms without extra carbon available.

Question 10

The breakdown of chemical bonds that were formed during the construction of plant and animal tissues is called ________.

Question 11

In an estuary,the zone of maximum vertical difference in density is called a(n)________.

Question 12

In decomposition,fungi generally

A)extend hyphae to invade litter and excrete hypha.
B)break down litter through shredding.
C)consume microbivores on tissues.
D)gain energy directly through photosynthesis.

Question 13

Animals that feed on bacteria and fungi are called ________.

Question 14

________ is the process by which plants absorb a portion of their nutrients from senescing tissues to be stored and used for the production of new tissues.

Question 15

Which of the following breaks down the slowest during decomposition?

A)simple sugars
B)cellulose
C)chitin
D)lignin

Question 16

The rate of net primary productivity can be limited directly by the availability of

A)organic nutrients in the soil solution.
B)inorganic nutrients in the soil solution.
C)organic carbon in the soil solution.
D)inorganic carbon in the soil solution.

Question 17

The release of organically bound nutrients into an inorganic form is called ________.

Question 18

The incorporation of mineral nutrients into an organic form is called ________.

Question 19

The process of decomposition releases ________ to bacteria and fungi.

A)oxygen
B)energy
C)glucose
D)protein

Question 20

In open water,the undissolved remains of dead organisms and other organic material that drifts toward the bottom is called ________ organic matter.

Question 21

Aquatic arthropods that fragment organic particles and also eat bacteria and fungi on the surface of the litter are called

A)shredders.
B)filtering collectors.
C)gathering collectors.
D)grazers.

Question 22

In an estuary,the zone of maximum vertical difference in density of water layers is called the

A)thermocline.
B)pycnocline.
C)mixing zone.
D)hypolimnion.

Question 23

During the process of decomposition,carbon quality typically declines.

Question 24

Aerobic decomposition occurs at a faster rate than anaerobic decomposition.

Question 25

A C:N ratio of 134:1 will usually lead to immobilization.

Question 26

Bacteria,fungi,and animals are all important in decomposition.

Question 27

Litterbags can be used to estimate the rate of decomposition.

Question 28

Coastal zones of contact between freshwater from streams and rivers and saltwater from the ocean are called

A)estuaries.
B)headwaters.
C)deltas.
D)coastal upwelling zones.

Question 29

The physical fragmentation of organic matter into smaller pieces is achieved primarily by invertebrate detritivores.

Question 30

Bacteria and fungi have higher C:N ratios than most of the plant litter they consume.

Question 31

The rate of nutrient cycling in an ecosystem

A)depends only on the rate of photosynthesis.
B)depends only on the rate of decomposition.
C)does not depend on the rate of photosynthesis or the rate of decomposition.
D)depends on both the rate of photosynthesis and the rate of decomposition.

Question 32

The rate of decomposition is faster for proteins,simple sugars,cellulose,and hemicellulose than it is for lignin.

Question 33

In which of the following is the process of nutrient cycling sometimes described as nutrient spiraling?

A)streams and rivers
B)oceans
C)lakes
D)forests

Question 34

Soil organic matter contains recalcitrant compounds that are of low quality and contain little energy for decomposers.

Question 35

All heterotrophs to some degree function as decomposers.

Question 36

The microbial loop results from

A)fungal attack on litter and subsequent consumption by microbivores.
B)leaching of litter that stimulates detritivores.
C)enhanced decomposition of labile litter materials enhancing food web turnover.
D)exudate release in the rhizosphere stimulating decomposition and nutrient release.

Question 37

In open-water ecosystems,decomposition occurs primarily in the

A)thermocline.
B)hypolimnion.
C)epilimnion.
D)benthic zone.

Question 38

Decomposition proceeds faster in moist environments than in dry environments.

Question 39

Most of the nutrients in the leaves of a deciduous plant are lost from the plant when the leaves senesce and drop to the ground.

Question 40

Decomposers are primarily autotrophs.

Question 41

The work of Edward Schuur (Schuur,2001,2003; and Schuur and Matson,2001)has found that in some ecosystems,rates of decomposition decline with increased precipitation.

Question 42

The region of the open ocean where the north and south equatorial currents meet is deficient in nutrients and supports little life.

Question 43

The rate of nutrient cycling in an ecosystem is a function of physical characteristics of the ecosystem,not biological processes such as photosynthesis and decomposition.

Question 44

Nitrogen fertilizers used for crops represent the main source of pollution in the ocean.

Question 45

In salt marshes,only a small portion of primary production is consumed by herbivores.

Question 46

Estuaries receive nutrients both from tides and from streams and rivers.

Question 47

In open-water systems such as lakes and oceans,decomposition occurs mostly in the surface layer.

Question 48

In open-water ecosystems,turnover prevents the movement of nutrients between the bottom and surface layers.