Chapter 23 Flashcards
During the past century, the concentration of carbon dioxide in the earth’s atmosphere has
increased rapidly from its pre‐industrial level of about __________ to its present level of about
385 ppm.
A) 0 ppm B) 100 ppm C) 280 ppm D) 350 ppm
C) 280 ppm
Characterize the pre‐industrial atmospheric carbon dioxide concentration in the context of the
earth’s geologic history.
A) It was probably at the highest level in the earth’s geologic history.
B) It was probably at an average level in the earth’s geologic history.
C) It was probably at the lowest level in the earth’s geologic history.
C) It was probably at the lowest level in the earth’s geologic history.
Some chemical transformations of elements in ecosystems take place in abiotic contexts. Which
of the following is an example of such a transformation?
A) weathering of bedrock
B) production of reduced nitrogen (in ammonia) by lightning
C) precipitation of calcium carbonate in the oceans
D) all of the above
D) all of the above
Most biochemical energy transformations are associated with the oxidation and reduction of
which of the following elements?
A) sodium, potassium, calcium, and magnesium
B) copper, iron, aluminum, and manganese
C) carbon, oxygen, nitrogen, and sulfur
D) nickel, cadmium, and zinc
C) carbon, oxygen, nitrogen, and sulfur
Energy transformations in biological systems typically link assimilatory and dissimilatory
processes. Which of the following is necessary for such transformations to occur?
A) The dissimilatory process must release less energy than that required by the assimilatory
process.
Chapter 23: Pathways of Elements in Ecosystems
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B) The dissimilatory process must release at least as much or more energy than that required
by the assimilatory process.
C) The energy released by the dissimilatory process must exactly balance the energy required
by the assimilatory process.
B) The dissimilatory process must release at least as much or more energy than that required
by the assimilatory process.
Which of the following is by far the largest reservoir of water on earth?
A) the oceans D) lakes and rivers
B) polar ice caps and glaciers E) soil moisture
C) underground aquifers
A) the oceans
What percentage of solar energy striking the earth provides the energy required to drive the
global water cycle?
A) 1% B) 2% C) 10% D) 25% E) 100%
D) 25%
Each year, the input (as water vapor) and output (as precipitation) of water to and from the
earth’s atmosphere is balanced. The inputs and outputs each amount to 65 cm of water, if this
water were spread evenly over the earth’s surface. The amount of water in the atmosphere at
any time would amount to 2.5 cm if spread evenly over the earth’s surface. What is the
approximate residence time (in years) of water in the atmosphere?
A) 40 years B) 26 years C) 4 years D) 0.4 years E) 0.04 years
E) 0.04 years
How many times longer is the residence time of water in soils, rivers, lakes, and oceans
(combined) compared to its residence time in the atmosphere?
A) 10 times longer D) 10,000 times longer
B) 100 times longer E) 100,000 times longer
C) 1000 times longer
E) 100,000 times longer
The global assimilation rate of carbon by photosynthesis is approximately 85 gigatons per year,
balanced by an equivalent rate of dissimilation by respiration. Given a global organic carbon
pool (excluding fossil carbon) of 2650 gigatons, what is the average residence time of carbon in
this pool?
A) 0.032 years B) 0.32 years C) 3.1 years D) 31 years
D) 31 years
In aquatic systems, there is a small net removal of soluble carbon from the water column,
primarily through precipitation of insoluble calcium carbonate. What balances this small net
loss?
A) inputs from rivers, which tend to carry dissolved carbonate sediments
B) inputs from wind‐blown dust carried from terrestrial limestone deposits
C) inputs from dissolution of insoluble aquatic calcium phosphate deposits
A) inputs from rivers, which tend to carry dissolved carbonate sediments
Geologist Gregory Retallack has studied fossilized Antarctic soils that formed during the
Devonian. His findings suggest that declining atmospheric carbon concentrations during the
Devonian were prompted by which of the following processes?
A) extensive fires in Devonian forests
B) cessation of soil development in the Devonian
C) increased weathering of calcium and magnesium from soils during the Devonian
D) increased respiration by soil invertebrates during the Devonian
C) increased weathering of calcium and magnesium from soils during the Devonian
The atmosphere contained vastly more carbon dioxide at the beginning of the Devonian (417
Mya) than it did toward the end of the Devonian (354 Mya). What was the ultimate fate of this
atmospheric carbon?
A) It was incorporated into carbonate sediments in the ocean basins.
B) It was incorporated into solid methane deposits in the ocean basins.
C) It was incorporated into the living biomass of the earth’s rapidly developing forests.
D) It was bound to clay minerals in paleosols.
A) It was incorporated into carbonate sediments in the ocean basins.
When Jack Morgan and colleagues exposed plots of Colorado grassland to an elevated
concentration of atmospheric carbon dioxide, they noted an increase in biomass accumulation
at the community level. When they investigated contributions of three dominant grass species
to this increase, what did they find?
A) All three species contributed equally to this increase.
B) Two of the three species actually declined in biomass, but the third more than
compensated for these declines.
C) Two of the three species showed little change in biomass accumulation, but the third
increased substantially.
C) Two of the three species showed little change in biomass accumulation, but the third
increased substantially.
In Morgan’s study of Colorado grassland exposed to an elevated concentration of atmospheric
carbon dioxide (previous question), what was an unexpected finding related to production of
needle grass?
A) Production of needle grass declined substantially, but digestibility increased.
B) Production of needle grass remained constant, but digestibility increased.
C) Production of needle grass remained constant, but digestibility declined.
D) Production of needle grass increased substantially, but digestibility declined.
D) Production of needle grass increased substantially, but digestibility declined.
Which of the following abiotic processes can result in the transformation of atmospheric nitrogen gas (N2) to ammonia (NH3) available to plants and microorganisms? A) landslides B) acidification of lakes C) lightning D) none of the above
C) lightning
What kinds of organism are capable of carrying out ammonification?
A) plants B) animals C) fungi D) microbes E) all organisms
E) all organisms
Is biological nitrogen fixation an assimilatory or dissimilatory process?
A) assimilatory B) dissimilatory C) neither of the above
A) assimilatory
