Deck 25: Cycling Carbon

Question 1

Which of the following equations is the chemical reaction for cellular respiration?

A)C₆H₁₂O₆ + 6O₂ $\rightarrow$ 6CO₂ + 6H₂O
B)6CO₂ + 6H₂O $\rightarrow$ C₆H₁₂O₆ +6O₂
C)CaSiO₃ +CO₂ $\rightarrow$ CaCO₃ +SiO₂
D)C₆H₁₂O₆ + 6CO₂ $\rightarrow$ 6O₂ + 6H₂O

Answer 1

C₆H₁₂O₆ + 6O₂ $\rightarrow$ 6CO₂ + 6H₂O

Question 2

Studies assessing the amounts of different carbon isotopes (¹²C, ¹³C, and ¹⁴C) in the atmosphere were important because they provided evidence that human activities were in fact adding CO₂ to the atmosphere. This is an example of what type of relationship?

A)correlation
B)causation
C)conduction
D)antagonism

Answer 2

B

Question 3

As shown in Figure 25.1 below, atmospheric CO₂ levels oscillate throughout the year. How would this trend change if it were spring for an entire year? Select the graph below that represents the atmospheric CO₂ levels of an Earth with a full year of spring (assume you are in the Northern Hemisphere).

A)graph A
B)graph B
C)graph C

Answer 3

C

Question 4

A positive feedback is one in which the products of a process act to increase the rate at which the process operates. Which of the following would constitute a positive feedback in the carbon cycle?

A)Increasing CO₂ causing an increase in rates of photosynthesis.
B)Increasing temperature causing an increase in rates of photosynthesis.
C)Increasing temperature causing an increase in rates of respiration.
D)Increasing temperature causing an increase in rates of continental weathering.

Question 5

Which correlates CLOSEST with the net increase in CO₂ levels over the past two centuries?

A)volcanic gases
B)carbon dissolved in the oceans
C)respiration
D)human activities

Question 6

When looking at the carbon isotopes present in the atmosphere, scientists determined that ¹³C and ¹⁴C levels have decreased over time. What did researchers conclude from these observations?

A)volcanic activity is responsible for increased atmospheric CO₂
B)the burning of forests is responsible for increased atmospheric CO₂
C)the use of fossil fuels is responsible for increased atmospheric CO₂
D)increased plant/animal respiration is responsible for increased atmospheric CO₂

Question 7

If plants consume CO₂ during photosynthesis, why hasn't all the atmospheric CO₂ been used up?

A)Photosynthesis also produces CO₂ as a product.
B)Respiration produces CO₂ as a product.
C)Both photosynthesis and respiration produce CO₂ as products.
D)Plants actually don't use CO₂ during photosynthesis; they use O₂.
E)Photosynthesis and respiration use one another's products as reactants.

Question 8

What can Antarctic ice core samples tell us about atmospheric CO₂ levels?

A)Nothing, because ice is made of H₂O and not CO₂.
B)CO₂ ice core data confirm CO₂ measurements taken directly from the atmosphere.
C)Ice cores can help scientists estimate atmospheric CO₂ levels from centuries ago.
D)Ice cores can tell scientists exactly what plants lived on Earth centuries ago.

Question 9

Which of the following processes are typically associated with the short-term carbon cycle?

A)respiration
B)plate tectonics
C)photosynthesis
D)chemical weathering

Question 10

In reviewing historical records and ice core data, researchers noted that atmospheric CO₂ levels started to rise as humans began to burn fossil fuels. This is an example of what type of relationship?

A)correlation
B)contradiction
C)causation
D)antagonism
E)conduction

Question 11

The process of cellular respiration consumes _____ and produces _____.

A)CO₂; O₂
B)O₂; CO₂
C)O₂; H₂O
D)CO₂; H₂O

Question 12

The CO₂ level is _____ during winter in the northern hemisphere compared to levels in the summer.

A)lower
B)higher
C)the same

Question 13

Consider the Keeling curve, which shows a steady increase in CO₂ levels over the past 50+ years. This steady rise has been attributed to both natural and human activity. Imagine if everyone in the world planted a fast-growing vine that was an annual (i.e., it grows large and fast, but dies after one year). Predict the effect this would hypothetically have on the level of CO₂ in the atmosphere over the next 20 years.

A)The level of CO₂ in the atmosphere will steadily decrease because of increased rates of photosynthesis.
B)The level of CO₂ in the atmosphere will steadily increase because decomposition of the annuals simply returns the CO₂ back into the atmosphere.
C)The level of CO₂ in the atmosphere will stay the same because the growing annuals will remove the extra CO₂ from human activity.

Question 14

Which of the below statements is true regarding the movement of carbon between organisms in a food web and the transfer of energy between organisms in different trophic levels?

A)Both energy and carbon can be continuously cycled.
B)Neither energy nor carbon can be continuously cycled.
C)Energy can be continuously cycled, but carbon cannot.
D)Carbon can be continuously cycled, but energy cannot.

Question 15

Over the last several decades, what have researchers discovered about atmospheric CO₂ levels?

A)They have decreased.
B)They have increased.
C)They have remained the same.
D)They increased for a period, but have now stabilized.

Question 16

CO₂ is added to the atmosphere by:

A)respiration.
B)photosynthesis.
C)deforestation.
D)the weathering of rocks.

Question 17

It is thought that approximately 90% of plant species went extinct during the Carboniferous Period (~320-290 mya). Which of the following graphs represent the changes that likely occurred in carbon dioxide and oxygen levels? (The solid black line depicts CO₂ levels, the dashed line represents O₂ levels) The left side of the x-axis represents the time of the extinction event.

A)graph M
B)graph H
C)graph K
D)graph L

Question 18

The Keeling curve in Figure 25.1, below, shows that while CO₂ levels oscillate on an annual basis, overall CO₂ levels increase from year to year. Why has this trend continued in the last 50 years?

A)increasing rates of aerobic respiration associated with the rise in world population
B)decreasing rates of oxygenic photosynthesis by plants and algae
C)clearing of forests to create agricultural land outside the tropics
D)combustion of fossil fuels

Question 19

Why are carbon-based organic compounds, such as C₆H₁₂O₆ (glucose), often referred to as "energy molecules"?

A)Energy is released when carbon-containing compounds are broken down.
B)Energy is stored in carbon-containing organic compounds.
C)Energy is required to build carbon-containing organic compounds.
D)None of the answer options is correct.

Question 20

The levels of CO₂ in the atmosphere have been:

A)increasing.
B)decreasing.
C)staying the same.

Question 21

The equation 6CO₂ + 6H₂O+ C₂H₁₂O₆ + 6O₂ represents the process of:

A)photosynthesis.
B)respiration.
C)None of the answer options is correct.

Question 22

Photosynthesis and respiration both play a major role in the _____ carbon cycle, and can affect atmospheric CO₂ levels on a seasonal or annual basis.

A)short-term
B)long-term
C)None of the answer options is correct.

Question 23

The equation C₆H₁₂O₆ + 6O₂ $\rightarrow$ 6CO₂ + 6H₂O represents the process of:

A)photosynthesis.
B)respiration.
C)None of the answer options is correct.

Question 24

Cellular respiration is a process unique to animals, and is not undertaken by plants.

Question 25

Photosynthesis _____ the atmosphere, whereas respiration _____ the atmosphere.

A)removes CO₂ from; introduces CO₂ to
B)introduces CO₂ to; removes CO₂ from

Question 26

Measuring the isotopic composition of atmospheric CO₂ shows that the burning of fossil fuels has led to _____ CO₂ levels over the last 200 years.

A)increasing
B)decreasing

Question 27

The rate of respiration _____ throughout the year.

A)remains more or less constant
B)varies significantly

Question 28

Imagine that a time traveler was able to successfully travel 2 billion years back in time and modified the environment so that photosynthesis and respiration were completely coupled (i.e., there was no "leakage" of products from respiration or photosynthesis). How would this affect Earth's present-day atmosphere, if at all?

A)Earth's atmosphere would be unaffected.
B)Atmospheric O₂ levels would increase.
C)Atmospheric O₂ levels would decrease.
D)Atmospheric CO₂ levels would increase, but O₂ levels would be unaffected.
E)Atmospheric O₂ levels would increase, but CO₂ levels would be unaffected.

Question 29

Recall that photosynthetic rates remain relatively constant in regions near the equator. Imagine that tropical environments persisted throughout Earth's northern and southern hemispheres (i.e., Earth's entire climate mirrored that near the equator). If Keeling had collected his atmospheric CO₂ data on such an Earth, what would you expect the Keeling Curve to look like?

A)a straight line sloping upward (atmospheric CO₂ levels would not seasonally oscillate, but would have increased over time)
B)a straight line sloping downward (atmospheric CO₂ levels would not seasonally oscillate, but would have decreased over time)
C)a sinusoidal curve sloping upward (atmospheric CO₂ levels would fluctuate seasonally, but would increase over time)
D)a sinusoidal curve sloping downward (atmospheric CO₂ levels would fluctuate seasonally, but would have decreased over time)
E)a straight line without a slope (atmospheric CO₂ levels would have remained constant over time)

Question 30

Photosynthesis and respiration affect atmospheric CO₂ levels on a _____ timescale, whereas volcanic eruptions affect atmospheric CO₂ levels on a _____ timescale.

A)yearly; century
B)century; yearly

Question 31

Hans Suess's work (and subsequent studies carried out by other researchers) determined that the amount of ¹³C in Earth's atmosphere has _____, and the amount of ¹⁴C in the atmosphere has _____.

A)decreased; increased
B)increased; decreased
C)decreased; also decreased
D)increased; also increased

Question 32

In the northern and southern hemispheres, the rate of photosynthesis is _____ in the summer and _____ in the winter.

A)highest; lowest
B)lowest; highest

Question 33

Which of the following processes is responsible for the changes scientists observed in atmospheric concentrations of ¹²C, ¹³C, and ¹⁴C over the last 200 years?

A)the burning of fossil fuels
B)volcanism
C)the clearing of forests
D)chemical weathering
E)subduction

Question 34

Which of the following is NOT considered a photosynthetic organism, and so would not remove atmospheric CO₂?

A)kelp
B)elm tree
C)human
D)moss
E)phytoplankton

Question 35

The ocean, much like the atmosphere, can serve as a sink for man-made CO₂. In fact, both Earth's atmosphere and the ocean store roughly equal amounts of man-made CO₂.

Question 36

Because the products of photosynthesis are used as the reactants of respiration, these two processes are said to be:

A)antagonistic.
B)complementary.
C)supplementary.
D)symbiotic.
E)tangential.

Question 37

A researcher is measuring atmospheric CO₂ levels on cloudy and sunny days. He notices that on sunny days, CO₂ levels appear slightly higher compared to levels on cloudy days. This is an example of:

A)causation.
B)fluxation.
C)correlation.
D)conjugation.
E)assimilation.

Question 38

Scientists can gain information about ancient atmospheric CO₂ levels through ice core data. This is primarily the result of sediments being trapped in glaciers, which scientists can subsequently assess for different carbon isotopes (¹³C, ¹²C, ¹⁴C).

Question 39

Recall that in the northern hemisphere, atmospheric CO₂ levels are highest in early spring and lowest in early fall. What accounts for this seasonal fluctuation in atmospheric CO₂ levels?

A)photosynthesis
B)human activities
C)respiration
D)biomineralization
E)plate tectonics

Question 40

If researchers never evaluated the amount of ¹⁴C in the atmosphere, they could still use ¹³C levels to demonstrate causation between human activities and increased atmospheric CO₂.

Question 41

Which of the following statements is TRUE regarding CO₂?

A)CO₂ is a greenhouse gas.
B)CO₂ plays a vital role in maintaining Earth's temperature.
C)CO₂ is released as a product of respiration.
D)CO₂ can be produced by natural and man-made processes.
E)All of these choices are correct.

Question 42

Which of the following is considered a carbon reservoir?

A)the Atlantic Ocean
B)Redwood National Park
C)the Great Barrier Reef
D)all the organisms on Earth

Question 43

Recall that over the last 400,000 years, atmospheric CO₂ levels have fluctuated, with the lowest levels occurring during glacial periods and the highest levels occurring during interglacial periods. Why might atmospheric CO₂ levels be lower during glacial periods?

A)During glacial periods, there are more volcanic eruptions.
B)During glacial periods, there are fewer photosynthesizing plants.
C)During glacial periods, more carbon is stored in ocean reservoirs.
D)During glacial periods, chemical weathering stops.

Question 44

A scientist studying a material has determined that ¹²C, ¹³C, and ¹⁴C occur in the material in a ratio of 1000:10:1. How did he MOST likely differentiate between these forms of carbon?

A)by the number of protons in ¹²C, ¹³C, and ¹⁴C
B)by the number of electrons in ¹²C, ¹³C, and ¹⁴C
C)by the number of neutrons in ¹²C, ¹³C, and ¹⁴C
D)by the biomasses of ¹²C, ¹³C, and ¹⁴C
E)by the number of positrons in ¹²C, ¹³C, and ¹⁴C

Question 45

What would be the environmental consequences if Earth's volcanoes all shut down tomorrow?

A)CO₂ levels in the atmosphere would slowly rise.
B)Continental weathering would decrease.
C)Rates of continental weathering would slowly increase.
D)Temperature would slowly increase.

Question 46

The movement of carbon from CO₂ in the atmosphere to HCO₃^-(a byproduct of chemical weathering) on rocks to CaCO₃ in coral skeletons and finally CaCO₃ in limestone are all steps in the _____ cycle.

A)short-term carbon
B)nitrogen
C)sulfur
D)long-term carbon

Question 47

Charles Keeling's work demonstrated that, over the last five decades, atmospheric CO₂ levels have increased.

Question 48

Nearly 150 years ago, man-made CO₂ was introduced into the atmosphere primarily through _____. Currently, _____ is the main contributing factor to increased levels of human-produced CO₂ in the atmosphere.

A)the burning of fossil fuels; deforestation
B)deforestation; the burning of fossil fuels
C)respiration; deforestation
D)deforestation; respiration
E)the burning of fossil fuels; the burning of fossil fuels

Question 49

How has Earth's atmosphere been influenced by the fact that, as part of the carbon cycle, some amount of organic carbon is stored in sedimentary rocks and is not immediately re-introduced back into the atmosphere?

A)The storing of organic carbon in sedimentary rocks allowed for Earth's atmosphere to remain the same for the last 4 billion years.
B)The storing of organic carbon in sedimentary rocks allowed for oxygen to become a main component of Earth's atmosphere.
C)The storing of organic carbon in sedimentary rocks resulted in carbon not becoming an integral part of Earth's atmosphere.
D)The carbon cycle is not related to the composition of Earth's atmosphere.

Question 50

Of the processes that release CO₂ to the atmosphere, which are influenced by human technology?

A)increased volcanic activity because of local earthquakes
B)wild fires set by lightning strikes in remote areas of forests
C)burning organic carbon that has been stored in sediments and sedimentary rocks
D)respiration rates dropping because of increased temperatures at the poles

Question 51

CO₂ is an example of a _____, a gas in the atmosphere that is transparent to solar radiation but can absorb heat emitted from Earth's surface.

A)photosynthesis product
B)synthetic carbon cycle product
C)greenhouse gas
D)None of the answer options is correct.

Question 52

What would be the environmental consequences if Earth's volcanoes all shut down tomorrow?

A)CO₂ levels in the atmosphere would slowly rise.
B)CO₂ levels in the atmosphere would slowly fall.
C)Rates of continental weathering would slowly increase.
D)Temperature would slowly increase.

Question 53

Which of the following processes are typically associated with the long-term carbon cycle?

A)respiration
B)burial of carbon in sediments
C)photosynthesis
D)volcanic eruptions

Question 54

Which of the processes listed below naturally release CO₂ into the atmosphere?

A)volcanism
B)chemical weathering
C)subduction
D)biomineralization
E)oxidation of fossil fuels (by bacteria)

Question 55

How is atmospheric oxygen linked to the carbon cycle?

A)More burial of organic carbon in sediments results in more oxygen in the atmosphere and oceans.
B)More photosynthesis leads to more oxygen in the atmosphere and oceans.
C)More volcanic CO₂ emission leads to more oxygen in the atmosphere and oceans.
D)Longer food chains with more consumers lead to more oxygen in the atmosphere and oceans.

Question 56

Seasonal respiration rates fluctuate in a similar manner as seasonal photosynthesis rates.

Question 57

A researcher is comparing atmospheric CO₂ levels in Earth's northern and southern hemispheres during June and August. Since more terrestrial plants are present in the northern hemisphere, what do you expect she will find?

A)Atmospheric CO₂ measurements will be greater in the northern hemisphere.
B)Atmospheric CO₂ measurements will be greater in the southern hemisphere
C)Because atmospheric CO₂ measurements represent global amounts, measurements in the northern and southern hemispheres will be (approximately)the same.

Question 58

Over the last 400,000 years, how have atmospheric CO₂ levels changed?

A)Atmospheric CO₂ levels have remained the same.
B)Atmospheric CO₂ levels have been steadily increasing overall.
C)Atmospheric CO₂ levels have been steadily decreasing overall.
D)Atmospheric CO₂ levels have fluctuated periodically.

Question 59

Which of the following statements is TRUE about photosynthesis and chemical weathering?

A)Both processes release CO₂ as a product (i.e., increase atmospheric CO₂ levels).
B)Both processes use CO₂ as a reactant (i.e., decrease atmospheric CO₂ levels).
C)Both processes are typically associated with the long-term carbon cycle.
D)Both processes are typically associated with the short-term carbon cycle.

Question 60

The observation that atmospheric CO₂ levels were typically low during glacial periods in Earth's history is an example of:

A)causation.
B)correlation.
C)communication.
D)confusion.

Question 61

The movement of the Earth's crust, plate tectonics, contributes to the long-term carbon cycle through all of the following EXCEPT:

A)subduction.
B)mountain lifting.
C)photosynthesis.
D)volcanic activity.
E)None of the answer options is correct.

Question 62

The term that describes the movement of Earth's crust and includes the process of subduction is _____.

Question 63

Which of the following relationships BEST depicts the amount of carbon stored in the atmosphere, sedimentary rocks, living organisms, and soil?

A)soil < the atmosphere < sedimentary rocks < living organisms
B)the atmosphere < soil < living organisms < sedimentary rocks
C)sedimentary rocks < soil < living organisms < the atmosphere
D)soil < living organisms < sedimentary rocks < the atmosphere
E)living organisms < the atmosphere < soil < sedimentary rocks

Question 64

Because CO₂ is a greenhouse gas, a rise in CO₂ levels correlates with a(n):

A)rise in respiration.
B)rise in temperature.
C)increase in the size of glaciers.
D)rise in photosynthesis.

Question 65

Which of the following processes INCREASES the amount of CO₂ in the atmosphere?

A)photosynthesis
B)volcanic eruptions
C)subduction
D)chemical weathering
E)respiration

Question 66

Which of the following statements is TRUE regarding atmospheric CO₂ levels during the last 400,000 years?

A)Atmospheric CO₂ levels have remained relatively constant, and have only increased since the 1800s.
B)Atmospheric CO₂ levels fluctuate periodically, with the highest levels occurring during interglacial periods.
C)Atmospheric CO₂ levels fluctuate periodically, with the highest levels occurring during glacial periods.
D)Correlation exists between low levels of atmospheric CO₂ and high temperatures.
E)Causation exists between low levels of atmospheric CO₂ and high temperatures.

Question 67

Recall that during the Paleozoic Era, atmospheric CO₂ levels decreased. Why?

A)New, extensive mountain ranges formed and chemical weathering decreased.
B)Earth's plate tectonics changed dramatically, and subduction increased.
C)Photosynthetic, woody plants first appeared during this period.
D)Volcanism decreased during this period.

Question 68

The long-term and short-term carbon cycles are connected by the fact that some of the carbon contained in C₆H₁₂O₆ (or other organic molecules) in plants is incorporated into sedimentary rocks or oil; it is not immediately reintroduced back into the atmosphere.

Question 69

Which of the following statements is TRUE regarding chemical weathering?

A)It plays a major role in the short-term carbon cycle.
B)It releases CO₂ into the atmosphere.
C)It relies on the acid SiO₂.
D)It contributes to the accumulation of CaCO₃ in oceans.
E)It relies on bacteria to break down rocks.

Question 70

When we think about the carbon cycle and human activities, it is important to differentiate between facts and hypotheses. Which of the following can be considered a fact?

A)The amount of carbon dioxide in the atmosphere has increased since 1950.
B)Increasing atmospheric carbon dioxide will cause mean global temperature to increase by 2 degrees Celsius over the next century.
C)The burning of fossil fuels contributes substantially to the ongoing rise of atmospheric CO₂.
D)In the past, atmospheric CO₂ levels reached levels higher than those observed today.

Question 71

Increased rate of photosynthesis is the most likely explanation as to why atmospheric CO₂ levels appear lowest during glacial periods of Earth's history.

Question 72

Currently, atmospheric CO₂ levels are the highest they have ever been in Earth's 4.6-billion-year history.

Question 73

Of the processes involved in the long-term carbon cycle, which removes CO₂ from the atmosphere?

A)chemical weathering
B)volcanism
C)respiration
D)photosynthesis
E)bacteria-based oxidation

Question 74

Which of the following are NOT geological processes that drive the long-term carbon cycle?

A)volcanism and plate tectonics
B)subduction and volcanism
C)photosynthesis and respiration
D)chemical weathering and plate tectonics
E)subduction and chemical weathering

Question 75

Imagine that a researcher has discovered a 500-million-year-old leaf fossil from the Cambrian Period. He notices that the leaf had very few stomata compared to present-day leaves. What does this tell the researcher about atmospheric CO₂ levels during the Cambrian Period?

A)Atmospheric CO₂ levels were higher during the Cambrian Period compared to today.
B)Atmospheric CO₂ levels were lower during the Cambrian Period compared to today.
C)Atmospheric CO₂ levels during the Cambrian Period were equal to present-day levels.
D)Atmospheric CO₂ levels are not correlated with numbers of stomata.

Question 76

Carbon is incorporated into the skeletons of corals and other marine organisms through the process of _____. The CaCO₃ making up these skeletons, in turn, becomes a major component of sedimentary rocks after these organisms die.

A)chemical weathering
B)subduction
C)biomineralization
D)inorganic mineralization
E)bacterial oxidation

Question 77

How can scientists determine what atmospheric CO₂ levels were like hundreds or thousands of years ago?

A)They can examine ice core samples from Antarctica.
B)They can examine CO₂ levels in the outermost layer of Earth's atmosphere.
C)They can examine the number of stomata in fossilized leaves.
D)They can examine the number of fossilized dinosaur skeletons from different eras.

Question 78

The _____ cycle deals with geological processes and carbon reservoirs, some of which have been built up (or take place) over a period of millennia. In contrast, the _____ cycle involves biological processes that are carried out on a daily and/or seasonal basis.

A)short-term carbon; long-term carbon
B)long-term carbon; short-term carbon
C)short-term carbon; rapid carbon
D)long-term carbon; intermediate carbon

Question 79

The majority of carbon stored in reservoirs is in the form of:

A)CO₂.
B)C₆H₁₂O₆.
C)H₂CO₃.
D)CaCO₃.
E)CH₄.

Question 80

Of the processes involved in the long-term carbon cycle, which introduces CO₂ back into the atmosphere?

A)chemical weathering
B)carbonate precipitation
C)volcanism
D)respiration
E)photosynthesis