Chapter 5
Ecosystems and the Physical Environment
Lecture Outline:
I. Biogeochemical cycles
A. The carbon cycle
i. The global movement of carbon between organisms and the abiotic
environment is known as the carbon cycle
1. Carbon is present in the atmosphere as carbon dioxide(CO2),
the ocean as carbonate and bicarbonate (CO32-, HCO3-) and
sedimentary rock as calcium carbonate (CaCO3)
2. Proteins, carbohydrates, and other molecules essential to life
contain carbon
3. Carbon makes up approximately 0.04% of the atmosphere as a
gas
ii. Carbon primarily cycles through both biotic and abiotic environments
via photosynthesis, cellular respiration and combustion (CO2)
1. Photosynthesis incorporates carbon from the abiotic
environment (CO2) into the biological compounds of producers
(sugars)
2. Producers, consumers and decomposers use sugars as fuel and
return CO2 to the atmosphere in a process called cellular
respiration
3. Carbon present in wood and fossil fuels (coal, oil, natural gas)
is returned to the atmosphere by the process of combustion
(burning)
4. The carbon-silicate cycle (which occurs on a geological
timescale involving millions of years) returns CO2 to the
atmosphere through volcanic eruptions and both chemical and
physical weathering processes
B. The nitrogen cycle
i. The global circulation of nitrogen between organisms and the abiotic
environment is know as the nitrogen cycle
1. Atmospheric nitrogen (N2) is so stable that it must first be
broken apart in a series of steps before it can combine with
other elements to form biological molecules
2. Nitrogen is an essential part of proteins and nucleic acids
(DNA)
3. The atmosphere is 78% nitrogen gas (N2)
ii. Five steps of the nitrogen cycle
1. Nitrogen fixation
a. Conversion of gaseous nitrogen (N2) to ammonia (NH3)
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b. Nitrogen-fixing bacteria (including cyanobacteria) fixes
nitrogen in soil and aquatic environments (anaerobic
process)
c. Combustion, volcanic action, lightning discharges, and
industrial processes also fix nitrogen
2. Nitrification
a. Conversion of ammonia (NH3) or ammonioum (NH4+)
to nitrate (NO3-)
b. Soil bacteria perform nitrification in a two-step process
(NH3 or NH4+ is converted to nitrite (NO2-) then to
NO3-)
c. Nitrifying bacteria is used in this process
3. Assimilation
a. Plant roots absorb NO3-, NO3 or NO4+ and assimilate the
nitrogen of these molecules into plant proteins and
nucleic acids
b. Animals assimilate nitrogen by consuming plant tissues
(conversion of aminio acids to proteins)
c. This step does not involve bacteria
4. Ammonification
a. Conversion of biological nitrogen compounds into NH3
and NH4+
b. NH3 is released into the abiotic environment through the
decomposition of nitrogen-containing waste products
such as urea and uric acid (birds), as well as the
nitrogen compounds that occur in dead organisms
c. Ammonifying bacteria is used in this process
5. Denitrification
a. Reduction of NO3- to N2
b. Anaerobic denitrifying bacteria reverse the action of
nitrogen-fixing and nitrifying bacteria
C. The phosphorus cycle
i. Phosphorus cycles from land to sediments in the ocean and back to
land
1. Phosphorus erodes from rock as inorganic phosphates and
plants absorb it from the soil
2. Animals obtain phosphorus from their diets, and decomposers
release inorganic phosphate into the environment
ii. Once in cells, phosphates are incorporated into biological molecules
such as nucleic acids and ATP (adenosine triphosphate)
iii. This cycle has no biologically important gaseous compounds
D. The sulfur cycle
i. Most sulfur is underground in sedimentary rocks and minerals or
dissolved in the ocean
ii. Sulfur gases enter the atmosphere from natural sources in both ocean
and land
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1. Sea spray, forest fires and dust storms deliver sulfates (SO42-)
into the air
2. Volcanoes release both hydrogen sulfide (H2S) and sulfur
oxides (Sox)
iii. A tiny fraction of global sulfur is present in living organisms
1. Sulfur is an essential component of proteins
2. Plant roots absorb SO42- and assimilate it by incorporating the
sulfur into plant proteins
3. Animals assimilate sulfur when they consume plant proteins
and covert them to animal proteins
iv. Bacteria drive the sulfur cycle
E. The hydrologic cycle
i. The hydrologic cycle is the global circulation of water for the
environment to living organisms and back to the environment
1. It provides a renewable supply of purified water for terrestrial
organisms
2. the hydrologic cylce results in a balance between water in the
ocean, on the land, and in the atmosphere
ii. Water moves from the atmosphere to the land and ocean in the form of
precipitation
iii. Water enters the atmosphere by evaporation and transpiration
iv. The volume of water entering the atmosphere each year is about
389,500 km3
II. Solar Radiation
A. The sun powers biogeochemical cycles (i.e., hydrologic, carbon) and is the
primary determinant of climate
B. Most of our fuels (i.e., wood, oil, coal, and natural gas) represent solar energy
captured by photosynthetic organisms
C. Approximately one billionth of the total energy released by the sun strikes our
atmosphere
i. Clouds, snow, ice, and the ocean reflect about 31% of the solar
radiation that falls on Earth
ii. Albedo is the proportional reflectance of solar energy from the Earth’s
surface
1. Glaciers and ice sheets have a high albedo and reflect 80 to 90% of the
sunlight hitting their surfaces
2. Asphalt pavement and buildings have a low albedo (10 to 15%)
3. Forests have a low albedo (about 5%)
iii. 69% of the solar radiation that falls on the Earth is absorbed and runs
the hydrologic cycle, drives winds and ocean currents, powers
photosynthesis, and warms the planet
D. Temperature changes with latitude
i. Near the equator, the sun’s rays hit vertically
1. Energy is more concentrated
2. Produces higher temperatures
3. Rays of light pass through a shallower envelope of air
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ii. Near the poles, the sun’s rays hit more obliquely
1. Energy is spread over a larger surface area (less concentrated)
2. Produces lower temperatures
3. Rays of light pass through a deeper envelope of air, causing the
sun’s energy to scatter and reflect back to space
E. Temperature changes with season
i. Season’s are determined primarily by Earth’s inclination on its axis
ii. March 21 to September 22 the Northern Hemisphere tilts toward the
sun (spring/summer)
iii. September 22 to March 21 the Northern Hemisphere tilts away from
the sun (fall/winter)
III. The Atmosphere
A. The atmosphere is an invisible layer of gases that envelops Earth and protects
it’s surface from lethal amounts of high energy radiation (i.e., UV rays, X rays
and cosmic rays)
i. 99% of dry air is composed of oxygen (21%) and nitrogen (78%)
ii. Argon, carbon dioxide, neon, and helium make up the remaining 1%
B. The interaction between atmosphere and solar energy is responsible for
weather and climate
C. Layers of the atmosphere vary in altitude and temperature with latitude and
season
i. Troposphere
1. Closest layer to Earth’s surface
2. Temperature decreases with increasing altitude
3. Extends to a height of approximately 10 km
4. Weather, including turbulent wind, storms, and most clouds
occurs in the troposphere
ii. Stratosphere
1. Temperature is more or less uniform, but does increase with
increasing altitude
2. Extends from 10 to 45 km above Earth's surface
3. Steady wind, but no turbulence (commercial jets fly here)
4. Contains ozone layer
iii. Mesosphere
1. Temperatures drop steadily (to lowest temperature in
atmosphere)
2. Extends from 45 to 80 km above Earth's surface
iv. Thermosphere
1. Very hot (nearly 1000˚C or more)
2. Extends from 80 to 500 km
3. Aurora borealis occurs in this level of the atmosphere
v. Exosphere
1. The outermost layer of the atmosphere
2. Begins about 500 km above Earth's surface
3. The exosphere continues to thin until it converges with
interplanetary space
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D. Differences in temperature caused by variations in the amount of solar energy
reaching different locations on Earth drive the circulation of the atmosphere
i. Air is heated by warm surfaces near the equator cause it to rise and
expand
ii. Due to subsequent chilling, air tends to sink to the surface at about 30
degrees north and south latitudes
iii. Similar upward movements of warm air and its subsequent flow
toward the poles occur at higher latitudes, farther from the equator
iv. This continuous turnover moderates temperatures over Earth's surface
E. Surface winds
i. Horizontal movements resulting from differences in atmospheric
pressure and from the Earth's rotation are called winds
ii. Winds tend to blow from areas of high atmospheric pressure to areas
of low pressure (greater difference = stronger winds)
ii. The influence of Earth's rotation, which tends to turn fluids (air and
water) toward the right in the Northern Hemisphere and toward the left
in the Southern Hemisphere is called the Coriolis effect
iv. The atmosphere has three prevailing winds
1. Polar easterlies blow from the northeast near the North Pole or
from the southeast near the South Pole
2. Westerlies generally blow in the midlatitudes from the
southwest in the Northern Hemisphere or the northwest in the
Southern Hemisphere
3. Trade winds (tropical winds) generally blow from the northeast
in the Northern Hemisphere or the southeast in the Southern
Hemisphere
IV. The Global Ocean
A. The global ocean is a single, continuous body of salt water that covers nearly
¾ of the Earth's surface
B. Geographers divide it into four sections separated by continents (Pacific,
Atlantic, Indian, and Arctic oceans)
C. Prevailing winds blowing over the ocean's surface and the position of land
masses influence patterns of circulation
i. Currents are mass movements of surface-ocean water
ii. Gyres are large, circular ocean current systems that often encompass
an entire ocean basin
iii. The Coriolis effect also influences the paths of surface-ocean currents
B. The varying density of seawater affects deep-ocean currents and creates a
vertical mixing of ocean water
i. The ocean conveyor belt moves cold, salty deep-sea water from higher
to lower latitudes
ii. The ocean conveyor belt affects regional and possibly global climate
and shifts from one equilibrium state to another in a relatively short
period (years to decades)
C. Ocean interactions with the atmosphere are partly responsible for climate
variability
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i. El Niño-Southern Oscillation (ENSO) is a periodic, large scale
warming of surface waters of the tropical eastern Pacific Ocean that
temporarily alters both ocean and atmospheric circulation patterns
1. Most ENSOs last 1 to 2 years
2. ENSO has a devastating effect on fisheries off South America
and alters global air currents (causing severe and unusual
weather worldwide)
ii. La Niña occurs when the surface water temperature in the eastern
Pacific Ocean becomes unusually cool, and westbound trade winds
become unusually strong
1. La Nina often occurs after an ENSO
2. La Nina also affects weather patterns around the world, but its
effects are more difficult to predict
V. Weather and Climate
A. Weather
i. Weather refers to the conditions in the atmosphere at a given place and
time
ii. Weather includes temperature, atmospheric pressure, precipitation,
cloudiness, humidity, and wind
iii. Weather is continuously changing (hour to hour, day to day)
B. Climate
i. The average weather conditions that occur in a place over a period of
years is termed climate
ii. Climate is determined by temperature and precipitation
iii. Other climate factors include wind, humidity, fog, cloud cover, and
occasionally lightning
C. Precipitation
i. Precipitation refers to any form of water that falls from the atmosphere
ii. Examples of precipitation include rain, snow sleet and hail
iii. Precipitation has a profound effect on the distribution and kinds of
organisms present
D. Rain shadows, tornadoes and tropical cyclones (hurricanes/typhoons) are
extreme forms of weather that can have a significant impact on regional
climate
VI. Internal Planetary Processes
A. Plate tectonics
i. Plate tectonics is the study of the dynamics of Earth’s lithosphere
(outermost rigid rock layer)
1. The lithosphere is composed of seven large plates, plus a few
smaller ones
2. The plates float on the asthenosphere (the region of the mantle
where rocks become hot and soft)
ii. Plate boundaries are typically sites of intense geologic activity –
earthquakes and volcanoes are common in such a region
B. Earthquakes
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i. Forces inside Earth sometimes push and stretch rocks in the
lithosphere
1. The energy is released as seismic waves causing earthquakes
2. Most earthquakes occur along fault zones
3. More than 1 million earthquakes are recorded each year
ii. Landslides and tsunamis are some of the side effects of earthquakes
E. Volcanoes
i. When one plate slides under or away from an adjacent plate, magma
may rise to the surface, forming a volcano
ii. Volcanoes occur at subduction zones, spreading centers, and above hot
spots
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In-Class Activities:
Instructor Notes for In-Class Activity 1
Title:
Anthropogenic Changes to the Hydrologic Cycle
Time:
5 – 10 Minutes prep; 40 – 60 minutes in class (or can assign research
between class periods)
None
None
Materials:
Handouts:
Procedures:
For – Against – Jury standard procedure. Randomly divide class into
three groups.
Statement: We need not be terribly concerned about human-caused
changes to the hydrologic cycle, since most or all of these changes are
local, occasional regional, and rarely global
Assign one group each to argue FOR or AGAINST the statement, and the
third group to serve as a JURY.
Each group should select a leader and a recorder.
The FOR group should research (not just think up!) information that
supports the statement. They should be explicit about their sources,
whether those are data, ethics, theories, or political positions. They
should then synthesize this into a five minute verbal argument, to be
made before the full class.
The AGAINST group should do the same for the opposite position. Their
original argument SHOULD NOT respond to items brought up by the
FOR group.
After each has made a five minute argument, each side will have two
minutes to respond to claims or statements made by the other side.
The JURY group will then deliberate openly; the FOR and AGAINST
groups will listen to the deliberations, but may not respond. The JURY
may challenge either group to provide evidence for up to three pieces of
information, and may ask up to three questions of each group (they may
ask the same question to both groups).
The JURY should then make two judgments:
1. Which, if either, provided the most credible INFORMATION
2. Which provided the most compelling overall argument.
3. Be sure students argue their points forcefully, whether or not they
believe them personally.
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See above
Student
Instructions:
Specific
Suggestions:
The instructor is likely to have to serve as a facilitator or moderator from
time to time
1. Do not allow personal assaults
2. Feel free to challenge pieces of information that you find dubious
if the JURY does not.
It will probably take a couple times through this debate process before
you and your class are comfortable with it.
Objectives:
Discuss human-caused changes to the hydrologic cycle.
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Instructor Notes for In-Class Activity 2
Title:
A Three Dimensional Look at the Planet
Time:
Materials:
Handouts:
10 – 25 minutes prep (practice); 15 – 25 minutes in class
Large globe (inflatable is handy), flashlight
None
Procedures:
Bring a large globe to class. Put Figures 5.13, 5.14 and 5.15 up (projector
or overhead). Use the globe to describe the various land masses and
ocean water flows depicted in these slides. Have students locate New
York City, and follow the latitude across the Atlantic to Europe. What
major European city is at the same latitude as New York City? What part
of North America is at the same latitude as Oslo? Describe how
prevailing winds crossing the Atlantic from East are warmed by ocean
currents, thereby warming Europe. Next, describe how the El Nino and
La Nina phenomena can have impacts in places thousands of miles apart.
Finally, use the flashlight to demonstrate the phenomena described in
figure 5.8
Working in groups of 3-4, answer the following questions:
Student
Instructions: Note to instructor: Give the students the next two questions only after
they have generated hypotheses.
Specific
Suggestions:
Be sure to practice this first!
Remember to bring notes along.
Objectives:



Describe the influences of the oceans on climate.
Discuss the roles of solar energy and the Coriolis effect in producing
global water flow patterns
Define El-Nino Southern Oscillation and La Nina and describe some
of their effects.
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Instructor Notes for In-Class Activity 3
Title:
Perturbing the carbon cycle
Time:
Materials:
Handouts:
5 minutes prep; 15 minutes in class
Projection of Figure 5.2
None
Procedures:
Have students get together in groups of 3 -5 and discuss the topics below
for 10 – 15 minutes. Then have them regroup and compare their answers.
Students will evaluate the long-term impacts of a quadrupling of carbon
released through fossil fuel combustion, and the alternatives to that
combustion.
Consider Figure 5.2. Assume that currently, most of the 6 x 1015 of
Student
Instructions: carbon released through combustion is produced by the energy demand
of only 1/3 of the 6 billion people now on the planet. Consider a time in
the next century when the population is 10 billion, and 2/3 of the
population want energy at current demand levels.
1. If all of this comes from fossil fuel combustion, how much more
carbon will be released to the atmosphere?
2. What changes would have to take place elsewhere in the carbon
cycle
3. Are there any ways that humans could intervene elsewhere in the
carbon cycle to accommodate this production? If so, how, and
how difficult do you think it would be?
4. In the IPAT model, if P and A (here, energy use) both go up as
described above, what changes in T would be required to keep I
constant? Do you think these changes are feasible? Why or why
not?
Specific
Suggestions:
None
Objectives:
Describe the carbon cycle, and human impacts on the carbon cycle.
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Instructor Notes for In-Class Activity 4
Title:
The Cycling of Materials within Ecosystems
Time:
40 – 60 minutes prep: 60 minutes in class(or can assign research
between class periods)
100 piece or less puzzle (kids puzzle), paint, varnish or laminate if
desired
1 copy of each of the cycles. See below Activity 5 for handouts.
Materials:
Handouts:
Procedures:
1. Divide the students into equal groups, give each group a cycle:
carbon, nitrogen, phosphorus, sulfur and hydrologic. Give them
the corresponding handout of the figure that represents their
group.
2. Have them put the puzzle together and paint over the picture part
of the puzzle. You can assign the different color for each group
or they can choose a color but each cycle will be a different color.
For example the carbon cycle is yellow, nitrogen cycle blue, etc.
Set the puzzles out to dry…
3. After the puzzles are dry have the students paste pictures of their
Cycle on the puzzle. Each will be similar but different according
to the cycle.
4. Use laminate or a sealant to seal the pictures to the puzzle.
After each group has finished making their puzzle, exchange puzzles
Student
Instructions: with the other groups and have them put the puzzles together. While they
are putting the puzzles together they are reviewing the differences
between the cycles and also the components in them.
Specific
Suggestions:
The teacher could make the puzzles as far as painting them, but have the
students put the pictures of their cycle on them.
Objectives:
Discuss each cycle and why they are different from each other. Can the
students identify the need for each cycle? How do they interrelate with
each other?
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Instructor Notes for In-Class 5
Title:
Cycles of the Ecosystems
Time:
Materials:
Handouts:
10 minutes prep
Copies of the Figures for each cycle
1 copy per group of one of the Cycles
Procedures:
1. Divide the class into equal groups
2. Let one student of the group pick from the stack of Figures (5.2-5.6)
face down so they cannot choose their cycle.
3. After the groups have their cycle explain to them they are the
components of their cycle. They must come up with a community
flag, set of rules or procedures on how they will have an impact on the
ecosystem. What are their components? Do they have a mascot?
Cheer? Fight Song? Etc.
4. During the weeks of this chapter have the students present their cycle
to the class. Let them be creative…..
Students are to research their cycle: nitrogen, carbon, sulfur, phosphorus
Student
Instructions: etc. They will present their cycle with a flag, mascot, fight song or other
creative way. In defining their cycle, they must describe the cycle, its
impact on the ecosystem and how does it make it different to the other
cycles.
Specific
Suggestions:
Objectives:
Make the teams equal and promote creativity.




Describe the influences the components of each cycle.
Discuss the roles of each cycle on the ecosystem.
Compare and contrast each cycle and its impact to the environment
List the differences in each cycle.
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Answers to Thinking About the Environment
End of Chapter Questions:
1. Scientists produce tentative conclusions based on a degree of uncertainty, whereas
politicians and others making public policies prefer to deal in absolutes. How does this
dichotomy relate to Hurricane Katrina and the restoration of New Orleans?
Ans: Scientists cannot predict exactly how much New Orleans will continue to subside or
how much sea level will continue to rise in the coming years. Nor can they predict the
exact degree that rebuilt levees and canals will hold up to another storm of Hurricane
Katrina’s magnitude or greater. Furthermore, further loss of the surrounding wetlands
could increase New Orleans’ vulnerability to hurricanes. Despite these uncertainties, city
planners and representatives of local, state, and federal governments are developing longterm plans to rebuild New Orleans. These plans range from a complete rebuilding of all
damaged areas to a scaled-back restoration of areas that are less vulnerable to future
hurricane damage. If these plans do not take into account varying estimates of changing
conditions the rebuilding of New Orleans may not be as successful as hoped.
2. What is a biogeochemical cycle? Why is the cycling of matter essential to the
continuance of life?
Ans: Biogeochemical cycles move matter from one organism to another and from living
organisms to the abiotic environment and back again. The cycles of matter- carbon,
nitrogen, phosphorus, sulfur and hydrologic- involve biological, geologic and chemical
interactions. These five cycles are particularly important to organisms, because these
materials make up the chemical compounds of cells.
3. Describe how organisms participate in each of these biogeochemical cycles: carbon,
nitrogen, phosphorus, and sulfur.
Ans: In the carbon cycle organisms fix, or incorporate, carbon from the atmosphere into
chemical compounds through photosynthesis. Organisms also release carbon during
cellular respiration. Other biological molecules that are not release during cellular
resipiration can be stored as fossil fuels for millions of years. Aquatic organisms
incorporate Ca2+ and HCO3- into their shells. When these organisms die their shells sink
to the ocean floor and become part of the sedimentary rock layer. The CO2 in these rock
layers will later be released due to weathering or subduction.
Atmospheric nitrogen is very stable and must be broken apart in order to combine with
other elements. Bacteria are exclusively involved in all five steps of the nitrogen cycle,
except assimilation. Nitrogen-fixing bacteria carry out biological nitrogen fixation in soil
and aquatic environments. Soil bacteria perform nitrification, a two step process. First
soil bacteria convert ammonia or ammonia to nitrite. Then other soil bacteria oxidize
nitrite to nitrate. The process of nitrification furnishes these bacteria with energy.
Ammonification begins when organisms produce nitrogen-containing waste products
such as urea and uric acid. These substances, as well as the nitrogen compounds that
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occur in dead organisms, are decomposed, releasing nitrogen into the abiotic
environment. Finally, denitrifying bacteria reverse the action of nitrogen-fixing and
nitrifying bacteria by returning nitrogen to the atmosphere.
In the phosphorus cycle plants roots absorb inorganic phosphates. Animals obtain most of
their required phosphate from the foods they eat. Phosphorus is then release back into the
soil when organisms die and decompose. In aquatic environments phosphorus is absorbed
and assimilated by algae and plants, which are then consumed by plankton and larger
organisms. A small portion of phosphate in the aquatic food web finds its way back to the
land in the manure of sea birds.
A tiny fraction of the global sulfur is present in living organisms. Plant roots absorb
sulfate and assimilate it by incorporating the sulfur into plant proteins. Animals
assimilate sulfur when they consume plant proteins and convert then to animal proteins.
Sulfur is returned to the atmosphere by bacteria which convert sulfates to hydrogen
sulfide gas.
4. How are photosynthesis and cellular respiration involved in the carbon cycle?
Ans: During photosynthesis, plants, algae, and certain bacteria remove CO2 from the air
and fix, or incorporate, it into chemical compounds such as sugar. Thus, photosynthesis
incorporates carbon from the abiotic environment into the biological compounds of
producers. Those compounds are used as fuel for cellular respiration by the producers
that made them, by a consumer that eats the producer, or by a decomposer that breaks
down the remains of the producer or consumer. Thus, cellular respiration returns CO2 to
the atmosphere.
5. What is the basic flow path of the nitrogen cycle?
Ans: There are five steps to the nitrogen cycle, in which nitrogen cycles between the
abiotic environment and organisms: nitrogen fixation, nitrification, assimilation,
ammonification and denitrification. Bacteria are exclusively involved in all of these steps
except assimilation.
6. A geologist or physical geographer would describe the phosphorus cycle as a
“sedimentary pathway.” Based on what you have learned about the phosphorus cycle in
this chapter, what do you think that means?
Ans: Phosphorus does not form compounds in the gaseous phase and does not
appreciably enter the atmosphere. In the phosphorus cycle, phosphorus cycles from the
land to sediments in the ocean and back to the land. Phosphorus in plants comes from
weathered sedimentary rock layers and returns to the ocean floor to be incorporated back
into rock.
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7. How have global air temperatures changed in the recent past? How is this change
related to the carbon cycle?
Ans: Global air temperatures have increased in the recent past. Since 1850, the advent of
the Industrial Revolution, our society has used a lot of energy, which we have obtained
by burning increasing amounts of fossil fuels. This has released CO2 into the atmosphere
at a rate greater than the carbon cycle can handle. Numerous studies indicate that the rise
of CO2 in the atmosphere is causing human-induced global warming.
8. Diagram the hydrologic cycle.
Ans: Answers will vary.
9. What are the two lower layers of the atmosphere? Cite at least two differences between
them.
Ans: The layer of the atmosphere closest to the Earth is the troposphere. The troposphere
extends to a height of approximately 10km (6.2mi). The temperature of the troposphere
decreases with increasing altitude about -6°C (-11oF) for every kilometer. Weather,
including turbulent wind, storms and most clouds, occur in the troposphere. The layer
directly above the troposphere is the stratosphere. The stratosphere extends from 10-45
km (6.2 to 28 mi) above the Earth’s surface and contains the ozone critical to life because
it absorbs much of the sun’s damaging ultraviolet radiation. There is a steady wind but no
turbulence. There is little water, and temperature is more or less uniform (-45°C to 75°C), however, the absorption of ultraviolet radiation by the ozone layer heats the air,
and so temperature increases with increasing altitude in the stratosphere.
10. Describe the general directions of atmospheric circulation.
Ans: Differences in temperature are caused by variations in the amount of solar energy
reaching different locations on Earth and drive the circulation of the atmosphere. The
warm surface near the equator heats the air in contact with it, causing this air to expand
and rise. As the warm air rises, it cools and then sinks again. Much of it recirculates
almost immediately to the same areas it has left, but the remainder of the heated air splits
and flows in two directions, toward the poles. The air chills enough to sink to the surface
at about 30 degrees north and south latitudes. This descending air splits and flows over
the surface in two directions. Similar upward movements of warm air and its subsequent
flow toward the poles occur at higher latitudes, farther from the equator. At the poles the
cold polar air sinks and flows toward the lower latitudes, generally beneath the sheets of
warm air that simultaneously flow toward the poles. The constant motion of air transfers
heat from the equator toward the poles, and as the air returns, it cools the land over which
it passes. This continuous turnover moderates temperatures over Earth’s surface.
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11. How do ocean currents affect climate on land?
Ans: The persistent prevailing winds blowing over the ocean produce currents, mass
movements of surface-ocean water. The prevailing winds generate gyres, circular ocean
currents. Although surface-ocean currents and winds tend to move in the same direction,
there are many variations on this general rule. The ocean and the atmosphere are strongly
linked, with wind from the atmosphere affecting the ocean currents and heat from the
ocean affecting atmospheric circulation. Ocean currents help establish consistent
circulation patterns that moderate the climate. When currents are altered the climate is
altered. One of the best examples of the interaction between ocean and atmosphere is the
El Niño-Southern Oscillation (ENSO) event, which is responsible for much of Earth's
interannual (from one year to the next) climate variability. ENSO alters global air
currents, directing unusual weather to areas far from the tropical Pacific.
12. How do atmospheric and oceanic circulations transport heat toward the poles?
Ans: The constant motion of air transfers heat from the equator toward the poles. The
process of atmospheric circulation transfers the more concentrated solar energy found at
the equator towards the poles. The warm surface near the equator heats the air in contact
with it, causing this air to expand and rise. As the warm air rises, it cools and then sinks
again. Much of it recirculates almost immediately to the same areas it has left, but the
remainder of the heated air splits and flows in two directions, toward the poles. The
constant motion of oceanic circulation also moves heat from the equator towards the
poles. Surface currents transfer immense amount of heat from the tropics to the higher
latitudes. As heat is transferred to the atmosphere water become colder and denser which
causes it to sink. As it sinks it forms deep ocean currents.
13. Relate the locations of earthquakes to plate tectonics.
Ans: Most earthquakes occur along faults, fractures where rock moves forward and
backward, up and down, or from side to side. Fault zones are often found at plate
boundaries- any area where two plates meet. Therefore, earthquakes are very common at
plate boundaries. Understanding plate tectonics has increased our knowledge of
earthquakes and predicting where they may occur.
14. Evaluate the area where you live with respect to natural dangers. Is there a threat of
possible earthquakes, volcanic eruptions, hurricanes, tornadoes, or tsunamis?
Ans: Answers will vary
15. The system encompassing Earth’s global mean surface temperature can be
diagrammed as follows:
Solar radiation absorbed by surface
Outgoing long-wave (infrared) heat energy
Affected by albedo
Affected by clouds and aerosols
Earth’s global mean surface temperature
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Please explain each part of this system.
Ans: The sun releases energy into space in the form of electromagnetic radiation. A small
fraction of this energy reaches the Earth’s surface and is absorbed and runs the
hydrologic cycle, drives winds and ocean currents, powers photosynthesis and warms the
plant. The amount of energy absorbed is affected by albedo. Albedo is the proportional
reflectance of solar energy from Earth’s surface, commonly expressed as a percentage.
Glaciers and ice sheets have high albedo, whereas ocean and forests have low albedo.
The more energy that is absorbed the greater the Earth’s global mean temperature will be.
Aerosols are tiny particles of air pollution consisting mostly of sulfates, nitrates, carbon,
mineral dusts, and smokestack ash Once in the atmosphere, aerosols enhance the
scattering and absorption of sunlight in the atmosphere and cause brighter clouds to form.
Both the clouds and the light-scattering effect in the atmosphere cause a warming of the
atmosphere and a threefold reduction in the amount of solar radiation reaching Earth's
surface, including the ocean. Ultimately, all of this energy is lost by the continual
radiation of long-wave infrared energy into space.
16. Examine the following changes that have been identified in the arctic hydrologic
system in the past few decades. Predict the effect of these changes on the salinity in the
North Atlantic Ocean.
Increasing precipitation in arctic
Melting arctic glaciers
Decreasing extent &
thickness of arctic sea ice
Arctic hydrologic system
Ans: Due to increased precipitation, melting of artic glaciers, and decreasing extent and
thickness of artic sea ice the salinity in the North Atlantic Ocean is likely to decrease.
Cold, salty warm is less dense than warm, less salty water. This physical property drives
the deep ocean conveyor. Scientists are therefore concerned that this decrease in salinity
could alter the ocean conveyor and the global climate.
Answers to Review Questions
Cycling of Materials within Ecosystems (page 97)
1. What roles do photosynthesis, cellular respiration, and combustion play in the carbon
cycle?
Ans: Photosynthesis removes carbon dioxide from the atmosphere and incorporates it
into chemical compounds. Cellular respiration and combustion both return carbon
dioxide to the atmosphere.
2. What are the five steps of the nitrogen cycle?
Ans: The steps include nitrogen fixation, nitrification, assimilation, ammonification and
denitrification.
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3. How does the phosphorus cycle differ from the carbon, nitrogen, and sulfur cycles?
Ans: Unlike the carbon, nitrogen and sulfur cycles the phosphorus cycle does not form
compounds in the gaseous phase and does not enter the atmosphere in appreciable
amounts.
4. What sulfur-containing gases are found in the atmosphere?
Ans: Sulfates (SO42-), calcium sulfate (CaSO4), hydrogen sulfide (H2S), sulfur oxides
(SOx) including sulfur dioxide (SO2), and sulfur trioxide (SO3).
Solar Radiation (page 98)
1. How does the sun affect temperature at different latitudes? Why?
Ans: The sun’s energy does not reach all places uniformly due to the tilt of the Earth on
its axis. The energy from the sun’s rays that hit the equator are therefore more
concentrated and produce higher temperatures. The solar energy that reaches the polar
regions is less concentrated and temperatures are lower.
2. What is albedo?
Ans: The proportional reflectance of solar energy from Earth’s surface, commonly
expressed as a percentage.
The Atmosphere (page 103)
1. What is the innermost layer of the atmosphere? Which layer of the atmosphere
contains ozone that absorbs much of the sun's ultraviolet radiation?
Ans: The inner most layer of atmosphere is the troposphere. The stratosphere contains
ozone that absorbs ultraviolet radiation.
2. What basic forces determine the circulation of the atmosphere?
Ans: Warm surfaces near the equator heats the air causing it to expand and rise. As warm
air rises it cools and then sinks again. Cold polar air sinks and moves towards the equator.
This constant motion of air moderates earth’s temperatures over its surface. In addition
to these global circulation patterns, the atmosphere exhibits winds, complex horizontal
movements that result in part from differences in atmospheric pressure and from the
Coriolis effect.
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The Global Ocean (page 106)
1. How are the sun's energy, prevailing winds, and surface ocean currents related?
Ans: The sun’s energy unevenly heats the Earth’s surface and the air. This uneven
heating results in air circulation and wind. The persistent prevailing winds blowing over
the ocean produce currents.
2. What is the El Niño-Southern Oscillation (ENSO)? What are some of its global
effects?
Ans: ENSO is a periodic, large scale warming of the surface waters of the tropical eastern
Pacific Ocean that temporarily alters both ocean and atmospheric circulation patterns.
ENSO alters global air currents, directing unusual weather to areas far from the tropical
Pacific. It is responsible for changing rain patterns that cause flooding and drought.
Weather and Climate (page 110)
1. How do you distinguish between weather and climate? What are the two most
important climate factors?
Ans: Weather refers to the conditions of the atmosphere at a given place and time. These
conditions may vary from hour to hour. Climate is the average weather conditions that
occur in a place over a period of years. The two most important factors that determine
climate are temperature and precipitation.
2. What are some of the environmental factors that produce areas of precipitation
extremes, such as rain forests and deserts?
Ans: The heavy rainfall of the tropics results mainly from the equatorial uplift of
moisture-laden air. As warm moisture-laden air rises and cools its water holding capacity
decreases. When it reaches the saturation point clouds form and it is released as
precipitation. Mountains, which force air to rise, remove moisture from humid air.
Precipitation occurs primarily on the windward slope of mountains creating rain forests.
On the other side of the mountain the dry air results in desert conditions.
3. Distinguish between tornadoes and tropical cyclones.
Ans: Tornadoes are powerful, rotating funnels of air associated with severe
thunderstorms. They form when warm and cool air collide. Tropical cyclones are giant
rotating tropical storms that form as strong winds pick up moisture over warm surface
waters of the tropical ocean and start to spin as a result of Earth’s rotation. One major
distinction is the scale of the two types of storms, tornadoes are typically much more
isolated events.
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Internal Planetary Processes (page 113)
1. What are tectonic plates and plate boundaries?
Ans: Tectonic plates are the large pieces of the Earth’s outermost rigid rock layer that
float on the hot and soft mantle. Any area where two plates meet a plate boundary forms.
These plate boundaries are site of intense geologic activity.
2. Where are earthquakes and volcanoes commonly located, and why?
Ans: Earthquakes and volcanoes are common at plate boundaries, the area where two
tectonic plates meet. When the two plates grind together, one of them sometimes
descends under the other, in the process of subduction. When two plates move apart, a
ridge of molten rock forms from the mantle wells up between them.
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