Mastering Concepts
38.1
1. What are the relationships among ecosystems, communities, biomes, and the
biosphere?
The biosphere contains all the ecosystems on earth. The biosphere is divided into biomes
or major types of ecosystems, each containing its own communities of living organisms.
2. What abiotic conditions influence the distribution of species in the biosphere?
Sunlight, temperature, moisture, nutrients, water, and dissolved oxygen are the major
abiotic factors.
3. How do the main factors affecting primary production differ between land and water?
In water, sunlight and nutrients can be scarce. Salinity and dissolved oxygen are also
main factors. On land sunlight, temperature, moisture, nutrients in the soil and
sometimes fire are important factors.
38.2
1. Explain why sunlight is most intense at the equator.
Sunlight is directly overhead all year and does not hit Earth at an oblique angle.
2. Moving outward from the equator, what are the major climatic regions of the world?
At the equator, the climate is warm and moist year round. Deserts occur at about 30o N
and S. Between 30o and 60o N or S, the climate is temperate. Above 60o N or S, the
climate is cold and dry.
3. How do prevailing winds, ocean currents, and mountain ranges affect climate?
Prevailing winds move air masses and moisture around the globe. Ocean currents
influence temperature and moisture in coastal regions. Mountain ranges affect climate on
a local scale by causing disruptions in the movement of air and moisture.
38.3
1. How do climate and soil composition determine the characteristics of terrestrial
biomes?
Climate and soil composition determine which plants and microorganisms can grow in a
particular area. The plants, in turn, influence the animals and other organisms that live
there.
2. List and describe the climate, soils, and inhabitants of each of the major terrestrial
biomes.
This table compares the climate, soils, and inhabitants of Earth’s major biomes:
Biome
Climate
Soils
Inhabitants
Tropical rain forest
Warm and wet
Reddish, nutrientLush and diverse
poor, low in organic plant and animal life
matter
Temperate
Winters mild,
Deep layer of
1 or 2 tree species
deciduous forest and rainfall constant
organic matter,
dominate; whitetail
temperate
through year
fertile soils
deer, gray squirrels,
coniferous forest
red foxes, snakes,
raccoons
Taiga
Long, cold winters
Damp, cold, acidic, Spruce, fir, pine and
last 6 months; short and nutrient-poor
tamarack; caribou,
growing season
porcupines, red
squirrels, snowshoe
hares, migratory
birds
Tropical savanna
Warm with wet and Rich
Perennial grasses
dry seasons
and patches of fireresistant trees; large
herds of herbivores;
diverse carnivores
Temperate grassland Low annual rainfall; Deep, fertile soils
Large herds of
can have cold and
grazing herbivores;
hot seasons
prairie chickens,
prairie dogs, coyotes
Deserts
Less than 20 cm of
Because of sparse
Plants adapted to
rain/ year; may be
biological activity,
little moisture;
cold or hot
soils are low in
nocturnal and
organic matter
burrowing animals
Tundra
Long, cold, dark
Rich in organic
Shallow-rooted
winters; short
matter; shallow soil shrubs, lichens, lowsummers; short
with permafrost
growing perennial
growing season
herbs; caribou,
musk oxen,
reindeer, lemmings,
snowy owls,
wolverines
Mediterranean
Hot, dry summers;
Sandy, retain little
Shrubby plants with
shrublands
mild, moist winters water
leathery leaves;
jackrabbits, mule
deer, rodents
3. Which biomes are supported by fire and grazing?
Temperate grasslands and savannas are supported by fire and grazing. Mediterranean
shrublands require periodic fires.
38.4
1. Describe the types of organisms that live in each zone of a lake or pond.
The shallow water of a pond’s littoral zone houses rooted plants, algae, and
cyanobacteria, along with many kinds of animals, including turtles, frogs, birds, fishes,
insects, crayfish, and spiders. In the limnetic zone are phytoplankton and fishes.
Scavengers and decomposers live in the profundal and benthic zones.
2. What is the difference between an oligotrophic and a eutrophic lake?
An oligotrophic lake has nutrient-poor, clear water, little plant life, and little animal life.
A eutrophic lake has nutrient-rich, murky water, and lots of plant and animal life.
3. How does a river changes from its headwaters to its mouth?
As a river flows from its headwaters it becomes slower-moving, wider, and richer in
sediments and nutrients.
38.5
1. Describe some of the adaptations that characterize organisms in estuaries, intertidal
zones, and coral reefs.
Organisms living in estuaries have adaptations that allow them to cope with the daily
tides, which bring extreme changes in salinity and moisture. Intertidal organisms have
adaptations that allow them to withstand daily periods of extreme dryness, wetness, heat,
and cold, along with protection against wave action. Coral reef organisms have
adaptations that allow them to live in the nooks and crannies of the reef.
2. List and define the major zones of the ocean.
The major zones of the ocean are the intertidal zone, between the high and low tide
marks; the neritic zone, which extends from the coast to the edge of the continental shelf;
the oceanic zone, or zone extending beyond the continental shelf; the pelagic zone, which
is composed of all water above the ocean floor; and the benthic zone, or ocean bottom.
The photic zone, or upper layer of sunlit water, extends from the coast to the open ocean.
-.
3. How is upwelling important to ocean ecosystems?
Upwelling brings nutrients up from the ocean floor, allowing phytoplankton to grow
abundantly. These, in turn, provide food for ocean food chains, making zones of
upwelling some of the richest ocean waters.
38.6
1. Explain how researchers tested the adaptive bleaching hypothesis.
Researchers observed coral communities before and after El Niño events where water
temperatures spiked. The researchers investigated DNA from different algae samples in
the coral and identified a type C and a type D. They then tested to see if the two types
had different photosynthetic rates at different temperatures. They discovered that the
type D algae are high-temperature specialists.
2. What are the benefits and limitations of field studies and lab experiments in testing the
adaptive bleaching hypothesis?
Field studies observe organisms in their natural habitat; however, this approach results in
a lot of uncontrolled variables that could affect results. Lab experiments can control
variables, but it is very hard to exactly reproduce the natural environment in the lab.
Write It Out
1. How does the fact that Earth is a sphere tilted on its axis influence the distribution of
life?
The fact that Earth is a sphere tilted on its axis affects a region’s sunlight, temperature,
and moisture, which are major determinants of climates. Solar energy is most intense at
the equator, where the sun is directly overhead. The average temperature falls with
distance from the equator because the same amount of solar energy is distributed over a
larger area. Earth’s major convection cells, composed of rising and falling air masses,
mean that moisture availability also varies worldwide.
2. Explain why the climate on the west side of Oregon’s Cascade Mountains is much
wetter than on the east side of the mountain range.
The climate on the west side of Oregon’s Cascade Mountains is much wetter than on the
east side of the mountain range because the mountains often block wind and moistureladen clouds on their upwind side, producing a rain shadow.
3. List adaptations that characterize organisms in each of the following biomes: tropical
rain forest, savanna, temperate grassland, tundra, desert, taiga, the rocky intertidal zone,
the bottom of a lake.
- The tropical rain forest has a constantly warm and moist climate that favors plant
growth year-round. Plants in the rainforest are adapted to high moisture levels and poor
soils.
- In a savanna, the weather is warm year-round, with distinct wet and dry seasons. Fire
plays a role in the savanna ecosystem, so plants are fire-resistant.
- Temperate grasslands have deep, rich soils that support extensive growth of grasses, but
annual rainfall is insufficient to support trees. Grasses resprout from their bases, an
adaptation to both grazing and fire.
- In the tundra, soils are rich in organic matter, but shallow. Only plants that tolerate cold
winters and have shallow root systems grow in the tundra.
- Deserts are dry; desert plants have adaptations that enable them to store water.
- The taiga is cold and snowy, with scarce moisture and a short growing season. Plant
roots have adaptations to acidic, nutrient-poor soils.
- The rocky intertidal zone is alternately exposed and covered by water. Organisms that
live there have adaptations that enable them to hold tightly to their substrates.
- The bottom of a deep lake has no light penetration; the inhabitants are scavengers and
decomposers that can detect food by scent, not sight.
4. How can the tropical rain forest support diverse and abundant life with such poor soil?
The tropical rain forest can support diverse and abundant life with such poor soil because
the plant and animals populations are constantly recycling nutrients without returning
them to the soil.
5. What is permafrost, where does it occur, and how does it affect primary production in
that biome?
The permafrost is below the tundra topsoil and never thaws. Because roots cannot
penetrate the frozen soil, root systems must be shallow and plants must be small.
6. Polar bears live on the ice cap near the North Pole. Their numbers are dwindling,
apparently because of both pollution and global climate change. Ice on Canada’s Hudson
Bay, for example, is melting about 3 weeks earlier in the year than it was some 30 years
ago. List some specific ways that this change in habitat might affect polar bear
populations.
Warming temperatures may change the mating and migration patterns of polar bears and
their prey. In addition, a warm surface layer of water can prevent cold, nutrient-rich
water below from rising to the surface. The lack of nutrients might cause smaller
organisms to disappear, and the larger organisms also may starve. Since polar bears eat
these larger organisms, they may starve as well.
7. A watershed is an area of land in which all of the precipitation drains into the same
body of water. The central United States, for example, is in the Mississippi River’s
watershed, which itself consists of many smaller watersheds. Why would cities and towns
that share a watershed want to cooperate to manage water resources? Why might one part
of a watershed face different issues from another part?
Each town removes water from the river and returns it as wastewater, which becomes a
downstream town’s water supply. Not only is the water within a watershed shared, but so
are problems such as drought or pollution. Each part of the watershed may face different
issues because of differences in population size, irrigation and industrial needs, flooding
frequency, and pollution sources. .
8. Poultry farmers apply large amounts of nutrient-rich animal waste onto the land, where
it runs off into nearby lakes and streams. What effect might this nutrient input have on
the aquatic ecosystems? Lawmakers in some states have debated whether animal waste, a
natural substance, should legally qualify as a hazardous waste. Do you think it should?
The nutrient influx causes algae to thrive; decomposers eventually eat their dead bodies,
depleting the water’s oxygen and releasing noxious chemicals that cause fish to suffocate.
Although poultry waste is a natural substance, the Environmental Protection Agency
defines a hazardous waste as having “… properties that make it dangerous or potentially
harmful to human health or the environment.” By this definition, poultry waste is a
hazard to aquatic ecosystems.
9. Nuisance aquatic plants such as Hydrilla can disrupt the ecology of the littoral zone of
a lake. Two of the most common ways to control nuisance aquatic plants are herbicides
(chemicals that kill plants) and biological control (introducing fungi or animals that
consume the plants). How might each strategy help or harm the lake ecosystem?
The herbicides could help by reducing the plant before it chokes out resources; however,
it may also kill beneficial plants, disrupting the food sources of other organisms.
Biological controls could also reduce the nuisance plant without introducing toxins.
However, the introduced organisms could begin killing desirable plants, or they may
themselves become a nuisance.
10. Describe how and why photosynthetic activity differs in the zones of a lake or ocean.
Because light penetrates water to different degrees at different depths, photosynthetic
activity is highest near the surface and declines with depth. In both lakes and the ocean,
the photic zone is the only area where photosynthesis can occur. Photosynthetic rates are
generally highest near the shore, where nutrients are most abundant.
11. Describe the physical and chemical differences between the water in a mountain
stream and the water near the mouth of the Mississippi River.
At the headwaters of a stream, the water is relatively clear, the channel is narrow, the
current is fast, and the water is rich in O2 but low in nutrients. As the stream moves
toward the ocean, it continues to pick up sediment and nutrients from the channel, the
river widens, the water is murky, the O2 content is low, and the current slows.
12. Make a concept map depicting the relationships among the zones of the ocean. What
is the main energy source in each zone?
[Answers will be visual]
13. The biomes described in this chapter do not include those that humans create, such as
cities, villages, croplands, rangelands, and tree farms. How are these biomes similar to
and different from the biomes in this chapter?
Human created biomes also rely on abiotic factors like energy availability and water, and
they are interconnected. However, human created biomes are not necessarily determined
by latitude, temperature, and moisture since these factors can be controlled or
manipulated. In addition, human created biomes are typically less diverse than those
described in the chapter, and they emphasize species that can coexist with humans
without threatening our safety.
14. Use the Internet to learn about cave ecosystems. What are some possible energy
sources in a cave? How do cave ecosystems interact with other ecosystems? How might
the abiotic conditions in a cave select for unique adaptations in cave-dwelling organisms?
How do human activities affect caves?
Possible energy sources include bat guano, detritus that comes in with floodwaters, and
chemoautotrophic microorganisms. The bat guano and detritus originate from other
ecosystems. The bats would feed on insects in other ecosystems, and the cave could act
as a shelter for larger organisms that extend their habitat into other ecosystems. Water in
the cave could flow out into other ecosystems as well. The lack of sunlight could select
for such adaptations as sonar in bats, small or absent eyes, and lack of pigmentation. Low
nutrient levels could select for small body size. Cave ecosystems are delicately balanced,
and human activities like spelunking can easily damage that balance. In addition,
removal of guano reduces nutrient levels, and pollution can damage the water supply.
15. Some scientists are currently attempting to catalog all of the world’s biodiversity.
What are some of the technical problems they may encounter?
Cataloging all of the world’s diversity would be nearly impossible. Many organisms live
in inaccessible places, and many microorganisms cannot be grown in laboratory culture
(making them difficult to identify). Describing a new species and comparing it to known
species is extremely time-consuming. Moreover, communities change over time, so even
if all life were documented in an area, the habitat may change, and new species may enter
and others may go locally extinct.
16. Suppose you are exploring the chaparral ecosystem in California. You encounter a
shrub species that you think may be fire-adapted, and you wonder whether the plant can
reproduce in the absence of fire. Design an experiment that would help answer your
question.
One way to answer the question would be to set aside a plot of chaparral from which fire
was excluded. You could then take seeds from the shrub and plant them in the fireprotected plot and observe the plants over time to see whether they can complete their life
cycles in the absence of fire.
17. Researchers and citizens in Prairie City, Iowa, are reconstructing the prairie by
collecting seeds from remnants of native grasslands and reintroducing animals. Which
other biomes discussed in the chapter might it be possible to reconstruct and which not?
Biomes in which only a few plant species dominate might be the easiest to reconstruct;
examples include temperate forests and taiga. The tropical forest would be virtually
impossible to reconstruct, both because of its poor soils and because of the intricate
relationships among the organisms that live there.
18. Hundreds of millions of years ago, Earth’s land masses were joined into one
supercontinent, Pangaea. If Pangaea had never broken up, do you think there would be
more biodiversity, less biodiversity, or the same amount of diversity as today? Explain
your answer.
With one supercontinent there would not be land masses spread across the surface of the
earth at different latitudes and in different hemispheres. This, coupled with the reduced
coastline, would decrease the diversity of biomes.
Pull it Together
1. What factors determine the location of each biome on Earth?
For terrestrial biomes, the amount of water, altitude, distance from the oceans, and
latitude are important factors. For aquatic biomes, distance from shore, light penetration,
depth/pressure, latitude, current strength, and salinity are important.
2. What types of forests occur on Earth, and what combination of conditions favors each
type?
The main types of forests are rainforests, temperature deciduous forests, temperate
coniferous forests, and taiga. High rainfall and warm temperatures throughout the year
favor the rainforest. In temperate deciduous forests, rainfall is evenly distributed
throughout the year, summers are warm, and winters are cold. Temperate coniferous
forests usually grow where winters are milder and summers are cooler. Taiga forests
grow where winters are very long and cold.
3. How do tropical savannas differ from temperate grasslands?
Tropical savannas are characterized by grasses and scattered trees, whereas trees are
typically absent from a temperate grassland. In addition, tropical savannas and temperate
grasslands differ in terms of seasonal extremes. In tropical areas the temperature never
drops to freezing, and cold spells are rare, whereas temperate areas have seasonal
changes with sub-freezing winters.
4. List examples of coastal ecosystems.
Examples of coastal ecosystems include estuaries, intertidal zones and coral reefs.
Estuaries are where fresh water from rivers meets ocean water, resulting in brackish
water and currents that sustain all sorts of unique organisms. Intertidal zones describe the
areas of the shore that are alternately submerged and exposed with the tide. Coral reefs
form in warm shallow waters along tropical shorelines.