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Chapter 21
Ocean Water
Review
Choose the best response. Write the letter of that choice in the space provided.
1. The gas that dissolves most easily in ocean water is
a. carbon dioxide. b. argon.
c. nitrogen.
d. oxygen.
2. The amount of dissolved solids in ocean water is called its
a. salinity.
b. nekton.
c. plankton.
d. density.
3. A thin floating layer of ice that covers an ocean surface is called
a. an iceberg.
b. a thermocline.
c. pack ice.
d. benthos.
4. A zone of rapid water temperature change with increasing depth is called
a. a benthos.
b. an abyssal zone. c. a bathyal zone.
d. a thermocline.
5. When liquid water is warmed, its density
Copyright © by Holt, Rinehart and Winston. All rights reserved.
a. increases.
b. decreases.
c. remains the same.
d. doubles.
6. Although most of the various wavelengths of visible light are absorbed by ocean water,
the one wavelength that tends to be reflected is the color
a. violet.
b. green.
c. yellow.
d. blue.
7. The process by which surface water is blown farther offshore and nutrient-rich deep
water rises to take its place is called
a. desalination.
b. distillation.
c. upwelling.
d. aquaculture.
8. Drifting marine plants and animals are known as
a. plankton.
b. benthos.
c. nekton.
d. tube worms.
9. Marine animals that can swim to search for food and avoid predators are called
a. phytoplankton. b. zooplankton.
c. nekton.
d. benthos.
c. benthos.
d. phytoplankton.
10. Sea anemones are an example of
a. zooplankton.
b. nekton.
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Chapter 21
Choose the best response. Write the letter of that choice in the space provided.
11. Perhaps the most unstable ocean environment is the
a. intertidal zone. b. abyssal zone.
c. bathyal zone.
d. neritic zone.
12. The pelagic zone that has abundant sunlight, a fairly constant temperature, and relatively
low pressure is the
a. bathyal zone.
b. neritic zone.
c. abyssal zone.
d. intertidal zone.
13. Which of the following is not a method for producing fresh water by desalinating ocean
water?
a. distillation
b. evaporation
c. reverse osmosis d. aquaculture
14. Lumps of minerals on the ocean floor are called
a. nekton.
b. nodules.
c. benthos.
d. plankton.
15. Aquaculture is another name for
a. desalination.
c. ocean farming.
b. distillation.
d. rapid temperature changes.
16. In the future, scientists may be able to fertilize the ocean through
b. artificial upwelling.
d. dissolving gases.
Critical Thinking
Read each question or statement and answer it in the space provided.
1. Suppose that climatic conditions over the earth’s oceans changed dramatically. The changes
resulted in a complete absence of upwelling and wave action. Explain what would happen to the
marine life and why.
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a. distillation.
c. mining nodules.
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Chapter 21
Read each question or statement and answer it in the space provided.
2. How would a significant decrease in sunlight affect phytoplankton?
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3. What impact would the decrease in sunlight discussed in Question 2 have on other forms of
marine life?
4. When oceanographers first explored the deep ocean basin along mid-ocean ridges, they
discovered a variety of marine life, including sightless crabs. Explain why these crabs are not
handicapped by their sightlessness.
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Chapter 21
Application
Read each question or statement and answer it in the space provided.
1. Suppose you are contracted to build a desalination system for the state of Florida. In order to
make your system as efficient as possible, you want to locate it in an area of the ocean where
the salinity of the water is low. Where along the coast of Florida would you choose to build the
site, near Miami or Tallahassee?
2. You have collected samples of ocean water from the three locations: a site just off the coast of
Israel; a site on Prudhoe Bay, off the coast of northern Alaska; and a site off the coast of
Sweden, on the Baltic Sea. All three samples have been brought to room temperature. From
which location would the water have the greatest density? Why?
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Chapter 21
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3. You have decided to start an aquatic farm. In which of the zones of ocean life should you locate
your farm? Why?
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words phytoplankton (from the Greek word phyto,
meaning “plant”) and zooplankton (from the Greek
word zoe, meaning “life”).
Pages 417–421: Discussion
(Reinforcement)
To reinforce students’ understanding of resources in
the ocean, put the following headings on the chalkboard: “Material Resources,” “Energy Resources,”
“Food Resources,” and “Recreational Resources.”
Have students list ocean resources in each category.
You may wish to point out that in 1983 President
Ronald Reagan established that the ocean resources
from the coasts of the United States and its territories to 320 km offshore belong to the United
States. Scientists from the U.S. Geological Survey
and National Oceanic and Atmospheric Administration have carefully mapped this zone, which
contains offshore mineral and oil resources.
Pages 418–419: Science & Technology
You may wish to explain that water normally flows
by osmosis from a dilute solution through a membrane to a more concentrated solution. In reverse
osmosis, pressure is applied to the concentrated
solution. Pure water is obtained by applying pressure to sea water—the more concentrated solution—
and forcing it through a membrane that prevents
ions and other substances from passing through it.
Small-Scale Investigation
Chapter 21 Review
Answers to Review
1. a
2. a
3. c
4. d
5. b
6. d
7. c
8. a
9. c
10. c
11. a
12. b
13. d
14. b
15. c
16. b
Answers to Critical Thinking
1. All but the bottom dwellers would die out
because the nutrient-rich material would never
return to the surface.
2. The absence of sunlight would halt the growth of
phytoplankton.
3. Other marine life would be devastated because
phytoplankton form the foundation of the marine
food web.
4. Because there is no light, sight is unnecessary.
Answers to Application
1. The waters of the Gulf of Mexico off Tallahassee
have a lower salinity than the waters of the
Atlantic Ocean off Miami; therefore, Tallahassee
would be the better choice.
2. off the coast of Israel, because highly saline
water has an abundance of dissolved solids and is
thus denser
3. neritic; because it is the most hospitable to
marine life
Density Factors (p. 411)
Science Process Skills: hypothesizing, recording
data, comparing and contrasting
In-Depth Investigation
Answers to Analysis and Conclusions
Ocean Water Density (pp. 424–425)
1. Answers will vary. Typical answers will include
salt water, cold water, and distilled water, ranked
from most dense to least dense. As the density
decreases, the straw will sink deeper below the
water’s surface.
2. Answers will vary. A typical answer would be to
warm the water.
3. It would decrease the water’s density.
4. Answers will vary. A typical answer would be
that the water will be least dense in areas where
the water has a low salinity or is very warm, or
where there is an infusion of fresh water. The
water will be most dense in areas where the water
has a high salinity or is very cold.
Approximate time: 1 class period
Objectives: to observe the effects of temperature
and salinity on the density of water
Skills: measuring, observing, comparing, determining cause and effect, inferring
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Chapter 21
Prelab Discussion
Discuss with students the effect of salinity in ocean
water as fresh water enters the ocean from large
rivers and heavy rainfall. Explain to students that
ocean water is approximately 96.5 percent pure
water and 3.5 percent dissolved salts. Ask them if
slight variations in salinity change the density of
ocean water.