1. If the Earth was not tilted on its axis of rotation, the annual cycle of seasons in the northern and southern hemispheres— a. would be reversed b. would stay the same c. would be reduced d. would not exist
The correct answer is d—
A. Answer a is incorrect. The tilt is responsible for reduced and increased incidence of solar radiation at different times of the year. Without the tilt, such annual variation would not exist.
The correct answer is d—
B. Answer b is incorrect. Without the tilt, the pattern of seasonality would disappear.
The correct answer is d—
C. Answer c is incorrect. Without some tilt, annual variation in the incidence of solar radiation would disappear.
The correct answer is d—would not exist
D. Answer d is correct. Tilt on the axis of rotation drives seasonality away from the equator.
2. The Coriolis effect— a. drives the rotation of the Earth b. is responsible for the relative lack of seasonality at the equator c. drives global wind circulation patterns d. drives global wind and ocean circulation patterns
The correct answer is d—
A. Answer a is incorrect. The Coriolis effect arises from the rotation of the Earth; it doesn’t produce it.
The correct answer is d—
B. Answer b is incorrect. Reduced seasonality at the equator results from the relative constancy of solar radiation input throughout the year.
The correct answer is d—
C. Answer c is incorrect. Although the Coriolis effect is responsible for global wind circulation patterns, it is not the best answer.
The correct answer is d—drives global wind and ocean circulation patterns
D. Answer d is correct. Both wind and ocean circulation patterns derive from forces that result from the spin of the Earth.
3. What two factors are most important in biome distribution?

a. Temperature and latitude b. Rainfall and temperature c. Latitude and rainfall d. Temperature and soil type
The correct answer is b—
A. Answer a is incorrect. Rainfall and temperature are the two most important factors in biome distribution.
The correct answer is b—Rainfall and temperature
B. Answer b is correct. Rainfall and temperature are the two most important factors in biome distribution.
The correct answer is b—
C. Answer c is incorrect. Rainfall and temperature are the two most important factors in biome distribution.
The correct answer is b—
D. Answer d is incorrect. Rainfall and temperature are the two most important factors in biome distribution.
Hint : There are eight major biome categories (some ecologists recognize more) that are defined by average annual rainfall (or available moisture) and average annual temperatures.
4. In a rain shadow, air is cooled as it rises and heated as it descends, often producing a wet and dry side because the water-holding capacity of the air— a. is directly related to air temperature b. inversely related to air temperature c. is unaffected by air temperature d. produces changes in air temperature
The correct answer is a—is directly related to air temperature
A. Answer a is correct. Air that is warm can hold more water than air that is cold.
The correct answer is a—
B. Answer b is incorrect. An inverse relationship would lead to air holding more water as it was cooled.
The correct answer is a—
C. Answer c is incorrect. The temperature of the air is the primary determinant of its water content.
The correct answer is a—
D. Answer d is incorrect. The water-holding capacity is the consequence of temperature change, not the cause.

5. The main cause(s) driving the difference between a tropical rain forest and a temperate evergreen forest is— a. the amount of average annual rainfall b. the average annual temperature c. temperature and rainfall d. none of the above
The correct answer is b—
A. Answer a is incorrect. There are many examples of tropical rainforests that get less annual rainfall than the majority of temperate evergreen forests.
The correct answer is b—the average annual temperature
B. Answer b is correct. The primary driver is annual temperature. Tropical forests are warmer than temperate evergreen forests, but many do not get more rain.
The correct answer is b—
C. Answer c is incorrect. The two factors do not differ; it is primarily an issue of temperature differences.
The correct answer is b—
D. Answer d is incorrect. One of the answers is correct.
6. Thermal stratification in a lake— a. is not modified by fall and spring overturn b. leads to higher oxygen in deep versus surface waters c. leads to higher oxygen in surface versus deep waters d. is reduced when ice forms on the surface of the lake
The correct answer is c—
A. Answer a in incorrect. The spring and fall overturns actually lead to a mixing of the lake, removing stratification.
The correct answer is c—
B. Answer b is incorrect. When there is thermal stratification, oxygen movement into the deeper waters of a lake is reduced, but its loss due to consumption by organisms may not be reduced, with the overall effect of low-oxygen concentrations expected at greater depths.
The correct answer is c—leads to higher oxygen in surface versus deep waters
C. Answer c is correct. Surface waters continue to take up oxygen from the atmosphere, but movement into deeper parts of a lake would be highly reduced.
The correct answer is c—
D. Answer d is incorrect. The formation of ice may further the degree of stratification in a lake.

7. Oligotrophic lakes have— a. low oxygen, and high nutrient availability b. high oxygen, and high nutrient availability c. high oxygen, and low nutrient availability d. low oxygen, and low nutrient availability
The correct answer is c—
A. Answer a is incorrect. These are the conditions associated with a eutrophic lake.
The correct answer is c—
B. Answer b in incorrect. High oxygen and nutrient availability are often at odds with each other. High nutrient availability drives high algal productivity which usually leads to conditions that reduce oxygen (decomposition rates and reduced penetration of solar radiation).
The correct answer is c—high oxygen, and low nutrient availability
C. Answer c is correct. High oxygen results when nutrients are low, keeping algal productivity down and oxygen consumption by organisms low.
The correct answer is c—
D. Answer d is incorrect. The two factors are usually inversely related, with oligotrophic lakes being characterized by high oxygen availability and low nutrient availability.
8. Oligotrophic lakes can be turned into eutrophic lakes as a result of human activities such as— a. overfishing of sensitive species, which disrupts fish communities b. introducing nutrients into the water, which stimulates plant and algal growth c. disrupting terrestrial vegetation near the shore, which causes soil to run into the lake d. spraying pesticides into the water to control aquatic insect populations
The correct answer is b—
A. Answer a is incorrect. Overfishing is a problem that affects some lakes, but it does not turn oligotrophic lakes into eutrophic lakes.
The correct answer is b—introducing nutrients into the water, which stimulates plant and algal growth
B. Answer b is correct. Oligotrophic lakes can be made eutrophic if excess nutrients are introduced into the lake.
The correct answer is b—

C. Answer c is incorrect. Many lakes are negatively affected by the removal of vegetation near the shore, which causes problems with soil runoff. However, this does not turn an oligotrophic lake eutrophic.
The correct answer is b—
D. Answer d is incorrect. Pesticides in the water can negatively affect water quality, but it does not cause an oligotrophic lake to become eutrophic.
9. Deep sea hydrothermal vent communities— a. get their energy from photosynthesis in the photic zone near the surface b. use bioluminescence to generate food c. are built on the energy produced by the activity of chemoautotrophs that oxidize sulfur d. contain only bacteria and other microorganisms
The correct answer is c—
A. Answer a is incorrect. Although there is enough primary production in the photic zone to support some deep sea life, the hydrothermal vent communities are unique in the density and diversity of organisms that survive at great depths in the oceans. The amount of energy from photosynthesis, literally thousands of feet above, is simply not enough to support such an abundance.
The correct answer is c—
B. Answer b is incorrect. Bioluminescence does not generate energy; it uses energy to generate light.
The correct answer is c—are built on the energy produced by the activity of chemoautotrophs that oxidize sulfur
C. Answer c is correct. Whole food chains that make the large abundance of organisms possible in vent communities rely on the use of hydrogen sulfide by chemoautotrophic bacteria.
The correct answer is c—
D. Answer d is incorrect. A great diversity and abundance of large invertebrates
(especially different kinds of worms) also characterize these habitats.
10. Biological magnification occurs when— a. pollutants increase in concentration in tissues at higher trophic levels b. the effect of a pollutant is magnified by chemical interactions within organisms c. an organism is placed under a dissecting scope
The correct answer is a—pollutants increase in concentration in tissues at higher trophic levels d. a pollutant has a greater-than-expected effect once ingested by an organism

A. Answer a is correct. As with DDT, a pesticide may be harmful at low concentrations, but when it is concentrated by moving up the food chain, exposure may actually be higher and the harmful consequences greater. In this case, biological magnification has occurred.
The correct answer is a—
B. Answer b is incorrect. Chemical interactions within an organism are usually the source of injury or mortality for an individual organism when exposed to a pollutant, but it is the increasing concentration with trophic level that matters in biological magnification.
The correct answer is a—
C. Answer c is incorrect. Biological magnification does not refer to magnifying our view of an organism.
The correct answer is a—
D. Answer d is incorrect. Biological magnification does not refer to effects of a pollutant once ingested.
11. Which of the following is a point source of pollution? a. Lawns b. Smokestacks of coal-fired power plants c. Factory effluent pipe draining into a river d. Acid rain
The correct answer is c—
A. Answer a is incorrect. Lawns represent a diffuse input of pollution into the environment.
The correct answer is c—
B. Answer b is incorrect. Smokestacks, although localized, put pollutants into a diffuse sink, the atmosphere.
The correct answer is c—factory effluent pipe draining into a river
C. Answer c is correct. The input of an effluent pipe is concentrated, localized, and traceable.
The correct answer is c—
D. Answer d is incorrect. Acid rain is an indirect source of pollution, resulting from many prior inputs (such as from point sources) that may be transported long distances.
12. Statements that CO
2 is increasing compared with historical levels— a. are based on theory only b. are based on data c. are irrelevant with respect to global warming

d. are the basis for a theory that the Earth’s global temperature is decreasing
The correct answer is b—
A. Answer a is incorrect. Increasing levels of CO
2
are not theoretical; they are based on data.
The correct answer is b—are based on data
B. Answer b is correct. Since about 1960, levels of CO
2 have been accurately measured as increasing.
The correct answer is b—
C. Answer c is incorrect. CO
2
is a major greenhouse gas, expected to help trap energy within the Earth and its atmosphere.
The correct answer is b—
D. Answer d is incorrect. The theory predicts the opposite, that the Earth’s temperature is increasing.
13. The loss of the ozone layer has serious implications for the quality of the environment because— a. ozone (O
3
) protects organisms from ultraviolet radiation that can cause cancer b. a depleted ozone layer causes rainwater to have a lower pH that kills plant life c. loss of the ozone layer causes the Sun’s rays to get trapped in the atmosphere and increase global temperatures d. a depleted ozone layer can interact with toxic chemicals to increase their effect on organismal health
The correct answer is a—ozone (O
3
) protects organisms from ultraviolet radiation that can cause cancer
A. Answer a is correct. The ozone layer helps to shield the Earth from ultraviolet radiation. UV radiation can mutate DNA and cause cancer and other diseases.
The correct answer is a—
B. Answer b is incorrect. Acid precipitation is due to the release of nitric and sulfuric acids into the atmosphere.
The correct answer is a—
C. Answer c is incorrect. The release of greenhouse gases (such as carbon dioxide) into the atmosphere creates a situation known as the greenhouse effect. Solar radiation that would normally be reflected back into space becomes trapped in the atmosphere and causes the atmosphere to heat up. This situation has resulted in global warming.
The correct answer is a—

D. Answer d is incorrect. The depleted ozone layer does not interact with toxic chemicals to increase their effect.
Challenge Questions
1. Discuss how Figure 58.1 explains the pattern observed in Figure 58.2.
Answer
—The Earth is tilted on its axis such that regions away from the equator receive less incident solar radiation per unit surface area (because the angle of incidence is oblique). The northern and southern hemispheres alternate between angling towards vs. away from the Sun on the Earth’s annual orbit. These two facts mean that the annual mean temperature will decline as you move away from the equator, and that variation in the mean temperatures of the northern and southern hemispheres will be complementary to each other; when one is hot, the other will be cold.
2. Why are most of the Earth’s deserts found at approximately 30° latitude?
Answer
—Energy absorbed by the Earth is maximized at the equator because of the angle of incidence. Because there are large expanses of ocean at the equator, warmed air picks up moisture and rises. As it rises, equatorial air, now saturated with moisture, cools and releases rain, the air falling back to Earth’s surface displaced north and south to approximately 30°. The air, warming as it descends, absorbs moisture from the land and vegetation below, resulting in desiccation in the latitudes around 30°.
3. Rainshadows are expected when prevailing winds carrying moist air intercept high mountains. What kind of rainshadow would you expect if the prevailing winds arrive on the windward side relatively dry?
Answer
—If the mountains are high enough, any moisture, even if there is only a small amount, will tend to be released as rain. On the leeward side, the dry, warming air would desiccate the soil and vegetation. A dramatic difference between windward and leeward sides might not develop (such as, forest versus desert) if the windward side never receives a tremendous amount of rain, but the leeward side would nevertheless be dried out by descending dry air.
4. What is the distinction between global warming and changes in average CO
2 levels?
Answer
—Global warming is the predicted outcome of increasing CO
2
levels in our atmosphere. Given both recent historical records and records from other sources (ice cores, etc.), we can be fairly certain that CO
2
levels are increasing at an unprecedented rate. Alternatively, given the complexity of global climate patterns and their sources, knowing exactly the impact of higher CO
2
is difficult but the consensus is that it will lead to a warning of the Earth’s surface. Such warming will likely have myriad consequences, including rising sea levels, desertification, flooding, severity of storms, among others.

5. If a pesticide is harmless at low concentrations (such as, DDT) and used properly, how can it become a threat to nontarget organisms?
Answer
—Two characteristics can lead to a phenomenon known as biological magnification. First, if a pesticide actually persists in the bodies of target species (that is, it doesn’t degrade after having its effect), then depending on its chemical composition, it might actually be sequestered in the bodies of animals that eat the target species. Because large numbers of prey are consumed at each trophic level (due to the 10% rate of transfer of energy), large amounts of the pesticide may be passed up the food chain. So, persistence and magnification can lead to toxic exposures at the top of food chains.