Practice Exam 3 - Environmental Science - page 286

A. Keystone species
B. Indicator species
C. Foundation species
D. Specialist species
E. Generalist species

33. One of the biggest threats to rangeland is overgrazing of vegetation by livestock. All the following are
consequences of overgrazing EXCEPT:
A. Soil erosion
B. Soil compaction
C. Desertification
D. The proliferation of invasive species
E. An increase in native biodiversity

Question 34 refers to the following table.

Changes in Concentration of Greenhouse Gases
Greenhouse GasPreindustrial Levels (ppm) Current Level (ppm)

Carbon dioxide 280 388

Methane 700 1,745

Nitric oxide 270 314

CFCs 0 533

34. The table shows dramatic increases in greenhouse-gas levels. Combustion of fossil fuels accounts for
changes in CO 2 and NO levels. The increasing populations of cattle and other animals for human con-
sumption accounts for the increase in CH 4 . What accounts for the change in CFCs?
A. CFCs were not used prior to the Industrial Revolution.
B. CFCs were discovered and manufactured starting in the 1930s.
C. CFCs are a secondary air pollutant, and levels were not significant until concentrations of primary
air pollutants were high.
D. CFCs were in the atmosphere prior to the Industrial Revolution, but humans did not have the means
to measure the gases until instruments were developed.
E. CFCs are released in the processing of uranium for use as a fuel in nuclear reactors and, therefore,
were not produced until the 1950s, when reactors were first developed.

Questions 35-38 refer to the following answer choices.

A. Ammonification
B. Denitrification
C. Nitrification
D. Nitrogen fixation
E. Assimilation

35. NO 3 is converted to N 2 .
36. NH 4 + is converted into NO 2 - and then into NO 3 - .