Passage VI

The concentration of dissolved oxygen (DO) in river water affects the fish in the river. Many freshwater fish species, including crappie, perch, and bass, require a minimum average DO concentration of 5 parts per million (ppm) to thrive. Other fish, such as carp and gar, can tolerate average DO concentrations as low as 3 ppm. Table 1 shows the DO concentration at saturation for water at various temperatures. Figures 1 and 2 show the measured changes in a river's water temperature and DO concentration, respectively, over a 24-hour period in midsummer. Table 2 shows how the DO concentration affects fish species in a river.

Table 1 and Figures 1 and 2 adapted from American ChemicalSociety, ChemCom: Chemistry in the Community, 2nd ed. ©1993 by American Chemical Society.

32. According to Figure 1 and Figure 2, which of the following best describes what happens to the water temperature and the DO concentration between 2 A. M.and7 A. M.?

Water temperature ---- DO concentration

Answer and Explanation

Your Answer is

Correct Answer is H

Explanation

Look at figure 1, when the abscissa is 2 -7 AM, the river water temperature is constant at 19°, and it is the lowest temperature of the day;

Look at figure 2 again, the DO concentration at this time is also Constant