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.

33. According to Table 1 and Table 2, river water at a temperature in which of the following ranges would most likely have a low enough DO concentration to endanger moșt fish species living in that water?

Answer and Explanation

Your Answer is

Correct Answer is D

Explanation

Look at table 2 first, when DO concentration<1, fish die;

Look at table 1 again, when the water temperature is 35° C, DO concentration is 7.0, and if it is higher than 35° , DO concentration will decrease, and may eventually drop to less than 1, resulting in fish death