Pollution has many causes and can affect the air and water quality in a variety of ways. Nitrates are a common pollutant found in agricultural runoff. Four groups of students designed experiments to determine the effect of nitrates on algae growth. Which group of students designed an experiment whose variables would lead to the most valid results? Group 1 varied both the temperature and the amount of nitrates.
Group 2 kept both the temperature and the amount of nitrates constant.
Group 3 kept the temperature constant and varied the amount of nitrates.
Group 4 varied the temperature and kept the amount of nitrates constant.