Passage I

Herbicides are used to control the growth of weeds. A herbicide that may be used safely with one crop species may damage another crop if the latter crop is planted in soil containing residual amounts of the herbicide from an earlier application. Two experiments were performed to study this effect.

Experiment 1

A botanist filled 90 pots with Soil Type 1. No herbicide was added to the soil in 10 pots. The other pots were divided into groups of 10 and the soil in each group was treated with 10, 20, 50, or 100 ppm of either Herbicide A or B. All other factors were held constant. Ten seeds of a corn hybrid were planted in each pot. After 40 days, the plants were uprooted, oven-dried, and weighed. The results are shown in Table 1.

Experiment 2

Experiment 1 was repeated with 90 pots of Soil Type 1 and 90 pots of Soil Type 2. The same herbicide doses and corn hybrid were used. All other factors were held constant. After 40 days, the heights of the plants were measured. The results are shown in Table 2.

Information on the two soil types used is given in Table 3.

4. Assume that there is a direct correlation between plant height and plant mass. If Experiment 1 were repeated using Soil Type 2, one would predict that the average plant mass would be lowest under which of the following conditions?

Answer and Explanation

Your Answer is

Correct Answer is H

Explanation

The stem of the question says that the plant mass is small, and the plant height is short. The smallest plant mass in Table 1 is Herbicide A with 100 ppm. From this, it is speculated that if the soil type 2 is replaced, the plant mass is the smallest and the plant height is the shortest in this group