ACT Science Practice Test 50

PASSAGE VII

Several scientists considered some different environmental factors and their influence on the growth of certain bacteria. The following experiments used Salmonella bacteria to measure the effect of pH levels, nutrients, and temperature on the number of bacteria produced within a given time period.

Experiment 1

A known quantity of Salmonella bacteria was placed in each of 3 Petri dishes with the same nutrient concentration at the same temperature. The pH level of each nutrient concentration in each dish was varied according to Table 1. On the pH scale, 7 represents neutral, values less than 7 indicate an acid, and values greater than 7 indicate a base. The lids of the Petri dishes were replaced after the bacteria were added and the dishes were left alone. After 6 hours, the percent growth of Salmonella bacteria was recorded (Table 1).

Experiment 2

A known quantity of Salmonella bacteria was placed in each of 3 Petri dishes with different nutrient concentrations in the form of organic compounds. The temperature and pH level (neutral 7) were held constant in each sample. The lids of the Petri dishes were replaced after the bacteria were added and the dishes were left alone. After 6 hours, the percent growth of Salmonella bacteria was recorded (Table 2).

Experiment 3

A known quantity of Salmonella bacteria was placed in each of 3 Petri dishes at different temperatures. The pH level and nutrient concentrations were held constant. The lids of the Petri dishes were replaced after the bacteria were added and the dishes were left alone. After 6 hours, the percent growth of Salmonella bacteria was recorded (Table 3).

PASSAGE I

Friction is the resistance to the movement of one object past another object with which the first object is in contact. A group of students performed several experiments using rectangular blocks of various materials and a smooth inclined plane 2 meters in length. To compare how different materials are affected by friction, the blocks were placed at the top of the plane and released to travel the 2-meter distance. The time in seconds (s) that it took for each block to reach the end of the inclined plane was recorded.

Experiment 1

The group of students wanted to know which materials moved down the plane in the shortest amount of time. The students used blocks of wood, steel, aluminum, glass, plastic, and concrete. The dimensions of each block were the same, the volume of each block remained constant, and the mass of the blocks was varied. The incline of the plane was set at 45° for each trial. The students conducted 3 trials for each material, and recorded the results in Table 1.

Experiment 2

The students conducted a similar experiment as in Experiment 1 to test the effect of volume on the time that it took for the blocks to move down the inclined plane. The results are shown in Table 2.

Experiment 3

Objects can be rated according to their ability to move efficiently. The students created a scale from 5 to 30 (least to most resistant to motion due to friction) and tested four objects of a known rating. Three trials were conducted for each object, using the same methods as in Experiment 1. The results are shown in Table 3.