AccelePrep for the ACT Test 2nd Edition Student Text

212 • S URGE TO S UCCESS ! S CIENCE T EST P REP

UNDERSTANDING EXPERIMENTAL DESIGN

Understanding Design of Experiment items ask about what is represented by a particular part of an experiment. These items require an understanding of the information stated in the passage about the design and implementation of the various experiments, as well as any results. In the ear model example, a typical item would ask what the metal hoop represents (the supporting bone for the eardrum). Another item might focus on the controlled variables in the experiment (the rubber sheet and the metal hoop). To test the hypothesis that all antibiotics are equally effective in preventing bacterial growth, the following three experiments ™‡”‡…ƒ””‹‡† ‘—– —•‹‰…Ž‡ƒ” ’Žƒ•–‹…’Žƒ–‡• ϐ‹ŽŽ‡† ™‹–Š —–”‹‡– ƒ‰ƒ” ȋƒ mixture of ingredients that supports the growth of bacteria). When bacteria reproduce successfully, colonies form on the agar, giving it a cloudy appearance. Experiment 1 Three plates (A, B, and C) of agar were set up, each with an equal amount of bacterial culture (Bacterium X) spread over the agar surface and with a paper disk placed in the center. Plate A’s disk was soaked in Antibiotic I; Plate B’s disk was soaked in Antibiotic II; Plate ǯ• †‹• ™ƒ• •‘ƒ‡† ‹ ’Žƒ‹ ™ƒ–‡”Ǥ ˆ–‡” ‹…—„ƒ–‹‘ ‘˜‡”‹‰Š– ƒ– ͵͹ι (body temperature), Plates A and B had a clear area, 2” in diameter surrounding the paper disk, but beyond this 2” region, the plates were cloudy. Plate C was entirely cloudy, including the area adjacent to the paper disk. Experiment 2 Identical procedures were followed except that Plates A, B, ƒ† ™‡”‡ ‹…—„ƒ–‡† ‘˜‡”‹‰Š– ƒ– ʹʹι ȋ”‘‘ –‡’‡”ƒ–—”‡ȌǤ ˆ–‡” incubation, Plate A had a clear area, 2” in diameter, surrounding the paper disk. Plates B and C were entirely cloudy. Experiment 3 Identical procedures were followed except that the concentrations of Antibiotic I (Plate A) and Antibiotic II (Plate B) ™‡”‡ ƒ†‡ –™‹…‡ ƒ• •–”‘‰Ǥ ˆ–‡” ‹…—„ƒ–‹‘ ‘˜‡”‹‰Š– ƒ– ʹʹι ǡ Žƒ–‡• A and B both had clear, 2” areas around the paper disk, while Plate C remained entirely cloudy. 1. After incubation, a clear area around a previously soaked paper disk represents a region where: A. agar had washed away. B. decomposition had occurred due to high incubation temperatures. C. bacterial growth did not occur. D. bacteria grew best.

Examples:

Explanations for the example questions are included later in the chapter. Circle your answers now. Later when you reach the explanations at the end of the section, come back and check to make sure you answered the questions correctly.