PSAT Writing and Language Practice Question 334
Question: 334
Gause's Law: It's a Competition
By the nineteenth and early twentieth centuries, scientists had observed many ecological 1 principles, including the principle of competition. In this principle, different organisms or species compete for a limited supply of a certain resource. Scientists posited that whenever two species are in competition, they will not coexist with constant population sizes. 2 To prevent going extinct, a species can either evolve or develop a new niche—the species's unique role in a certain environment. While this idea had been proposed earlier, biologist Georgy Gause was 3 born in Moscow, Russia, in 1910.
[1] In order to demonstrate this theory, Gause conducted a laboratory experiment. [2] He used two species of Paramecium (a type of microscopic organism) known as P. aurelia and P. caudatum. [3] To test the theory of competitive exclusion, Gause also combined the two species and observed what happened. [4] For the experiment, he created separate groups of each organism as control groups. [5] He provided the control and combined groups with the same amount of food and water and used a sample to determine the population of each species every day. [6] He wanted to see whether the two species would grow equally 4 well or whether, as the principle of competitive exclusion suggests, one group would become dominant and overtake the other. 5
6 The experiment contradicted scientists' expectations. In the control groups, the two species had similar populations to each other. However, in the group that was combined, 7 Gause saw no clear pattern: as the two species competed for resources, P. aurelia emerged as the dominant organism. Initially, the two species grew at a similar rate, but P. aurelia soon surpassed P. caudatum and approached the population levels seen in the individual groups. P. caudatum decreased in population, 8 but it later increased and caused the P. aurelia to go extinct.
Scientists continue to study competitive exclusion today, among plants, animals, and even humans, and Gause's experiments are credited for demonstrating this ecological idea experimentally. 9 Ecologists know that, at least under the controlled conditions of a laboratory, 10 when two species compete for the same resources, one will overtake the other one.
Which choice most effectively combines the sentences at the underlined portion?
Correct Answer: D
Explanation:
Note the question! The question asks how to effectively combine the underlined sentences, so it's testing precision and concision. Start with the shortest answer, which is (C). Choice (C) implies that the act of observing many ecological principles is competition, which is not consistent with the original sentence. It could also be read as a list of three things, which it shouldn't be. Eliminate (C). Consider the shortest of the remaining choices, which is (B). Choice (B) implies that scientists only observed ecological principles related to competition, not that competition is one of the ecological principles they studied. This is not consistent with the original sentences, so eliminate (B). Consider the shorter of the remaining choices, which is (D). Choice (D) preserves the meaning of the original sentence, so keep it. Choice (A) uses a comma to separate two complete ideas, which is not allowed. Eliminate (A). The correct answer is (D).