PSAT 8/9 Writing and Language Practice Test 3: Gause's Law: It's a Competition

Questions 1-10 refer to the following information.

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.

10 questions 8 minutesAll test questions

1. Which choice most effectively combines the sentences at the underlined portion?

A. principles, this includes competition, in which

B. competition principles, in which

C. principles, competition, and

D. principles, including competition, in which

2. At this point, the writer is considering adding the following sentence.

That is, one species will benefit from a certain advantage it has and increase its population, and the other species could eventually go extinct.

Should the writer make this addition here?

A. Yes, because it elaborates on a concept and clarifies the connection between competition and extinction.

B. Yes, because it explains the significance of Gause's research.

C. No, because it provides information that is unrelated to the paragraph's main idea.

D. No, because it contradicts information given earlier in the paragraph.

3. Which choice best sets up the information that follows in the passage?

A. NO CHANGE

B. the first to prove the validity of the principle of competitive exclusion, in 1932.

C. later awarded a prize for his life-saving work on antibiotic medications.

D. an ecologist who published a number of influential books.

4. Which choice best maintains the style and tone of the passage?

A. NO CHANGE

B. nicely

C. amazingly

D. wonderfully

5. To make this paragraph most logical, sentence 4 should be placed

A. where it is now.

B. after sentence 1.

C. after sentence 2.

D. after sentence 5.

6. Which choice, if added here, would most effectively introduce the main topic of the paragraph?

A. NO CHANGE

B. Gause's results confirmed the theory.

C. It is important for scientific experiments to contain control groups.

D. Gause eventually published his results in a book.

7. Which choice most effectively sets up the results that follow in the sentence?

A. NO CHANGE

B. both species continued to grow at the same rate:

C. Gause saw a difference in the populations emerge:

D. Gause decided to do more experiments:

8. Which choice uses information from the graph to accurately describe P. caudatum over the 16-day span?

A. NO CHANGE

B. never containing more than 5 cells.

C. going extinct in fewer than 10 days.

D. eventually being eliminated entirely from the sample.

9. At this point, the writer is considering adding the following information:

Gause had earned his first degree at Moscow University a few years before publishing his results.

Should the writer add the sentence here?

A. Yes, because it shows that Gause's scientific research was trustworthy.

B. Yes, because it helps the reader understand the passage's main points.

C. No, because it contradicts the author's claim about Gause in the previous sentence.

D. No, because it adds unnecessary information that is unrelated to the main topic of the paragraph.

10. The author wants a conclusion that summarizes the main finding of Gause's experiment. Which choice best accomplishes this goal?

A. NO CHANGE

B. two species can coexist without competing for resources.

C. competition for resources causes both organisms to go extinct.

D. when two species compete, one will adapt to find a new niche.

PSAT 8/9 Writing and Language Practice Test 3: Gause's Law: It's a Competition

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