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Science Reasoning Sample Questions

Click on the letter choices to determine if you have the correct answer and for question explanations.

(An actual ACT Science Test contains 40 questions to be answered in 35 minutes.)
 


DIRECTIONS: The passage in this test is followed by several questions. After reading the passage, choose the best answer to each question and fill in the corresponding oval on your answer document. You may refer to the passage as often as necessary. You are NOT permitted to use a calculator on this test.


Abandoned cornfields have been the sites of investigations concerning ecological succession, the orderly progression of changes in the plant and/or animal life of an area over time (see Figure 1). (Note: The plants are ordered according to their appearance during ecological succession.)  During the early stages of succession, the principal community (living unit) that dominates is the pioneer community. Pioneer plants are depicted in Figure 2.  The final stage of ecological succession is characterized by the presence of the climax community, the oak-hickory forest. Figure 3 depicts the gradual change from pine to hardwoods.  Figures adapted from Eugene P. Odum, Fundamentals of Ecology. ©1971 by Saunders College Publishing/Holt, Rinehart, and Winston, Inc.


1. On the basis of the data presented in Figure 1, approximately 80 years after the abandonment of cropland, the land would contain:
  A. pine seedlings only.
  B. oak-hickory hardwood forests only.
  C. early invading species like horseweed, aster, and broomsedge.
  D. large pine trees with an understory of hardwood trees.
   
2. According to the information in Figure 3, a 150-year-old climax community would contain oak and hickory trees with a density of approximately:
  F. 3,000 trees per unit area.
  G. 5,000 trees per unit area.
  H. 15,000 trees per unit area.
  J. 20,000 trees per unit area.
   
3. On the basis of the data depicting the gradual change from pine forest to an oak-hickory forest, after 100 years, as the density of the pine trees:
  A. increases, the density of the oak-hickory trees increases.
  B. increases, the density of the oak-hickory trees decreases.
  C. decreases, the density of the oak-hickory trees increases.
  D. decreases, the density of the oak-hickory trees decreases.
 
   
4. Given the information in Figure 1, which of the following conclusions concerning ecological succession in an abandoned cornfield is most correct?
  F. Succession in an abandoned cornfield begins on bare rock.
  G. Succession is characterized by the replacement of one plant community by another until a climax community has been achieved.
  H. The height of the plants in the communities decreases as succession progresses to the climax stage.
  J. The plant species change continuously during succession, but the change is more rapid in the later stages than in the earlier stages.
   
5. According to Figure 2, pioneer plant(s) showing a progressive increase in summed diameter of stems per unit area over the course of several years of succession is(are):
  A. horseweed only.
  B. broomsedge only.
  C. aster and broomsedge only.
  D. horseweed, aster, and broomsedge.