PreACT Practice Test 14
10 free PreACT practice questions in the real exam format, covering the official content areas, with an explanation for every answer.
Question 1 of 10
ScienceEach year, a tree adds a layer of wood called a growth ring; a wide ring means the tree grew well that year. Researchers took core samples from 30 oak trees in a forest and measured the average ring width for 1984 through 1990 (Table 1). The rings for 1986, 1987 and 1988 were unusually narrow. Three students explain the narrow rings.
| Year | Average oak ring width (mm) |
|---|---|
| 1984 | 2.1 |
| 1985 | 2.0 |
| 1986 | 0.9 |
| 1987 | 0.7 |
| 1988 | 0.8 |
| 1989 | 1.9 |
| 1990 | 2.1 |
Three explanations
Student 1: From 1986 through 1988 the forest had a drought. With little water in the soil, the trees closed the pores in their leaves to save water, which reduced photosynthesis and left less sugar for growth. A drought affects every tree species in the forest, although trees on wet, low-lying soil would be affected less than trees on dry ridges.
Student 2: From 1986 through 1988 a leaf-eating caterpillar population exploded in the forest. The caterpillars stripped much of the oaks' foliage, and with fewer leaves the trees carried out less photosynthesis and grew less. These caterpillars feed only on oaks and a few related broadleaf trees, so the forest's pines would not have been affected. The damage would not depend on soil moisture.
Student 3: In 1986, 1987 and 1988, hard frosts struck in late spring, just after the oaks had opened their new leaves. The frost killed the young leaves, and the trees used stored energy to grow replacement leaves, so photosynthesis was reduced during the early growing season. Pines, which keep their needles all year and were not opening new leaves at that time, would not have been affected. Frosts are more frequent at the higher, colder elevations of the forest.
According to Student 2, the oak rings for 1986–1988 were narrow mainly because: