ACT Science Practice Test 62

PASSAGE III

Predation is an interaction between individuals of 2 species in which one is harmed (the prey), and the other is helped (the predator). Predation can occur among plants and animals as well as between plants and animals. Some biologists contend that herbivores, or plant eaters, are predators. Table 1 indicates some characteristics and examples of certain predators.

Predation is very important in maintaining a natural balance in any given ecosystem. For example, without predators, prey populations tend to grow exponentially. Without prey, predator populations tend to decline exponentially. Predators consume individual members of the prey population, thereby controlling the overall numbers in the ecosystem. The number of prey consumed depends on the number of prey present as well as the number of predators present. The rate of change in the number of prey is a function of the birth of new prey minus the death of other prey, due either to predation or other causes. The death rate is assumed to depend on the number of prey available and the number of predators. The rate of change in the number of predators is a function of the births of new predators-which depends on the number of prey-minus the death of some predators.

Over long periods of time, predator and prey tend to balance each other out. This is called the predator-prey cycle. Prey numbers will increase when predator numbers decrease. When the number of prey reaches a certain point, predators will start to increase until they eat enough prey to cause a decline in prey numbers. When this happens, the number of predators will begin to decrease because they can't find enough prey to eat, and the cycle will begin again. Figure 1 represents an example of a predator-prey cycle.

Figure 1

PASSAGE IV

The term weathering refers to the processes that cause surface rock to disintegrate into smaller particles or dissolve in water. These processes are often slow, taking place over thousands of years. The amount of time that rock has been exposed to the elements (primarily wind and water) influences the degree to which the rock will weather.

Weathering processes are divided into three categories: physical, chemical, and biological.

Table 1 shows some of the factors that contribute to physical weathering.

Chemical weathering occurs when minerals in rock are chemically altered. Table 2 shows some of the factors that contribute to chemical weathering.

Plants and bacteria contribute to biological weathering. The ultimate product of biological agents on rock is soil. Table 3 shows some factors of biological weathering.