AccelePrep for the ACT Test 2nd Edition Student Text

186 • S URGE TO S UCCESS ! S CIENCE T EST P REP

POWER PRACTICE 2 DIRECTIONS: The passage below is followed by several items. After reading the passage, choose the best answer to each item. You may refer to the passage as often as necessary. You are NOT permitted the use of a calculator. To investigate the factors affecting the rate at which starch is broken down to sugar by the digestive enzyme salivary amylase, two experiments were performed. In both experiments, starch (in the form of a cracker) was mixed in a beaker with the enzyme, and samples were removed every 3 minutes. Special sugar indicators were dipped in

the sample to determine the presence of starch (indicating that the cracker had not yet been completely digested). Experiment 1 To test the effects of different pH levels on enzyme activity rate, one cracker and a standard amount of enzyme were placed in three beakers, each containing buffers of different pH. This procedure was repeated using standard amounts of water in place of the enzyme. All tests were carried out at optimal temperature, 37 degrees Celsius. Starch and sugar levels (starch/sugar) from selected

samples are shown in Table 1. TABLE 1

Approximate pH Levels

Levels of Starch/Sugar

Contents of Beakers

After 3 minutes cracker + enzyme + buffer 5 7 9 high/none moderate/moderate high/none high/none low/high high/none high/low none/high high/low moderate/moderate none/high moderate/moderate cracker + water + buffer 5 7 9 high/none high/none high/none high/none high/none high/none high/none high/none high/none high/none high/none high/none After 9 minutes After 15 minutes After 60 minutes

standard amounts of water in place of the enzyme. All tests were carried out at optimal pH, 7.40. Starch and sugar levels (starch/sugar) from selected samples are shown in Table 2.

Experiment 2 To test the effects of temperature on enzyme activity rate, one cracker and a standard amount of enzyme were placed in three beakers, each kept at different temperatures. This was also repeated using

TABLE 2

Levels of Starch/Sugar

Contents of Beakers Temperatures

After 3 minutes After 9 minutes After 15 minutes After 60 minutes cracker + enzyme 25°C 37°C 45°C high/none moderate/moderate high/none high/none low/high high/none high/low none/high high/low moderate/moderate none/high moderate/moderate cracker + water 25°C 37°C 45°C high/none high/none high/none high/none high/none high/none high/none high/none high/none high/none high/none high/none