ACT Science Practice Test 47

PASSAGE I

Amino acids are considered the building blocks of protein in the body. Amino acids combine with each other to form chains called peptides, which then combine to form proteins. The human body requires twenty different amino acids, whose combinations produce every essential protein in the body. When amino acids form peptides, the residue is what is left after the amino acid sheds a molecule of water (a hydrogen ion from one end and a hydroxide ion from the other end). The reaction rate is the factor by which the protein is able to build itself up through the combination of peptides. Figures 1-3 show the effects that changes in temperature, water volume, and residue concentration have on the rate of reaction when Amino Acids A and B are present. Figure 4 shows the effects that changes in the concentrations of Amino Acids A and B have on the rates of reaction in solutions of the same concentration.

Figure 1

Figure 2

Figure 3

Figure 4

PASSAGE II

The Great Lakes are a group of five large lakes located in the United States and Canada. They make up the largest group of fresh water lakes in the world, and the Great Lakes-St. Lawrence River system is the largest freshwater system in the world. Recently, near-historic low water levels have plagued the water system. Two scientists discuss the causes of low lake levels in the Great Lakes.

Scientist 1

Water levels are part of the ebb and flow of nature. The determining factor in whether the water level will rise, fall, or remain stable is the difference between the amount of water coming into a lake and the amount going out. When several months of above-average precipitation occur with cooler, cloudy conditions that cause less evaporation, the lake levels gradually rise. Likewise, the lowering of water levels will result from prolonged periods of lower-than-average precipitation and warmer temperatures.

The recent decline of water levels in the Great Lakes, now at lows not seen since the mid-1960s, is due to a number of causes. Higher degrees of evaporation from warmer than usual temperatures in recent years, a series of mild winters, and below-average snow pack in the Lake Superior basin all contribute to the phenomenon. Since precipitation, evaporation, and runoff are the major factors affecting the water supply to the lakes, levels cannot be controlled or accurately predicted for more than a few weeks into the future. Further, the influence of human regulation on lake levels is inconsequential. Because water is added through snow and rain and taken away through evaporation, nature has most of the control over lake levels.

Scientist 2

Several human activities have significantly affected levels and flow of the water in the Great Lakes. For example, structures have been built to regulate the outflows of both Lake Superior and Lake Ontario. Lake Superior has been regulated since 1921 as a result of hydroelectric and navigation developments in the St. Mary's River, such as the Soo Locks. Lake Ontario has been regulated since 1960 after completion of the St. Lawrence Seaway and Power Project. Diversions bring water into, and take water out of, the Great Lakes. Many such diversions were constructed for hydropower generation and logging. For example, the Lake Michigan diversion at Chicago moves water out of Lake Michigan and into the Mississippi River for domestic, navigation, hydroelectric, and sanitation purposes.

In addition, the St. Clair and Detroit rivers have been dredged and modified. This has caused some drop in the levels of Lake Michigan and Lake Huron. Channel and shoreline modifications in connecting the channels of the Great Lakes have affected lake levels and flows as well, because the infilling of shoreline areas can reduce the flow carrying-capacity of the river. Further, the extensive use of groundwater deposited in massive aquifers (underground layers of water-bearing permeable rock) in the Midwest has affected the lake levels. Vast quantities of water deposited in aquifers surrounding the Great Lakes are taken to population centers outside of the Great Lakes' watershed (region of land whose water drains into a specified body of water). Thus, the water in the lakes is not replenished.