ACT Science Practice Test 3

Organic compounds are molecules that frequently contain carbon (C), hydrogen (H), and oxygen (O) joined together by covalent bonds (symbolized by straight lines in chemical notation). As the number of bonds to oxygen atoms increases in a carbon chain, the overall molecule is increasingly oxidized. For example, aldehydes are more oxidized than alcohols, which are more oxidized than alkanes as shown in Table 1. The melting points of these compounds are listed in Table 2, and their viscosities (resistance to flow, or "stickiness,") are listed in Table 3.

A mass suspended by a lightweight thread and swinging back and forth approximates the motion of a simple gravity pendulum, a system in which gravity is the only force acting on the mass, causing an acceleration of 9.8 m/sec². The time to complete one cycle of swinging back and forth is the period and is inversely related to gravitational acceleration.

Using the same type and length of thread, 2 cubes were suspended, lifted to the same starting angle, and let go. The amount of time required for each pendulum to complete one swinging cycle (1 period) was recorded with a timer capable of reading to the nearest 0.01 sec. The measured times were used to calculate acceleration.

Experiment 1

A cube of lead (11.3 grams) and a cube of tin (7.4 grams) were suspended from a 0.5 m length of thread. Both cubes had the same length. (Note: A cube's volume is proportional to its length cubed; its surface area is proportional to its length squared.) The cubes were set in motion from a fixed starting angle, and the period for each was recorded.

The average periods were 1.46 sec and 1.48 sec for the lead and tin cubes, respectively. The average accelerations were 9.3 m/sec² for lead and 9.1 m/sec² for tin.

Experiment 2

The same procedures used in Experiment 1 were repeated using a thread length of 1.0 m and the same fixed starting angle. Results were recorded in Table 2.

The average periods were 2.06 sec and 2.09 sec for the lead and tin cubes, respectively. The average accelerations were 9.3 m/sec² for lead and 9.0 m/sec² for tin.

Experiment 3

Given the results of the first 2 experiments, the accuracy of the timer was tested. The procedures of Experiment 1 were repeated using only the lead cube. The trials were recorded on digital video at 100 frames per second. The video was then reviewed to obtain precise measurements of the period for each trial and results are shown in Table 3.

The average period recorded in Table 3 was 1.47 sec.

Accepted classification systems of life do not include viruses. Although viruses possess certain features of cellular organisms, including genetic material that codes for making new viral particles, they cannot replicate (make copies of) themselves without first infecting a living cell. Biologists agree that viruses originated from genetic material called nucleic acid, but it is difficult to prove any single theory regarding how this occurred. Three hypotheses of viral origin are presented here.

Coevolution Hypothesis

Some biologists argue that viruses evolved alongside other organisms over billions of years. They suggest that simple molecules of ribonucleic acid (RNA), a nucleotide that forms the genetic code for proteins, joined to form more complex sequences. These RNA sequences developed enzyme-like abilities including the ability to self-replicate and insert themselves into other nucleotide sequences. While some RNA sequences became incorporated into membrane-bound cells, others were packaged inside proteins as the first viral particles that could replicate after infecting cellular organisms (see Figure 1).

Figure 1

Cellular Origin Hypothesis

Some biologists claim that nucleotide sequences within prokaryotic (non-nucleated) and eukaryotic (nucleated) cellular organisms incorporated into a protein coating and escaped from the cell as a viral particle. Initially, DNA or RNA nucleotide sequences gained the code required for other cells to replicate them. Next, these sequences associated with proteins to form an outer capsid. Finally, the virion (viral particle) became capable of passing through the cell membrane and infecting other cells where it could be replicated. After the initial escape, viruses evolved independently from their initial host and ultimately could infect either prokaryotic or eukaryotic cells.

Regressive Evolution Hypothesis

An alternative explanation of viral origin is that viruses evolved from cellular organisms. Some cellular organisms, particularly certain bacteria, are obligate intracellular parasites because they must infect a host cell in order to reproduce. Regressive evolution suggests that some bacterial parasites gradually lost the structures required for survival outside of a cell. The result was a virus particle containing only nucleotides, a capsid (protein coating), and at times an outer membrane or envelope. This would account readily for viruses that contain complex deoxyribonucleic acid (DNA) similar to that found in bacteria and other cellular organisms (see Figure 2).

Figure 2

Wind causes topsoil deflation, a type of erosion that is affected by plant and organic cover as well as water content of the soil. Scientists performed 2 experiments using equal-sized fields containing the same volume of soil. The soil samples were primarily a mixture of sand and silt, but differed in the percentage of clay they contained. Soil X was composed of 5% clay and soil Y was composed of 40% clay. Large fans were used to simulate wind. Topsoil deflation was measured in kilograms per hectare (kg/ha) following 10 hours of wind.

Experiment 1

A mixture of compost and straw was used to represent plant and organic cover. The percentage of soil covered with the mixture was considered to approximate an equivalent percentage of natural vegetative cover. One field remained uncovered, and the other fields were covered with different percentages of compost and straw. The topsoil deflation from each field was recorded in Table 1.

Experiment 2

Rainfall was simulated using a sprinkler system. Sprinklers were turned on for either 4 hours or 8 hours for fields of each kind of soil. Two additional fields composed of each type of soil were left unwatered. Afterward, soil samples were taken from all of the fields to determine their water content percentage, which was recorded in Table 2. Wind was applied as in Experiment 1 and topsoil deflation for all fields was recorded in Table 3.