October 25, 2017

CLEP Natural Sciences Exam Answer Key

1. C
2. E
3. E
4. D
5. B
6. C
7. A
8. B
9. E
10. C

Answer Explanations

1. (C) Cellulose is a polysaccharide. It is the most common chemical and the strongest substance present in a plant’s primary cell wall.

2. (E) High reproductive rates and adults not caring for their young are both characteristics that are r-selected. These are also known as opportunistic life strategies. However, the size and longevity of sea turtles (assuming they do reach adulthood) are characteristics that are k-selected. These are also known as equilibreal life strategies. Thus, sea turtles possess both r- and k-selected traits.

3. (E) Basalt is a type of extrusive igneous rock formed from the cooling of lava. Coal (C) and limestone (D) are sedimentary rocks made up of organic plant and animal remains. Sandstone (A) and shale (B) are sedimentary rocks made from the clastic material of sand and clay, respectively.

4. (D) The Paleozoic Era was characterized by the evolution of the first fish and, later, the first amphibians. Reptiles did not appear until some time during the Mesozoic Era.

5. (B) The number of deposit feeders at all sites is directly proportional to the percentage of silt and clay present in the area. Deposit feeders are found in greater numbers where there is a high percentage of silt and clay. They are found in lower numbers where there is a lower percentage of silt and clay. This suggests that deposit feeders are more affected by changes in the amount of silt and clay than are suspension feeders. The number of suspension feeders is indirectly related to the percentage of silt and clay at all sites.

6. (C) Cells continually make ATP through the synthesis of ADP, inorganic phosphate, and energy.
7. (A) Crossing over occurs during the first prophase stage of meiosis I. Two chromosomes of a homologous pair may exchange segments. This breaking and reforming of homologous chromosomes allows genes to change the chromosome they are linked to. This is important in producing a greater possibility of genetic variation.

8. (B) The Sun is composed mostly of hydrogen gas, which reacts with other hydrogen gas to form helium. Some matter is lost during the reactions, as 4 H atoms combine to form 1 He atom. This lost matter is converted to energy. These reactions occur continually, and billions occur every second.

9. (E) Glycogen phosphorylase is the enzyme that breaks down glycogen to glucose. This process is called glycogenolysis. To increase the rate at which glycogenolysis occurs, a liver cell must increase the catalytic rate of glycogen phosphorylase.
10. (C) The Moon appears illuminated because it reflects light from the Sun. The Moon does not produce or emit its own light. The part of the Moon that is illuminated when viewed from Earth is dependent on the angle between the Earth, Moon, and Sun.