E T S Praxis Series

Middle School Science (0439)

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Answers

  1. The correct answer is D. Although there are additional gases such as methane and water vapor that are considered to be greenhouse gases, carbon dioxide accounts for the largest percentage of the annual human-caused input of these gases.

  2. The correct answer is D. Substances whose water solutions conduct an electric current are called electrolytes. Electrolytes, when in solution, break down into smaller particles called ions.

  3. The correct answer is B. Isotopes are atoms of the same element that have different atomic masses. In order to be the same element, they must have the same number of protons. Therefore, they must possess different numbers of neutrons if they are isotopes.

  4. The correct answer is C. In order for us to smell a particular substance, it must enter the nasal cavity via the air. In addition, it must be sufficiently soluble in water to dissolve in the fluid coating of the cells lining the nasal cavity.

  5. The correct answer is C. The car having a constant value for linear acceleration would constantly increase its speed over time. Therefore, a car that constantly accelerated would cover a given distance in the shortest time and most likely win a race against cars with constant values for the other parameters listed.

  6. The correct answer is A. The other options are true of both tornadoes and hurricanes. However, hurricanes require warm ocean surface waters in order to develop and it is from these warm waters and the release of latent heat that they derive their energy. Tornadoes are associated with thunderstorms, form over land, and are most likely to occur when large differences in temperature and moisture exist between two air masses and the boundary between the air masses is sharp.

  7. The correct answer is C. While the agents given in the other options do influence and change the appearance of Earth's surface, water is constantly acting upon terrestrial features in the form of precipitation, glaciers, streams, rivers, and oceans. Therefore, it contributes to the chemical and mechanical weathering of the land surface in most parts of the globe.

  8. The correct answer is A. According to the cell theory, the basic biological unit of structure and function is the cell, and cells come from other cells. Although the other options could be found in living material or material of biological origin, they are not unique to it and would not clearly confirm that the sample was biological in nature.

  9. The correct answer is D. In response to rising levels of glucose in the blood, cells in the pancreas secrete the hormone insulin. Circulating insulin lowers blood sugar levels by enhancing the transport of glucose and other simple sugars into body cells, especially muscle cells.

  10. The correct answer is B. In this diagram the path of the circuit is such that current will be diverted from passing through the resistor and the bulb. When the part of a circuit with the most resistance is bypassed, and all of the current flows through the part with zero (negligible) resistance, a short circuit is said to exist.

  11. The correct answer is D. The green filter absorbs all colors except green, which it passes. Therefore, the red light will be absorbed by the filter, which will pass no light. The paper will not be illuminated, and so it will appear black, regardless of its initial color.

  12. The correct answer is A. 36 grams of water is 2 moles (2 x 18.0 grams). A 2-mole sample of O2 contains the same number of molecules as does 2 moles of any other substance. A 2-mole sample of O2 would have a mass of 2 x 32.0 grams = 64.0 grams.

  13. The correct answer is A. Both graphs indicate more rapid growth for the treated samples than for the untreated samples. The other options describe results not tested in the experiments and so not indicated by the data.

  14. The correct answer is A. Seasons are best explained as resulting from the Earth's axial tilt and not from distance variations, sunspot activity, atmospheric transparency, or rotation.

  15. The correct answer is A. S has the smallest atomic radius. The relative atomic radii of the atoms of various elements can be predicted from the position of the element on the periodic table. Going across a row of the periodic table from left to right, the radii get smaller, and going down a column, the radii get larger. The correct order of atomic radii for elements in this question is Ba > Na > Al > S.

  16. The correct answer is B. Most chordates posses a vertebral column (backbone) that surrounds a dorsal nerve cord. Mollusks (e.g., clams and mussels) and echinoderms (e.g., sea stars and sea urchins) are invertebrates that lack a vertebral column and dorsal nerve cord.

  17. The correct answer is D. The Sun's corona has extremely low density and is visible only during a total solar eclipse.

  18. The correct answer is D. The measurements differ from the true length by 0.39 cm, 0.19 cm, and -0.11 cm. Thus, the measurements are quite different in value from the true value, which means that they are not accurate. The measurements are also quite different in value from one another (not repeatable), which means that they are not precise.