Praxis PT#2 Middle School Science
EXAM QUESTIONS AND CORRECT
DETAILED ANSWERS (VERIFIED
ANSWERS) |ALREADY GRADED A+
1. A sample contains 8 g 8 gramsof a radioisotope that has a
half-life of 10 years. How much time is required for the sample
to decay until approximately 1 g one gramof the isotope
remains in the sample? - ✔✔ANSWER✔✔->>>>>>>>30 years is
correct. If the half-life of the substance is 10 years, then every
10 years the amount of the isotope is decreased by half. Thus, it
requires three half-lives, or 30 years, for the isotope to decay
until approximately 1 gone gram remains in the sample.
2. Which of the following is a balanced chemical equation? -
✔✔ANSWER✔✔->>>>>>>>Cl2 + 2 NaBr →→Br2 + 2 NaCl
,3. Which of the following objects exerts the greatest
gravitational force on another object located 5 million
kilometers away? - ✔✔ANSWER✔✔->>>>>>>>A star is correct.
At a given distance, the greatest gravitational force is exerted by
the object with the greatest mass. Of the four objects listed, a
star has the greatest mass.
4. The Challenger Deep is the deepest surveyed location in the
oceans. The Challenger Deep is most likely associated with
which of the following ocean features? - ✔✔ANSWER✔✔-
>>>>>>>>A trench is correct. An oceanic trench is a feature
associated with a convergent plate boundary where one
lithospheric plate is subducted beneath another, less dense
plate. Trenches can extend several kilometers below the level of
the surrounding ocean floor. In the Pacific Ocean, the Pacific
Plate is being subducted beneath the Mariana Plate. This
interaction created the Mariana Trench, parts of which extend
more than 11,000 meters (36,000 feet) below sea level. The
deepest point in the world's oceans, the Challenger Deep, is in
the Mariana Trench.
5. Which of the following are major structural components of
plasma membranes? - ✔✔ANSWER✔✔->>>>>>>>Phospholipids
is correct. They are major structural components of plasma
,membranes. In aqueous environments, phospholipids form lipid
bilayers that are the basis for cellular membranes.
6. Which of the following is true of the recessively inherited
disease sickle-cell anemia that is caused by a mutated
hemoglobin protein? - ✔✔ANSWER✔✔->>>>>>>>A single base
pair substitution in a hemoglobin gene leads to an amino acid
substitution in the hemoglobin protein.
7. The gravity on the Moon is 1/6one sixth as strong as the
gravity on Earth. With respect to the weight (W) and mass (M)
of two identical bricks that are placed on the surfaces of Earth
and the Moon, which of the following is true? -
✔✔ANSWER✔✔->>>>>>>>M Earth = M Moon is correct. The
weight of an object is equal to the force of gravity acting on the
object; thus for identical objects, the weight on the Moon will
be less than the weight on Earth. The mass of an object does
not depend on the location of the object, which means that the
masses of identical objects will be equal.
8. Which of the following often occurs when water-soluble
fertilizers are spread on farmland? - ✔✔ANSWER✔✔-
>>>>>>>>Nearby waterways undergo eutrophication. Excess
water-soluble fertilizers are washed into nearby waterways. The
increased nitrate and phosphate levels often promote excessive
, phytoplankton (e.g., algae) growth and decay in the waterways.
The decomposition of additional plant matter depletes the
dissolved oxygen. This process is called eutrophication.
9. An investigation to study the factors that affect the rate of
reaction is conducted. In an experiment, one calcium carbonate
tablet each is added to equal volumes of hydrochloric acid with
different concentrations. The mass of carbon dioxide gas
produced over time is recorded. Which of the following is the
independent variable in the experiment? - ✔✔ANSWER✔✔-
>>>>>>>>The concentration of hydrochloric acid is correct. The
concentration of aqueous hydrochloric acid is the variable that
is manipulated and thus is the independent variable. The mass
of carbon dioxide produced over time is the dependent
variable, since it may change as the independent variable is
changed. The number of tablets is constant, and the volume of
the hydrochloric acid is constant.
10. In cold weather, it is more difficult to make people
comfortable in a room with a high ceiling than in a room with a
low ceiling primarily because - ✔✔ANSWER✔✔->>>>>>>>Cold
air is more dense than warm air is correct. Since cold air is more
dense than warm air, convection currents will develop, with
warmer air rising to the ceiling and cooler air dropping toward
the floor. When the ceiling is high, there will be a greater
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