Praxis Middle School Science (5442)

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? 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? 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? 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? 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? 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? 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? 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.