MCAT Practice test exam with 100% correct answers

Why are triacylglycerols used in the human body for energy storage? A) They are highly hydrated, and therefore can store lots of energy. B) They always have short fatty acid chains, for easy access by metabolic enzymes. C) The carbon atoms of the fatty acid chains are highly reduced, and therefore yield more energy upon oxidation. D) Polysaccharides, which would actually be a better energy storage form, would dissolve in the body. - correct answer️️C Triacylglycerols are highly hydrophobic and therefore not highly hydrated (which would add extra weight from the water of hydration, taking away from the energy density of these molecules), eliminating choice (A). The fatty acid chains produce twice as much energy as polysaccharides during oxidation because they are highly reduced. The fatty acid chains vary in length and saturation. Action potentials travel down neural axons that resist the flow of current. In considering a theoretical circuit, one normally assumes that the wire has no resistivity. In the real world, however, wire resistivity is an important consideration. Which of the following is a way to increase resistance? A) Lengthen the wire B) Widen the wire C) Lower the temperature D) Change from tungsten to copper wire - correct answer️️A This question tests your knowledge of resistance in wires. An electrical wire's resistance is directly proportional to its length and inversely proportional to its cross-sectional area. Think of it as gravel in a pipe—the wider the pipe and the shorter the pipe, the easier it is for water to go through it. B is incorrect because when a wire's cross-sectional area is increased, its resistivity is decreased. C is incorrect because lowering temperature decreases resistivity. Think superconductors. D is incorrect because tungsten has higher resistivity than copper. Tungsten is used for lightbulb filaments because of its higher resistivity. Sexually reproducing species have a selective advantage over asexually reproducing species, because sexual reproduction: A) is more energy efficient. B) creates novel genetic recombinations. C) decreases the likelihood of mutations. D) always decreases offspring survival rate. - correct answer️️B The reason those species that reproduce sexually have a selective advantage is because gene recombination is a given with every fertilization—two genetically unique nuclei—the sperm nucleus and the egg nucleus--fuse to form an equally genetically unique zygote. This is the main means of introducing phenotypic variability into a population. Pus is primarily composed of phagocytosed bacterial remnants. Which of the following would you expect to find in a microscopic sample of pus? A) Red blood cells, white blood cells, and platelets B) Granulocytes, monocytes, and macrophages C) Eosinophils, basophils, and neutrophils D) Collagen, white blood cells, and calcium - correct answer️️B Phagocytosis plays an important role in both the nonspecific and humoral response to foreign pathogens. At the level of the skin, macrophages dwell in the connective tissue surrounding the organs of the body. Neutrophils are recruited to the site of entry and become part of the non-specific response to invading bacteria, working in combination with monocytes and macrophages to completely decompose bacteria. The cell-mediated branch of the immune system does not result in pus formation. Which of the following is true about cholesterol? A) Cholesterol always increases membrane fluidity in cells. B) Cholesterol is a steroid precursor. C) Cholesterol is a precursor for vitamin A, which is produced in the skin. D) Cholesterol interacts only with the hydrophobic tails of phospholipids. - correct answer️️B Cholesterol is a steroid precursor that has variable effects on membrane fluidity depending on temperature, eliminating choice (A). It interacts with both the hydrophobic tails and the hydrophilic heads of membrane lipids, nullifying choice (D). It is also a precursor for vitamin D (not vitamin A), which can be produced in the skin in a UV-driven reaction, eliminating choice (C). Osteogenesis imperfecta is an autosomal dominant disease that results in abnormal collagen synthesis and fragile bone structure. What is true regarding the probability that the sister of an affected man will have the disease, if their mother was unaffected?