MCAT Practice Questions Answered 100% correct 2023

MCAT Practice Questions Answered 100% correct 2023 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. C 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 A 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. B 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 B 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. B 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? A) The probability equals 50%. B) The probability depends on the genotype of the father, which cannot be determined from the given information. C) The probability depends on the genotype of the mother, which cannot be determined from the given information. D) The probability depends on the genotype of the brother, which cannot be determined from the given information. B If the disease is autosomal dominant, from the passage, we know the mother had two good alleles. Therefore, the father had at least 1 diseased allele: heterozygous or homozygous dominant (i.e. diseased). If the father were homozygous, the sister would have a 100% chance of getting the disease. If the father were heterozygous, the sister would have a 50% chance. Therefore, choice (B) is correct (A) No, it depends on the father's genotype. (C) We know that the mother is homozygous recessive since she is unaffected. (D) The brother's genotype is not important and can be determined: it is heterozygous. Which of the following statements regarding fetal circulation is FALSE? A) In the umbilical cord, there are more arteries than veins. B) The foramen ovale is the only shunt that connects two chambers of the heart. C) Blood flow in the ductus arteriosus is from the aorta to the pulmonary artery. D) The ductus venosus is the only shunt that bypasses the liver. C Blood flow in the ductus arteriosus is from the pulmonary artery to the aorta. The direction of flow is determined by the pressure differential between the right side of the heart (and pulmonary circulation) vs. the left side of the heart (and systemic circulation). Unlike in adults, the right side of the heart is at a higher pressure during prenatal life than the left side, so blood will shunt from the pulmonary circulation to the systemic circulation through both the foramen ovale and ductus arteriosus. Researchers discover that polymorphisms in the DRD2 gene can be associated with thrill-seeking behavior, and that individuals with certain forms of the gene are more likely to become extreme athletes and have more dangerous hobbies. Which of the following theories is supported by this discovery? I. The social cognitive perspective II. The behavioral perspective III. The biological perspective A) I only B) III only C) I and III only D) II and III only C This research supports a link between genetic expression and behavior, which is a central tenet of the biological perspective. The social cognitive perspective also holds that people's behaviors and traits shape their environments, which in turn have an effect on their identity, so the discovery also supports this perspective. Behaviorism is not supported, as the discovery is not related to rewards and punishments. Most of the CO2 in the blood travels as HCO3- and H+ ions in the plasma. Which of the following would a physician most likely find upon examining a person who has recently had Acute Mountain Sickness (Altitude Sickness)? A) Increased levels of O2 in the plasma B) A decreased rate of ventilation C) An increased red blood cell count D) An increased white blood cell count C Altitude sickness occurs when a person climbs faster than his body can adjust. One of the ways that the body compensates for the lack of O2 at high altitude is by releasing erythropoitin, a hormone that increases the RBC mass after a period ranging from a few days to several weeks. Chemical extraction is a simple, but powerful, means of isolating a desired compound, and this technique is used to isolate many pharmacological agents. A chemist requires that a mixture of two species be separated. In order to do this, the chemist allows the mixture to separate and extracts the top, non-polar layer. Based on this information, what is least likely to be true of the original two species? A) The densities of the species are different. B) The original species rotate plane-polarized light in opposite directions. C) The bottom layer is hydrophobic. D) The two species have the same molecular weight. B describes the species as enantiomers. If the two species can be separated through ordinary means, without first changing them chemically, they cannot be enantiomers! Enantiomers cannot be separated by physical properties alone.