TPR MCAT review Ptest 1
Speed of light
3X10^8
Given F2 > Cl2 > O2 > Br2 > I2 . Which of the following elements is the least likely to undergo a displacement reaction with Na2S? A.O B.Cl C.K D.Mg
?????D. For nonmetals, reactivity increases with the tendency to gain an electron. For metals, reactivity increases with the tendency to lose an electron. The passage shows that reactivity for group VII nonmetals decreases down the column regardless of electron affinity. The same applies for Group VI nonmetals, making oxygen the most reactive of that group. If O is more reactive than S, and Cl is more reactive than O (from the series in the passage), then choices A and B are eliminated. The trend is reversed for metals. Reactivity of metals increases going down a group. K is more reactive than Na, eliminating choice C and leaving choice D as the correct answer. Mg has a higher ionization energy than Na and is less reactive.
What is the role of luteinizing hormone in men? A.Induce the interstitial cells to produce testosterone B.Stimulate the sustenacular cells to undergo mitosis C.Induce the interstitial cells to undergo mitosis D.To negatively inhibit further sperm production
A. Luteinizing hormone in men stimulates the interstitial (or Leydig) cells to produce testosterone (choice A is correct and choice C is wrong). The sustenacular (Sertoli) cells are stimulated by FSH (not LH, choice B is wrong) to assist in the process of spermatogenesis. Finally, inhibin, not LH, is secreted by the sustenacular cells to inhibit FSH release; this suppresses further spermatogenesis (choice D is wrong).
A scientist has a vial of cells that can be grown on plates in the lab. She does a transformation experiment on these cells and isolates the RNA a few days later. Which of the following is true about the cells under study? A.To extract the RNA, the researcher would have to break down the cell wall and the plasma membrane. B.They have lysosomes and peroxisomes. C.They have more than one chromosome, made of double stranded DNA. D.The cells would not be susceptible to any bacteriophage.
A. Since the scientist did a transformation experiment, the cells under study must be prokaryotic (note that both prokaryotic and eukaryotic cells can be grown on plates in the lab, but the similar technique for eukaryotic cells is called transfection). Prokaryotic cells have a plasma membrane and a cell wall, both of which must be degraded to extract the intracellular RNA. Since the cells are prokaryotes, they do not have any membrane-bound organelles (choice B is wrong), have only one, double-stranded DNA chromosome (choice C is wrong), and may be susceptible to a bacteriophage, or a virus which uses bacteria as its host (choice D is wrong).
At a distance d below the surface of pure water, a balloon experiences buoyant force Fb. If the balloon is submerged to distance 4d, what is the magnitude of the buoyant force that it experiences? (Assume no atmospheric pressure, that the density of water is constant, and that the volume of the balloon is inversely proportional to the pressure being exerted on it.) A.0.25Fb B.0.5Fb C.Fb D.4Fb
A.0.25Fb. Archimedes principle (Fb = ρfluidVsubg) Pressure depends on depth, bouyant force does not!. if the volume of the balloon decreases four times, then the buoyant force decreases four times as well.
The correct ranking of electron affinity magnitude for the lightest halogens is: A.F > Cl > Br > I. B.Cl > F > Br > I. C.I > Br > F > Cl. D.I > Br > Cl > F.
Although choice A is expected from general periodic trends, the electron affinity magnitude of fluorine (-331 kJ/mol) is actually less than that of chlorine (-352 kJ/mol). This exception also applies to the electron affinity of oxygen compared to sulfur. At first glance, it may seem that adding an electron to a 2p valence subshell would release more energy than adding an electron to a 3p valence subshell because 2p is closer to the positively charged nucleus. However, fluorine is much smaller than chlorine, and the tightly packed electrons in the 2p subshell have a repelling effect on the incoming electron. This is a challenging question and the MCAT is much more likely to ask about scenarios where the rule rather than the exception applies to periodic trends.
In an attempt to speed up her experiment, the researcher runs her reactions at 50°C rather than 25°C. However, this decreased the reaction rates. Which of the following best explains this result? A.The increased temperature decreased the average energy of the molecules in solution. B.The increased temperature reduced the solubility of the gas being bubbled through the solution. C.The increased temperature reduced the solubility of the ionic solid in aqueous solution. D.The reactions are exothermic.
B. Increasing temperature decreases the solubility of gases in liquids. This decreases the concentration of a reactant in the displacement and decreases the rate of reaction, making choice B the best answer. Choice D states a thermodynamic property of the reaction, whereas rate of reaction is a kinetic property.
n aqueous solutions, HF is a much weaker acid than HCl. However, when combined with Lewis acids, fluorinated systems make much stronger superacids than chlorinated ones. Which of the following best accounts for this phenomenon? A.Aqueous, solvated F- ions are more stable in aqueous media than Cl- ions. B.F- forms very stable complex anions through strong bonding to Lewis acids. C.The basicity of the Cl- ion hinders its inclusion in complex anions. D.The larger size of the Cl- anion sterically prevents its inclusion in the complex anion with a metal like Sb.
B. The same property that makes HF a weak acid in aqueous systems (relative instability of F-) makes it a very strong acid in the Lewis/Brønsted acid partner. F-, being unstable on its own, makes strong bonds to Lewis acids and very stable complex anions. Choice A is incorrect because F- is less stable in aqueous media than Cl- based on the charge density of its small radius. Choice C is incorrect because F- is more basic than Cl-. Choice D is incorrect because, while Cl- is larger than F-, it isn't large enough to create steric issues. Steric issues are generally only taken into account with bulky ligands on metals; such as large organic entities.
A reaction vessel at 1 atm total pressure and 1000 K contains 3 moles of SO2, 2.5 moles of O2, and 4.5 moles of SO3. For these conditions: Kp = 1.88 (at 1000 K). SO2+(1/2)O2 => SO3 A.ΔG = 0. B.ΔG is positive for the forward reaction. C.ΔG is negative for the forward reaction. D.ΔG = Keq.
B. ΔG cannot equal Keq. K is equilibrium. Partial pressure x. 1/2 coeff becomes exp. (4.5/10) =3 [(3/10)(2.5/10)^.5] 3>1.88 will go reverse.
Which of the following are possible causes of prerenal acute renal failure? which the passage states is caused by a lack of blood flow. I. Hemorrhage II. Diabetes mellitus III. Myocardial infarction A.I only B.II only C.I and III only D.I, II and III
C. ACUTE!!!! diabetes is not acute. Diabetes can contribute to chronic renal failure.
How will a smoke detector behave if it were exposed to an environment composed of fluorine and neon rather than nitrogen and oxygen? A.It will be less sensitive since fluorine and neon have higher ionization energies. B.It will be less sensitive since fluorine and neon have lower ionization energies. C.It will be more sensitive since fluorine and neon have higher ionization energies. D.It will be more sensitive since fluorine and neon have lower ionization energies.
C. In a fluorine and neon atmosphere, a smaller proportion of molecules between the plates will be ions, making the detector more sensitive to any factors that may neutralize them. For example, if 1 ion is neutralized, this will have a greater percentage impact on a detector with only 100 ions between the plates compared to one with 100,000 ions between the plates.
Patients suffering from Guillain-Barre syndrome, a demyelinating illness of the peripheral nerves, often need to be artificially ventilated until they recover. What is the most likely explanation for why these patients have difficulty breathing? A.Peripheral chemoreceptors do not sense increased concentrations of CO2 properly. B.Peripheral chemoreceptors do not sense decreased concentrations of O2 properly. C.The speed of nerve conduction to muscle is decreased. D.The amplitude of nerve conduction to muscle is decreased.
C. Myelination speeds up nerve conduction by allowing action potentials to "skip over" myelinated regions of the neuron; these action potentials are instead transmitted between the nodes of Ranvier on the axon. Demyelination due to illness slows nerve conduction enough that patients have difficulty contracting their diaphragms (choice C is correct). An action potential, once initiated, is "all or none"; it cannot have a large or small amplitude (choice D is incorrect). Finally, Guillain-Barre disease is demyelinating and should not affect receptor function. It could be argued that the receptor's signal would not be sent quickly enough, but although peripheral O2 and CO2 chemoreceptors both affect respiratory rate, the main respiratory drive comes from CO2-sensitive chemoreceptors within the medulla. Since Guillain-Barre syndrome is a disease of the peripheral neurons, these patients should still be able to maintain an adequate respiratory rate despite potential interference from peripheral chemoreceptors (choices A and B are incorrect).
In which phase of spermatogenesis could a single nondisjunction event occur with the lowest probability of eventually forming a zygote with a Down syndrome karyotype? A.Prophase I B.Anaphase I C.Anaphase II D.Telophase II
C. Nondisjunction involves the failure of homologous chromosomes or sister chromatids to separate; this does not occur in prophase or telophase (choices A and D can be eliminated). If a single nondisjunction event occurred in anaphase II of spermatogenesis, it would only affect two out of the four resulting gametes. The primary spermatocyte would generate two normal secondary spermatocytes. One of the secondary spermatocytes would perform normal anaphase II and would generate two normal spermatids. The secondary spermatocyte that undergoes nondisjunction in anaphase II would produce two abnormal spermatids, one that would fertilize an egg to cause trisomy and another that would fertilize an egg and cause monosomy. Thus, the probability of Down syndrome occurring if nondisjunction occurred in anaphase II of spermatogenesis would be 25% (choice C is correct). If the nondisjunction event occurred in anaphase I, both secondary spermatocytes would be affected and all four spermatids would be affected; two would generate zygotes with trisomy and two would generate zygotes with monosomy. Thus, the probability of Down syndrome occurring if nondisjunction occurs in anaphase I is 50% (choice B is wrong).
What of the following could be a mechanism by which prerenal acute renal failure could lead to irreversible kidney damage? A.Damage to the glomeruli can lead to recruitment of immune cells, which can cause blockage of some tubules, and leakage of others. This can cause damage to the glomeruli that is beyond repair. B.As blood flow to the kidneys is reduced, insufficient O2 is delivered to maintain the sodium chloride reabsorption. This hypoxia then results in tissue damage and cell death. C.Blood flow to the kidneys is reduced, which decreases the amount of sodium chloride reabsorbed by the nephron, thus decreasing ATP requirements and O2 consumption. Decreased GFR below basal requirements causes tissues to become hypoxic which can lead to cell death. D.Prerenal acute renal failure cannot lead to irreversible damage since all ATP consumption is in reabsorption of sodium chloride, which can be turned off in states of severe hypoxia.
C. Paragraph 2 describes prerenal acute renal failure as a reduced blood flow to the kidneys (choice A can be eliminated, as it is an example of intrarenal acute renal failure). It further states that reduced flow results in a reduced GFR, and reduced reabsorption in general. Virtually all reabsorption in the kidney is via active transport, so a reduction in reabsorption could conserve ATP and reduce oxygen consumption. However, if blood flow to the kidney continues to fall, eventually it will fall below the basal level needed to keep the kidney cells alive. At that point, cell death and damage to the tubules will occur (choice C is correct). It may be true that insufficient oxygen is delivered to maintain sodium chloride reabsorption at its normal high level, but this reabsorption is not the thing keeping the cell alive. Sodium chloride reabsorption could stop altogether, and as long as blood flow was at or above basal level, the cells would not die. In any case, the passage states that as flow drops, reabsorption drops, and thus so would oxygen demand, so it may be that the O2 delivered is adequate to maintain whatever limited reabsorption is still occurring (choice B is wrong). Finally, ATP consumption is not used for reabsorption of sodium chloride exclusively; other substances are also actively reabsorbed (choice D is wrong).
F2 > Cl2 > O2 > Br2 > I2 . the reactivity series for nonmetals is best predicted by: A.electron affinity. B.electronegativity. C.reduction potential. D.oxidation state.
C. The passage states that the electron affinity for fluorine is less negative than that of chlorine Therefore, choice A eliminated. Oxygen is more electronegative than chlorine, yet is less reactive according to the series in the passage, eliminating choice B. All of the elements in the reactivity series in the passage have a zero oxidation state in their diatomic form, eliminating choice D. Choice C is the best answer, since Reaction 1 is fundamentally a redox reaction. In this reaction F2 is reduced and I- is oxidized, meaning F2 has a greater reduction potential than I2.
Although HCN can be poisonous and interfere with cellular respiration, cyanide is an important component of chemical reactions for all of the following reasons EXCEPT: A.it can make carbon-carbon bonds via SN2 replacement of a halogen or other leaving group. B.the cyanide group can be readily converted to other functional groups by reduction or hydrolysis. C.cyanide is an excellent nucleophile that can be reacted in both basic and acidic conditions. D.its reactivity with aldehydes allows it to play an important role in the synthesis of some carbohydrates.
C. Unlike many nucleophiles, the CN- is nucleophilic at a carbon atom, allowing for the synthesis of carbon-carbon bonds via SN2 reactions, making A true, so it is eliminated. As a good nucleophile, it also can attack aldehyde groups such as those on sugars participating in the synthesis of some carbohydrates, which makes choice D true, so it should be eliminated. In addition, the cyanide can be converted readily to other functional groups by reduction (to amine) or hydrolysis (to amide and carboxylic acid) making choice B true and eliminated. As with other strong nucleophiles, CN- is easily protonated by acidic solutions, rendering it no longer nucleophilic. As such C is the false statement, and therefore the correct answer choice.
Consumption of alcohol leads to an increased production of urine. How can this be explained? A.Alcohol decreases the release of ADH from the posterior pituitary. This leads to decreased release of aldosterone from the adrenal medulla. Aldosterone, which regulates sodium reabsorption, indirectly leads to water reabsorption from the distal nephron. Therefore, decreased aldosterone levels result in less water reabsorption, and a greater volume of dilute urine. B.Alcohol inhibits the release of vasopressin from the posterior pituitary. This increases the secretion of water into the distal tubule via aquaporins, resulting in a greater volume of dilute urine. C.Alcohol inhibits the transcription of ADH in the posterior pituitary. The resulting decrease in the amount of ADH decreases the number of aquaporins inserted in the distal nephron and collecting duct, which limits water reabsorption and results in a greater volume of dilute urine D.Alcohol inhibits the release of ADH from the posterior pituitary. This decreases the number of aquaporins inserted in the distal nephron and collecting duct, which limits water reabsorption and results in a greater volume of dilute urine.
D. ADH (also known as vasopressin) is produced in the hypothalamus and travels down the axons of the neurons into the posterior pituitary, where it is released; it is not transcribed in the pituitary (choice C is wrong). ADH does not affect aldosterone release (choice A is wrong). ADH causes the insertion of aquaporins in the distal nephron and collecting duct to allow water reabsorption (not secretion, choice B is wrong), thus its absence leads to less reabsorption of water and an increase in urine volume (choice D is correct).
A positive charge is brought near a neutral conducting sphere. After equilibrium within the sphere is established, which of the following is true? I.The sphere feels an attractive force toward the charge II.The electric field inside the sphere is zero. III.The electric potential on every point of the sphere is a constant. A.I only B.II only C.II and III D.I, II and III
D. Since the electrostatic force is stronger when charges are closer together, the electrons in the sphere are attracted to the charge with a greater force than the protons are repelled. Therefore Item I is true; choices B and C can be eliminated and choice D is correct. Looking at Item III, remember that electrons always move to regions of high electric potential. The fact that the sphere is in equilibrium (and hence, no motion) tells us there must be no regions where the potential is higher than any other. Therefore, Item III is also true.
A medical student in New York rents a studio apartment with surprisingly inexpensive rent but soon discovers that the elevated train passes outside her window every night and prevents her from sleeping. She begins looking for a new apartment but one month later finds she's having no difficulty sleeping through the night. Which area of the brain is most likely involved in this response? A.Occipital lobes B.Cerebellum C.Medulla D.Thalamus
D. The thalamus is the major relay center for sensory information on its way to the cortex, and is the most likely region of the brain to be involved in an adaptation to a sensation (noise; choice D is the correct answer). The occipital lobes are responsible for visual processing (which would not be active if a person was trying to sleep and their eyes were closed, choice A is wrong), and the cerebellum is responsible for movement and coordination (again, not so much an issue for a person trying to sleep, choice B is wrong) The medulla is responsible for maintaining blood pressure, respiratory rate, reflexes etc. and would not be involved in sensory processing (choice C is wrong).
Amphoteric vs. Amphipathic.
Detergents are amphipathic (or amphiphilic) molecules because they are both hydrophilic and hydrophobic Amphoteric molecules can act as either acids or bases. Examples of amphoteric molecules are amino acids (due to their amino and carboxyl ends) or bicarbonate (HCO3-) which neutralizes stomach acid in the duodenum and functions as a blood buffer.
Temperature and condition for growing Ecoli
Like humans, E. coli grow best at 37°C; this can be inferred from the fact that our colons are full of these bacteria (E. coli) that flourish at our body temperature of 37°C. If bacteria are growing in liquid culture, they must be continuously shaken to ensure proper mixing and distribution of nutrients, and to provide a constant oxygen supply.
Which of the following statements regarding acetylcholine is true? A.ACh released onto cardiac muscle cells blocks voltage-gated K+ channels to prevent cardiac muscle repolarization. B.ACh released onto cardiac muscle cells blocks voltage-gated Ca2+ channels to prevent cardiac muscle depolarization. C.ACh released onto skeletal muscle cells opens ligand-gated Na+ channels and leads to muscle cell depolarization. D.ACh released onto skeletal muscle cells can be stimulatory in some cases and inhibitory in other cases.
Muscular system. Am I really supposed to know this?? C. The binding of ACh to receptors on skeletal muscle cells leads to the opening of ligand-gated Na+ channels, influx of Na+, depolarization of the muscle cell, and contraction (choice C is correct). This is the case in every instance; ACh is always stimulatory to skeletal muscle cells (choice D is wrong). ACh causes the inhibition of cardiac muscle cells by opening K+ channels via a G-protein-mediated mechanism (choices A and B are wrong). The resulting efflux of K+ hyperpolarizes (and thus inhibits) the cell.
A member of the woodwinds section is late for his concert and is practicing his flute, playing a note that has a frequency of 480 Hz, while riding in the back of the bus traveling at 100 m/s. What is the frequency he hears of the note's echo from the canyon wall that is 200 m straight ahead on the road? A.280 Hz B.480 Hz C.680 Hz D.880 Hz
The detected frequency by the wall is fdetected = fsource(v / (v - vsource)) = (480 Hz)((340 m/s) / (340 m/s - 100 m/s)) = (480 Hz)(340 / 240) = (2 Hz)(340) = 680 Hz. This frequency is then reflected back to the bus so the source is the wall with the detector moving toward the wall, and the plus sign is used in the numerator of the Doppler equation. The frequency detected by the member is fdetected = fsource((v + vdetector) / v) = (680 Hz)((340 m/s + 100 m/s) / 340 m/s) = (680 Hz)(440 / 340) = (2 Hz)(440) = 880 Hz.
Histamine bound to H1 receptors on vascular smooth muscle causes vasodilation; this induces separation of cellular junctions and results in increased vascular permeability. Which of the following is NOT true about the H1 receptors? A.H1 receptors are proteins that begin their translation in the cytoplasm but are eventually found on the cell membrane. B.H1 receptors are integral proteins that begin their translation in the cytoplasm and have a hydrophobic signal sequence. C.H1 receptors are transmembrane proteins that have hydrophobic sequences as part of the functional end product. D.H1 receptors are peripheral proteins that bind to hydrophobic hormones on the surface of the cell membrane.
You Chose C because you didnt read the NOT in the Q. You also did not know that the secretory pathway begins in the cytoplasm and proceeds by two mechanism to get the protein into the ER. Translation always starts in the cytoplasm, moved to the ER either co-translationally in which the beginning section of protein is signal for ER, or after translation whole Pt is brought to ER. Then only D is false as all the other answers overlap each other!
Reducing sugars
benedict's test: + in the presence of reducing sugars eg. aldehydes, ketones, hemiacetals are reducing all monosaccharides are reducing, di- and polysaccharides w/ hemiacetals anomeric C's *Sucrose is non-reducing (b/c both anomeric carbons are acetals)
Resonance vs Inductive stabilization of radical
can eliminate the resonance if it leads to "texas carbons" Question states that inductive are "not obvious"????
ΔG =
ΔG = ΔG° + RT ln Q, and when the reaction is at equilibrium ΔG° = -RT ln K.
