Practice Test 5 - MCAT Chemical and Physical Foundations of Biological Systems

20 questions. Answer them in any order, then submit to see your score and every explanation.

Start practice test

1. A solubility study examines CaF in the presence of added NaF. The equilibrium is: CaF(s) cc Cababa(aq) + 2Fe(aq). A researcher adds NaF to a saturated CaF solution while keeping temperature constant. Which outcome would be expected from the described ion interaction?
2. A mechanical wave travels along a nerve-mimicking gel filament under constant tension. The wave speed is observed to stay constant over time. If the source frequency is decreased, what change is expected for the wavelength along the filament?
3. A researcher compares two small ultrasound transducers used in a tissue-mimicking gel. Both emit the same frequency. Transducer X moves toward a stationary hydrophone at speed $v$, while transducer Y moves toward the same hydrophone at speed $2v$ (both speeds are much less than the speed of sound in the gel). Based on the scenario, which frequency shift would be expected?
4. A researcher compares emission from two different discharge tubes: one containing hydrogen gas and one containing helium gas. Each tube produces a discrete set of bright lines at specific wavelengths. The researcher notes that increasing the tube current changes brightness but does not create a continuum. Constants: $c = 3.00\times10^8\ \text{m/s}$. Which statement best explains why both gases produce line spectra rather than continuous spectra under these conditions?
5. A lab evaluates whether mixing two solutions will form $\text{AgBr}$ precipitate. At 25°C, $\text{AgBr}(s) \rightleftharpoons \text{Ag}^+ + \text{Br}^-$ with $K_{sp}=5.0\times10^{-13}$. After mixing, $[\text{Ag}^+] = 1.0\times10^{-6}\,\text{M}$ and $[\text{Br}^-] = 1.0\times10^{-6}\,\text{M}$. Which statement best predicts the outcome?
6. In permeabilized cells, malate was provided to drive NAD+-dependent malate dehydrogenase in the mitochondrial matrix, generating NADH. Under control conditions, ATP production increased. When cyanide (Complex IV inhibitor) was added, oxygen consumption ceased and matrix NADH fluorescence increased. Which statement best reflects the redox process described?
7. A chemist tests the hypothesis that increasing acid concentration increases the rate of magnesium dissolution because more $\text{H}^+$ is available for the redox reaction producing $\text{H}_2(g)$. Identical Mg ribbons (same mass and surface area) are placed into 50 mL of HCl at 25°C. The only variable changed is HCl concentration. The time to collect 25 mL of $\text{H}_2$ gas is measured with an inverted graduated cylinder. Results: - 0.50 M HCl: 80 s - 1.0 M HCl: 42 s - 2.0 M HCl: 21 s What conclusion can be drawn about the variable change?
8. A solution of a nonvolatile solute is prepared in water. The researcher models boiling point elevation using colligative properties: $\Delta T_b = iK_b m$. Two solutions have the same molality $m$; solution 1 contains glucose ($i=1$) and solution 2 contains NaCl (assume ideal dissociation, $i\approx 2$). Which prediction is most consistent with the model?
9. A lab investigates how glycosylation affects protein solubility. Two versions of the same secreted protein are produced: Protein 1 is expressed in mammalian cells and is heavily glycosylated; Protein 2 is expressed in bacteria and lacks glycosylation. At physiological pH, Protein 1 remains soluble at higher concentrations, while Protein 2 precipitates more readily. Which property of the carbohydrate modification most likely explains the increased solubility of Protein 1? Reference: Carbohydrates often contain multiple hydroxyl groups and can introduce charged residues (e.g., sialic acid) depending on composition.
10. A lab clamp holds a horizontal rod at a pivot. A 9 N force is applied at 0.10 m from the pivot, perpendicular to the rod. The force is moved to 0.30 m from the pivot with the same direction and magnitude. Which outcome is most consistent with torque principles?
11. A small, single-domain protein (90 residues) is studied to model folding in the crowded cytosol. In dilute buffer at 25b0C, it folds cooperatively to a native state dominated by a hydrophobic core. In 6 M urea, the protein becomes unfolded; when urea is rapidly diluted to 0.5 M, folding is slower if 10 mM dithiothreitol (DTT) is present, despite no change in primary sequence. The protein contains two cysteines that are close in the native structure. Based on the vignette, how does the environment influence protein folding?
12. A sealed syringe contains an ideal gas at 300 K. The plunger is slowly compressed so the process is isothermal. The ideal gas law is $PV=nRT$. Which change is most consistent with an isothermal compression at constant $n$?
13. A diverging lens is incorporated into a smartphone attachment to allow closer focusing on skin lesions. The attachment lens has $f=-5.0\,\text{cm}$. A lesion is $d_o=10\,\text{cm}$ in front of the lens. Based on the thin-lens equation as the central concept, which outcome is most consistent with the described optics principle?
14. In an acid-catalyzed hydrolysis study of an ester (R–CO2R′) at pH 2.0, a student proposes that the key intermediate is a tetrahedral species formed after water attacks the carbonyl carbon. Concept probed: mechanistic intermediates in nucleophilic acyl substitution. Which description is most consistent with the structure of the tetrahedral intermediate formed immediately after nucleophilic attack (before collapse)?
15. In a constant-pressure biochemical assay, a reaction releases $12\ \text{kJ/mol}$ of heat to the surroundings. Interpreting thermodynamic quantities, which statement is most consistent with the sign of $\Delta H$ for the reaction as written?
16. A hospital uses a handheld ultrasound probe and applies more pressure, slightly increasing the contact force but not changing the emitted frequency. The tissue is assumed approximately linear for these small changes, so sound speed in tissue remains $v=1540\ \text{m/s}$. Which statement best describes the wave behavior in this scenario for the ultrasound wavelength $\lambda$ in tissue?
17. An investigator uses a fluorescent intercalator that binds preferentially between stacked base pairs in double-stranded DNA. Fluorescence increases strongly upon adding the dye to dsDNA but increases only weakly with ssDNA of the same sequence. Which process best explains the data observed?
18. A lab is developing a new contrast agent for MRI and plans first-in-human testing. The PI wants to recruit from a clinic where many patients have limited English proficiency. The consent form is only in English, and the PI says, "We can summarize it quickly; the chemistry is too complex anyway." A coordinator suggests translated documents and certified interpretation. Based on the scenario, what is the most ethical course of action?
19. In a sealed calorimetry chamber, a researcher measures the heat released by hydrolysis of a high-energy phosphate compound at constant pressure. The reaction is exothermic and produces more moles of aqueous solute but no net gas. Using the convention $\Delta H = q_p$, which statement is most consistent with the measurement at constant pressure?
20. In a TOF mass spectrometer, ions are accelerated through the same potential difference $V$ before entering a field-free drift region. The principle used is $z e V = \tfrac{1}{2}mv^2$, so for fixed $V$, ions with larger $m/z$ have lower velocity and arrive later. If an ion with $m/z=50$ arrives at the detector later than an ion with $m/z=25$ under identical conditions, which statement is most consistent with the principle? Constants: $e = 1.60\times 10^{-19}\ \text{C}$; $1\ \text{amu} = 1.66\times 10^{-27}\ \text{kg}$.

Practice tests