An inhibitor that blocks the proton channel of ATP synthase is added to a suspension of actively respiring mitochondria. Which change occurs first?

The proton gradient across the inner membrane grows steeper, and oxygen consumption slows.

The proton gradient across the inner membrane collapses, and oxygen consumption rises.

Protons accumulate in the mitochondrial matrix, and the matrix becomes acidic.

NADH is oxidized more rapidly, and ATP production increases.

Why was the gene-silencing experiment an important complement to the experiments in yeast and bacteria?

It showed that the proteins protect tardigrades themselves, not only cells that are given the genes artificially.

It showed that yeast and bacteria make the same proteins naturally.

It measured the animals' metabolic rate during anhydrobiosis.

It proved that trehalose is harmful to tardigrades.

Glucose enters a cell by facilitated diffusion, and the carrier proteins are already saturated. Which change would most increase the rate of glucose uptake?

Increasing the number of glucose carrier proteins in the membrane

Raising the extracellular glucose concentration further

Supplying the cell with additional ATP

Lowering the temperature of the medium

OAT

Free OAT Practice Questions

10 sample questions for the OAT, with the correct answer and an explanation for each. No account needed. Try each one before you open the answer.

Sections covered on the exam: Survey Of The Natural Sciences, Quantitative Reasoning, Biology, Organic Chemistry, Generalchemistry, Organicchemistry, Passage-Based, Kinematics, Thermodynamics, Rotationalandharmonicmotion, Wavesandsound, Optics, Numericalcalculations, Quantitativecomparison, Probabilityandstatistics.

Question 1 · Survey Of The Natural Sciences
An inhibitor that blocks the proton channel of ATP synthase is added to a suspension of actively respiring mitochondria. Which change occurs first?
- A.The proton gradient across the inner membrane grows steeper, and oxygen consumption slows.
- B.The proton gradient across the inner membrane collapses, and oxygen consumption rises.
- C.Protons accumulate in the mitochondrial matrix, and the matrix becomes acidic.
- D.NADH is oxidized more rapidly, and ATP production increases.
Show answer and explanation
Answer: A. The proton gradient across the inner membrane grows steeper, and oxygen consumption slows.
With ATP synthase blocked, protons pumped into the intermembrane space can no longer flow back into the matrix, so the gradient steepens. The steep gradient makes further proton pumping harder, which slows electron transport and therefore oxygen consumption; ATP synthesis stops rather than increases.
Question 2 · Generalchemistry
What is the ground-state electron configuration of the Fe2+ ion (Fe, Z = 26)?
- A.[Ar] 4s2 3d6
- B.[Ar] 4s2 3d4
- C.[Ar] 3d6
- D.[Ar] 4s1 3d5
Show answer and explanation
Answer: C. [Ar] 3d6
Neutral iron is [Ar] 4s2 3d6. Transition metals lose their 4s electrons before their 3d electrons when they form cations, so Fe2+ is [Ar] 3d6. The configuration [Ar] 4s2 3d6 is neutral iron.
Question 3 · Organicchemistry
An unknown compound shows a strong, sharp IR absorption at 1715 cm−1 and no absorption between 2500 and 3550 cm−1 other than C–H stretches near 2900 cm−1. Which compound fits these data?
- A.Butanoic acid
- B.But-1-yne
- C.Butanone
- D.Butan-1-ol
Show answer and explanation
Answer: C. Butanone
A strong band near 1715 cm−1 indicates a C=O. Butanoic acid also has C=O but would show a very broad O–H band from 2500 to 3300 cm−1. The alcohol has no carbonyl and a broad O–H band, and the terminal alkyne shows C≡C and ≡C–H bands instead. Butanone fits.
Question 4 · Passage-Based
Why was the gene-silencing experiment an important complement to the experiments in yeast and bacteria?
- A.It showed that the proteins protect tardigrades themselves, not only cells that are given the genes artificially.
- B.It showed that yeast and bacteria make the same proteins naturally.
- C.It measured the animals' metabolic rate during anhydrobiosis.
- D.It proved that trehalose is harmful to tardigrades.
Show answer and explanation
Answer: A. It showed that the proteins protect tardigrades themselves, not only cells that are given the genes artificially.
Inserting the genes into yeast and bacteria showed that the proteins can protect other cells. Silencing them in tardigrades and observing lower survival showed that the animals depend on these proteins, strengthening the conclusion that the proteins contribute to tardigrade tolerance.
Question 5 · Optics
A patient's corrective lens has a focal length of −25 cm. What is the power of the lens?
- A.+4.0 diopters
- B.−25 diopters
- C.−4.0 diopters
- D.−0.25 diopter
Show answer and explanation
Answer: C. −4.0 diopters
Lens power is P = 1/f with f in meters: P = 1/(−0.25 m) = −4.0 diopters. The negative power indicates a diverging lens, the type used to correct myopia.
Question 6 · Survey Of The Natural Sciences
Glucose enters a cell by facilitated diffusion, and the carrier proteins are already saturated. Which change would most increase the rate of glucose uptake?
- A.Raising the extracellular glucose concentration further
- B.Increasing the number of glucose carrier proteins in the membrane
- C.Supplying the cell with additional ATP
- D.Lowering the temperature of the medium
Show answer and explanation
Answer: B. Increasing the number of glucose carrier proteins in the membrane
Once every carrier is occupied, adding more glucose cannot raise the rate; only more carriers can increase the maximum transport rate. Facilitated diffusion is passive, so ATP does not help, and lowering the temperature slows transport.
Question 7 · Generalchemistry
Which element has the highest first ionization energy?
- A.Oxygen
- B.Carbon
- C.Boron
- D.Nitrogen
Show answer and explanation
Answer: D. Nitrogen
Ionization energy generally increases across period 2, but oxygen is lower than nitrogen. Nitrogen's half-filled 2p subshell is especially stable, while oxygen's fourth 2p electron is paired and repelled by its partner, so it is removed more easily.
Question 8 · Organicchemistry
Which species is aromatic?
- A.The cyclopentadienyl anion
- B.Cyclobutadiene
- C.Cyclopentadiene
- D.Cyclooctatetraene
Show answer and explanation
Answer: A. The cyclopentadienyl anion
Aromaticity requires a planar, cyclic, fully conjugated ring with 4n + 2 π electrons. The cyclopentadienyl anion has 6 π electrons (n = 1) delocalized over five sp2 carbons. Cyclobutadiene has 4 π electrons (antiaromatic), cyclopentadiene has an sp3 carbon that breaks the conjugation, and cyclooctatetraene is nonplanar with 8 π electrons.
Question 9 · Passage-Based
As used in the third paragraph, the word "depleted" most nearly means
- A.poisoned.
- B.drained of energy reserves.
- C.broken apart.
- D.overcrowded.
Show answer and explanation
Answer: B. drained of energy reserves.
The paragraph describes a bleached coral as "starving," so corals that are too "depleted" to recover have exhausted their energy reserves after losing the sugar supplied by their algae.
Question 10 · Optics
A diver is 20 m below the surface of a freshwater lake. What is the absolute pressure on the diver? (Atmospheric pressure ≈ 1.0 × 105 Pa; ρwater = 1000 kg/m³; g = 10 m/s²)
- A.2.0 × 105 Pa
- B.3.0 × 105 Pa
- C.2.1 × 106 Pa
- D.1.0 × 105 Pa
Show answer and explanation
Answer: B. 3.0 × 105 Pa
P = P0 + ρgh = 1.0 × 105 + (1000)(10)(20) = 1.0 × 105 + 2.0 × 105 = 3.0 × 105 Pa. The value 2.0 × 105 Pa is the gauge pressure alone.

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