Mixed Deck — All OAT Topics Flashcards

A battery of EMF 12 V and internal resistance 1 Ω is connected to a 5 Ω external resistor. What is the terminal voltage?

Answer: 10 V

Current I = 12/(1+5) = 2 A; terminal voltage = EMF − Ir = 12 − 2(1) = 10 V.

Which of the following is the strongest acid?

Answer: Acetic acid (pKa ≈ 4.75)

Acetic acid has the lowest pKa (~4.75), meaning it donates a proton most readily due to resonance stabilization of the acetate anion.

Which phase of mitosis is characterized by chromosomes aligning along the cell's equatorial plate?

Answer: Metaphase

During metaphase, spindle fibers attach to kinetochores and align chromosomes at the metaphase plate.

What product forms when an ester is treated with excess Grignard reagent followed by aqueous workup?

Answer: Tertiary alcohol

Excess Grignard reacts twice with the ester—first to give a ketone intermediate, then again—yielding a tertiary alcohol.

An OAT reading passage compares two studies on intraocular pressure. The first study concludes pressure increases with age; the second finds no such correlation. What is the BEST characterization of the passage's purpose?

Answer: To present conflicting evidence and highlight an unresolved scientific question

Presenting two contradictory studies signals that the passage aims to illustrate ongoing scientific debate rather than establish a definitive conclusion.

Which reagent sequence converts a primary alkyl halide into a primary amine via the Gabriel synthesis?

Answer: Phthalimide/K2CO3, then N2H4

Gabriel synthesis alkylates potassium phthalimide, and hydrazinolysis cleaves the imide to yield the primary amine.

Which type of mutation results in a premature stop codon?

Answer: Nonsense mutation

A nonsense mutation changes a codon that encodes an amino acid into a stop codon (UAA, UAG, or UGA), causing premature termination of translation.

What is the major product when 1-butyne reacts with 2 equivalents of HBr?

Answer: 1,1-dibromobutane

Two Markovnikov additions of HBr to the terminal alkyne place both bromines on C-1, giving 1,1-dibromobutane (gem-dibromide).

In eukaryotes, which histone modification is most strongly associated with transcriptionally active chromatin?

Answer: H3K4 trimethylation

H3K4me3 marks active gene promoters and is associated with open, transcriptionally permissive chromatin.

Which stage of cellular respiration produces the most ATP per glucose molecule?

Answer: Oxidative phosphorylation

Oxidative phosphorylation (electron transport chain + chemiosmosis) generates approximately 32-34 ATP per glucose, far more than the other stages.

Which type of symbiosis is demonstrated when a barnacle attaches to a whale, benefiting the barnacle while neither helping nor harming the whale?

Answer: Commensalism

Commensalism describes a relationship where one organism benefits and the other is neither helped nor harmed.

What is the primary role of the corpus luteum after ovulation?

Answer: Secrete progesterone to maintain the uterine lining

The corpus luteum, formed from the ruptured follicle after ovulation, secretes progesterone (and some estrogen) to maintain the endometrium for potential implantation.

Sensory neurons that carry impulses FROM sensory receptors TO the central nervous system are called:

Answer: Afferent neurons

Afferent (sensory) neurons transmit signals from receptors toward the CNS; efferent neurons carry signals away.

A plane mirror forms an image that is:

Answer: Virtual, upright, and same size

A plane mirror always produces a virtual, upright image at the same distance behind the mirror, with magnification = 1.

The resting membrane potential of a typical neuron is approximately:

Answer: -70 mV

The resting membrane potential of most neurons is approximately −70 mV, maintained by K⁺ leakage and the Na⁺/K⁺ pump.

In a class of 30 students, 18 play soccer and 14 play basketball. If 5 play neither sport, how many play both?

Answer: 7

Students playing at least one sport = 25; by inclusion-exclusion: 18 + 14 − both = 25 → both = 7.

A convex lens has a focal length of 20 cm. An object is placed 30 cm from the lens. Where is the image formed?

Answer: 60 cm on the opposite side

1/v − 1/u = 1/f → 1/v = 1/20 + 1/30 = 5/60 → v = 60 cm on the opposite side (real image).

All enzymes in the synaptic cleft are shown to be denatured by a chemical agent. How will this agent affect acetylcholine?

Answer: Acetylcholine will not be degraded in the synaptic cleft

Acetylcholine (ACh) is a neurotransmitter that transmits signals across the synaptic cleft. After binding to receptors on the postsynaptic membrane, its action is terminated by the enzyme acetylcholinesterase (AChE), which degrades ACh in the synaptic cleft. If all enzymes in the synaptic cleft, including AChE, are denatured, they will lose their function. This means acetylcholine will not be broken down and will persist in the cleft, continuing to bind to receptors and prolonging its effect.

A biologist observes a mule, which is the offspring of a male donkey and a female horse. The mule is healthy and strong but is sterile. This is an example of which type of reproductive isolating mechanism?

Answer: Hybrid sterility

Hybrid sterility is a post-zygotic isolating mechanism where the hybrid offspring of two different species is viable but unable to produce functional gametes, and is therefore sterile. A mule is a classic example of hybrid sterility. Hybrid inviability means the hybrid zygote fails to develop or dies before birth. Hybrid breakdown refers to when F1 hybrids are fertile, but their F2 offspring are inviable or sterile. Gametic isolation is a pre-zygotic barrier where gametes from different species are incompatible.

Which of the following has the highest boiling point?

Answer: NH3

NH3 has the highest boiling point due to strong intermolecular hydrogen bonding.