Giving a single IV injection of phenylephrine can be used to normalize a rapid heart rate in paroxysmal supraventricular tachycardia (PSVT). How does phenylephrine do this?

Correct Answer: C

Rationale: Correct Answer: C Rationale: 1. Phenylephrine is a vasoconstrictor that raises blood pressure. 2. Increased blood pressure activates the baroreceptor reflex. 3. Baroreceptor reflex detects elevated blood pressure and sends signals to the brain. 4. The brain then signals the heart to slow down, thus normalizing the rapid heart rate in PSVT. Summary: A: Blocking beta-receptors would have the opposite effect, as beta-blockers slow down the heart rate. B: Stimulating norepinephrine release would increase heart rate, not slow it down. D: ACh esterase is involved in the breakdown of acetylcholine, not relevant to the mechanism of action of phenylephrine in PSVT.

Correct Answer: B

Rationale: The correct answer is B: Only some bacteria will be killed by some antibiotics. Antibiotic resistance refers to the ability of bacteria to survive and grow despite the presence of an antibiotic. This occurs when bacteria evolve and develop mechanisms to defend against antibiotics. It is not accurate to say that no bacteria will be killed by any antibiotic (choice A) as some bacteria may still be susceptible to certain antibiotics. Antibiotics are not effective against viruses, so choice C and D are incorrect. In summary, antibiotic resistance specifically pertains to bacteria developing the ability to survive some antibiotics, making choice B the correct answer.

Correct Answer: B

Rationale: The correct answer is B: neutralisation, yellow. In a neutralization reaction between an acid and a base, the acidic and basic properties neutralize each other, resulting in a salt and water. The indicator phenolphthalein is commonly used in acid-base titrations, turning pink in basic solutions and colorless in acidic solutions. When the reaction is complete and the solution is neutral (pH 7), phenolphthalein appears yellow. Therefore, the color of the mixture at the end of a neutralization reaction is yellow. Choices A, C, and D are incorrect because neutralization reactions typically result in a yellow color, not orange, and redox reactions do not involve the same color changes as neutralization reactions.

Correct Answer: D

Rationale: The correct answer is D. In circuit symbols, a heater is typically represented by a zigzag line enclosed in a rectangle. This symbol signifies the generation of heat through resistance. Option A does not resemble a heater symbol, Option B is a resistor symbol, and Option C is a light bulb symbol. Therefore, the correct answer is D as it accurately represents a heater in circuit diagrams.

Correct Answer: B

Rationale: The correct answer is B: paracrine. Paracrine signaling involves the release of signaling molecules into the extracellular fluid to affect nearby target cells. This type of signaling is localized and affects cells within close proximity. Autocrine signaling (A) involves cells releasing signals that act on themselves, endocrine signaling (C) involves signaling molecules being released into the bloodstream to affect distant target cells, and neural signaling (D) involves the transmission of signals through neurons. In this case, paracrine signaling specifically targets local cells by releasing chemicals into the extracellular fluid, making it the correct choice.