Nitroglycerin is a vasodilator used in the treatment of angina. A common side effect of its vasodilator activity is a reflex increase in heart rate, which is sometimes dangerous. Which drug could inhibit this reflex cardiac stimulation?

Correct Answer: D

Rationale: The correct answer is D: Propranolol. Propranolol is a beta-blocker that blocks the beta-adrenergic receptors in the heart, preventing the reflex increase in heart rate caused by nitroglycerin. This action helps to counteract the potentially dangerous side effect of increased heart rate. A: Atropine is not the correct answer because it is an anticholinergic drug that increases heart rate, which would exacerbate the reflex cardiac stimulation caused by nitroglycerin. B: Cocaine is a stimulant drug that can further increase heart rate and is not used to inhibit reflex cardiac stimulation. C: Phentolamine is an alpha-blocker that primarily acts on alpha-adrenergic receptors and is not the preferred drug for inhibiting the reflex increase in heart rate caused by nitroglycerin.

Correct Answer: D

Rationale: The correct answer is D because biodiversity refers to the variety of living organisms in an ecosystem, specifically the number of different species present. This term encompasses all forms of life, from bacteria to plants to animals. Choice A is incorrect as it only focuses on the increase in the number of species, not the overall diversity. Choice B is incorrect as it describes the interaction between organisms and their environment, not the diversity of species. Choice C is incorrect as it limits biodiversity to only animals, neglecting the importance of other living organisms in an ecosystem.

Correct Answer: C

Rationale: When aqueous silver nitrate is added to a mixture, a yellow precipitate forms if there are chloride ions present. This is due to the formation of silver chloride, which is insoluble in water. The reaction is AgNO3 + Cl- → AgCl↓ + NO3-. Therefore, choice C is correct. Choice A (white precipitate) is incorrect because silver chloride is yellow, not white. Choice B (white solution) is incorrect as a precipitate forms, not a solution. Choice D (yellow solution) is incorrect because the product is a solid precipitate, not a solution.

Correct Answer: C

Rationale: The correct answer is C: kidneys. The kidneys are not considered a major endocrine organ, but they do produce hormones such as erythropoietin and renin as part of their major function of regulating fluid balance and blood pressure. The pancreas (A) is a major endocrine organ producing insulin and glucagon. The thymus (B) is involved in immune function and produces hormones like thymosin. The pituitary (D) is often referred to as the master gland and secretes various hormones that regulate other endocrine glands.

Correct Answer: B

Rationale: The correct answer is B: DNA. Hormone response elements are specific DNA sequences where hormone receptors bind to regulate gene expression. This binding initiates the transcription of target genes. Choices A, C, and D are incorrect because hormone response elements are not located on the cell membrane, RNA, or enzymes. The key is understanding that hormone receptors act on DNA to regulate gene expression, making choice B the most appropriate answer.