The following statements concerning prazosin and phentolamine are correct EXCEPT:

Correct Answer: B

Rationale: Correct Answer: B Rationale: 1. Prazosin and phentolamine both antagonize alpha1-receptors, leading to vasodilation and decreased blood pressure. 2. Both drugs are competitive antagonists, competing with norepinephrine at alpha1-receptors. 3. However, phentolamine causes reflex tachycardia due to its non-selective alpha-adrenergic blockade, unlike prazosin. 4. Therefore, the statement that both cause the same degree of tachycardia is incorrect based on their pharmacological differences.

Correct Answer: C

Rationale: The correct answer is C - Phentolamine plus propranolol. Phentolamine is an alpha-adrenergic blocker that can counteract the effects of high noradrenaline levels, while propranolol is a non-selective beta blocker that can further control the symptoms by blocking beta-adrenergic receptors. Combining both drugs can effectively block all adrenergic receptors and normalize the signs and symptoms of pheochromocytoma. A: Propranolol alone cannot block all adrenergic receptors, as it only targets beta receptors. B: Phentolamine alone can block alpha receptors but does not address the beta receptors. D: Atropine plus phenylephrine combination does not cover all adrenergic receptors involved in pheochromocytoma.

Correct Answer: D

Rationale: The correct answer is D because X, a mixture of amphetamines, works by releasing neuronal noradrenaline, causing excessive sympathetic effects like severe rises in blood pressure. This is how the drug helps manage ADHD symptoms. The other choices are incorrect because A (blocking muscarinic receptors) would not be related to the autonomic effects seen with X, B (blocking β2 receptors) would not explain the fatal autonomic effects, and C (inhibiting MAO) would not lead to the described autonomic effects. Therefore, D is the correct choice based on how X works in the body to produce its effects on the sympathetic nervous system.

Correct Answer: B

Rationale: The correct answer is B: a length of DNA that codes for a protein. Genes are specific sequences of DNA that encode instructions for building proteins. This is the fundamental role of genes in the process of protein synthesis. Choice A is incorrect because not all DNA in a cell controls metabolic reactions; some DNA is non-coding. Choice C is incorrect as it refers to the entire nucleus and its contents, not just the gene. Choice D is incorrect as genes do not solely determine the inheritance of sex; they also code for other traits. In summary, the definition of a gene as a segment of DNA that codes for a protein aligns with the known function and role of genes in genetics and molecular biology.

Correct Answer: D

Rationale: Certainly! The correct answer is D because it includes statements 3 and 4, which are both true. Statement 3 is correct, as air pollutants can lead to various health issues. Statement 4 is also accurate, as air pollutants can contribute to environmental degradation. Statements 1 and 2 are incorrect as they are not included in the correct answer. Statement 1 may not be universally applicable, and statement 2 does not cover the broad impact of air pollutants on both health and the environment as indicated in statements 3 and 4. Therefore, choice D is the most accurate based on the information provided.