Pheochromocytoma is a tumor of the adrenal medulla. The tumor results in extraordinarily high blood noradrenaline levels. What drug or drug combination can block all of the adrenergic receptors and normalize all the signs and symptoms caused by pheochromocytoma?

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: 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.

Correct Answer: D

Rationale: The correct answer is D: red supergiant → supernova → black hole. This sequence is part of the life cycle of a very large mass star. Red supergiants are massive stars in the later stages of their evolution. When a red supergiant goes supernova, it explodes in a massive stellar explosion, leaving behind a remnant that can collapse into a black hole due to the immense gravitational forces. Choices A and B are incorrect because planetary nebulae form from the outer layers of lower mass stars, not very large mass stars. Choice C is incorrect as neutron stars are more likely to form from the remnants of less massive stars.

Correct Answer: A

Rationale: The correct answer is A. Eicosanoids are not true hormones because they act locally, not on distal organs like true hormones. Eicosanoids are produced and released in response to specific stimuli at the site of action, affecting nearby cells. This local action distinguishes them from true hormones, which are produced in one part of the body and travel through the bloodstream to distant target organs to elicit a response. Choices B, C, and D are incorrect because eicosanoids do have target organs (B), mediate inflammatory reactions (C), and are lipid in nature (D), but these characteristics do not define them as hormones.