What is a light-year?

Correct Answer: A

Rationale: The correct answer is A: the distance travelled by light in a vacuum in 1 year. Light-year is a unit of astronomical distance, not time. Light travels at a constant speed in a vacuum, approximately 299,792 kilometers per second. In one year, light can travel about 9.46 trillion kilometers, which is defined as one light-year. Choices B, C, and D are incorrect because they do not accurately define a light-year in terms of distance traveled by light in a vacuum over a specific time period.

Correct Answer: C

Rationale: The correct answer is C because somatostatin acts on nearby cells other than those that secrete it, which is the definition of paracrine signaling. This type of signaling involves the release of signaling molecules that affect neighboring cells within the same tissue or organ. Choices A and B are incorrect because paracrine signaling does not target the cells that secrete the signaling molecule or distant target organs. Choice D is incorrect because the hypothalamus is not typically the target of somatostatin action in the pancreas.

Correct Answer: A

Rationale: The correct answer is A: External laryngeal nerve. This nerve runs along the medial surface of the thyroid gland, providing motor innervation to the cricothyroid muscle. The other choices are incorrect because: B: Hypoglossal nerve innervates the tongue, C: Internal laryngeal nerve supplies sensory innervation to the larynx, and D: Vagus nerve innervates various organs in the thorax and abdomen.

Correct Answer: a

Rationale: The correct answer is A: This muscle is optimized for endurance training. Dark (red) muscle contains more myoglobin, which stores oxygen and enhances endurance performance. This muscle type is rich in mitochondria, allowing for sustained energy production. Choice B is incorrect because dark muscle actually has more mitochondria. Choice C is incorrect because dark muscle contains more slow-twitch fibers, which are fatigue-resistant and contribute to endurance. Choice D is incorrect because dark muscle predominantly consists of slow-twitch fibers, making it optimized for endurance rather than speed.

Correct Answer: C

Rationale: The correct answer is C: High plasma levels of glucose. When blood glucose levels rise after a meal, pancreatic beta cells sense this increase and release insulin to facilitate glucose uptake into cells for energy production or storage. This is known as the glucose-stimulated insulin release mechanism. Low plasma levels of calcium (choice A), high plasma levels of potassium (choice B), and low blood volume (choice D) do not directly stimulate insulin release and are unrelated to the regulation of insulin secretion.