Which statement about catalysts is correct?

Correct Answer: A

Rationale: The correct answer is A. Catalysts decrease the activation energy required for a reaction, speeding up the reaction without being consumed in the process. They provide an alternative pathway for the reaction to proceed, facilitating the reaction without being altered themselves. This is why they are unchanged at the end of the reaction. Choice B is incorrect because catalysts are not used up in the reaction. Choices C and D are also incorrect as catalysts do not increase the time taken for a reaction to finish nor are they consumed in the reaction.

Correct Answer: C

Rationale: The correct answer is C, the anterior pituitary gland. The hypophyseal portal system is a network of blood vessels that connects the hypothalamus to the anterior pituitary gland. This system allows the hypothalamus to release hormones that regulate the secretion of hormones from the anterior pituitary gland. The releasing and inhibiting hormones travel through this portal system directly to the anterior pituitary gland to exert their effects. Choices A, B, and D are incorrect because the hypophyseal portal system specifically targets the anterior pituitary gland, not the parathyroid glands, thyroid gland, or adrenal glands.

Correct Answer: D

Rationale: The correct answer is D: peroxidase enzymes. Peroxidase enzymes are responsible for catalyzing the iodination process of thyroid hormones in the thyroid gland. They facilitate the incorporation of iodine atoms into tyrosine residues within thyroglobulin to form thyroid hormones T3 and T4. Lysosomes (choice A) are involved in cellular waste disposal, not iodination. The Golgi apparatus (choice B) is responsible for processing and packaging proteins, not iodination. Colloid endocytosis (choice C) is the process of internalizing colloid-containing vesicles in thyroid follicular cells, but it is not directly involved in iodination.

Correct Answer: D

Rationale: The correct answer is D: Splenic vein. The splenic vein lies posterior to the body of the pancreas. Step 1: Locate the pancreas in the abdominal cavity. Step 2: Identify the structures behind the body of the pancreas. Step 3: The splenic vein runs posterior to the body of the pancreas, making it the correct answer. Other choices are incorrect because A: IVC is located more inferiorly, B: Portal vein is located more superiorly, and C: Common bile duct is located more anteriorly to the body of the pancreas.

Correct Answer: a

Rationale: The correct answer is A: Calcitonin-parathyroid hormone. 1. Calcitonin lowers blood calcium levels by inhibiting bone breakdown, while parathyroid hormone raises blood calcium levels by stimulating bone breakdown. 2. This hormone pair directly opposes each other in regulating blood calcium levels. 3. Choices B, C, and D do not involve hormones with antagonistic effects on the same physiological process.