Complete the following sentence: Hormones are chemical messengers that…

Correct Answer: D

Rationale: The correct answer is D because hormones alter the activity of target tissues to regulate various physiological processes in the body. Hormones act on specific receptors in target tissues to initiate a response. Option A is incorrect because hormone levels fluctuate to maintain homeostasis. Option B is incorrect because hormones are typically synthesized by endocrine glands, not plasma proteins. Option C is incorrect because hormones are produced throughout life, not just after puberty.

Correct Answer: B

Rationale: The correct answer is B because glucose, galactose, and fructose are transported across the basolateral membrane by the GLUT2 transporter. This occurs after they are absorbed into enterocytes through various transport mechanisms. Choice A is incorrect because SGLT-2 transporter is responsible for glucose and galactose absorption, not fructose. Choice C is incorrect as fructose is absorbed through facilitated diffusion, not secondary active transport. Choice D is incorrect because insulin actually increases carbohydrate absorption by upregulating GLUT2 expression.

Correct Answer: B

Rationale: Chief cells in the stomach secrete pepsinogen, which is the inactive precursor of pepsin, an enzyme that helps break down proteins. This is the correct answer because pepsinogen is the primary product secreted by chief cells. HCl is secreted by parietal cells, intrinsic factor is secreted by parietal cells in the stomach, and HCO3- is secreted by the pancreas to neutralize stomach acid in the duodenum.

Correct Answer: D

Rationale: Step-by-step rationale for choice D being correct: 1. ATP is an energy carrier molecule. 2. Adenosine triphosphate (ATP) is a precursor of cyclic AMP. 3. Cyclic AMP is a secondary messenger involved in cellular signaling. 4. Therefore, choice D is true. Summary of incorrect choices: A: Adenosine triphosphate is a high-energy phosphate, not low. B: Reduction involves gain, not loss, of electrons. C: Oxidative phosphorylation occurs in the mitochondria, not the endoplasmic reticulum.

Correct Answer: B

Rationale: The correct answer is B because antidiuretic hormone (ADH) actually causes urine volume to decrease as blood volume decreases, not increase. ADH acts on the kidneys to reabsorb water, leading to concentrated urine and conservation of body fluids. Rationale summary: A: True, hyposecretion of FSH or LH can lead to sterility in both males and females. C: False, oxytocin is also released during sexual activity, breastfeeding, social bonding, and stress responses, not just during childbirth and nursing. D: True, luteinizing hormone triggers ovulation and stimulates the production of progesterone and some estrogens.