Pepsinogen secreted by the gastric cells is converted into pepsin by:

Correct Answer: B

Rationale: Pepsinogen is converted into its active form, pepsin, by hydrochloric acid in the stomach. Hydrochloric acid helps in unfolding the pepsinogen molecule to transform it into pepsin, which is crucial for protein digestion. Therefore, the correct answer is hydrochloric acid (choice B). Enterokinase (choice A) is an enzyme produced in the small intestine that activates trypsinogen into trypsin, not pepsinogen. Gastric lipase (choice C) is an enzyme that digests fats, not involved in converting pepsinogen to pepsin. Pancreatic lipase (choice D) is an enzyme produced by the pancreas that aids in breaking down fats in the small intestine, not part of the process of pepsin activation.

Correct Answer: D

Rationale: The correct answer is D: By enterokinase. Trypsin is activated by enterokinase, an enzyme secreted by the small intestine. Enterokinase plays a crucial role in converting trypsinogen into its active form, trypsin. Choices A, B, and C are incorrect because trypsin is specifically activated by enterokinase, not by zymogen, bile, or gastrin.

Correct Answer: C

Rationale: Chymotrypsin is an enzyme found in pancreatic secretions that plays a role in protein digestion. Rennin is primarily found in the stomach and is involved in milk digestion. Pepsin is also a stomach enzyme that aids in protein breakdown. Casein is a protein found in milk, not an enzyme involved in pancreatic secretions. Therefore, the correct answer is Chymotrypsin.

Correct Answer: A

Rationale: Albumin is the correct answer. It is a plasma protein that helps maintain osmotic pressure, thereby playing a vital role in regulating fluid balance in the body. Fibrinogen is involved in blood clotting, not fluid balance. Hemoglobin is responsible for oxygen transport in red blood cells, not fluid balance. Collagen is a structural protein found in connective tissues, not directly involved in fluid balance.

Correct Answer: B

Rationale: A nursing infant receives antibodies from its mother through the absorption of antibodies present in breast milk. Choice A is incorrect as anabolism and catabolism refer to metabolic processes, not the transfer of antibodies. Choice C is incorrect as the infant does not need to synthesize antibodies but directly receives them. Choice D is incorrect because while genetic inheritance plays a role in the immune system, in this case, the direct transfer of antibodies occurs through breast milk.