Infections are common in people who have inadequate protein intake because of an insufficient quantity of:

Correct Answer: C

Rationale: Inadequate protein intake can lead to a decrease in antibody production, making individuals more susceptible to infections. Insulin (Choice A) is a hormone involved in regulating blood sugar levels, not related to protein intake. Lipoprotein (Choice B) is a type of lipid-protein complex involved in lipid transport, not directly related to antibody production. Albumin (Choice D) is a protein that helps maintain oncotic pressure and carries various substances in the blood, but it is not primarily responsible for fighting infections like antibodies.

Correct Answer: A

Rationale: The correct answer is A: Forming neurotransmitters. Methionine, tyrosine, and tryptophan are important amino acids involved in the production of neurotransmitters in the body. Neurotransmitters are chemical messengers that transmit signals across nerve cells, influencing various functions such as mood, memory, and muscle control. Choices B, C, and D are incorrect because these amino acids do not primarily play a role in blocking protein breakdown, increasing insulin and thyroxine production, or decreasing energy expenditure.

Correct Answer: A

Rationale: Branched chain amino acids, such as leucine, isoleucine, and valine, are essential in preventing muscle breakdown. Therefore, they may be particularly important for a patient with cancer-related malnutrition, where maintaining muscle mass is crucial. Marasmus is a severe form of malnutrition characterized by energy deficiency, not specifically related to cancer. Cardiovascular disease and severe depression do not have a direct correlation with the need for branched chain amino acids to prevent muscle breakdown.

Correct Answer: C

Rationale: The correct answer is C: amino acids. Proteins are broken down by digestive enzymes into amino acids before being absorbed in the small intestine. Amino acids are the building blocks of proteins and are the form in which they are primarily absorbed. Choice A (fatty acids) is incorrect as fatty acids are the end products of fat digestion, not protein digestion. Choice B (disaccharides) is incorrect because disaccharides are sugars that are broken down into monosaccharides, not proteins. Choice D (polypeptides) is incorrect as proteins are broken down into amino acids and not absorbed as polypeptides.

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.