Correct Answer: B

Rationale: Hemoglobin is a protein that carries oxygen in the blood, making it the correct answer. Choice A, Saline, is a salt solution and not a protein. Choice C, Cellulose, is a complex carbohydrate found in the cell walls of plants, not a protein. Choice D, Prostaglandins, are lipid compounds with hormone-like effects, not proteins.

Correct Answer: A

Rationale: Oligosaccharides are carbohydrates composed of 3 to 10 monosaccharide units, making choice A the correct answer. Choice B is incorrect as oligosaccharides do not contain partially digested starch. Choice C is incorrect as nonnutritive sweeteners are a different category of compounds. Choice D is incorrect as oligosaccharides are not primarily used for weight management.

Correct Answer: A

Rationale: The correct answer is A: act as buffers. Amino acids can act as buffers by helping to maintain the pH balance in the body. Choice B is incorrect because amino acids do not primarily facilitate glucose storage. Choice C is incorrect as amino acids do not regulate the heartbeat. Choice D is also incorrect because amino acids do not control the level of blood cholesterol.

Correct Answer: A

Rationale: The correct answer is 'tissue and plasma.' Protein turnover involves the continuous exchange of proteins between body tissues and the bloodstream (plasma) as part of normal metabolic processes. This process ensures a balance in protein levels throughout the body. Choices B, C, and D are incorrect as they do not represent the primary sites for protein turnover in the body.

Correct Answer: C

Rationale: Vitamin B12 is primarily found in animal-derived foods like meats. Choices A, B, and D are incorrect as whole grains, nuts, and legumes do not naturally contain significant amounts of Vitamin B12. Therefore, the correct answer is 'C: Meats.'