One characteristic of an essential fatty acid is that it:

Correct Answer: C

Rationale: The correct answer is C because essential fatty acids are not manufactured by the body and must be obtained through the diet. Choice A is incorrect because essential fatty acids can come from plant sources as well. Choice B is incorrect as essential fatty acids are primarily derived from plant sources. Choice D is incorrect because essential fatty acids cannot be produced by the body. Therefore, the only accurate statement is that essential fatty acids are not manufactured by the body.

Correct Answer: B

Rationale: Beta cells in the islets of Langerhans in the pancreas are responsible for the production and secretion of insulin, which is crucial for regulating blood glucose levels. Alpha cells, on the other hand, produce glucagon, a hormone that raises blood glucose levels. Gamma cells and Delta cells do not exist in the islets of Langerhans; therefore, they are incorrect choices.

Correct Answer: B

Rationale: Malnutrition is a common comorbidity in patients with Chronic Kidney Disease (CKD). This is mainly due to factors such as dietary restrictions, poor appetite, and the body's increased nutritional needs as it struggles to deal with the disease. Liver disease (Choice A) is not typically associated directly with CKD, although both conditions may coexist in some patients. Acute renal failure (Choice C) is not a comorbidity but a severe and potentially lethal progression of CKD. Difficulty breathing (Choice D) is not a comorbidity but can be a symptom of severe kidney disease or other underlying conditions. However, malnutrition is more commonly observed in CKD patients compared to difficulty breathing.

Correct Answer: B

Rationale: The correct answer is B. The classification of the 20 common amino acids is not based on the properties of their side chains, but rather on the structure of their amino and carboxyl groups. These groups are consistent among all amino acids, while the side chains, also known as R groups, are what vary and give each amino acid its unique properties. Choice A is correct because proteins are indeed composed of amino acids. Choice C is incorrect because while the side chains of amino acids can vary, the general structure of an amino acid - a central carbon atom bonded to an amino group, a carboxyl group, a hydrogen atom, and a side chain - is consistent. Choice D is correct because amino acids do polymerize to form long chains called polypeptides, which can then fold into complex shapes to form proteins.

Correct Answer: A

Rationale: The first statement is correct as bacterial plaque can indeed metabolize sucrose, lactose, and fructose. However, the second statement is inaccurate. Fructose, despite being found naturally in honey and known also as levulose, is not less cariogenic than either sucrose or lactose. This means that its consumption does not result in fewer cavities or tooth decay. Therefore, the correct answer is that bacterial plaque can metabolize these sugars, but fructose is not less cariogenic. Choices B, C, and D are incorrect because they either wrongly assert that bacterial plaque cannot metabolize these sugars or wrongly claim that fructose is less cariogenic.