Which statement best compares and contrasts lipids and carbohydrates?

• A. Both lipids and carbohydrates are primarily composed of amino acids.
• B. Lipids are generally nonpolar and insoluble in water, while carbohydrates are polar and soluble in water.
• C. Carbohydrates store more energy per gram than lipids.
• D. Lipids and carbohydrates both contain nitrogen as a major component.

Answer: (B)

Verified step by step guidance

1. Understand the composition of lipids and carbohydrates: Lipids are primarily composed of carbon, hydrogen, and oxygen, while carbohydrates are also composed of carbon, hydrogen, and oxygen but in a specific ratio (C:H:O = 1:2:1). Neither lipids nor carbohydrates are composed of amino acids, which are the building blocks of proteins.
2. Analyze the solubility and polarity: Lipids are generally nonpolar molecules, meaning they do not dissolve well in water (hydrophobic). Carbohydrates, on the other hand, are polar molecules due to the presence of hydroxyl (-OH) groups, making them soluble in water (hydrophilic).
3. Compare energy storage: Lipids store more energy per gram than carbohydrates because lipids have long hydrocarbon chains that are highly reduced, allowing them to release more energy upon oxidation. Carbohydrates, while also energy-rich, store less energy per gram compared to lipids.
4. Evaluate the presence of nitrogen: Neither lipids nor carbohydrates contain nitrogen as a major component. Nitrogen is primarily found in proteins and nucleic acids, not in lipids or carbohydrates.
5. Identify the correct comparison: Based on the analysis, the correct statement is that lipids are generally nonpolar and insoluble in water, while carbohydrates are polar and soluble in water. This distinction is key to understanding their roles in biological systems.