Final answer:
The correct answer is D) Only steroids have a four-ring carbon structure. This structure is distinctive to steroids, like cholesterol, and is not found in phospholipids, which are major components of the cell membrane.
Step-by-step explanation:
Differences Between Steroids and Phospholipids
When comparing steroids and phospholipids, there are some key differences to consider. Steroids are characterized by a fused four-ring carbon structure. This distinct feature is unique to steroids and is not found in phospholipids, which consist of two fatty acids and a phosphate group attached to a glycerol backbone. In contrast, phospholipids are significant components of the cell membrane and have both hydrophilic (water-attracting) and hydrophobic (water-repelling) properties, helping them to form bilayers that makeup cell membranes.
Another difference is that many steroids, known as sterols, contain an -OH functional group, classifying them as alcohols. This hydroxyl group lends a polar, hydrophilic property to an otherwise hydrophobic molecule. For instance, cholesterol is a sterol that is essential for cell membrane structure and as a precursor for steroid hormones. Comparatively, phospholipids do not typically have ring structures but instead contain fatty acid chains.
In summary, option D) "Only steroids have a four-ring carbon structure" correctly explains a fundamental difference between steroids and phospholipids, making it the accurate choice.