Compared with proteins, the rate of diffusion for steroid molecules is generally

• A. Slow
• B. Rapid
• C. Not at all
• D. Highly variable

Answer: (B)

Small, nonpolar molecules like steroid hormones diffuse rapidly because they readily dissolve in the lipid bilayer and move down their concentration gradient without needing help from transport proteins. Proteins, in contrast, are large and often polar, so they diffuse more slowly and typically require channels, carriers, or other mechanisms. So, steroid molecules generally diffuse faster than proteins.