Which best describes passive diffusion?

Which best describes passive diffusion?

• A. Spontaneous diffusion from high to low concentration with no energy required
• B. Requires ATP to move against gradient
• C. Diffusion from low to high concentration for lipophilic substances
• D. Movement only occurs in presence of enzymes

Answer: (A)

Passive diffusion is the spontaneous movement of molecules down their concentration gradient without any energy input. Molecules move from regions of higher concentration to lower concentration simply because of random thermal motion, and this process does not require ATP or any transport proteins. The description that it moves against the gradient or requires energy is describing active transport, not passive diffusion. Likewise, diffusion from low to high concentration contradicts the fundamental downward gradient of passive diffusion, and diffusion does not inherently depend on enzymes.

Passive diffusion is the spontaneous movement of molecules down their concentration gradient without any energy input. Molecules move from regions of higher concentration to lower concentration simply because of random thermal motion, and this process does not require ATP or any transport proteins. The description that it moves against the gradient or requires energy is describing active transport, not passive diffusion. Likewise, diffusion from low to high concentration contradicts the fundamental downward gradient of passive diffusion, and diffusion does not inherently depend on enzymes.