Passive Diffusion Requires No Energy

Steps:

• Identify processes needing energy: active transport, muscle contraction, and synthesis use ATP.
• Recognize diffusion as passive: oxygen moves down its concentration gradient without energy.
• Evaluate choices: A, C, D involve active cellular work; B is simple diffusion.
• Confirm B: oxygen enters blood via passive diffusion in lungs.

Why B is correct:

• Diffusion follows Fick's law, moving substances down concentration gradients without ATP expenditure.

Why the others are wrong:

• A: Muscle contraction uses ATP for myosin-actin sliding.
• C: Nerve impulses require ATP for ion pumps maintaining gradients.
• D: Protein synthesis needs ATP and GTP for ribosomal assembly and translation.

Final answer: B