Which statement accurately distinguishes between substrate-level phosphorylation and oxidative phosphorylation?

• A. Substrate-level phosphorylation occurs in the mitochondria only, while oxidative phosphorylation occurs in the cytoplasm.
• B. Substrate-level phosphorylation directly transfers a phosphate group to ADP, while oxidative phosphorylation uses a proton gradient.
• C. Substrate-level phosphorylation relies on oxygen, while oxidative phosphorylation does not.
• D. Both substrate-level and oxidative phosphorylation produce ATP using the same mechanism.

Answer: (B)