The electron transport chain pumps H⁺ ions into which location of the mitochondria?
a) Mitochondrial intermembrane space. 
b) Mitochondrial matrix.
c)  Mitochondrial inner membrane.
d) The H⁺ ions are pumped out of the mitochondria.

• A. Mitochondrial intermembrane space.
• B. Mitochondrial inner membrane.
• C. Mitochondrial matrix.
• D. The H⁺ ions are pumped out of the mitochondria.

Answer: (A)

Verified step by step guidance

1. Understand the role of the electron transport chain (ETC) in cellular respiration, which is to create a proton gradient across the mitochondrial membrane.
2. Identify the location of the electron transport chain, which is embedded in the inner mitochondrial membrane.
3. Recognize that as electrons are transferred through the complexes of the ETC, protons (H+ ions) are pumped from the mitochondrial matrix to the intermembrane space.
4. This movement of protons creates a high concentration of H+ ions in the intermembrane space, establishing a proton gradient.
5. The proton gradient is then used by ATP synthase to drive the synthesis of ATP as protons flow back into the mitochondrial matrix.