Cellular respiration — In eukaryotic cells, where does electron transport (the electron transport chain responsible for oxidative phosphorylation) occur?

Introduction / Context:
Electron transport uses a chain of redox centers embedded in a membrane to convert the energy of electrons into a proton gradient that powers ATP synthase. Correctly localizing this machinery in eukaryotes is fundamental to understanding oxidative phosphorylation.

Given Data / Assumptions:

• The mitochondrial inner membrane houses complexes I–IV and ATP synthase.
• Electron carriers include ubiquinone (coenzyme Q) and cytochrome c.
• Protons are pumped from the mitochondrial matrix to the intermembrane space.

Concept / Approach:
Match process to organelle and membrane. The eukaryotic ETC operates on the inner mitochondrial membrane. While photosynthetic eukaryotes also have a photosynthetic electron transport chain in thylakoid membranes (chloroplasts), the question refers to respiratory electron transport for ATP production in most eukaryotic cells, which is mitochondrial, not ER or cytosolic.

Step-by-Step Solution:

Verification / Alternative check:
Electron micrographs and biochemical fractionation show ETC proteins in mitochondrial cristae membranes; ER lacks the respiratory chain complexes I–IV.

Why Other Options Are Wrong:

Common Pitfalls:
Conflating mitochondrial electron transport with other cellular redox systems (peroxisomes, ER detoxification).

Final Answer:
Inner mitochondrial membrane in mitochondria.