October 2026 - Cellular Respiration Study Guide

Core ideas to know

Learn the relationships, not a string of isolated definitions. These are the facts that let you reason through unfamiliar wording.

• The overall aerobic process uses glucose and oxygen and produces carbon dioxide, water and usable energy captured mainly as ATP.
• Glycolysis occurs in the cytosol, splits one glucose into two pyruvate and makes a small net amount of ATP and NADH.
• Pyruvate oxidation and the citric acid cycle occur in the mitochondrial matrix and release carbon dioxide while loading electron carriers.
• The electron transport chain in the inner mitochondrial membrane builds a proton gradient used by ATP synthase.
• Oxygen is the final electron acceptor; without it, fermentation regenerates NAD+ so glycolysis can continue but yields little ATP.

A reliable way to answer

Use the same short process every time so the wording of the question does not decide your method for you.

1. Identify whether the question asks about carbon flow, electrons, location or ATP production.
2. Place the stage in cytosol, mitochondrial matrix or inner mitochondrial membrane.
3. Follow energy carriers from glycolysis and the cycle to the electron transport chain.
4. When oxygen is absent, separate what stops from glycolysis, which can continue if NAD+ is regenerated.

Distinctions that earn marks

Terms to know

ATP

The cell’s immediate, transferable energy currency.

NADH

An electron carrier that delivers high-energy electrons to the transport chain.

Fermentation

A pathway that regenerates NAD+ without using an electron transport chain.

Key points

• Glycolysis occurs outside mitochondria and does not directly require oxygen.
• Most aerobic ATP is associated with oxidative phosphorylation at the inner mitochondrial membrane.
• Oxygen accepts electrons at the end of the transport chain and water forms.