Summary

In this lesson, the following essential questions were explored:

• How does the presence of oxygen affect cellular respiration?
• How does aerobic cellular respiration release potential energy from organic compounds?

Oxygen is required in aerobic respiration as a final electron acceptor in the electron transport chain. This chain is located in the inner membrane of the mitochondrial matrix. Oxygen accepts electrons from oxidized glucose and combines with hydrogen molecules to produce water. When oxygen is present, 36 molecules of ATP are produced compared to 2 molecules of ATP during anaerobic respiration.

ATP Totals for Aerobic Respiration

Glycolysis	2 ATP
Krebs Cycle	2 ATP
Electron Transport Chain	32 ATP
Cellular Respiration	36 ATP from 1 glucose

The production of ATP occurs through a series of metabolic pathways. In each step of aerobic respiration, glucose (or an intermediate carbon molecule) is oxidized and ATP is synthesized. For every glucose that is completely oxidized, glycolysis produces 2 ATP, the Krebs cycle produces 2 ATP, and the electron transport chain synthesizes the largest amount, 32 ATP molecules. Cells will use the energy to fuel activities such as active transport, muscle contraction, and biochemical synthesis. Since multicellular organisms have high energy demands, it makes sense that these organisms function aerobically.

Lesson Glossary

glycolysis: a metabolic pathway in which one glucose molecule is broken down to form two, 3-carbon molecules and a small amount of ATP. Glycolysis is the first step in both anaerobic and aerobic respiration.

pyruvate: three-carbon molecules produced by glycolysis

phosphorylation: the process of adding a phosphate to a molecule to activate it; occurs in at the onset of cellular respiration

acetyl CoA: a molecule formed from a coenzyme and a 2-carbon molecule which is used to start the Krebs cycle

FADH₂ : an important coenzyme produced during the Krebs cycle

Krebs cycle: a metabolic pathway consisting of a series of reactions that break down the end products of glycolysis, producing carbon dioxide and generating a large amount of ATP; also known as the citric acid cycle; named after the 1953 Nobel Prize-winning scientist who made the discovery

NADH: a high-energy electron carrier