Chapter 8, Problem 41A

Summary Introduction

To state:

The origin of oxygen atoms in carbon dioxide and water and the end products of cellular respiration.

Introduction:

Organisms obtain energy through a process called cellular respiration. This process occurs in two stages; glycolysis and aerobic respiration. Glycolysis is an anaerobic process. Aerobic respiration includes Krebs cycle and electron transport.

Answer to Problem 41A

The oxygen atoms in carbon dioxide come from the glucose molecule and the oxygen in water comes from the air or atmosphere.

Explanation of Solution

The end products of cellular respiration are carbon dioxide and water. The first stage is glycolysis during which glucose molecule is broken down in the cytoplasm of cells to form pyruvate.

During the second stage called Krebs cycle, pyruvate is transported into the mitochondrial matrix, where it is finally converted to carbon dioxide. So the oxygen in carbon dioxide comes from the glucose molecule.

During electron transport which is the final step in breakdown of glucose, oxygen is the final electron acceptor which combines with hydrogen ions to form water. This oxygen comes from air that is taken in during breathing.