9.1 Cellular Respiration: An Overview

Organisms get the energy they need from food.

Cellular respiration is the process that releases energy from food in the presence of oxygen.

Photosynthesis removes carbon dioxide from the atmosphere, and cellular respiration puts it back. Photosynthesis releases oxygen into the atmosphere, and cellular respiration uses that oxygen to release energy from food.

• calorie (250)

• cellular respiration (251)

• aerobic (252)

• anaerobic (252)

9.2 The Process of Cellular Respiration

During glycolysis, 1 molecule of glucose, a 6-carbon compound, is transformed into 2 molecules of pyruvic acid, a 3-carbon compound.

During the Krebs cycle, pyruvic acid is broken down into carbon dioxide in a series of energy-extracting reactions.

The electron transport chain uses the high-energy electrons from glycolysis and the Krebs cycle to convert ADP into ATP.

Together, glycolysis, the Krebs cycle, and the electron transport chain release about 36 molecules of ATP per molecule of glucose.

• glycolysis (254)

• NAD⁺ (255)

• Krebs cycle (256)

• matrix (256)

9.3 Fermentation

In the absence of oxygen, fermentation releases energy from food molecules by producing ATP.

For short, quick bursts of energy, the body uses ATP already in muscles as well as ATP made by lactic acid fermentation.

For exercise longer than about 90 seconds, cellular respiration is the only way to continue generating a supply of ATP.

• fermentation (262)

Think Visually Using the information in this chapter, complete the following compare/contrast table about cellular respiration and fermentation:

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