Chapter 9: Cellular Respiration and Fermentation

Introduction

Cellular respiration and fermentation are essential metabolic processes by which cells extract energy from organic molecules. These processes are central to the survival of both plant and animal cells, enabling them to generate ATP, the molecule that powers most cellular work.

Chemical Energy in Food and ATP Generation

Overview of Energy Transformation

• Plant and animal cells break down organic molecules by cellular respiration in the mitochondria.

• The chemical energy in food is transformed into chemical energy in ATP molecules, which are used to power cellular work.

• Some energy is released to the environment as heat.

Example: Photosynthesis stores energy in organic molecules, while cellular respiration releases that energy for cellular activities.

Catabolic Pathways and Energy Yield

Catabolic Pathways Release Energy by Oxidizing Organic Molecules

• Energy enters ecosystems as light and exits as heat.

• Chemical elements essential to life are recycled.

• Photosynthesis uses CO2 and H2O to make organic molecules and O2.

• Cellular respiration uses O2 and organic molecules to make ATP; CO2 and H2O are produced as waste.

Mechanisms of Catabolic Pathways

• Catabolic pathways release stored energy by breaking down complex molecules.

• Electron transfer from food molecules to other molecules plays a major role in these pathways.

• These processes are central to cellular respiration.

Types of Catabolic Pathways and ATP Production

Fermentation and Respiration

• Fermentation is a partial degradation of sugars that occurs without oxygen.

• Aerobic respiration consumes organic molecules and oxygen, yielding ATP.

• Anaerobic respiration is similar to aerobic respiration but consumes compounds other than oxygen.

Key Point: The breakdown of organic molecules is exergonic (releases energy).

Cellular Respiration: Definition and Equation

• Cellular respiration includes both aerobic and anaerobic respiration but often refers to aerobic respiration.

• Carbohydrates, fats, and proteins can all be consumed as fuel, but glucose is commonly used to trace the process.

Overall Equation for Cellular Respiration:

ATP and Cellular Work

• Catabolic pathways do not directly power cellular work; they are linked to work by ATP.

• Cells must constantly regenerate their supply of ATP from ADP and phosphate.

Additional info: ATP (adenosine triphosphate) is the universal energy currency in cells, used for mechanical, transport, and chemical work.