1. 9-1 Cell Respiration: An Overview
Chapter 9 Cellular Respiration
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9-1 Cell Respiration: An Overview
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9-1 Chemical Pathways
Food serves as a source of raw materials from which the cells in the body can synthesize new molecules. Food is also a source of energy.
Animal Cells
Animal
Mitochondrion
Plant
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Plant Cells
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Both plant and animal cells carry out the final stages of cellular respiration in the mitochondria.
Outer membrane
Intermembrane space
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Inner membrane
Matrix
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4. Chemical Energy and Food
One gram of the sugar glucose (C6H12O6), when burned in the presence of oxygen, releases 3811 calories of heat energy.
A calorie is the amount of energy needed to raise the temperature of 1 gram of water 1 degree Celsius. It is a unit of energy.
1000 calories = 1 Calorie
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Cells use all sorts of molecules for food, including fats, proteins, and carbohydrates. The energy stored in each of these molecules varies because their chemical structures, and therefore their energy-storing bonds, differ. Cells break down food molecules gradually and use the energy stored in the chemical bonds to produce compounds such as ATP that power the activities of the cell. The cell has to release the chemical energy in food molecules (like glucose) gradually, otherwise most of the energy would be lost in the form of heat and light.
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6. Overview of Cellular Respiration
If oxygen is available, organisms can obtain energy from food by a process called cellular respiration. The summary of cellular respiration is presented below.
In symbols:
6 O2 + C6H12O6  6 CO2 + 6 H2O + Energy
In words:
Oxygen + Glucose  Carbon dioxide + Water +
Energy
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7. Overview of Cellular Respiration
Cellular respiration is the process that releases energy by breaking down glucose and other food molecules in the presence of oxygen.
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8. Stages of Cellular Respiration
The three main stages of cellular respiration are glycolysis, the Krebs cycle, and the electron transport chain.

9. Overview of Cellular Respiration
Glycolysis takes place in the cytoplasm. The Krebs cycle and electron transport take place in the mitochondria.
Glycolysis
Cellular respiration is the process that releases energy by breaking down food molecules in the presence of oxygen. Glycolysis takes place in the cytoplasm. The Krebs cycle and electron transport take place inside the mitochondria.
Cytoplasm
Mitochondrion
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10. Overview of Cellular Respiration
Each of the three stages of cellular respiration – glycolysis, the electron transport chain, and the Krebs cycle - captures some of the chemical energy available in food molecules and uses it to produce ATP.
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11. Stages of Cellular Respiration
Glycolysis produces only a small amount of energy. Most of glucose’s energy (90%) remains locked in the chemical bonds of pyruvic acid at the end of glycolysis.
During the Krebs cycle, a little more energy is generated from pyruvic acid.
The electron transport chain produces the bulk of the energy in cellular respiration by using oxygen, a powerful electron acceptor.

12. Oxygen and Energy
The pathways of cellular respiration that require oxygen are called aerobic. The Krebs cycle and electron transport chain are both aerobic processes.
Gylcolysis is an anaerobic process. It does not directly require oxygen, nor does it rely on an oxygen-requiring process to run. However, it is still considered part of cellular respiration.

13. Comparing Photosynthesis and Cellular Respiration

14. Comparing Photosynthesis and Cellular Respiration
Photosynthesis and cellular respiration are opposite processes.
The energy flows in opposite directions. Photosynthesis “deposits” energy, and cellular respiration “withdraws” energy.
The reactants of cellular respiration are the products of photosynthesis and vice versa.
Respiration takes place in all living things. Photosynthesis takes place only in plants, algae, and some bacteria.