1. Cellular Respiration

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Chemical Pathways
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Chemical Pathways
Food serves as a source of raw materials for the cells in the body and as a source of energy.
Animal Cells
Animal
Mitochondrion
Plant
Photo Credits: left: ©Bob Gurr/DRK Photo; middle bottom: ©John Durham/Science Photo Library/Photo Researchers, Inc. ; middle top: ©Ron Boardman/Stone; right: ©Keith Porter/Photo Researchers, Inc.
Plant Cells
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4. Overview of Cellular Respiration
What is cellular respiration?
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5. 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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6. Overview of Cellular Respiration
The equation for cellular respiration is:
6O2 + C6H12O6 → 6CO2 + 6H2O + Energy
oxygen + glucose → carbon dioxide + water + Energy
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7. 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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What happens during the process of glycolysis?
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Glycolysis
ATP Production
At the beginning of glycolysis, the cell uses up 2 molecules of ATP to start the reaction.
2 ATP
2 ADP
4 ADP
4 ATP
Glycolysis is the first stage in cellular respiration. During glycolysis, glucose is broken down into 2 molecules of pyruvic acid.
Glucose
2 Pyruvic
acid
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Glycolysis
When glycolysis is complete, 4 ATP molecules have been produced.
2 ATP
2 ADP
4 ADP
4 ATP
Glucose
2 Pyruvic
acid
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Glycolysis
This gives the cell a net gain of 2 ATP molecules.
2 ATP
2 ADP
4 ADP
4 ATP
Glucose
2 Pyruvic
acid
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Glycolysis
The Advantages of Glycolysis
The process of glycolysis is so fast that cells can produce thousands of ATP molecules in a few milliseconds.
Glycolysis does not require oxygen.
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Fermentation
Fermentation
When oxygen is not present, glycolysis is followed by a different pathway. The combined process of this pathway and glycolysis is called fermentation.
Fermentation releases energy from food molecules by producing ATP in the absence of oxygen.
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Fermentation
What are the two main types of fermentation?
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Fermentation
Alcoholic Fermentation
Yeasts and a few other microorganisms use alcoholic fermentation, forming ethyl alcohol and carbon dioxide as wastes.
The equation for alcoholic fermentation after glycolysis is:
pyruvic acid + NADH → alcohol + CO2 + NAD+
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Fermentation
Lactic Acid Fermentation
In many cells, pyruvic acid that accumulates as a result of glycolysis can be converted to lactic acid.
This type of fermentation is called lactic acid fermentation. It regenerates NAD+ so that glycolysis can continue.
The equation for lactic acid fermentation after glycolysis is:
pyruvic acid + NADH → lactic acid + NAD+
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17. The Krebs Cycle and Electron Transport
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18. 9-2 The Krebs Cycle and Electron Transport
Oxygen is required for the final steps of cellular respiration.
Because the pathways of cellular respiration require oxygen, they are aerobic.
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The Krebs Cycle
What happens during the Krebs cycle?
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The Krebs Cycle
During the Krebs cycle, pyruvic acid(end product of glycolysis) is broken down into carbon dioxide in a series of energy-extracting reactions.
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Electron Transport
How are high-energy electrons used by the electron transport chain?
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Electron Transport
Electron Transport
The electron transport chain uses the high-energy electrons from the Krebs cycle to convert ADP into ATP.
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The Totals
The Totals
Glycolysis produces just 2 ATP molecules per molecule of glucose.
The complete breakdown of glucose through cellular respiration, including glycolysis, results in the production of 36 molecules of ATP.
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24. Comparing Photosynthesis and Cellular Respiration
The energy flows in photosynthesis and cellular respiration take place in opposite directions.
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25. Comparing Photosynthesis and Cellular Respiration
On a global level, photosynthesis and cellular respiration are also opposites.
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.
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