Wize High School Grade 11 Biology Textbook > Biochemistry of Metabolism
Cellular Respiration: Beyond Oxygen Consumption
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Fermentation & Alcoholic Beverages
Alcohol fermentation is used by bacteria and yeast in the absence of oxygen to keep their cells alive. Humans have discovered that this process is very useful for the production of alcoholic beverages!
Using Microorganisms to Make Alcoholic Beverages
To make alcoholic beverages, you need:
- A source of fermentable sugar (e.g., grapes, barley)
- Yeast (can be added, or can occur naturally on grapes, for example)
- A air-tight container to prevent oxygen from entering
Yeast will ferment the sugars in the absence of oxygen. This leads to the production of carbon dioxide and ethanol.
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Fermentation & Food Production
Fermentation is used in many types of food and beverages. It is the process of taking sugars and converting them to alcohol or acids using microorganisms. Foods that are produced through fermentation include:
- Bread: Yeast ferments the sugars in wheat, producing CO2 as a biproduct (leads to levening of bread)
- Yogurt: Bacteria ferment sugars in milk to produce lactic acid
- Vinegar: Bacteria ferment alcohol or sugars to produce acetic acid
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Cellular Respiration & Human Health
Lack of oxygen
The human body cannot survive long in the absence of oxygen. This is because brain cells are very sensitive to lack of oxygen. Without oxygen, they cannot carry out cellular respiration or produce ATP. The lack of ATP production leads to brain cell damage and death.
Cellular Respiration in Cancer Cells
Cancer cells reprogram their metabolism to enable rapid cellular replication and spread throughout the body.
- A key aspect of the metabolism of cancer cells is that they have an enhanced rate of glycolysis during periods of fast growth.
- Cancer cells consume more than 20x more glucose compared to normal cells
- Instead of breaking glucose down to CO2, they undergo fermentation and produce lactic acid
Fermentation produces less ATP than cellular respiration. So why do cancer cells do this?
- While cancer cells produce far less ATP per molecule of glucose, they produce it much faster
- Cancer cells use this process to produce many intermediate molecules that are used to create DNA, proteins, and other biomolecules that are needed for rapid cell growth and division.
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Cellular Respiration & Exercise
Muscle cells during strenuous exercise
Have you ever felt that intense burn in your thighs when hiking a mountain or climbing stairs? This feeling comes from lack of oxygen in your muscles. Your muscle cells are working so hard that they use up more oxygen than can be delivered to them by the bloodstream. The result is fermentation.
- Under oxygen deprivation, muscle cells switch to lactic acid fermentation
- This is because oxygen is not present in high enough amounts to keep aerobic cellular respiration running
- The build up of lactic acid leads to the burning sensation in your muscles
Muscle cells during rest
Fermentation is not efficient long term. Eventually, too much lactic acid will accumulate and muscle cells will become damaged. So, when oxygen is abundant, muscle cells undergo normal cellular respiration.
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Example: Cellular Respiration & Respiration
Describe what happens at the cellular level when someone is unable to breath?
When someone is unable to breath, oxygen levels in the bloodstream will become depleted. As the cells in the body begin to experience oxygen depletion, the electron transport chain will slow.
In order to continue producing ATP by glycolysis, cells switch to fermentation and produce lactic acid as a biproduct. But eventually, lactic acid will build up and cells won't be able to sustain life.
Practice
Fill in the blanks: Fermentation is ________________ and generates _______________
in humans and __________________ in yeast.
Practice
Which of the following is a metabolic pathway shared by both cellular respiration and fermentation?
Practice
Fermentation is a limited way of obtaining energy because