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Questions and Answers
What is the primary difference between anaerobic and aerobic respiration?
Which of the following statements about ATP yield in anaerobic respiration is true?
Why is the oxidation of NADH back to NAD+ important during fermentation?
Which process occurs first in both anaerobic respiration and fermentation?
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What type of organisms can perform fermentation?
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What is NOT a common final electron acceptor in anaerobic respiration?
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Which of the following fermentation processes produces lactic acid?
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How many ATP molecules are produced during glycolysis?
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Which of the following is a result of yeast fermentation?
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What distinguishes alcohol fermentation from acid fermentation?
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What gas is released during the fermentation process that causes holes in Swiss cheese?
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What is the primary reason organisms will choose fermentation over aerobic respiration?
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Which of the following best describes E. coli’s metabolic flexibility?
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What outcome indicates that a sugar was fermented with gas production in phenol red broth?
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What does the red color of phenol red broth indicate about sugar fermentation?
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Which type of medium is used to determine the oxygen requirements of an organism?
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In fluid thioglycolate medium, where would aerobes be expected to grow?
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Which of the following organisms is likely to grow at the bottom of the fluid thioglycolate medium?
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Which of the following is NOT a result of fermentation indicated by phenol red broth?
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What advantage does fermentation offer to cells under anaerobic conditions?
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Anaerobic respiration is more common than aerobic respiration.
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Only prokaryotes are capable of performing anaerobic respiration.
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The final electron acceptor in anaerobic respiration is always oxygen.
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The ATP yield for anaerobic respiration can range from 10 to 24 ATP per glucose molecule.
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Fermentation can only occur in the absence of oxygen.
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Fermentation produces more ATP than glycolysis.
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Propionibacterium fermentation produces acetic acid as its main product.
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Fermentation is only performed by eukaryotes under anaerobic conditions.
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E. coli can perform fermentation when both oxygen and salt are absent.
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Yeasts are commonly used in the production of alcohol due to their ability to ferment sugars.
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In phenol red broth, the medium turns red if the sugar is fermented.
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During fermentation, carbon dioxide gas is always released as a byproduct.
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Lactobacillus fermentation results in lactic acid production.
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Fluid thioglycolate medium allows the growth of anaerobes at the top of the tube.
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The process of fermentation is essential for converting NADH back to NAD+.
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Aerobic respiration yields more ATP compared to fermentation.
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Gluconobacter and Acetobacterium are involved in the fermentation process that creates yogurt.
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Anaerobes can survive and grow in environments where oxygen is present.
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A yellow color in phenol red broth indicates that gas was produced during sugar fermentation.
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Facultative anaerobes can grow in both the presence and absence of oxygen.
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Study Notes
Anaerobic Respiration
- Anaerobic respiration is less common than aerobic respiration.
- Only some prokaryotes are capable of anaerobic respiration.
- Anaerobic respiration begins like aerobic respiration, utilizing glycolysis and the TCA cycle.
- The difference lies in the electron transport system, where the final electron acceptor is an inorganic salt, not oxygen.
- Common inorganic salts utilized include sulfate, nitrate, nitrite, and fumarate.
- The amount of ATP produced varies depending on the specific salt, but is always lower than aerobic respiration.
- ATP yield for anaerobic respiration is typically between 10-24 ATP/glucose.
Fermentation
- Fermentation is a catabolic strategy employed by some prokaryotes and eukaryotes in the absence of oxygen.
- Fermentation can be categorized into two main pathways: alcohol fermentation and acid fermentation.
- Both pathways start with glycolysis, yielding 2 pyruvate, 2 NADH, and 2 ATP.
- Pyruvate is then further broken down into an acid or an alcohol.
- CO2 release can occur during fermentation but no additional ATP is produced beyond the initial 2 from glycolysis.
- The most important aspect of fermentation is the oxidation of NADH back to NAD+, preventing the halt of glycolysis.
- Various forms of fermentation exist, producing a mixture of acids and/or alcohols.
- Fermentation products have practical applications in food production, for example:
- Yeast fermentation for alcohol production in beer, wine, and spirits.
- Yeast fermentation for bread rising.
- Lactobacillus fermentation of milk for lactic acid production, leading to yogurt and cheese production.
- Propionibacterium fermentation for propionic acid production, resulting in the mild acid taste and holes in Swiss cheese.
- Gluconobacter and Acetobacterium fermentation for acetic acid production, a key step in vinegar making.
Oxygen Requirements for Fermentation
- Organisms capable of fermentation can also perform aerobic respiration.
- Aerobic respiration is preferred due to its higher ATP yield (38 ATP/glucose) compared to fermentation (2 ATP/glucose).
- Fermentation is only utilized when oxygen is unavailable for aerobic respiration.
- Some bacteria, such as E. coli, can utilize all three catabolic strategies: aerobic respiration, anaerobic respiration, and fermentation.
- E. coli prioritizes aerobic respiration when oxygen is present, followed by anaerobic respiration if suitable salts are available, and finally fermentation if neither oxygen nor salts are present.
Identification of Fermentation Capability
- Carbohydrate fermentation media, such as phenol red broth, is used to determine if an organism can ferment a specific sugar.
- Phenol red broth contains the sugar being tested and a pH indicator that turns yellow in acidic conditions.
- If fermentation occurs, the media turns yellow due to the released acid.
- A gas bubble in the inverted tube indicates gas production during fermentation.
- Possible results include:
- Yellow with a gas bubble: fermentation with gas production.
- Yellow without a gas bubble: fermentation without gas production.
- Red: no fermentation.
Comparison of Catabolic Strategies
- There are three main ways to generate ATP: aerobic respiration, anaerobic respiration, and fermentation.
- Aerobic respiration uses oxygen as the final electron acceptor in the electron transport chain, producing the highest ATP yield.
- Anaerobic respiration utilizes inorganic salts as the final electron acceptor, resulting in a lower ATP yield than aerobic respiration.
- Fermentation does not involve an electron transport chain but rather re-oxidizes NADH to NAD+ through the breakdown of pyruvate, yielding only 2 ATP per glucose.
Oxygen Requirements and Growth
- Organisms can be classified based on their oxygen requirements:
- Aerobes: require oxygen for growth.
- Anaerobes: cannot tolerate oxygen and may even be harmed by it.
- Facultative anaerobes: can grow with or without oxygen, preferring oxygen when available.
- Fluid thioglycolate is a reducing medium that absorbs or slows oxygen penetration, creating an oxygen gradient within the media.
- Growth patterns in fluid thioglycolate media indicate oxygen requirements:
- Aerobes grow at the top, where oxygen is present.
- Anaerobes grow at the bottom, where oxygen is absent.
- Facultative anaerobes grow throughout the media.
Anaerobic Respiration
- Only occurs in some prokaryotes, not eukaryotes.
- Starts with glycolysis and the TCA cycle, same as aerobic respiration.
- Uses inorganic salts as the final electron acceptor in the electron transport system, instead of oxygen.
- Examples of salts used: sulfate, nitrate, nitrite, and fumarate.
- ATP yield varies based on the salt used, but always lower than aerobic respiration.
- Typical ATP yield for anaerobic respiration: 10-24 ATP/glucose.
Fermentation
- Occurs in some prokaryotes and eukaryotes when oxygen is unavailable.
- Divided into two categories: alcohol fermentation and acid fermentation.
- Begins with glycolysis, producing 2 pyruvate, 2 NADH, and 2 ATP.
- Pyruvate is then broken down into an acid or alcohol through a fermentation pathway.
- No additional ATP is produced beyond the initial 2 from glycolysis.
- Key function: oxidizes NADH back to NAD+, essential for glycolysis to continue.
Fermentation Examples
- Yeast fermentation produces alcohol, used in beer, wine, and spirits.
- Yeast fermentation also causes bread to rise.
- Lactobacillus fermentation of milk produces lactic acid, important for yogurt and cheese making.
- Propionibacterium fermentation releases propionic acid, responsible for the mild acid taste of Swiss cheese and the formation of holes due to released carbon dioxide.
- Gluconobacter and Acetobacterium fermentation produces acetic acid, the first step in vinegar production.
Comparing Catabolic Strategies
- Three main ways organisms produce ATP: aerobic respiration, anaerobic respiration, and fermentation.
- Aerobic respiration generates the most ATP (38 ATP/glucose) and is preferred when oxygen is available.
- Anaerobic respiration generates less ATP than aerobic respiration (10-24 ATP/glucose) and occurs when oxygen is unavailable and a suitable inorganic salt is present.
- Fermentation generates the least ATP (2 ATP/glucose) and is used when oxygen is unavailable and no suitable salts are present.
Identifying Fermentation in Lab
- Phenol red broth is a media used to test for fermentation of a specific sugar.
- It contains the sugar being tested (glucose, sucrose, lactose, etc.) and a pH indicator that changes color based on acidity.
- Red broth indicates neutral pH, yellow broth indicates acidic pH.
- An inverted tube collects gas bubbles if gas is produced during fermentation.
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Possible results:
- Yellow with gas bubble: Sugar fermented and gas produced.
- Yellow without gas bubble: Sugar fermented without gas production.
- Red: Sugar not fermented.
Oxygen Requirements
- Fluid thioglycolate is a reducing media used to determine oxygen requirements of an organism.
- It absorbs or slows the penetration of oxygen, creating an oxygen gradient – oxygen at the top, no oxygen at the bottom.
- Possible growth patterns:
- Aerobes: Grow only at the top (oxygen present).
- Anaerobes: Grow only at the bottom (no oxygen present).
- Facultative anaerobes: Grow both at the top and the bottom (can use oxygen but can also survive without oxygen).
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Description
Explore the fascinating processes of anaerobic respiration and fermentation, focusing on their mechanisms, pathways, and ATP yield. This quiz delves into the biological significance of these processes, particularly in prokaryotes and eukaryotes. Test your knowledge on the differences between anaerobic and aerobic respiration, as well as the types of fermentation.
