10. Anerobic Respiration

Fermentation

10. Anerobic Respiration

Fermentation: Videos & Practice Problems

Topic summary

Fermentation is a crucial process in anaerobic respiration, breaking down sugar to produce ATP without oxygen. It involves glycolysis, which generates NADH and pyruvate, and fermentation, which regenerates NAD⁺ to sustain glycolysis. There are two main types: alcoholic fermentation, producing ethanol and CO₂, primarily in yeast, and lactic acid fermentation, producing lactate, used by muscles during intense activity. While anaerobic respiration yields only about 4 ATP, aerobic respiration can produce 32-34 ATP, highlighting the inefficiency of anaerobic pathways.

concept

Fermentation

Video duration:

Fermentation Video Summary

Fermentation is a crucial process in anaerobic respiration, which occurs in the absence of oxygen. It involves the breakdown of sugar to produce adenosine triphosphate (ATP), the energy currency of cells. The process begins with glycolysis, which does not require oxygen and occurs in both aerobic and anaerobic organisms. During glycolysis, glucose is converted into two molecules of pyruvate, generating a net gain of two ATP and two molecules of nicotinamide adenine dinucleotide (NADH), an important electron carrier.

In anaerobic conditions, NADH cannot be oxidized back to NAD⁺ through the electron transport chain, as it would in aerobic respiration. This is where fermentation plays a vital role. It regenerates NAD⁺ by transferring electrons from NADH to pyruvate, allowing glycolysis to continue and produce ATP. There are two primary types of fermentation: alcohol fermentation and lactic acid fermentation.

Alcohol fermentation occurs in yeast and some bacteria. In this process, pyruvate is converted into acetaldehyde, which is then reduced to ethanol, releasing carbon dioxide (CO₂) in the process. This pathway is essential for producing alcoholic beverages and for baking, as the CO₂ helps bread rise.

Lactic acid fermentation, on the other hand, occurs in muscle cells during intense exercise when oxygen is scarce. Here, pyruvate is directly converted into lactic acid, regenerating NAD⁺ in the process. This type of fermentation is also utilized in the production of dairy products like cheese and yogurt.

While fermentation allows organisms to generate ATP without oxygen, it is significantly less efficient than aerobic respiration, which can produce approximately 32 to 34 ATP molecules per glucose molecule. In contrast, fermentation yields only about 4 ATP. The byproducts of fermentation, such as ethanol and lactic acid, can accumulate and may lead to muscle soreness or other metabolic limitations. Therefore, while fermentation is a vital survival mechanism for organisms in anaerobic environments, aerobic respiration is generally preferred for its higher energy yield.

Problem

Which of the following is not associated with fermentation?

It occurs in the absence of oxygen

It results in a variety of byproducts

It regenerates NAD+

It uses ATP

Problem

The purpose of fermentation is to produce what?

ATP

NADH

NAD+

H₂O

Problem

True or False:The creation of pyruvate in the absence of oxygen is more energetically favorable than the creation of pyruvate in the presence of oxygen.

True

False

Do you want more practice?

We have more practice problems on Fermentation

Here’s what students ask on this topic:

What is fermentation in cellular respiration?

Fermentation is a metabolic process that breaks down sugar to produce ATP in the absence of oxygen. It is a key step in anaerobic respiration, which occurs when oxygen is not available. The process involves glycolysis, which generates NADH and pyruvate. Fermentation then regenerates NAD⁺ from NADH, allowing glycolysis to continue producing ATP. There are two main types of fermentation: alcoholic fermentation, which produces ethanol and CO₂, and lactic acid fermentation, which produces lactate. While anaerobic respiration yields only about 4 ATP, aerobic respiration can produce 32-34 ATP, making anaerobic pathways less efficient.

What are the main types of fermentation?

The two main types of fermentation are alcoholic fermentation and lactic acid fermentation. Alcoholic fermentation occurs primarily in yeast and some bacteria, producing ethanol and CO₂. This process is used in brewing beer and making bread rise. Lactic acid fermentation occurs in muscle cells during intense activity when oxygen is scarce, producing lactate. This type of fermentation is also used in the production of dairy products like cheese and yogurt. Both types of fermentation regenerate NAD⁺ from NADH, allowing glycolysis to continue in the absence of oxygen.

How does fermentation regenerate NAD⁺?

Fermentation regenerates NAD⁺ by transferring electrons from NADH to pyruvate, the end product of glycolysis. In alcoholic fermentation, pyruvate is first converted to acetaldehyde, which then accepts electrons from NADH to form ethanol and CO₂. In lactic acid fermentation, pyruvate directly accepts electrons from NADH to form lactate. This regeneration of NAD⁺ is crucial because it allows glycolysis to continue producing ATP in the absence of oxygen.

Why is anaerobic respiration less efficient than aerobic respiration?

Anaerobic respiration is less efficient than aerobic respiration because it produces significantly less ATP. Anaerobic pathways, including glycolysis and fermentation, yield only about 4 ATP per glucose molecule. In contrast, aerobic respiration, which includes glycolysis, the citric acid cycle, and the electron transport chain, can produce 32-34 ATP per glucose molecule. Additionally, anaerobic respiration results in byproducts like ethanol and lactic acid, which are not further utilized for energy production, making the process less efficient overall.

What role does glycolysis play in fermentation?

Glycolysis is the initial step in both aerobic and anaerobic respiration, including fermentation. It breaks down one glucose molecule into two pyruvate molecules, producing a net gain of 2 ATP and 2 NADH. In the absence of oxygen, fermentation follows glycolysis to regenerate NAD⁺ from NADH, allowing glycolysis to continue. Without this regeneration, glycolysis would halt, and ATP production would stop. Thus, glycolysis is essential for providing the substrates and initial energy yield that fermentation processes rely on.