Cellular Respiration & Lactic Acid Fermentation



Lactic Acid Fermentation

Cellular Respiration:

Cellular respiration takes place in the mitochondria of every cell that is found in a living organism. Cellular respiration converts sugars into usable energy for the cell. This energy is called ATP. In order for cellular respiration to happen, oxygen must be present. Because this process uses oxygen, cellular respiration is a type of aerobic respiration. Humans obtain oxygen by breathing in. This oxygen is then incorporated into the blood and transported through the cell membrane so that it can be used by the mitochondria.

Lactic Acid Fermentation:

When oxygen is not present or present in very low quantities, mitochondria produce energy through a process called lactic acid fermentation. Lactic acid fermentation still uses sugars to make ATP like in cellular respiration, but oxygen is not needed for the reaction. Because this process does not use oxygen, lactic acid fermentation is a type of anaerobic respiration. ATP isn’t the only product of lactic acid fermentation. As you might imagine, a molecule called lactic acid (lactate) is also produced! Check out the reaction below.

Exercise:

Lactic acid fermentation can be used to make foods such as yogurt, pickles, sauerkraut, etc. Lactic acid fermentation also takes place in human muscle cells during intense exercise. During strenuous physical activities such as sprinting, oxygen that is taken in by breathing is quickly used up by the mitochondria in the muscle cells. When there is no longer enough oxygen, mitochondria switch to lactic acid fermentation instead. While lactic acid fermentation is still able to produce ATP like cellular respiration, it does not produce nearly as much. Unfortunately, lactic acid fermentation also produces lactic acid which can cause muscles to cramp. When lactic acid builds up in the body during intense exercise, the blood often becomes too acidic. Normally, blood should be at a pH of around 7.35. However, when a large amount of lactic acid fermentation takes place, the blood pH decreases (becomes more acidic). This condition is called acidosis and it can result in hyperventilation (increased respiration rate).

Case Study – Herman

Herman is a 21-year-old male who is on the men’s swim team at California State University, San Marcos. After swimming in a 400 meter freestyle race, Herman decided to do a butterfly workout. At first, Herman was feeling okay, and then his muscles cramped and he began to hyperventilate. His coaches pulled him out of the water and quickly drove him to the hospital. In order to diagnose Herman, the doctors ran a series of tests. This evidence is listed below.

Evidence #1:

The doctors first took a sample of Herman’s blood and tested how much lactic acid was present in the sample. This test is usually a good indicator of how much lactic acid has built up in the muscle cells. Herman’s blood had a lactic acid level of 9 mmol/L. Check the chart below to see if Herman’s lactic acid level indicates that he is suffering from acidosis.

|Lactic Acid Level (mmol/L): |Symptoms of Acidosis: |

|> 10 |Severe |

|5-10 |Moderate |

|2-5 |Mild |

|< 2 |Not Present |

Evidence #2:

Herman’s respiration (breathing) rate was also measured when he first arrived at the hospital. The doctors determined that Herman was taking an average of 40 breaths per minute. Take a look at the chart below to determine if this respiration rate is normal for Herman’s age.

Evidence #3:

Herman’s doctors also took a second sample of his blood and tested its pH. They found that Herman’s blood pH was at 7.15. Take a look at the blood pH scale below to determine if Herman’s blood pH is within the normal range.

***Note: The tests mentioned above are NOT how doctors typically make a diagnosis.

Brainstorming

Directions: Using all of the evidence and information given to you on the first two pages of this assignment, work with a partner to answer the questions below.  

1. Compare cellular respiration and lactic acid fermentation. How are these two processes similar and different? When does the body use each process?

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2. During intense exercise, the mitochondria start to use lactic acid fermentation instead of cellular respiration. Why does this switch happen? Why is it dangerous for too much lactic acid fermentation to take place?

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3. What condition is Herman suffering from? _____________________________________

a. Explain how you know this using evidence from the lactic acid level chart on page #2.

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b. Explain how you know this using evidence from the respiration rate chart on page #2.

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c. Explain how you know this using the blood pH scale on page #2.

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4. Explain why Herman’s intense swim workout caused his condition.

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Essay Response

Directions: On a separate sheet of paper, write your own response to the following prompt.

Compare and contrast cellular respiration and lactic acid fermentation. Describe why the body switches to lactic acid fermentation during intense exercise. Then, create a hypothesis that predicts which condition Herman is suffering from. Use all three pieces of evidence from page 2 and the reading from the first page to support and explain your decision. Use the rubric on page 4 to help guide you as you write your essay. The easiest way to receive full points is to include all of the components that you and your partner brainstormed about (1-3) in your response. Your essay should be 10-12 sentences in length.

Rubric:

Directions: This rubric will be used to evaluate your essay response. Please attach this sheet to your paper when you turn it in.

| |Advanced |Partially Proficient |Not Proficient |

| |(5) |(3) |(1) |

|Comparing Cell |You have thoroughly and |Your response is not accurate |Your response is |

|Respiration and |accurately compared cell |or thorough enough to include |neither thorough nor |

|Lactic Acid |respiration and lactic acid |all requirements. |accurate. |

|Fermentation |fermentation and described why | | |

| |the body switches to | | |

| |fermentation during intense | | |

| |exercise. | | |

|Hypothesis and |You have correctly identified |You have correctly identified |Your hypothesis is not |

|Evidence |Herman’s condition and have |Herman’s condition, but have |correct or you have |

| |directly connected all three |only connected two pieces of |included little to no |

| |pieces of evidence to your |evidence to your hypothesis or |evidence. |

| |hypothesis. |the connections are unclear. | |

Total = _____/10

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