Question

Part Three: Acid/Base Homeostasis in the Human Body

Beginning Questions:

1. Carbon dioxide is formed during cellular respiration and then diffuses out of cells into the interstitial fluid and then into the bloodstream. Most of the carbon dioxide is transported in our blood as bicarbonate. Write the chemical equation for the formation of bicarbonate and hydrogen ions from carbon dioxide and water below.

2. Under which of the following situations would the formation of bicarbonate and hydrogen ions be greater? Circle your answer.

At Rest After Exercise

Change in pH after exercise.

Calculate the percentage change in pH for both procedures and record your values in the table below

• % change in pH = ((control pH – experimental pH)/control pH) * 100

Condition:	Breaths/Min	Control pH	Experimental pH	% pH Change	Class Avg of % pH Change
At Rest	13	6.8	6.2	8.8%	9.2%
After Exercise	34	7.1	5.8	18.3%	15.6%

Questions:

1. Explain how blowing air into water caused the change in pH.

2. Describe why exercise caused the observed change in pH.

Answer 1

Q. Write the chemical equation for the formation of bicarbonate and hydrogen ions from carbon dioxide and water below.

This is the equation that shows the formation of bicarbonate and hydrogen ions from water and carbon dioxide. This is a reversible reaction. It is catalyzed by the enzyme Carbonic anhydrase. This equation also forms the basis of the bicarbonate buffer system that tightly regulates the pH of the blood. Carbonic anhydrase, enzyme found in red blood cells, gastric mucosa, pancreatic cells, and renal tubules.

Q. Under which of the following situations would the formation of bicarbonate and hydrogen ions be greater?

At Rest After Exercise

Change in pH after exercise.

Explanation: The change in pH after exercise is greater. This is because a large amount of carbon dioxide is generated. This increases the number of H+ ions. Thus causing a change in pH. Also, the actively contracting muscle may use anaerobic glycolysis leading to the production of lactic acid. This lactic acid may further reduce the pH.

Q. Explain how blowing air into water caused the change in pH.

The expired air has a higher concentration of carbon dioxide. When one blows air into the water, the expired carbon dioxide forms bicarbonate and hydrogen ions according to the equation shown above. This is the cause of the change in pH when air is blown into the water.

Q. Describe why exercise caused the observed change in pH.

This is because a large amount of carbon dioxide is generated. This increases the number of H+ ions. Also, the actively contracting muscles may generate ATP using anaerobic glycolysis leading to the production of lactic acid. This lactic acid may further reduce the pH. This is the reason why the change in pH was observed after exercise.