Biochemistry : pH Regulation

Study concepts, example questions & explanations for Biochemistry

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Example Questions

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Example Question #11 : Homeostasis And The Biological Environment

A nervous student begins hyperventilating before a test. What immediate effects does hyperventilation have on  and blood pH?

Possible Answers:

 decreases and blood pH decreases

 increases and blood pH increases

 increases and blood pH decreases

 increases, and blood pH remains constant

 decreases and blood pH increases

Correct answer:

 decreases and blood pH increases

Explanation:

Hyperventilation involves expelling carbon dioxide from the body, so the amount of  in the blood would decrease. Since carbon dioxide is directly associated with acid and  ion production, pH would increase upon elimination of .

Example Question #1 : P H Regulation

Which of the following conditions would a person who has diabetic ketoacidosis be likely to experience?

Possible Answers:

High levels of intracellular glucose

Reduced glucagon output by the liver

Reduced breakdown of fat in the body

Decreased rate of gluconeogenesis in the liver

Decreased blood pH

Correct answer:

Decreased blood pH

Explanation:

Diabetic ketoacidosis is a condition that can occur in people who have diabetes. In this situation, there is a deficiency in insulin production. Consequently, the glucose that is present in the blood has no way of entering cells. These cells, in turn, become starved for energy, causing the body to burn fat and produce acidic ketone bodies as an alternative energy source. The energy deficit that cells experience as a result of not having access to glucose causes significant production of these acidic ketone bodies. In fact, so many of these ketone bodies are produced that it overwhelms the body's normal pH buffering capacity, and thus the blood can become dangerously acidic. High levels of intracellular glucose is incorrect because the lack of insulin causes glucose to be unable to enter these cells. Gluconeogenesis in the liver is also increased because the energy starved cells alert the body that they need energy. The body is "tricked" into "thinking" that the cells aren't getting energy due to a shortage of glucose, even though plenty of glucose is actually available. Thus, gluconeogenesis exacerbates the high blood glucose levels. Fat breakdown in the body is also increased. It is this breakdown of fat that provides the ketone bodies as an alternative fuel source for the body. Glucagon output is also increased because, as explained above, the body "thinks" it is energy starved due to there not being enough glucose even though there is plenty. This hormone increases gluconeogenesis and fat breakdown, as described above.

Example Question #2 : P H Regulation

Given that the pKa of pyruvic acid is 2.50, what is the ratio of pyruvic acid to sodium pyruvate in a pyruvic acid solution with pH 3.5?

Possible Answers:

Correct answer:

Explanation:

Thus the ratio of  is equal to , or the ratio of  is equal to 

Example Question #3 : P H Regulation

Listed below are the pKa values of five common biochemical buffers.

Formic acid: 3.75

Acetic acid: 4.76

2-(N-Morpholino)ethanesulfonic acid (MES): 6.09

Tris(hydroxymethyl)aminomethane (Tris): 8.08

Glycine: 9.78

Which of the following would have the best buffering capacity in a solution with pH 4.0?

Possible Answers:

Tris

Glycine

MES

Acetic acid

Formic acid

Correct answer:

Formic acid

Explanation:

The best buffering capacity occurs when pH = pKa. When this is true, the ratio of ionized to unionized form of the buffer is 1:1. Thus the solution can best resist changes in pH, as hydrogen ions can be quenched or donated to solution to resist change. Acetic acid would have almost the same buffering capacity since its pKa is almost as close to 4.0 as that of formic acid.

Example Question #4 : P H Regulation

Upon running lab tests, you determine that a patient has very low blood pH. Which of the following could have caused this low pH?

Possible Answers:

Hypoventilation

Hyperventilation

Increased iron in blood

Increased red blood cells

Correct answer:

Hypoventilation

Explanation:

Low blood pH suggests that the patient has high concentration of hydrogen ions. To solve this question, we need to look at the following reaction, which represents the major blood buffer system:

One way the body controls the amount of hydrogen ions in the blood is by altering the amount of carbon dioxide. Recall that, according to Le Chatelier’s principle, increasing carbon dioxide will push the reaction the right and increase hydrogen ion concentration whereas decreasing carbon dioxide will decrease hydrogen ion concentration.

Body controls carbon dioxide levels via breathing. Hyperventilation refers to increased breathing whereas hypoventilation refers to decreased breathing. During hyperventilation the person breathes out excess carbon dioxide (decreasing the hydrogen ion concentration). During hypoventilation, on the other hand, a person breathes slowly and retains carbon dioxide (increasing the hydrogen ion concentration). The patient in this question has low blood pH (high hydrogen ion concentration); therefore, of the options, the patient must be hypoventilating.

Example Question #5 : P H Regulation

What buffer system is most important for maintaining blood pH?

Possible Answers:

Bicarbonate/carbonic acid

Phosphate ions/phosphoric acid

Chloride ions/hydrochloric acid

Acetate/acetic acid

Correct answer:

Bicarbonate/carbonic acid

Explanation:

A buffer system occurs when equal amounts of a weak acid and its conjugate base (or vice versa) is added together. Maintaining blood pH is a very important aspect in maintaining homeostasis. The body does this utilizing the carbonic acid/bicarbonate buffer system. The concentrations of the base and acid are altered accordingly to maintain a constant blood pH.

Hydrochloric acid is found in the stomach to maintain an acidic pH, phosphoric acid does play a role in buffering the blood, but is not the major buffer. Acetic acid is found in vinegar and does not play a major role in regulating blood pH.

Example Question #6 : P H Regulation

Which of the following molecule(s) will increase in response to high blood pH?

Possible Answers:

None of these

Bicarbonate ions only

Carbon dioxide only

Carbon dioxide and bicarbonate ions

Correct answer:

None of these

Explanation:

Blood pH is maintained via the lungs and the kidneys. Lungs alter the amount of carbon dioxide expelled to maintain blood pH. Consider the reaction below.

Carbon dioxide is decreased when pH is low (high hydrogen ion concentration). Decreasing carbon dioxide will shift the reaction to the left and decrease the hydrogen ion concentration. Similarly, the body compensates for high blood pH by increasing carbon dioxide.

Kidneys alter blood pH by increasing or decreasing the excretion of bicarbonate ions. Using the reaction above, we can determine that increasing bicarbonate ion in blood will decrease hydrogen ion concentration whereas decreasing bicarbonate ion will increase hydrogen ion concentration. To combat high blood pH (low hydrogen ion concentration), the bicarbonate ion needs to increased in the blood. The kidneys do this by decreasing the excretion of the bicarbonate ions.

Example Question #7 : P H Regulation

What is the pH of a solution of ?

Possible Answers:

Correct answer:

Explanation:

pH is calculated via the following equation:

refers to the concentration of hydrogen ions in the solution, which in this case is the same as the concentration of the acid since hydrochloric acid is a strong acid and will fully dissociate in solution. Thus, we have:

Example Question #8 : P H Regulation

What is buffering capacity?

Possible Answers:

The extent to which a buffer can counteract the effect of added acid or base

The effectiveness of commercial antacids

The amount of buffer present in a solution

The molecular weight of the substance used as a buffer

The pH of a buffer solution

Correct answer:

The extent to which a buffer can counteract the effect of added acid or base

Explanation:

Buffering capacity refers to how well a buffer works. A buffer is a substance that maintains a specific pH regardless of added acid or base. Thus, buffering capacity refers to how well a buffer maintains the pH of a solution despite the the effects of added acid or base. The other choices do not apply to this definition.

Example Question #9 : P H Regulation

What is the pOH of a 0.5 M  solution?

Possible Answers:

Correct answer:

Explanation:

Recall the equation for pH. Here is the calculation that should be performed:

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