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Multiple Choice
Which change in blood chemistry causes an increase in respiration rate?
A
An increase in blood pH
B
A decrease in blood $\mathrm{CO_2}$ concentration
C
A decrease in blood $\mathrm{O_2}$ concentration
D
An increase in blood $\mathrm{CO_2}$ concentration
Verified step by step guidance
1
Understand the relationship between blood chemistry and respiration rate: Respiration rate is regulated by the body's need to maintain homeostasis, particularly in response to changes in blood levels of oxygen ($\mathrm{O_2}$), carbon dioxide ($\mathrm{CO_2}$), and pH.
Recognize the role of carbon dioxide ($\mathrm{CO_2}$): When $\mathrm{CO_2}$ levels in the blood increase, it reacts with water ($\mathrm{H_2O}$) to form carbonic acid ($\mathrm{H_2CO_3}$), which dissociates into hydrogen ions ($\mathrm{H^+}$) and bicarbonate ions ($\mathrm{HCO_3^-}$). This process lowers blood pH, making it more acidic.
Understand the body's response to increased $\mathrm{CO_2}$: Chemoreceptors in the brainstem (specifically in the medulla oblongata) and in peripheral areas like the carotid and aortic bodies detect the increase in $\mathrm{CO_2}$ and the associated drop in pH. These chemoreceptors signal the respiratory center to increase the rate and depth of breathing.
Compare the effects of other changes: An increase in blood pH (alkalosis) or a decrease in $\mathrm{CO_2}$ concentration would typically decrease respiration rate, as the body perceives less need to expel $\mathrm{CO_2}$. A decrease in $\mathrm{O_2}$ concentration can also increase respiration rate, but this effect is less sensitive compared to $\mathrm{CO_2}$ levels.
Conclude that the correct answer is an increase in blood $\mathrm{CO_2}$ concentration, as it directly triggers an increase in respiration rate to expel excess $\mathrm{CO_2}$ and restore pH balance.