Which of the following has an effect on the pH of blood?

• A. Red blood cell count
• B. Carbon dioxide levels
• C. Blood pressure
• D. Heart rate

Answer: (B)

Verified step by step guidance

1. Understand that pH is a measure of the hydrogen ion concentration in a solution, with lower pH values indicating higher acidity.
2. Recognize that carbon dioxide (CO2) in the blood can combine with water to form carbonic acid (H2CO3), which dissociates into hydrogen ions (H+) and bicarbonate ions (HCO3-). This reaction can be represented as: ${\mathrm{CO}}_2+H_2{O}_2\leftrightarrow H_2{\mathrm{CO}}_3\leftrightarrow H_{+}+{\mathrm{HCO}}_3-$
3. Realize that an increase in carbon dioxide levels in the blood will lead to an increase in hydrogen ion concentration, thus lowering the pH and making the blood more acidic.
4. Consider that red blood cell count, blood pressure, and heart rate do not directly affect the pH of the blood in the same way that carbon dioxide levels do.
5. Conclude that among the given options, carbon dioxide levels have a direct effect on the pH of blood due to their role in the formation of carbonic acid and subsequent release of hydrogen ions.