Which of the following molecules would decrease the electrochemical gradient across a membrane?

• A. Calcium ion (Ca2+)
• B. Proton (H+)
• C. Potassium ion (K+)
• D. Sodium chloride (NaCl)

Answer: (B)

Verified step by step guidance

1. Understand the concept of an electrochemical gradient: It is the combined effect of an ion's concentration gradient and the electrical potential across a membrane.
2. Identify the ions involved: Calcium ion (Ca²⁺), Proton (H⁺), Potassium ion (K⁺), and Sodium chloride (NaCl).
3. Consider the charge of each ion: Ca²⁺ has a +2 charge, H⁺ has a +1 charge, K⁺ has a +1 charge, and NaCl dissociates into Na⁺ and Cl^-.
4. Analyze how each ion affects the membrane potential: Protons (H⁺) are directly involved in creating and maintaining the electrochemical gradient, especially in processes like ATP synthesis in mitochondria.
5. Conclude that the movement of protons (H⁺) across the membrane is crucial for decreasing the electrochemical gradient, as they are directly involved in processes that utilize this gradient.