Final answer:
The cell membrane voltage and which side is positive is determined by the functioning of ion pumps like the sodium-potassium pump, which create an electrochemical gradient across the cell membrane. The proton pump mentioned would contribute to this but in a different way, specifically affecting protons. However, we would need additional information to calculate the exact membrane voltage in this scenario.
Step-by-step explanation:
The student's question involves determining the cell membrane voltage and identifying which side of the membrane is positive, given the inside pH of 7.8 and the outside pH of 7.2. To understand this, we look at the role of pumps like the sodium-potassium pump (Na+-K+ ATPase), which are crucial in maintaining the electrochemical gradient across the cell membrane by actively transporting ions against their concentration gradients. Specifically, this pump moves three Na+ ions out of the cell for every two K+ ions it moves in, which creates a net positive charge outside the cell and a net negative charge inside the cell, contributing to the membrane potential.
The voltage across a cell membrane, also known as the membrane potential, is the electrical potential energy caused by a separation of charges with more positive ions outside than inside the cell. This creates a voltage that is crucial for functions like the conduction of electrical impulses along nerve cells. However, the question relates to a proton pump, which specifically moves protons (H+ ions) across a membrane and thus can affect the pH and charge distribution differently than the Na+-K+ ATPase would.