Pre-Lab Questions: 1. Which ion is more concentrated on the outside of the cell?

Question

Pre-Lab Questions: 1. Which ion is more concentrated on the outside of the cell? Which ion is more concentrated inside? 2. If Na could suddenly move freely in either direction through the membrane, which direction would it go? Explain your reasoning (Hint: There are 2 reasons.) 3. If Na did move as you describe above, what effect would that have on the potential? 4. If K could suddenly move freely in either direction through the membrane, which direction would it go? Explain your reasoning (Hint: 1 reason.) 5. If K did move as you describe above, what effect would that have on the potential? The resting potential of animal cells is a negative voltage. Considering your answers to the questions above, which ion (sodium or potassium) is the membrane more permeable to at rest? Which type of channel is responsible for this permeability? 6.

Explanation / Answer

1) Ions are not equally distributed between the inside and the outside of a cell. Na+ is nearly 10 times more concentrated outside the cell than inside and K+ is nearly 30 times more concentrated inside the cell than outside.

2) If Na+ could suddenly move freely in either direction through the membrane, the concentration of Na+ is greater outside the cell than inside. Therefore it will flow into the cell.

3) This causes hyperpolarization of the membrane, because of the flow of Na+ into the cell, the internal surroundings becomes more positive.

4) If K+ could suddenly move freely in either direction through the membrane, the concentration of K+ is greater inside the cell. Therefore it will move outside the cell if left freely.

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