Chapter 25, Problem 1BS.1QC

Summary Introduction

To determine:

The variables which will restrict the movement of water across the plasma membrane.

Introduction:

Water is transported across the plasma membrane through osmosis and pressure potential generated. Osmosis is the process by which water is diffused from higher concentration to lower across the cell membrane without any expenditure of energy. Pressure potential is the effect of pressure on water.

Explanation of Solution

The chemical energy possessed by water is water potential. Water has a tendency to move from higher water potential to lower water potential. Water pressure and solute concentration are two main factors that influence the water potential which in return affect the movement of water across plasma membrane:

1.

If the pressure exerted by water increases inside the cell, it will result in the turgid cell. At this point, the water potential inside and outside of the cell is equal. If the water pressure inside the cell is less it will become plasmolyzed and the water would be required by the plant. This is explained by the variable called pressure potential. If the water pressure is high, the water potential will be high.

2.

Solute concentration inside and outside the membrane also affect the movement of water. The semipermeable membrane allows the movement of selected solutes to enter the cell by osmotic potential which changes as the solute concentration change. The presence of solute prevents the movement of water as water is linked to solute by molecular bonds. Water moves from the lower solute concentration to the higher solute concentration.

Conclusion

Water potential and osmotic potential will restrict the movement of water across the plasma membrane.