Explore BrainMass

Movement of Water Across Semi-Permeable Membranes

1. As a person becomes very dehydrated, the concentration of water in her blood decreases. In which direction will water move across the plasma membranes of her blood cells? What will happen to the volume of the cells as a consequence? Why is proper hydration important for multicellular organisms?

2. Oops! You were cleaning out the aquariums in the biology lab and you accidentally placed the saltwater fish in the freshwater tank. What will happen to the cells of these fish?

3. In some countries, human waste is used as a fertilizer. If produce is grown in this type of fertilizer, it is possible that it will be contaminated with the protozoan that causes amoebic dysentery. One method of removing the protest without ruining the food is to place the produce in a 5% salt solution. Explain how this would kill the protest. If you cleaned your lettuce this way, what would happen to the lettuce cells? How could you return them to normal?

Solution Preview

I. Movement of water across semi-permeable membranes is dependent on osmotic pressure. It the concentration of solute in the liquid is higher on one side compared to the concentration of solutes on the other side, the liquid will move across the membrane from the side with the higher concentration to the side with the lower concentration until the concentrations are equal on both sides. For example:

1. Assume a semi-permeable membrane is surrounded by water on both sides.
2. 1 g of sugar is dissolved in 1 L of water on one side of the membrane (equivalent to 1g/L)
3. 1 g of sugar is also present in half the volume of water on the other side of the membrane (equivalent to 1g/0.5 L or 2g/L)
4. Water will move out of the side with 1g/L to the side with 2g/L until the concentration is equal on both ...

Solution Summary

The solution discusses the movement of water across semi-permeable membranes.