Explain why when the hands are placed in fresh water, the fingertips become wrinkled after sometime but these do not happen when the hands are placed in salt water.
In freshwater, the concentrations of the two fluids i.e. the fluid in the cells and the water are different. This results in water moving into the epidermal cells of the skin by osmosis. As the epidermal cells become stretched, the surface area of this layer increases. However, the inner layer of cells does not absorb any water. Hence the horny layer appears wrinkled. In saltwater, the concentration of the saltwater and that of the fluid in the cells are somewhat similar. Hence osmosis does not take place. Therefore, there is no stretching of the epidermis and the skin does not appear wrinkled.