Question

If a swimmer cuts her foot on a seashell while wading in the ocean and bleeds into the seawater, her red blood cells will shrink. what does this tell us about the relative tonicity of seawater. (is it hypotonic, hypertonic, isotonic to the the red blood cells?) explain what causes her red blood cells to shrink.

Answer 1

The red blood cells shrink due to movement if water from the RBCs to the outside in the process known as exosmosis. This indicates that the solution, i.e., seawater is much more concentrated than the intracellular environment of RBCs. Thus, seawater is hypertonic to red blood cells. The plasma membrane of red blood cells is a semi-permeable membrane which allows only the movement of water and restricts the solute movement. When RBCs are placed in a hypertonic environment such as seawater, water moves out of the cell through a process known as osmosis, causing the cells to shrink. In contrast, if the red blood cells were placed in fresh water, the cells would have swelled because of movement of water into the cell, since fresh water is hypotonic to RBCs.