Question

Look up the Osmotic Pressure in your blood and discuss why sea water will kill you if you drink it. (I know that it is more to do with kidneys than blood… but that is too much biology for this worksheet.)

Answer 1

Cell membranes or the cell walls act as selectively permeable membranes. Cells let water pass freely, but strictly controlling the amount and type of other ions that can pass the membrane. And hence, subjects the cells to the same osmotic pressure we observe in other osmotic systems. This means that cells thrive best in when placed in environments where the solution they are immersed in have the same concentration of solute as the cell interior, i.e. in an Isotonic solution.

If we place a cell in a watery solution which contains more solute, i.e. a Hypertonic solution, (in this case sea water) water will rush out of the cell, causing it to shrink and become dysfunctional, a process called crenation. If we place the cell in water with fewer solutes, i.e. Hypotonic solution, water will rush into the cell, causing it to swell and eventually rupture in haemolysis. These osmotic movements are the reason why drinking sea water causes dehydration or lethal for normal human being.