If you were stranded on an island, what would you do to obtain drinking water?

Ms. Springstroh/Marine Biology

 Contains many solutes, or dissolved materials ◦ Can be almost any dissolvable material ◦ Most solutes in sea water are sodium (Na + ) and chloride (Cl - ) ions (charged particles), which, when bonded together, form salts (ex: NaCl) ◦ Most come from hydrothermal vents  Evaporates  leaves behind ions (charged particles, ex. Na + )  ions combine to form salts

 The total amount of salt dissolved in sea water ◦ If 1000 grams of sea water evaporate and 35 grams of salt are left behind, the salinity = 35 ppt (parts per thousand)

 Ions are left behind in the unfrozen water ◦ Increases the salinity of unfrozen water surrounding the ice ◦ Icebergs are not salty  Water is added back to the ocean via precipitation– rain and snow

 HUGE effect on marine organisms! ◦ Most marine organisms would die in fresh water  Even small changes in salinity can greatly affect marine organisms. ◦ Luckily, the ocean’s salinity hardly changes.  Organisms living in areas where salinity fluctuates (river mouths) have evolved to cope with changes in salinity

 Ions (ex. Na + ) and other solute molecules move around just like water ◦ Always want to “spread out”– go from areas of high concentration to low concentration until evenly distributed… this is called diffusion  Substances move into and out of cells via diffusion

 If a fish’s cells contain less sodium than the seawater, sodium will diffuse (move) into the fish’s cells. ◦ Can be a problem if the fish is sensitive to sodium Too much sodium diffuses in = Nemo has a problem

 How can this problem be solved? ◦ With a barrier!!!  What is that barrier? ◦ The cell membrane!  The cell membrane is selectively permeable ◦ Allows some substances (ex: O 2 & CO 2 ), but not all substances (ex: Na +, Cl -, NaCl, proteins) to diffuse across the membrane

 Diffusion of water molecules across a selectively permeable membrane  Water diffuses easily across cell membranes because it has no overall charge, just like the majority of the membrane itself

 IF: ◦ total concentration of solutes (dissolved substances) inside the cell < outside the cell  (This means the concentration of water inside the cell is greater than outside the cell)  THEN: ◦ Water will move out of the cell  RESULT: ◦ The cell may shrivel

 IF: ◦ total concentration of solutes (dissolved substances) inside the cell > outside the cell  (This means the concentration of water inside the cell is less than outside the cell)  THEN: ◦ Water will move into the cell  RESULT: ◦ The cell swell and burst