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

Salinity & Osmosis

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

Seawater

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)

Salinity

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

When water freezes

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

Salinity’s effect on marine organisms

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

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: O2 & CO2), 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

Osmosis

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