Osmosis and Diffusion

We know that the human body is comprised of 70-80% water.

But, how does it move in and out of our cells? Is it pushed … pulled …does it flow freely through holes?  What happens when other substances like salt or calcium are present? 

  Diffusion Movement of dissolved molecules in a fluid or a gas from an area of higher concentration to an area of lower concentration.

What is a “Concentration Gradient?”

Molecules are like passengers on a bus.

They spread from areas of higher concentration to areas of lower concentration.

Diffusion

osmosis Diffusion of water molecules across a semipermeable membrane from an area of higher water concentration to an area of lower water concentration.

Different Types of Solutions

isotonic A solution that has the same concentration of dissolved particles as a cell.

“iso” means the same. If the concentration of solute is equal on both sides of a cell membrane, water will move back and forth but it won’t have any result on the overall amount of water on either side.

  hypertonic A solution that has a higher concentration of dissolved particles than a cell.  

“HYPER” The word "HYPER" means more. For example, more solute (salt) molecules outside the cell, causes water to be sucked in that direction.

In plant cells, the central vacuole loses water and the cells shrink, causing wilting. In animal cells, the cells also shrink. In both cases, the cell may die.

Snails and Salt

What happens when you pour salt on a snail? This is because the salt sucks out the water from the snails cells. The salt is hypertonic.

The Rhyme of the Ancient Mariner

Samuel Taylor Coleridge The Rhyme of the Ancient Mariner was a poem written in 1798 by an English poet named Samuel Taylor Coleridge. The poem is about a mariner (someone who guides a boat). The mariner and the ship’s crew is lost at sea.

Water, water everywhere but not a drop to drink. What do you think this most famous line from the poem is about?

Hypertonic! Remember salt water would be a hypertonic solution to your cells. This would suck all the water OUT of your cells.

This is why it is dangerous to drink sea water They used to say it would drive you insane It’s a myth that it will drive you insane, but people marooned at sea will speed up dehydration (and death) by drinking sea water.

Scorched Earth Policy This is also why "salting fields" was a common tactic during war. In ancient times, conquerors would scorch and salt fields to kill crops. This caused food shortages for the conquered people. Romans used this tactic. The Germans used it against Russia in WWII.

HYPERTONIC! Salting the fields made the soil HYPERTONIC to crops and kept new fields from growing.

hypotonic A solution that has lower concentration of dissolved particles as a cell.

Hypotonic The word "HYPO" means less, in this case there are less solute (salt) molecules outside the cell, since salt sucks the water, water will move into the cell. The cell will gain water and grow larger. In plant cells, the central vacuoles will fill and the plant becomes stiff and rigid, the cell wall keeps the plant from bursting.

Osmosis allowed water to flow into our eggs.