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Wednesday, November 23, 2011

Osmosis demonstration using eggs

Remember this? Today we are going t need 2 of those, maybe more if you want to go a little further.
Today we are going to play and learn about osmosis.

Before continuing:
Cells have several transport mechanisms, in other words, several different ways to make the molecules to pass from inside to outside and vice versa. On of those mechanisms is called osmosis, and we can say for sure "that's all about concentration".

Osmosis is the movement of solvent molecules through a membrane from a region of  lower solute  concentration, to a region of higher concentration.
In other words, and considering the solvent is water, osmosis is the movement of water molecules from "in" or "out" the cell, aiming to match the concentration on both sides of the membrane.

In general we only can see a cell with a microscope. You don’t need a super microscope like electronic, a optical is enough.

In Nature there is a group of cells witch don't need a microscope to be "seen”, the eggs of species that "lay eggs." Ostrich eggs are the biggest eggs (not extinct specie), humming birds are the smallest, to "make" one ostrich egg we need 24 chicken eggs.

The egg is a cell, full of potential, to become a new being; only our frying pan or a starving predator can stop it from happen.
This cell have, like any other cell, a membrane (works as envelope for white and yolk), this membrane is double layered and is easy to observe on the blunt region where it forms a air pouch.

Let's start our demonstration. Before anything else we need to "undress" 2 eggs, you can see how here.

Let’s go

What we need
  • 2 jars with lid, big enough to place the egg inside,
  • marker, to write on glass,
  • water,
  • 2 naked eggs,
  • honey.
How to:
  1. Put a "naked egg" in each jar;
  2. Fill the first with water;
  3. Fill the second with honey;
  4. Close the two jars;
  5. Label them with the marker, write on the first "H2O" or "water" and in the second "honey";
  6. Place the jars in the refrigerator;
  7. Wait 24 hours;
  8. Take the eggs of the jars.
  9. What do you see?
The egg in the water jar looks like swollen and smooth.
The egg in the honey jar looks like wrinkled.

The white part of the egg has 90% water and the honey has only about 18%. We placed our cell (the egg) in two different environments, the water (with 100% water molecules, or close enough) and the honey (with about 18% H2O).

In the first case the water flow goes from a 100% environment to a 90% environment, from the water to the cell (egg), theoretically until the two concentrations are set at 95%, the egg swells.
In the second jar the water flows from the 90% environment to the 18% environment, from the cell to the water, theoretically until the two concentrations are set at 54%, the egg wrinkles.

At this process, where solvent molecules move (in this example H2O) to find a equilibrium concentration, in two different environments, separated by a membrane, we call osmosis.

  • |X| here the outside H2O concentration match the inside concentration;
  • |>X| here the concentration outside the cell/egg membrane is lower then the concentration inside it, the honey example.
  • |<X| here the concentration outside the cell/egg membrane is higher then the concentration inside it, the water flask example;
Make this an experiment
Try other variables; remember to write down all your observations:
  • Use water with food coloring;
  • Use alcohol;
  • Use salt water;
  • Use Vinegar;
  • Or simply, place your "honey naked egg" in a jar with water and wait another 24h, what do you think it will happen?

Et voilá!
Play with eggs, learn from them


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