A quick summary of the egg lab Arslan Aziz SSWIMS December 2002
What did we do? • Test our predictions for what would happen to an egg treated with weak acids, corn syrup, and distilled water.
water water water water water water water water What did we find? • The egg shell dissolves in weak acids. • Once the shell is gone, eggs will swell due to the influx of water. • Water is moving from an area of greater concentration to an area of lesser concentration (Osmosis)
water water water water What about in corn syrup? water • The egg now sits in a solution that has a lower concentration of water than the egg itself. • The egg then shrinks due to the outflow of water. water water water water water
What allows for the movement of water? • A semi-permeable membrane • Remember: Semi-permeable membranes are selective. Some things can move across the membrane while others cannot. • What drives the movement? • All substances are moving towards their respective chemical potentials. • In other words, left alone, particles will spread out until they are evenly distributed.
PERMEABILITY A barrier like this one would be permeable to golf balls, but not tennis nor basketballs…
What about in the egg? The egg is actually covered by a semipermeable membrane. Vinegar is too large to fit through but water passes through easily.
DIFFUSION Involves the movement of much smaller things, like water molecules. The overall effect is the same, though: over time, there would be an equal number of particles on both sides of the barrier. HIGHER CONCENTRATION LOWER CONCENTRATION
OSMOSIS Is a special type of diffusion, where there is a barrier that only allows certain things through, like water molecules, but does not let things like salt through… HIGHER CONCENTRATION LOWER CONCENTRATION
So why does this matter? • We use semi-permeable membranes everywhere! • Examples include: Gore-Tex (water droplets are too big to move in, water vapor is small Enough to move out)
Water for everyone? • In an effort to make more fresh water available for the growing number of people in the world, we may turn to reverse osmosis using semi-permeable membranes.
Why does this matter in living things? • The cells of all living things are made of semi-permeable membranes!
Our cells are exposed to the environment. • Ex: the cells in the lining of your lungs lose moisture through evaporation as you breath.
Osmosis • The diffusion of water. • Water will move from an area of greater concentration to an area of lesser concentration.
ACTIVE vs. PASSIVE Passive transport involves creating an opening from things to move from a higher concentration to a lower concentration- they do this spontaneously, so no energy is needed… Active transport involves “pumping” things from a lower concentration to a higher concentration: this requires energy, and special pumping structures;