1. Diffusion and Semi-Permeable Membranes
Great way to introduce the characteristics of the cell membrane and have students
use their observations to explain how materials enter or leave the cells in their body.
Procedure:
Have students set up a data table in their notebooks to record predictions,
observations and measurements.
Day 1: Weigh a raw egg.
Place the egg in a large beaker, add 200ml of vinegar. Cover and leave overnight.
(The shell will disintegrate leaving the membrane visible).
Day 2: Weigh the egg and measure the amount of vinegar in the beaker.
Place the egg in a large beaker, add 200ml of light corn syrup. Cover and leave overnight.
Day 3: Weigh the egg and measure the amount of liquid in the beaker.
(The egg will be shriveled up and there will be an increase in the ml present in beaker).
Place the egg in a large beaker, add 200ml of water. Cover and leave overnight.
Day 4: Weigh the egg and measure the amount of liquid in the beaker.
When you put a naked egg in corn syrup, you are creating a situation where the egg
membrane separates two solutions with different concentrations of water. The egg white
is about 90% water; corn syrup is about 25% water. In this situation, random movements
of water molecules cause them to move from the side of the membrane where they are
more abundant to the side where they are less abundant. So water migrates from inside
the egg to outside the egg, leaving the egg limp and flabby.