Purpose : to demonstrate two critical conditions that influence osmosis
Things Required:
Table salt
Potato
Measuring cup (250 ml)
Measuring spoon-teaspoon (5 ml)
Two small bowls
Clock
Directions:
Mix 3 spoons of salt in 1 cup of water. Pour the salt water mixture into one of the small bowls.
Pour 1 cup of water into the second bowl. Ask an adult to cut the potato into slices, about one-fourth inch (6 mm) thick. Place half of the potato slices into the bowl of water and the remaining slices into the bowl of salt water.
After 15 minutes pick up potato slices from each bowl with your fingers and test their hardness or turgor pressure by trying to bend the slices.
What differences do you feel?
This Is What Happens:
The potato slices in the water are very stiff and do not bend easily. The slices in the salt water are very limp and bend very easily.
Science Behind It:
Two critical factors affecting osmosis are:
- The amount of water and dissolved material inside the cell.
- The amount of water and dissolved material outside the cell
Osmosis is the movement of a material such as water across a membrane. Water always moves through a membrane towards the side containing the most dissolved material and the lesser amount of water. In this experiment, the dissolved material will be salt.
Salt and water are only two of the chemicals found inside all potatoes. The potato slices placed in the bowl of water keep the original amount of water in their cells. In addition to it, more water from the bowl moves into the slices through cell membranes. This extra water makes the slices stiff.
The amount of salt inside each potato slice is less than that mixed with the water in the salt water mixture. The slices soaked in the salt water feel limp because they have lost some of the original water inside their cells. The water from inside each potato slice moves out of the potato through cell membranes and into the bowl of salt water. The slices are only partially filled and feel limp.
