Carry out the following osmosis experiment:
Take four peeled potato halves and scoop each one out to make potato cups. One of these potato cups should be made from a boiled potato. Put each potato cup in a trough containing water.
- Keep cup A empty
- Put one teaspoon sugar solution in cup B
- Put one teaspoon salt solution in cup C
- Put one teaspoon sugar solution in the boiled potato cup D. Keep these for two hours.
Then observe the four potato cups and answer the following:
- Explain why water gathers in the hollowed portion of B and C.
- Why is potato A necessary for this experiment?
- Explain why water does not gather in the hollowed out portions of A and D.
Substances move from areas of high concentration to areas of low concentration through a semipermeable membrane . This process is called osmosis .
Water also follows this principle.
i. In the first cup ,
- There is no movement of water through the potato alone .
- Potato cup A is necessary in the experiment as a ‘ control experiment ’ for providing comparisons with situations created in potato cups B, C and D.
For osmosis, there should be a gradient in concentration .
In this case there is water outside the cup but none inside the cup and hence no concentration gradient . Thus, water will not flow through the membrane.
ii. Cups B and C contain sugar and salt solutions
- This means that the concentration of water inside the cups is lesser than that outside .
- Hence, water gathers in cup B and C due to Osmosis .
iii. In the case of cup D ,
- The potato is boiled . Heating the cell membrane (which is made of proteins) leads to the destruction of the cell membrane due to the proteins being denatured .
- The destroyed cell membrane cannot act as a semi permeable membrane .
- Without a semi permeable membrane osmosis will not take place .