Osmosis is a physical process that conditions on the functioning of the majority of cells in live organisms. It was discovered by Jean Antoine Nollet in 1748. However, its full discovery started in one hundred years. There are several experiments that clearly demonstrate the process.
The aim of the following experiment is defying the osmosis potential in parenchyma tissue of a potato tuber. The object of the research is three pieces of parenchyma tissue. The subject is an ability of the tissue to absorb and excrete moisture depending on the chemical features of the environment.
Three equal cubes of parenchyma tissue of potato tuber were cut out. Each of them was dipped into a can with water. In one can a little amount of salt (sodium chloride) was added. The maximum amount of salt was added to the second can. The third can was untouched.
In one or two hours the visible changes in cubes’ appearance can be observed. The cube with a little amount of salt remained the same. The second one (which was dipped into a strong solution of salt) squeezed and became much smaller. The dimensions of the third cube increased.
This was an obvious evidence of osmosis. Osmosis is a one-side diffusion of a dissolvent through the membrane. It can be explained as the aim of the system to come to the thermodynamic balance. During the dissolving process, the molecules of a substance penetrate into the dissolvent and its molecules take place of the solution.
This diffusion leads to the compression of concentrations of the dissolved substance and the dissolvent through the whole volume. Now let’s imagine the situation when the substance and the dissolvent are divided by the membrane. It lets the molecules of the dissolvent and stops those belonging to the dissolved substance. Obviously, the compression can be performed only by a one-sided diffusion.
The molecules of the dissolvent will move from the solution with smaller concentration to the more concentrated one, causing the increase of moist amount in the latter. In other words, the dissolvent gets into the solution under the influence of so-called osmosis pressure. As soon as the hydrostatic pressure equals the osmosis pressure, the process ends.
So, in the first can with the little amount of salt the concentration of the latter was equal both in potato cells and the environment. The osmosis pressure did not appear. In the second can, where the concentration of salt was the highest, we could observe the osmosis. The water from the potato cells has penetrated through the cell membrane to the more concentrated solution.
That is why the potato cube has shrined – all water has gone from it. In the third can we could observe the reverse process – the water with lack of salt penetrated into potato cells, making the cube tissue bigger.
- Zwolinski, Bruno J., Eyring Henry, and Reese Cecil E. “Diffusion and Membrane Permeability.” The Journal of Physical Chemistry, vol. 53, no. 9, 1949, pp. 1426–453. ACS Publications, https://pubs.acs.org/doi/abs/10.1021/j150474a012. Accessed 21 Apr. 2018.
- Kahlenberg, Louis. “On the Nature of the Process of Osmosis and Osmotic Pressure with Observations Concerning Dialysis.” The Journal of Physical Chemistry, vol. 10, no. 3, 1905, pp. 141–209. ACS Publications, https://pubs.acs.org/doi/abs/10.1021/j150075a001. Accessed 21 Apr. 2018.
- Pryde, Lucy T., and Powers George B. “Osmosis and diffusion.” Journal of Chemical Education, vol. 65, no. 1, 1988, p. A22. ACS Publications, https://pubs.acs.org/doi/pdf/10.1021/ed065pA22. Accessed 21 Apr. 2018.
- Traxler, Ralph N., and Huntzicker Harry N. “Influence of the Presence of a Solute on Rate of Osmosis.” The Journal of Physical Chemistry, vol. 39, no. 3, 1934, pp. 431–36. ACS Publications, https://pubs.acs.org/doi/abs/10.1021/j150363a012. Accessed 21 Apr. 2018.