A Comparison of the Water Potential of Potato and Sweet Potato Tubers
Aim
The aim of this experiment is to compare the water potential of two
different plant tissues, potato and sweet potato tubers, by measuring
the gain or loss of water when samples of the tissue are placed in a
range of concentrations of sucrose solutions.
Background information
Osmosis is the movement of water molecules from a region of their
higher concentration to a region of their lower concentration through
a semi permeably membrane. If the cell is surrounded by pure water
(which has a water potential of zero), or by a solution that has a
lower concentration and therefore a higher water potential, than that
of the cell’s contents water flows into the cell by osmosis and the
cell would swell up (become turgid). The external solution is said to
be hypotonic to the solution in the cell (hypo meaning lower than and
applies to the solute concentration).
If the reverse was to occur and the cell was surrounded by a solution
whose concentration is higher and whose water potential is lower then
that of the cell, the water would flow out of the cell into the
solution. In this case the external solution would be known as
hypertonic to the solution in the cell. If the cell has the same
solute concentration and water potential as the surrounding solution,
there would be no flow of water into or out of the cell so the cell
stays the same size. In this case the external solution is called
isotonic, meaning it is the same as.
We have seen evidence of using hypo and hypertonic solutions during an
experiment using onion cells. Both onion cells were placed onto a
microscope slide, a drop of water (hypotonic solution) was then added
to slide A, and a salt solute (hypertonic solution) to slide B, below
are photos that were taken of the cells during this experiment.
[IMAGE][IMAGE]
Slide A Slide B
If we say that the right hand side in picture 1 is the potato, and the
* Note the mass down in the table at the end of the first page.
In osmosis, water can travel in three different ways. If the molecules outside the cell are lower than the concentration in the cytosol, the solution is said to be hypotonic to the cytosol, in this process, water diffuses into the cell until equilibrium is established. If the molecules outside the cell are higher than the concentration in the cytosol, the solution is said to be hypertonic to the cytosol, in this process, water diffuses out of the cell until equilibrium exists. If the molecules outside and inside the cell are equal, the solution is said to be isotonic to the cytosol, in this process, water diffuses into and out of the cell at equal rates, causing no net movement of water. In osmosis the cell is selectively permeable, meaning that it only allows certain substances to be transferred into and out of the cell.
molecules go in and out of the cell. There is no net movement of water
The water molecules move freely through the semi-permeable membrane; this is a passive process. We will do this experiment by placing potato chips in different strength solutions and checking for mass increase/decrease. Prediction I hypothesize that if we place potato chips in different strength solutions that there should be different results, some with noticeable changes in mass, the other will be nearly the same. The potatoes should gain/lose mass by the movement of water. If there is a change in mass, it is because water has entered or left the cell.
I am going to carry out an experiment to measure the change in mass of
cork borer and a ruler. I will keep the potato chips the same size in
In life, it is critical to understand what substances can permeate the cell membrane. This is important because the substances that are able to permeate the cell membrane can be necessary for the cell to function. Likewise, it is important to have a semi-permeable membrane in the cell due to the fact that it can help guard against harmful items that want to enter the cell. In addition, it is critical to understand how water moves through the cell through osmosis because if solute concentration is unregulated, net osmosis can occur outside or inside the cell, causing issues such as plasmolysis and cytolysis. The plasma membrane of a cell can be modeled various ways, but dialysis tubing is especially helpful to model what substances will diffuse or be transported out of a cell membrane. The experiment seeks to expose what substances would be permeable to the cell membrane through the use of dialysis tubing, starch, glucose, salt, and various solute indicators. However, before analyzing which of the solutes (starch, glucose, and salt) is likely to pass through the membrane, it is critical to understand how the dialysis tubing compares to the cell membrane.
If a plant cell is places in a hypotonic solution the cell has a lower water concentration to that of the solution. Water will move into the cell by osmosis from a high water concentration outside the cell to a lower water concentration inside the cell through a selectively permeable membrane. The cell becomes turbid
repeat the process 3 times in total to ensure a fair test. At the end
When I am not using them I will place them away from my experiment and
Osmosis in Potato Tubes Osmosis: Osmosis is the movement of water molecules through a semi-permeable membrane from a high concentration to a low concentration. Diagram: [IMAGE] [IMAGE] Aim: To see the effects of different concentration of sugar solution on Osmosis in potato tubes. Key factor: In the investigation we change the sugar solution from: 0%-10%-20%-30%-40%-50% this is the independent variable; the dependant variable is the change in mass. Prediction: I predict that all the potato tubes in pure water or low concentration sugar solution will swell because water enters their cells by osmosis.
water in the potato, then the water will go out of the potato and into
The tissue would gain in mass and length and will become turgid and sabotaging. If plant tissue has a higher water potential than
The strong cells wall prevents bursting. The cell is turgid. If plant cells lose water the cells become limp and flaccid. Water is essential for support in plants.