125 test tubes: To test each plant tuber or root with the different molar solutions i.e. 5 different plant tuber/ root and 5 molar solutions and 5 for each molar solution.
Ruler: To measure the length of each plant tuber/ root after being bored
100ml volumetric flask: To make 1 molar solution of glucose by completely dissolving 1 mole sucrose in 1000ml distilled water
Labels: To identify which beaker, plant root/ tuber or test tubes is which
PLANNING:
In order to ensure accuracy and have a full understanding on the process involved in the experiment, I’ll need to carryout some concrete research on Osmosis and its effect on different plant root/ tubers. I would also need to make a dilution of 1 molar sucrose, and to do this, I’ll weigh 1 mole of sucrose by using the formula of Mole = Mass/RAM where RAM of sucrose is 342. To get the desired amount, a mass of 342 sucrose will give exactly 1 mole and this would be dissolved in a 1000ml volumetric flask filled to about 2/3 rd with distilled water. By shaking the flask, I’ll dissolve the sucrose until partially clear then using a teat pipette, I’ll add 1 drop after another of distilled water until the meniscus reaches the 1000ml mark and finally shake until a solution is perfectly clear.
The reason I have chosen to use the apparatus men tined is because;
- A teat pipette allows 1 drop to be added hence the accuracy and measurements are almost perfect.
- A volumetric flask is also more accurate as the 1000ml mark has an indication of where the 1000ml mark is. Its also more accurate than using a beaker as the accuracy can be judged by the meniscus however a beakers actual volume is not specified, in addition the flask makes it easier to shake the solution without spillage.
Another point to consider is the plant tuber/ root, this is important because it helps to identify if there’s any relationship between the plant tuber/ root and Osmosis e.g. the isotonic etc. From research and secondary source, I’ve decided to use a Swede, potato, sweet potato, carrot and parsnips. More also, the water potential in the plants tuber/ root has to be considered, although it’s unlikely for there to be variations in the water potential as they’re all grown in the same climate however, it could be different due to environmental conditions. For example, if planted indoors the soil yield could be either better or worse than the outside, same for vice versa. Some suggested point s that could affect it are;
1. Quantity and quality of fertilizer
2. Frequency and amount of water added
Furthermore, I’ll need a way to control the experiment to avoid errors. On the one hand, I’ll need to perform the experiment under the same room temperature so as not to temper with the result. Keep the cut pieces in each molar solution for 1hr as it eliminates the chances of error across the range of solution. By planning ahead some of the stages involved, it would lead to a very well performed experiment, and as all the information needed is known, it should give a reliable result at the end.
SECONDARY SOURCE:
From research across a variety of sources which included the Internet, books, encyclopaedias etc, I was able to find lots of information on Osmosis and this as further increased my knowledge on how, why, and the situation and outcomes of Osmosis. As the experiment is on plants, I carried out a preliminary work on Yams and this should help when explaining my hypothesis i.e. range of effects of Osmosis by the different molarities. The table below shows the result of my preliminary work:
The above table shows the result of the yams both before and after the cut pieces where left in a range of solutions for 1hr. The results show that 0.2 molar has an overall increase in weight, this suggests that there’s a higher water potential outside than inside the cell hence the gain. This is therefore true as 0.2 molar has less solute than the rest, therefore the net movement of water down the gradient and into the cell. The external solution in this case is said to be ‘hypo tonic’. The 0.4 molar seems to have the same mass both before and after, this therefore suggests that the concentration of solution both in and out the cell are the same, thus solution is said to be ‘Isotonic’ with cell. The rest of the molar solutions have decreased in mass, this suggests that there’s more water potential inside the cell than outside which causes the net movement of the water molecules down the gradient and outside the cell, hence the external solution is said to be ‘hyper tonic’. Based on this, I hope the result of my experiment will be similar to the preliminary work and reliable to draw conclusions and evaluate.
HYPOTHESIS:
As Osmosis is the movement or passage of water molecules from a region of high concentration to a region of low concentration via a partially permeable membrane. In this experiment, the same process applies as it’s the molar solutions that diffuse in or out of the tiny holes of the plant tuber or root, where the serve as the partial membrane. Based on the evidence of the result, I predict for all the plant tuber/root that when the molar solution is lower, the net movement goes down the concentration gradient, as there’s more solute inside the cell than outside. This will be true for 0.2 molar solutions, as it’s got less solute hence this increases its water potential compared to the rest. More also, I predict that the higher molar solution would have a net movement outside the cell this happens because there’s more solute in the solution outside than inside the cell, hence a movement down the gradient out of the cell. This should be true for 0.8 molar and 1.0 as there’s more part solute than water therefore a loss in mass as water molecules get out of the cell.
However, there will be a molar solution which is the same for both inside and outside the cell, here there will be no significant change in mass as the net movement are at equilibrium, and from the preliminary work this is likely to happen between 0.4- 0.5 molar solution (Isotonic).
I also predict that both turgidity and flaccidity are likely to happen in certain molar solutions. I predict turgidity is likely to happen in full distilled water of 0 molar, however because I’m not testing 0 molar, the turgidity should happen in the 0.2 molar solution, this is because there’s a higher osmotic concentration in the 0.2 molar solution than the cell, it thus causes the drawing in of water via the living cells of the potato which act as the semi permeable membrane, as the solution diffuses into the potato it enters the vacuole of the potato cell, which increases the volume of cell sap, which in turn causes an increase in pressure as the contents of the cell pushes against the cell wall, which prevents it from bursting unlike that of the animal cell. The pressure exerted is turgor pressure and is counteracted by a pressure equal in magnitude but in the opposite direction of turgor to a point where its equalled to the resistance of the cell, thus 0.2 molar gains mass due to the factors of turgor pressure.
More also, I predict that for a solution of 0.8 0r 1.0 molar, the mass is likely to decrease because of the term plasmolysis, which happens due to the fact there’s a lower osmotic concentration in theses molar solutions than inside the cell, hence movement of water out of the cell down the gradient. The reason for this prediction is that, as the cell loses it’s water the cytoplasm shrinks and the plasmodesmata gets detached from the cell wall. From the secondary source/ research and based on my hypothesis, the result should backup the hypothesis as well as highlight the noticeable effect of osmosis on the different molar solutions. For example which molar solution would be Hypotonic i.e. where the cells of the plant tuber/ root takes in water because there’s more solute in the cell than the outside solution which then causes water molecules to pass into the cell by osmosis and swell up. Another prediction, which I hope will reflect in the result is the molar solution that appears to be Hpertonic i.e. the molar solution which has a high concentration inside the cell than out, hence the plant tuber/ root cells lose water causing it to shrink thereby leading to a loss in mass. And finally the molar solution that is Isotonic i.e. where there’s no change in mass (both solutions in equilibrium).
Fair test/ Safety:
In other to ensure reliability and accuracy of the experimental procedure, it has to be a fair test. To make sure of this there are certain variables that will be changed and some kept constant. On one hand some of the variables that would need to be changed include the molar solution strength as each is been tested, the plant tuber/ root tested will also change as I’m carrying out the experiment on 5 different ones, on the other hand some variables will need to be constant e.g. the diameter of the plant tuber/ root, the length of the plant tuber/ root, the volumes of the molar solution strength.
Other significant factors to ensure a fair test include; leaving the cut pieces for a period of 1 hr for all sets, ensuring the room temperature during which the experiments are carried out is constant, starting the clock as soon as the plant tuber/ root (s) are immersed in the solution, weighing the cut pieces within 1 minute of taking them out that is after partly drying the water drops left on the cut pieces by rolling on tissue paper to remove the excess water, ensuring the clock is stopped at the exact time for all sets (allow enough time spacing ) and make sure the apparatus are rinsed with distilled water before each experiment. In addition, I’ll also use a balance/ scale of 2d.p that helps to increase accuracy, by taking into consideration all these points, I’m sure that it would not only give accurate result but at the same time reliable results which would give good analysis.
Another important aspect is safety, and this must be observed in all experiment and therefore no exception in this investigation. One safety procedure is to use the scalpel or knife carefully as they are sharp, but more importantly ensure it doesn’t cut the skin as the blades are rusty and could easily inflict Tetanus. Take care when using the glass apparatus as they are fragile and if accidentally cracked could easily pierce the skin. However, apart from this there’re no other safety measures.
Method:
. Firstly I need to get the dilution of 1 mole of sucrose as mentioned earlier in the planning as this is the most important aspect in other for the experiment to proceed.
. Rinse all the test tubes carefully using distilled water as it gets rid of any previous residues left in them, then carefully measure the molar strength using the tables from the planning as a guide into 125 test tubes ensuring the right apparatus are used e.g. measuring cylinders (10 and 50 cubic cm) taking measurements from the meniscus and a pipette to ensure accuracy by adding droplets of solution.
. Take of the plant tuber/ root, then using a 13mm diameter cork borer, bore into 25 cylindrical pieces, then using a ruler cut each piece to a length of 30mm. This is the same for all the sets to ensure a fair test also make sure the experiment is carried out one at a time because if two are cut, then the time taken for one to be bored while the other is left on the tile would cause the it to dry out therefore affecting result
. Separate the 25 pieces into a tally of 5 per group i.e. 5 groups, label each test-tube carefully with the right molar solution it contains so as to make the identification easier. Then weigh the first group, and take note of the mass, thereafter place in the each molar solution for first set. Repeat for the remaining 4 sets and then for the other plant tuber/ root.
. Immerse the 5 cut pieces into the corresponding labelled test tubes and time for 1 hr, repeat for the remaining molar strength, sets and plant tuber/ root.
. After 1 hr, take out each piece and roll on a tissue paper gently to remove excess water droplets left on the cut pieces, then weigh on a balance/ scale taking note of the mass to the corresponding mass of before experiment. Repeat this for the remaining molar strengths, sets and other plant tuber/ root, thereafter average results and calculate % gain or loss in mass.
Analysis/ Conclusion:
From my result, I can conclude that the result I obtained supported my hypothesis to some extent i.e. the molar strength where turgidity (gain in mass) and plasmolysis (loo in mass) are to occur, however it also disagrees because I noticed a relationship between the tuber/ root which I’ had initially not expected. The result show that the plant tuber/ root both gained / lost mass, due to the concentration of water molecules inside and outside the cell. It could be seen that all the plant tuber/ root gained mass in the 0.2 molar solution, this is because it has the lowest solute potential which increases the water potential than that of inside the cell, hence causing osmosis to occur down the gradient as water molecules enter the plant tuber/ root cells, this in turn makes it turgid which in turn causes the gain in mass. During the experiment, the observation I noticed for the 0.2 molar strength was the cut pieces were floating in the test tube, this also supports my prediction as well as suggest the solution is Hypotonic.
In addition, it can be seen that all the cut pieces immersed in the 0.6- 1.0 molar strength solution had a loss in mass, this is because they had a high solute potential than that of inside the cell therefore reduces the water potential resulting in osmosis to occur down the gradient outside the cell. A s the on going process continues, the protoplast shrinks which eventually causes he cell contents to shrink as water is being lost, this therefore causes full plasmolyis to occur to occur due to the main fact that the molar strength solute concentration is higher than that of the cell sap. This 0.6- 1.0 molar strength solutions that causes the shrinking is referred to as an Hypertonic solution. One other evidence from the result is the molar solution that doesn’t seem to affect the mass. This molar strength solution is in equilibrium with that of inside the cell and noticeable at around the 0.4 molar strength, this is because the mass after the experiment isn’t of big difference to the original mass (0.1 id.p) hence, makes me conclude this solution strength is Isotonic. The correlation I noticed was a huge surprise because I never expected there to be a relationship. From the table it could be seen that the potato had the lowest gain in mass, however most of the water molecules diffuses out, and this might be due to factors such as species of potato or responsiveness of the potato cells. The 1.0 molar strength lost the most mass (0.586), which is 6 times the mass in a 0.2 molar strength out of all the other tuber/ roots. On the other hand, the parsnip had the least mass (0.098) in the 1.0 molar strength. By comparison the results suggests osmosis out of the cell occurs quicker in a potato and least in the parsnip, in addition the Swede had the highest gain in mass and this might be due to it’s soft inner core that allows water molecules to diffuse easily. And as for the sweet potato, it had the slowest drop in mass between the 0.2 – 0.4 strengths (0.08), hence suggests osmosis occurs slower in sweet potatoes may be due to its structure. (Stringy) To summarize the evidence of the result, I can represent it diagrammatically as shown below whilst indicating the main molar strength which have an effect on the cut pieces;
The above shows the events that ensue if a plant tuber/ root is placed in A) an Hypotonic solution and B) an Hpertonic solution
Evaluation:
Overall, I think the experiment went alright although I wasn’t expecting the outcome of relationships between the tuber/roots. There was an anomalous result between the 5 different plant tuber/ root for the Isotonic point due to the variation in % difference. On the one hand the anomalous result could have occurred because of human error, for example when drying the cut pieces, I might have compressed to hard forcing some water out of it and this would certainly have affected the result. Another reason that might account for the anomalous result might be lack of resources e.g. the plant tuber/ roots where of irregular (varied) size although cut to same length and diameter and this in conjunction with the vegetation or source they were grown might be a reason for such anomalous result. To add to this, the relationship will be due to the structural formula of the tuber i.e. the hardness (parsnips), stringiness (sweet potato) or softness (Swede).
More also, the freshness might affect the result in that the longer the tuber/ root has been on the shelf the less water present in its cells, in addition the errors might have happened due to % errors that happened in the length measurement when using the ruler. The % error can be worked out, and expressed as;
0.5 / 3 * 100% =
where 0.5cm is the error of ruler, 3cm is the length of the cut pieces.
In terms of the apparatus with the exception of the ruler, had no major errors because for example the burette has an insignificant error due to its 0.05cubic cm degree of accuracy
Having looked at the results critically, there could have been improvements to help give more reliable and more accurate results. One of the improvements could have been allowing more than enough time difference between the sets of experiment so as to create more time to move the pieces from test tube to balance if weighing, although I mentioned I would allow enough time in the planning, this became rather impossible due to lack of time. Another improvement could be to use more types of molar strength solutions that would allow the specific strength at which the effects of osmosis occur, also experimenting for longer and repeating the sets about 10 times will surely increase reliability, produce sufficient accurate result, eliminate any chance of errors in the mass 9gained or lost) and help identify the saturation point (where the cut tubers/ roots cannot take in water any more) and dehydration point (where the cut tubers/ roots cannot lose water anymore) as well as test similar types of plant tuber/ root.. Furthermore, I could have used a microscope to look at the cut pieces which would show in great detail the full extent the molar strength had on the process of osmosis, but having said I’ll need to devise a method to get the cells.
