The Osmosis of Potato Strips

Aim

To investigate the change in mass in potato strips over a period of two hours when immersed in distilled water (hypotonic solution) and salty water (hypertonic solution).

Research Question

How does the size of potato strips when immersed in both distilled water and salty water change over a period of 2 and half hours measured at 30 minutes intervals?

Background Information

Osmosis is one of the physiological processes in living organisms, among them active transport and diffusion. Osmosis is the movement of water molecules from a region of low concentration to a region of high concentration across the semi-permeable membrane. Os miss is impo4ettnt in both plants and animals. In plants it makes cells to be turgid while in animals it offsets the osmotic pressures in the cell. Plant cells are hypertonic because they have a cell sap, so when they are pout in distilled water (hypotonic solution), it absorbs water by osmosis, swells up and become turgid. They do not burst because they have a cell wall that develops a wall pressure that balances the turgor pressure exerted by turgid cells. As the plant gains turgidity, its volume increases until it achieves maximum turgidity, water will then start moving out of the cell to balance the pressure in the cells and outside environment.

When a plant cell is placed in the hypertonic solution for example solution containing NaCl (aq), it loses water due to osmosis, shrinks and become flaccid (plasmolysis). This is because the salt concentration is high then the concentration in the cell sap.

It is important to know how plant cells when placed in different solutions first to satisfy curiosity and understand water relations in plants that can be applied in studying various physiological processes in fields such as plant biochemistry and pathology among others.

Variables

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Dependent: the change in potatoes depends on the molarity (concentration) of salt solution. As the salt concentration increases, there is a decrease in mass of potato tissue.

Independent variable: time here is an independent variable; its change is not affected by either mass of potato tissue or the change in salt concentration. Will be measured at 30 minutes intervals and the dependent variable (mass of potato) will be got at that time.

Mass of potato tissue is calculated as;

Change in Mass = Initial Mass - Final Mass

Initial mass is the mass of fresh potato before adding any salt solution while the final mass is the mass of potato after adding salt solution at a specific time interval.

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For safety reasons, there was no need of gloves since the reagents used and the entire requirements are not harmful. However, the knife was held firmly while using it to avoid cuts. Care was observed when handling glass apparatus since they are fragile and can easily when they slide over the working bench.

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Materials and Apparatus

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Procedure

Potatoes were measured using a weighing balance and their masses recorded. 100 ml of distilled water was measured and put it in five different beakers. The first beaker was not added any NaCl (aq), second, third and fourth beakers were added different masses of NaCl (aq) as follows respectively, 3.656g, 7.311g, 14.625g and 29.25g and the salt were allowed to dissolve completely. The measure potatoes were immersed in each of the beakers containing different concentrations of NaCl (aq) solution at the same time. Their masses were recorded for each of the beakers after every 30 minutes for two and half hours.

Results

Table 1: Mass of potato strips at 30 minutes intervals in salty water 0f 0.0 molarity

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Table 2: Mass of potato strips at 30 minutes intervals in salty water 0f 0.12 molarity

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Table 3: Mass of potato strips at 30 minutes intervals in salty water 0f 0.25 molarity

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Table 4: Mass of potato strips at 30 minutes intervals in salty water

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Table 5: Mass of potato strips at 30 minutes intervals in salty water 0f 1.0 molarity

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Data Analysis

Table 6: Average change in mass at 30 minutes intervals and the overall change in mass after 2 hours 30 minutes

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Table 7: Initial and Final Mass of Potato Tissue

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Table 8: Mean, SD and 33.33% of the mean

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As all Standard deviation values are less than 33.33% of the mean and hence can be seen as accurate values.

Graph 1: Mean mass of potatoes with standard deviation

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The mass of potato tissues generally reduces with time for all experiments except one with distilled water

Graph 2: Percentage change in mass (g) against time in minutes

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Graph 3: Molarities of salt concentration against change in mass

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As the salt concentration is increased, there is a large reduction in mass.

Calculations Involved and other Adjustments

Average Mass is obtained by adding masses of;

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Change in mass is obtained by;

Final Mass - Initial Mass

Percentage change in mass is obtained by;

Standard deviation is calculated using the formula;

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Where Abbildung in dieser Leseprobe nicht enthalten is the mean,

X1 is each individual mass ,

N is the number of values,

Σ is Summation and

σ is Standard deviation.

Standard deviation was calculated from each individual values from Table 7 as follows,

i. Work out the mean of all numbers in the range
ii. Then for each number: subtract the Mean and square the result
iii. Then work out the mean of those squared differences.
iv. Finally, take the square root of the differences

33.33% of the mean is calculated as;

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The data obtained is nearly accurate because the errors are minor. The areas will be further discussed at evolution (at the end).

Measurement of the volume of water was nearly accurate using beakers. The concentrations of solutions were nearly accurate also due to using of electronic balance though there are human errors which cannot be assumed.

Interpretation

From the results, it is clear that as the concentration of salt solution increases, there is a larger decrease in the size of the potato. For example, at 0.0 concentration, that is, distilled water, percentage change is 11.660%, at 0.12 molarity, change is 2.702%, at 0.25 molarity, change is -11.088%, at 0.5 molarity, change is-27.980%, while at 1.0 molarity, change is -21.423%.

Discussion

In osmosis, water which is uncharged molecules passes through the cell membrane. A cell membrane is a semi-permeable membrane, that is, it only allows small particles to go through it. Osmosis depends on its concentration gradient, from a region of low concentration as it moves to a region of high concentration. It is dependent on temperature, size of the molecule, thinness of the membrane and the concentration gradient. In this activity, osmosis in potato cell was studied. Salty water with Cl- (aq) is concentrated as compared to the cell sap, that is, hypertonic solution. The cell sap, therefore, loses water by osmosis and shrink. From the results, as the concentration of salts increases, the mass of potato reduces, therefore solution with 0.0 molarity of NaCl (aq) recorded an increase in mass while the ones with 1.0 molarity of NaCl (aq) recorded a great decrease in mass. The process where a plane cell loses water, shrink and become flaccid is called deplasmolysis. A plasmolyzed cell can be made turgid by immersing it in distilled water for some time (deplasmolysis) (Odom et al, 2017).

Therefore for osmosis to occur, the two solutions must be separated by a semi-permeable, membrane, for this case, the potato cell membrane is only permeable to water molecules from potato cell but is not permeable to salt molecules from Cl-(aq) ions that are present in water solution. At 30 min, all of them showed a decrease in mass because water is drawn from potato tissue to the salt solution. As the time increases, the cell is continually losing water; to offset the osmotic imbalance. The overall change in mass is a decrease, in the end, the solutions become isotonic, that is, all solution s have attained the same concentration, and there is no net movement of water molecules from one solution to another.

The main aim of osmosis is to offset osmotic imbalances in bodies of living organisms to provide optimum conditions for body functions. Osmosis continues to take place until when the two solutions are almost equal in concentration.

As osmosis is taking place, a force will be created in the hypertonic solution that aims to prevent osmosis from taking place; such a force is called osmotic pressure. If osmotic pressure of a solution is high, it will draw a lot of water from the adjacent solution, and if it is low, it will draw little waiter. Osmotic pressure is, therefore, a measure of the total amount of dissolved salts in water (Xu et al, 2017).

Conclusion

As is can be seen from Table 6, there is generally a decrease in mass when a potato is placed in water containing NaCl (aq) solution. The potato sap has little solutes, and therefore it is hypotonic while the salt solution has more solutes. Therefore, it is hypertonic. Water molecules moved from a region of low concentration to a region of high concentration. The purpose of using five potato tissues is for the accuracy of the results obtained. The percentage change in mass calculated increased the increase in salt concentration. At 30 min, all of them showed a decrease in mass. This is due tote fact that a lot of water is drawn from potato tissue to the salt solution. As the time increases, the cell is continually losing water; there is no general trend as in others it increases from 30 minutes to 60 minutes while in others it decreases. Near to the end of the experiment, the cell increased slightly in mass, though it is still lower than the initial value. This is because the solution is isotonic, that is, all solution s have attained the same concentration, and there is no net movement of water molecules from one solution to another.

Though there is no specific theoretical value about the mass of potato used, the general conclusion is of a decrease in mass as the cells are losing water by osmosis (Odom et al, 2017).

Evaluation

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Reference List

Odom, A.L., Barrow, L.H. and Romine, W.L., 2017. Teaching Osmosis to Biology Students. The

American Biology Teacher, 79 (6), pp.473-479.

Xu, W., Chen, Q. and Ge, Q., 2017. Recent advances in forward osmosis (FO) membrane:

Chemical modifications on membranes for FO processes. Desalination, 419, pp.101-116.