Investigation: Osmosis

Learn how the concentration of the Sodium Chloride solution directly or indirectly affects the dependent variable of the experiment - the change in mass and ultimately the rate of osmosis in the plant cells of a potato cylinder!

Background

Osmosis is the movement of water molecules from a higher water potential to a lower water potential, down a water potential gradient across a partially-permeable cell membrane. It is a passive process, hence energy is not required to carry out this process. Tonicity is the ability of an extracellular solution to make water move into or out of the cell by osmosis. There are 3 classifications of tonicity - Hypotonic, Hypertonic and Isotonic. These types of solutions are used to describe the movement of water molecules into or out of the cell based on the molar value of sodium chloride and the water potential the solution possesses. The type of the extracellular solution can result in the cells increasing or decreasing in mass or staying at a constant mass, that is the cell either becomes turgid, plasmolyzed or flaccid.

Figure 1 - A diagram illustrating the process of Osmosis in cells using a beaker, the water will flow from the left compartment (containing higher concentration of sugar) to the right compartment of the cell (containing lower concentration of sugar) until the solutions are somewhat in equilibrium. (“What Is Osmosis? | Definition from Seneca Learning”)

Research Question

How does the independent variable of the experiment- the concentration of the Sodium Chloride solution directly or indirectly affect the dependent variable of the experiment - the change in mass and ultimately the rate of osmosis in the plant cells of a potato cylinder?

Aim of the Investigation

The aim of the ‘Osmosis Investigation’ is to investigate the direct or indirect relationship between the independent variable of the experiment, the concentration of the Sodium Chloride solutions, and the dependent variable of the experiment which is the change in mass and how this relationship affects the osmotic potential of a potato cell. The aim of this investigation will be achieved by manipulating the independent variable - the concentration of the sodium chloride solutions, this will be done by using 5 different concentrations of Sodium Chloride solutions, specifically - 0.0 M, 0.2M, 0.4M, 0.6M and 0.8M and placing a uniform potato cylinder in equal amounts of each solution for a fixed period of time. In this experiment, the solution containing 0.0M of sodium chloride contains zero molar value of sodium chloride/ lowest molar value of sodium chloride meanwhile the solution containing 0.8M of sodium chloride contains the highest molar value of sodium chloride. Whilst using these 5 constraints, the change in mass can be recorded using an electronic balance and these 5 solutions can be identified as having a Hypotonic, Hypertonic or Isotonic tonicity, ultimately helping in understanding the true relationship between the concentration of sodium chloride solution and the change in mass.

Hypothesis

It can be hypothesized that if a potato cylinder is placed in a sodium chloride solution which possesses a lower molar value of sodium chloride and a higher osmotic potential (the composition of a dilute solution) compared to that of a potato cylinder, the mass of the potato cylinder will increase. The scientific explanation for the following would be that the extracellular sodium chloride solution the potato is placed in is a hypotonic solution. A hypotonic solution “ is a solution that contains a lower amount of solute as compared with the solute concentration in the other solution across a semipermeable membrane”(“Hypotonic Solution”, para 2). Hence, it can be predicted that due to the higher osmotic potential possessed by the extracellular solution, the solution will enter the semi-permeable cell membrane of the potato cylinder and due to an increase in the water content, the potato cylinder will increase in mass.

It can also be predicted that if a potato cylinder is placed in a sodium chloride solution which possesses a higher molar value of sodium chloride and a lower osmotic potential compared to that of a potato cylinder, the mass of the potato will decrease. The scientific explanation for the following would be that the extracellular sodium chloride solution the potato is placed in is a hypertonic solution. A hypertonic solution is a “solution that contains more solute, such as sodium chloride and other electrolytes compared to the solute concentration in the other solution across a semipermeable membrane” (Sheil, William C, Davis, para 1). Therefore, it can be hypothesized that due to the extracellular solution possessing a lower osmotic potential and the semipermeable cell membrane of the potato cylinder possessing a higher osmotic potential, this will result in water moving out of the plant cells of the potato and entering the surrounding solution. Hence, the potato cells will lose water content and ultimately decrease in mass.

It can also be predicted that if the potato cylinder is placed in a sodium chloride solution which possesses the same molar value of sodium chloride and water potential as the potato cylinder, then the mass of the potato cylinder will be constant meaning there will be no increase or decrease in mass. The scientific explanation for the following would be that the extracellular sodium chloride solution of the potato is placed in an Isotonic solution. An isotonic solution “is (a solution) that has the same osmolarity or solute concentration as another solution” (“Isotonic Solutions Have a Same Boiling Point B Same Class 12 Chemistry CBSE”, para 5). Since both solutions are separated by the potato’s semi-permeable membrane, “the water will flow in equal parts out of each solution and into each other” (BD Editor, para 3) as there is no water potential gradient present. To conclude, since an equal amount of water is left and penetrated into the cell, “there is a zero water flow between both solutions although water is moving both ways”(BD Editors, para 3).

Predicted Graph

The hypothesized graph shows a downward trendline. The downward trend can be explained since the first concentration of 0.0M contains no molar value of sodium chloride it can be stated that this solution is Hypotonic, resulting in the potato significantly increasing in mass compared to the other solutions due to the solution's higher water potential compared to the potato. Therefore the graph shows the y-intercept having the highest value compared to the rest of the points on the graph. The second concentration of 0.2M can also be considered a Hypotonic solution as the concentration of 0.2M contains only a slightly larger molar value of Sodium Chloride compared to the solution with the concentration of 0.0M, therefore there will be an increase in mass in the potato cylinder, yet it can be assumed that the increase in mass of the potato cylinder is not as significant as it could be when placed in the 0.0M solution. Hence, for the solution containing 0.2M of sodium chloride, the mass can be seen to decrease. The third concentration of 0.4M can be considered the Isotonic point or the osmotic potential of the potato cells - the point 0.4M was taken by taking the average of 5 which is 2.5 and then rounding up. I believe this is the amount of sodium chloride concentration in the potato cells as there is no increase in mass due to the following reason. Therefore, the line is drawn hitting the x-axis as there is no y value because there is no increase or decrease in mass. Since the isotonic point/osmotic potential of the potato cell is hypothesized to be 0.4M, the solutions containing the concentrations of 0.6M and 0.8M can be considered Hypertonic as they have a greater molar value of sodium chloride compared to the potato resulting in a decrease in mass. As you can see, on the graph they are drawn in the fourth quadrant of the graph, the solution 0.6M is placed higher as it has a lower molar value of sodium chloride compared to the solution containing 0.8M.

To conclude, it is hypothesized that the concentrations of the sodium chloride solutions are inversely proportional to the change in mass, indicating if the salt concentration increases, there should be a decrease in mass.

Variables

Independent Variable (IV)

“The independent variable is the variable that is being manipulated/changed and it is assumed to have a direct effect on the dependent variable, the variable that’s measured” (McLeod, para 1). In this experiment, the independent variable is the concentration of the sodium chloride solution (sodium chloride solution) which is assumed to affect the rate of osmosis of the potato cylinder. A range of 5 different concentrations of sodium chloride solution will be used: 0.0M , 0.2M, 0.4M, 0.6M and 0.8M (contains the highest concentration of sodium chloride). ‘M’ which can also be written as mol/ dm³ is used to represent the unit of Molar, “Molar refers to the unit of concentration molarity, which is equal to the number of moles per liter of a solution” (Helmenstine Ph.D). As mentioned in the hypothesis and explanation for the predicted graph, the sodium chloride solution containing the concentration of 0.0.M has zero molar value of sodium chloride, hence distilled water will be used as it lacks sodium chloride and any other impurities which may hinder the result. All other solutions used in this experiment will contain distilled water.

Dependent Variable (DV)

“The dependent variable is the variable that is being tested and measured in an experiment” (McLeod).In this experiment, the dependent variable is the average change in mass (g) of potato cylinders which will be calculated by measuring the initial mass and the final mass and then subtracting the final mass from the initial mass. The ‘g’ stands for the CGI unit used to measure mass called ‘grams’. Both positive and negative values will be expected depending on the tonicity of the solutions used.

Controlled Variables CV)

“Control Variables are properties that researchers hold constant for all observations in an experiment…Keeping their values consistent helps the study establish the true relationships between the independent and dependent variables”- Frost (Frost), In this experiment, there are 7 main variables that need to be controlled - the source of the plant cell (no unit), the volume of the 5 different concentrations of Sodium Chloride (ml), the length and width of each potato cylinder (cm), measuring the initial mass, measuring the final mass, the room temperature and the duration at which the potato cylinder is placed in the solution.

How will the controlled variables be controlled? Why do these variables need to be controlled?

The source of plant cells

The source of the plant cell will be kept constant by using one large whole potato for all 3 trials of the experiment. The source of plant cells needs to be controlled in order to ensure that potato cylinders which will be cut later all have the same concentration of Sodium i.e salt concentration. If the concentration of sodium chloride is not the same for all cells, this can result in all different potatoes having different osmotic potentials/ isotonic points which can result in the true osmotic potential of the potato not being found.

The volume of the 5 different concentrations of the sodium chloride solutions (ml)

The volume of the different solutions will be kept constant by using a graduated cylinder which has a sensitivity of 5ml. This will allow us to accurately measure the liquid to 3ml. The graduated cylinder will then be viewed at eye level to prevent parallax error and in order to ensure that the volume of the solution is 3ml. ( The following process will be practised for all 3 trials of the experiment). The volume of the different concentrations of the sodium chloride solutions has to be controlled in order to ensure that the ratio of water to sodium chloride doesn’t change and the values of 0.0M, 0.2M, .4M, 0.6M, 0.8M are not altered to prove that the change in mass is caused due to the different concentrations of the sodium chloride solutions and not the different volumes of the sodium chloride solutions.

The length and width of each potato cylinder (cm)

The width of the potato cylinder will be kept constant by using a cork borer which will ensure that all the cylinders have a uniform width. To ensure that the width of the cylinder is uniform a Vernier Caliper will be used to check the width of each cylinder. Readings will be obtained by placing both the potato cylinder and vernier caliper on a flat surface and then taking the readings by viewing the cylinder from directly above the caliper at eye level in order to reduce/eliminate parallax error.

The length of the potato cylinder will be kept constant length of 1 cm by using a ruler to measure the length of the cylinder and then using a scalpel to trim the necessary amount. Readings will be obtained by placing both the potato cylinder and ruler on a flat surface and then taking the readings by viewing the cylinder from directly above the ruler at eye level in order to reduce/eliminate parallax error.

This variable needs to be controlled in order to ensure that all 5 potato cylinders have the same surface area to make sure that all cylinders can absorb the same amount of the concentrated solution to prevent the rate of osmosis from being negatively affected. This is because the larger the surface area - the increase in the rate of osmosis meanwhile the smaller the surface area - the decrease in the rate of osmosis.

Measuring the initial mass of the potato cylinder

When a petri dish is added on electronic balance it needs to be ensured that the ‘TARE’ button is pressed in order to ensure that the mass of the petri dish does not account for the mass of the potato. If the electronic balance does not have this button or problems are faced, the mass of the petri dish should first be noted down and later subtracted after measuring the mass of the potato cylinder and petri dish. The following variable has to be controlled in order to prevent the results from being negatively affected and giving a false positive/negative result when calculating the change.

Measuring the final mass of the potato cylinder

Use a dry paper towel to gently pat the potato cylinder dry to remove extra water and ensure that no excess mass is added.

When a petri dish is added on electronic balance it needs to be ensured that the ‘TARE’ button is pressed in order to ensure that the mass of the petri dish does not account for the mass of the potato. If the electronic balance does not have this button or problems are faced, the mass of the petri dish should first be noted down and later subtracted after measuring the mass of the potato cylinder and petri dish.

The following variable has to be controlled in order to prevent an excess mass from being added to the potato cylinder. This will allow us to find the true mass of the cylinder and prevent the results from being negatively affected and giving a false positive/negative result when calculating the change.

The room temperature (°C)

The room temperature should be kept constant by keeping the test tubes in a room with artificial light and closed windows and curtains in order to ensure that the light and heat from outside do not affect the test tubes. The room temperature has to be controlled as at a lower temperature, the rate of osmosis decreases and at a higher temperature, the rate of osmosis increases. Therefore keeping the temperature the same throughout the experiment can ensure that the rate of osmosis isn’t affected.

Duration of the potato cylinder in the solution

The duration of which the potato cylinders will be kept constant is by setting the timer with the sensitivity in hours at 16 hours, in order to ensure that all solutions will be kept in the 5 different solutions for the same period of time. The duration of the potato cylinder in the solution needs to be controlled because if some cylinders were left in the solution for longer, more osmosis would occur and if the potatoes were left for a shorter period of time then less osmosis would occur in the cells, this can result in the final mass and the average change in mass is affected resulting in a false positive or negative change.

Materials and Equipment needed to conduct 1st trial

• A whole, large potato - 1 unit

• Cork borer - 1 unit

• White cutting board with the dimensions of 12x8 inches - 1 unit

• Clear plastic ruler ( sensitivity ± 1 cm) - 1 unit

• Scalpel - 1 unit

• Glass beakers (no specific sensitivity) - 5 units

• Different coloured opaque, whiteboard markers - 5 units

• Test tubes (no specific sensitivity) - 5 units

• Test tube rack - 1 unit

• sodium chloride solution containing a concentration of 0.0 M - 3ml

• sodium chloride solution containing a concentration of 0.2 M - 3ml

• sodium chloride solution containing a concentration of 0.4 M - 3ml

• sodium chloride solution containing a concentration of 0.6 M - 3ml

• sodium chloride solution containing a concentration of 0.8 M - 3ml

• Graduated cylinder (sensitivity - 10ml) - 5 units

• Pipette - 1 unit

• Clear petri dish - 1 unit

• Electronic balance (sensitivity - 2 decimal places) - 1 unit

• Wooden Skewer - 1 unit

• Timer (sensitivity - hours) - 1 unit

• Paper towels - 2-3 units

• Word processing software ( preferably ‘Word’ or ‘Google Docs’)

• Graph paper - 1 unit

• Pencil - 1 unit

• Ruler - 1 unit

Safety precautions

The sodium chloride concentrations - Ensure that before starting the experiment all open wounds and scratches are covered to prevent the sodium chloride solution from having contact with skin, although the sodium chloride solution is not harmful, putting sodium chloride on wounds can directly raise the pain. If the following does happen, make sure to use a wet cloth and gently tap the affected area. Ensure that the sodium chloride solution also does not come in contact with the eyes as it can cause itchiness and redness. If sodium chloride accidentally does go into the eyes inform an adult and ensure to flush the affected eye/eyes, this can be done by placing the affected eye under the tap for a couple of minutes.

Scalpels - Scalpels are sharp, hence ensure that the scalpel is being held by the handle and is a safe distance away from the body and other people. Ensure that the scalpel is placed on the table and is not left on the ground or held in the hand when not in use. In case of a cut ensure that an adult is informed and the cut is cleaned using antiseptic and finally covered with a bandaid.

Cork borer - The cork borer will be inserted with a large amount of force into the potato, therefore it is important that the force doesn’t cause the cork borer to pierce the hands. To prevent this, ensure that when the dominant hand is holding the cork borer then the other hand should be holding the potato in place to prevent it from sliding across the surface resulting in injuries.

Step Up

Step 1 - Gather 5 beakers and 5 different coloured opaque whiteboard markers. The sensitivity of the beakers does not matter, however, ensure that all 5 beakers have the same scale in order to avoid confusion. Label each beaker with the sodium chloride concentrations of the 5 solutions using specific coloured markers to write each concentration on the surface of the beaker, for instance, the colour green could be used to write the concentration of “0.0 M” on the surface of the beaker.

Step 2 - Gather a test tube rack and 5 test tubes and the same 5 colours of the opaque whiteboard used in step 1. The sensitivity of the test tubes does not matter, however, ensure that all 5 test tubes have the same scale in order to avoid confusion. Label the 5 test tubes with the concentration of a solution using different colours, for organizational purposes, it is strongly recommended that the same colour used in step 1 is used to label the same concentration level on the surface of the test tube. For example, label the concentration of “0.0 M” on the surface of the test tube using a green marker. After labelling all 5 test tubes, place them into the test tube rack in an ascending order.

Method to conduct 1 trial

1. Place the large, whole potato on the surface of the white 12x8 inch cutting board, pick up the cork borer which is placed on the left-hand side (as per the setup) and hold the handle of the cork borer with your dominant hand and hold the potato in place with your other hand. Exert force in order to insert the cork borer vertically into the potato in one go. Once the cork borer passes through the potato, retract the cork borer and take out the potato cylinder which has been carved out by the cork borer.

2. Repeat step 1 until 5 potato cylinders have been collected. Ensure that all potato cylinders are placed at the upper right corner of the cutting board for convenience when doing the next step. The whole potato can now be taken off the cutting board.

3. Take a ruler with any sensitivity greater than or equal to 1 and place it in the centre of the cutting board. Take a potato cylinder from the upper right corner of the cutting board and place the cylinder directly above the ruler, ensuring that the ruler doesn’t scratch or pierce the potato cylinder as it can affect the surface area of the cylinder and in turn the rate osmosis. Measure the length of the cylinder, making sure that it has a fixed length of 1 cm. Ensure parallax error is reduced by viewing the ruler at eye level.

4. If it has the exact length of I cm, place the cylinder on the uppermost left side of the cutting board. If the length of the cylinder is too short, dispose of the potato cylinder and cut out a new cylinder using a cork borer, measure the cylinder in order to ensure that it is 1 cm long. Follow this step for all the potato cylinders which are either the perfect length or for those cylinders which are too short.

5. If the potato cylinder is too long, use a scalpel present on the left-hand side to trim the excess length until it is 1 cm. Follow the following step for all potato cylinders which are too long.

6. After ensuring that the length of all potato cylinders is 1cm, remove the ruler from the cutting board and place a vernier calliper in the centre of the board, take and use it to check that the widths of all cylinders are the same. This step isn’t required, however, doing this extra step will further ensure that all cylinders are uniform - ensuring that the controlled variable is well controlled. Ensure parallax error is reduced by viewing the caliper at eye level.

7. Gather an electronic balance which has a sensitivity of 2 decimal places and a clean petri dish. Turn on the electronic balance and ensure that the scale reads “0.00g” before placing any objects. Then, place the clear petri dish on the scale and press the red button on the balance labelled ‘ TARE’, this will bring the mass back to 0.0g, in order to ensure that the mass of the petri dish doesn’t affect the mass of the potato cylinders.

8. Ensure that all the potato cylinders are placed on the upper right-hand side of the cutting board in order to ensure easier transport of the cylinder. Use fingers to gently hold and transport one of the potato cylinders from the cutting board and place it into the petri dish. Ensure that the cylinders are not scratched or pierced as this could affect the surface area and therefore the rate of Osmosis.

9. Place each potato cylinder on the beam balance and ensure that all of the cylinders have somewhat of an equal mass. Note down the mass of each potato cylinder in a document as the initial values of the potato cylinders will be needed later onwards.

10. Place each potato cylinder into all 5 test tubes, then use a pipette to squeeze the solution containing the concentration of 0.0M and then pour it into a clean graduated cylinder with a sensitivity of 5ml. Fill the graduated cylinder with 3ml of the solution and avoid parallax error when measuring the volume of the solution by viewing the measuring cylinder at eye level.

11. Repeat step 10 for all 5 solutions. Ensure that both the pipette and graduated cylinder are cleaned properly to prevent the sodium chloride to water ratio changing which can affect the rate of osmosis.

12. After all test tubes have been filled with their respective solutions, use a timer with the sensitivity of hours to set the timer for 16 hours.

13. Leave the test tube in a room with constant temperature and light for 16 hours.

14. Ensure that this time is used productively in order to make 2 data tables - one to hold the initial, final and change in mass for all 3 trials and the second table to hold the change of mass and the average change in mass. An example of both results tables can be found on page….. ensure all titles are written as well as the concentration of sodium chloride solutions and initial masses of all potato cylinders are filled in.

15. After 16 hours, once again set up the electronic balance and Perri dish per step

16. Gently pour the solution in each of the 5 test tubes into the sink, ensuring that the potato does not fall into the sink. Ensure that a device with the image of the table created in step 14 is open and nearby.

17. Take the potato cylinder which was placed in the solution containing the sodium chloride concentration of 0.0M and then Gently pat it using a paper towel and then place it on the petri dish. Ensure that no extra water is on the petri dish as this can result in inaccurate results later on when calculating the average change in mass.

18. Repeat step 17, ensuring to write all the data collected in the digital table.

19. Once the first table for values is filled, copy and paste the change observed for each concentration for all 3 trials in the second table.

20. Calculate the average mass by adding all 3 masses And then dividing it by 3.

21. Clean all the equipment used thoroughly with soap and water

22. Gather graph paper, a pencil, an eraser and a ruler in order to sketch out a graph to better understand the relationship between independent and dependent variables.

23. To do the following draw a horizontal line of the 12fh bolded line on the graph and a horizontal line on the 5th line of the graph. Label the horizontal line/ x-axis "the salt concentration (M)” and the vertical line/y-axis “the average change in mass (g)”.

24. Use the scale of 0.010 in order to plot all the data points from the second table.

25. Draw the line of best fit by drawing a line “what divides the area that encloses the data in two evenly sized areas.”(“Constructing a Best Fit Line”).

Results table

Table 1 - The following table illustrates how manipulating the independent variable -the concentration of sodium chloride solutions (M mol/ dm³) by changing the concentration of sodium chloride can directly affect the mass of the 1 cm potatoes which were placed in 3ml of different solutions for 16 hours. For each trial of the experiment, the change has been calculated by subtracting the initial mass from the final mass (final mass - initial mass).

Table 2 - The following table illustrates the final changes of all the trials per solution and illustrates the average change (+/-) in the final column. The final change was calculated by adding all 3 final changes and then devising the total by 3 ( final change trial 1 + final change trial 2 + final change + final change trial 3 / 3)

Graph Analysis + Final Evaluation and Findings

The final graph titled “ A final graph illustrating the true relationship between the independent and dependent variable of the ‘Osmosis Investigation - How the different concentrations of the sodium chloride (M) affect the average change in mass (g)” has been drawn as per the standard graphing rules, with the independent variable on the x-axis and the dependent variable on the y-axis, the graph has been drawn from the range of -0.100 to +0.160 in order to present the data collected in the most logical and clear way as possible.

The final graph illustrates a downward trend as per the line of best fit which shows the values of average change in mass decreasing/ going in a descending order from +0.046 to +0.020 to +0.153 to -0.033 and finally to -0.050. The line of best fit drawn also illustrates the downward trend as the line passes from the y-intercept and cuts into the x-axis and forms a point in the fourth quadrant of the graph.

Since the mass decreases as the concentration of the Sodium Chloride solution increases, the true relationship between the independent and dependent variables can be described as the variables being inversely related but not inversely proportional. The term in inversely proportional can be defined as “ when two quantities are related to each other inversely when an increase in one quantity brings a decrease in the other and vice versa then they are said to be inversely proportional. In this, if one variable decreases, the other increases in the same proportion.”(“Inversely Proportional- Definition, Formula & Examples”, para 3.) The general formula of inverse proportionality can be written as y = k/x, the letter ‘x’ and ‘y’ represent the x and y axis respectively and the letter ‘k’ represents the constant of proportionality, therefore the relationship cannot be described as inversely proportional as both values are not increasing in the same proportion.

Due to the independent variable and dependent variable not being inversely proportional to one another, the general formula to cannot be derived by substituting the x and y values from the graph and into the formula y = k/x and then re-arranging it so that k= y*x, to find the value of the constant and therefore finding the general formula.To answer my research question that is “How does the independent variable of the experiment- the concentration of the Sodium Chloride solution directly or indirectly affect the dependent variable of the experiment - the change in mass and ultimately the rate of osmosis in the plant cells of a potato cylinder?”. The simple answer would be that both variables are inversely related.

To conclude, it can be stated at the y-intercept the mass is the greatest as the concentration of the solution - 0.0M has zero molar value of salt and higher osmotic potential, allowing the water from the solution (higher concentration) to flow into the cells of the potato (containing lower concentration), as the water content in the cells of the potato increasing the mass and the turgidity of the cell to generate a force (“Osmosis and Tonicity Review”, para 4), and the cell doesn’t burst due to the pressure due to the presence of the cell wall and the cell wall can “withstand the turgor pressure of the turgid cell contents by exerting counter wall pressure.”(Doubtnut, para 1 ). To continue, it can also be stated that the concentration containing 0.2M of sodium chloride is also a hypotonic solution as an increase in mass can be observed, but due to the presence of some sodium chloride, the mass didn’t significantly increase as compared to the solution containing 0.0M of salt. Therefore it can be confirmed that the higher the lower the salt concentration the greater the increase in mass (Constantopoulos, Jackson and Enke, para 1 ). The solution containing the sodium chloride concentration of 0.4M can be confirmed to be the isotonic point/ osmotic potential of the cell. This means that the concentration of Sodium chloride in a potato is 0.4M, therefore both the solution had the same concentration of salt and water potential resulting in the mass not being affected due to the lack of a water potential gradient. Therefore, the osmotic potential of the potato cells can be classified. The solution containing the sodium chloride concentration of 0.6M is a hypertonic solution as the solution contains a higher molar value of salt compared to the molar value of the potato which is 0.4M, therefore a decrease in mass can be observed. The last concentration of sodium chloride containing 0.8M is also a hypotonic solution as this solution possesses a greater molar value of salt as well as osmotic potential. However, the decrease in mass would be greater compared to the solution containing 0.6M of salt concentration therefore there would be a greater decrease in mass as presented in the graph from -0.033 to -0.50.

The results agree with the scientific reasonings stated in the hypothesis as the hypothesis written outlines the concepts of “the 3 tonicities of the salt solutions being hypotonic, hypertonic and isotonic”, and how each tonicity is different from the other in terms of molar value of salt and osmotic potential. The hypothesis also discusses the isotonic point/osmotic potential of the cells to be 0.4M, which is the same value which was obtained after sketching the final graph, proving the prediction to be correct. However, the one mistake which can be identified in my hypothesis is the statement that "To conclude, it is hypothesized that the concentration of the sodium chloride solutions are inversely proportional to the change in mass, meaning if the salt concentration is increased, that there should be a decrease in mass.” As stated in the above description of the relationship between the independent and dependent variables, the independent variable - the concentration of the different solutions (M) and the dependent variable - the average change in mass (g) can only be stated as having an inversely related relationship as both the independent and dependent variables do not increase and decrease respectively at the same rate.

Evaluation of the validity of the hypothesis based on the outcome of the investigation

A downward trend can be seen as the line of best-fit travels from the y-intercept on the graph which has the highest value of +0.046 to +0.020 to +0.153 to -0.033 and finally to -0.050 and it can be observed that the values of the average change in mass go down the graph in descending order as stated in the paragraph. 0.4M was predicted to be the osmotic potential of the cell, which is proven to be true. However as stated in the graph analysis, there is no inversely proportional relationship but rather an inversely related relationship between the 2 variables.

Evaluation of the validity of the method and potential improvements of the method that would benefit the investigation

The two main improvements that would benefit this investigation pertain to better controlling the control variables of the experiment as well as organizing data in a much clearer manner.

One of the control variables which has to be better controlled next time is the volume of the 5 different concentrations of the Sodium Chloride solutions, it can be believed that the wrong sensitivity was used for the graduated cylinder as the sensitivity of the 3 ml solution was measured using the scale going up by 5’s. Therefore a parallax error may have occurred even after viewing the graduated cylinder at eye level due to the extremely small values and incorrect sensitivity being used- hindering the data collected and causing a false positive/negative value for the average change in mass. Therefore, next time when the same experiment is being conducted, it should be important to use a graduated cylinder which has a sensitivity of 3ml.

Furthermore, another controlled variable which could have been better controlled is the room temperature, as stated in the method, the test tubes should be left for 16 hours and it was the majority decision made by the group to leave the test tubes overnight however the change in room temperature and light was never considered, and the setup and method was completed in the morning and according to the weather forecast on 5th April the temperature during the mid-day/ evening was 29.5°C and the temperature during the night was 28.7°C and when the results were collected the next morning on 6th April was 27 °C. It can be believed that the temperature did alter the rate of osmosis and the results as a whole due to close proximity of the value for each temperature. However, if the following experiment was conducted in the future, I would ensure to conduct the trial from early morning to mid-afternoon or consider placing it in the test tubes in a room with artificial light and closed curtains to keep this variable constant. It would also be beneficial to conduct more trials. The initial mass of the potato was also not the same for all 15 cylinders, therefore parallax error may have occurred when trimming the length or caused due to not measuring using a vernier caliper.

Extensions to the investigation

If I had the opportunity to conduct the ‘Osmosis investigation" again instead of investigating how the independent variable, the concentration of different sodium chloride solutions, affects the dependent variable, the average change in mass, I would like to investigate how the independent variable, different surface areas of potato cylinder, affect the dependent variable, the average change in mass. In order to conduct this experiment I would use potato cylinders of different sizes such as 1cm, 3cm, 5cm, 7cm and 9cm. The different sizes can be obtained by using different-sized cork borers. The controlled variables for this experiment would be the concentration of the glucose solution (M), the volume of the glucose solution (ml), the source of potato cells, measuring the initial and final mass of the potato cylinders (g) and the duration the cylinders are placed in the solution. I would hypothesize that the smaller the pieces of the potato, the larger the surface area of the potato is exposed to the glucose extracellular solution which will have a constant molar value of 0.5. Therefore, it could be reinstated that the 1 cm cylinders would have the largest surface area exposed to the extracellular solution, hence the rate of osmosis would be the highest compared to other cylinders. Moreover, the cylinders with the least surface area which is 9 cm will be less exposed to the extracellular solution, resulting in the rate of osmosis being the lowest compared to other potato cylinders. To conclude, I believe that the surface area of the potato cylinder (cm²) will be inversely related to the average change in mass (g).

I would follow a similar method to the one conducted for this investigation. I would measure the initial mass of the different-sized potato cylinders using an electronic balance and then place the cylinders in a beaker with a sensitivity of 1ml and then pour the same glucose solution into each beaker which has a concentration of 0.5M. I would leave the beakers for 7 hours and then pat the cylinders dry and measure their final mass using an electronic balance, in order to find out the true relationship between the independent and dependent variables.

How does the investigation relate to the inquiry statement?

The inquiry statement is the structural form of plants that allows them to carry out their functions which form the basics for ecosystems and the interactions within them.“Osmosis is the movement of water molecules from a higher water potential to a lower water potential, down a water potential gradient across a partially-permeable cell membrane. Osmosis is a passive process, hence energy is not required to carry out this process" (“What Is Osmosis?”, para 1). The partially permeable cell membrane is the most important structural form needed in order for osmosis to take place in both plant and animal cells. The process of osmosis has a deep positive impact on the ecosystem as this passive process can be used to “cultivate and broth dewatering for the production of algae biofuels” (Hoover. A, A.Philip, Traferri, Yip, Elimelech, table 1), reducing and possibly eliminating the world’s biggest global issue of releasing abundant gaseous emissions and greenhouse gasses resulting in global warming. Another global issue that the process of osmosis has a positive effect on is the issue of soil erosion and deterioration. This is because “brackish water ion can be used for irrigation of crops and fertilizer”(Hoover. A, A.Philip, Traferri, Yip, Elimelech, table 1), reducing global warming will result in a richer ecological life support or in other terms biodiversity. Biodiversity can increase the supply of oxygen, control pests and increase the rate of pollination in plants. The benefits of using brackish water to prevent soil erosion and degradation increase soil fertility thereby resulting in richer crops being produced and positively affecting the crop yields.

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