Determining the Solute Concentration of a Potato Based on Change in

Percentage of Change in Mass Caused by Osmosis

Research question: What is the solute concentration of a potato (in terms of its

osmotic potential) as determined by the change in percentage mass when submerged

in different sucrose solution concentrations?

Variables:

1. Dependent variable: The percentage change in mass of the potato pieces after

being submerged in the sucrose solutions.

● Measurement: Mass will be measured using a digital balance.

● Units: Grams (g).

● Uncertainty: ±0.01 g (based on the precision of the balance).

2. Independent variable: The concentration of solution in which the potato pieces are

submerged.

● Levels:

○ 0.25% (0.0025 g/mL)

○ 0.5% (0.005 g/mL)

○ 0.75% (0.0075 g/mL)

○ 1% (0.01 g/mL)

Why these levels were chosen:

These levels provide a range of concentrations to capture a gradient from hypotonic to

hypertonic conditions, ensuring that the isotonic point (where there is no net mass
change) can be determined. Moreover, these are small increments, allowing a more

precise determination of the potato's osmotic potential.

3. Constant/controlled variables:

● Duration of submersion: Submersion of all potato pieces in solution for a fixed

amount of time of 15 minutes. Doing this prevents unequal exposure time, which

could lead to variations in osmotic equilibrium.

● Temperature of the environment: Conduct the experiment at room temperature or

in a controlled-temperature setting to prevent the impact of different temperatures

on the kinetic energy of molecules and the rate of osmosis.

● The volume of solution: 100mL of solution in each container to hinder the impact

of different submersion times on the rate or extent of osmosis.

Hypothesis: The percentage change in mass of the potato sample will decrease as the

concentration of NaCl in the solution increases. At an intermediate concentration, the

potato mass will remain relatively unchanged, indicating the isotonic point. This occurs

because of osmosis, where water moves from areas of high to low water potential. In

lower sodium chloride concentrations, water enters the potato cells, increasing their

mass. In higher concentrations, water leaves the cells, reducing their mass. At the

isotonic point, water movement is balanced, causing no significant mass change.

Material list:

-Salt Solutions (0.25%, 0.5%, 0.75%, 1%) 100ml each

-Potatoes
-4 Clear Plastic Cups

-Scale

-Cork borer

-Knife

-Tweezers

-Graduated Cylinder

-Masking tape

-Marker

Procedure:

Prepare the Potato Samples:

● Use the cork borer to extract cylindrical potato pieces from the potato.

● Trim the potato cylinders to equal lengths using the knife, ensuring uniform size.

● Measure and record the initial mass of each potato piece using the digital scale.

Prepare the Solutions and Containers:

● Use the graduated cylinder to measure 100 mL of each salt solution (0.25%,

0.5%, 0.75%, 1%).

● Pour each solution into a separate plastic cup.

● Label the cups with masking tape and a marker to indicate the solution

concentration.

Submerge the Potato Pieces:

the salt solution.

● Use tweezers to handle the potato pieces carefully.

Control the Conditions:

● Keep all cups at room temperature or in a controlled environment (approximately

25°C).

● Ensure all cups contain the same volume of solution (100 mL).

● Allow the potato pieces to soak in the solutions for a fixed duration of 15 mins.

Remove and Dry the Samples:

● After 15 mins, use tweezers to carefully remove the potato pieces from the cups.

● Gently blot the potato pieces dry with paper towels to remove excess surface

liquid.

Measure the Final Mass:

● Weigh each potato piece again using the digital scale and record the final mass.

Calculate Percentage Mass Change:

● Use the formula:

Percentage change in mass = [(Final mass - Initial mass) / Initial mass] x 100

Repeat the Experiment:

reliability of the results.

Analyze Results:

● Plot the percentage mass change against salt concentration to determine the

isotonic point, where no significant mass change occurs. This indicates the solute

concentration inside the potato cells.

Data presentation and analysis:

Individual data

Trial 1 Concentration of NaCI Solution

0.25% 0.5% 0.75% 1% 0%

Piece 1 Initial 1.50 1.53 1.39 1.70 1.68

(large) mass (g)

Final 1.60 1.58 1.43 1.71 `1.80

mass (g)

% change 6.67% 3.27% 2.88% 0.59% 7.14%

in mass
Piece 2 Initial 1.2 1.37 1.11 1.11 0.86

(smaller) mass (g)

Final 1.29 1.43 1.17 1.12 0.94

mass (g)

% change 7.5% 4.38% 5.41% 0.90% 9.30%

in mass

Group Data

% Change in mass(group data)

Concentratio 0% NaCl 0.25% NaCl 0.50% NaCl 0.75% NaCl 1.00% NaCl

n of solution

Piece 1 7.14 6.67 3.27 2.88 0.59

Piece 2 9.30 7.5 4.38 5.41 0.90

Piece 3 6.88 1.47 0.54 -1.52

Piece 4 7.46 2.42 0.00 1.45

Piece 5 6.13 7.14 1.74 0.00

Piece 6 6.99 7.03 0.83 -2.86

Piece 7 3.95 3.37 1.37 1.12

Average % 6.96 7.00 5.00 1.79 0.29

change in

mass

Standard 1.43 1.95 2.95 1.59 1.62

deviation

The data and graph demonstrate the effect of varying NaCl concentrations on the

percentage change in mass of tissue samples, illustrating the principles of osmosis. At

lower NaCl concentrations (0–0.25%), the solution is hypotonic, leading to water entry

and mass gain, while higher concentrations (0.75–1%) are hypertonic, causing water
loss and a mass decrease. The regression line indicates that the isotonic point, where

no net mass change occurs, is approximately 1.07% NaCl, suggesting that the solute

concentration inside the potato cells is about 1.07%. At this concentration, the osmotic

potential inside and outside the cells is balanced, resulting in no net movement of water.

This predicted solute concentration aligns with the data trend and reinforces the

principles of osmosis, with group averages smoothing out variability and providing

clearer insights.

Conclusion:

The research aimed to determine the solute concentration of potato cells by analyzing

the percentage change in mass caused by osmosis when the cells were submerged in

NaCl solutions of varying concentrations. The hypothesis proposed that the percentage

change in mass would decrease as the NaCl concentration increased, with an isotonic

point where the mass change would be zero. The data supports the hypothesis,

showing a clear trend of mass gain in hypotonic solutions (0–0.25% NaCl) and mass

loss in hypertonic solutions (0.75–1.0% NaCl). The isotonic point, indicated by the

regression line, was approximately 1.07% NaCl, suggesting the potato cells' solute
concentration is around this value, where the osmotic potential is balanced and no net

water movement occurs.

This investigation had several strengths, including controlled variables such as solution

volume, submersion time, and temperature, ensuring consistency and reliability.

Additionally, using multiple trials and averaging group data minimized individual

variations and enhanced accuracy. However, there were limitations, such as slight

inconsistencies in the size and surface area of potato samples, which could influence

the rate of osmosis. The increments of NaCl concentration tested (0.25%) might not

have been fine enough to precisely pinpoint the isotonic point. To improve, future

experiments could use more uniform potato pieces, finer concentration increments, and

longer submersion times to allow for a more complete osmotic equilibrium.

The accuracy of the answer is relatively high, as the isotonic point was determined

using a regression line based on multiple trials and averaged data, reducing individual

variability. However, some factors may affect the precision, such as minor

inconsistencies in the size and surface area of potato samples and slight inaccuracies in

mass measurements.

To improve accuracy, the experiment could include:

1. Finer concentration increments: Using smaller steps (e.g., 0.1% instead of

0.25%) would allow for a more precise determination of the isotonic point.

2. More trials: Increasing the number of trials for each concentration would help

reduce the impact of random errors and enhance reliability.

pieces would ensure consistent size and surface area.

Further investigation could explore the effects of other solutes, such as sucrose, to

compare osmotic potentials across different plant tissues. Testing under varying

environmental conditions, such as temperature or pH, could provide additional insights

into factors affecting osmosis. This study has successfully identified the approximate

solute concentration of potato cells, and refining these methods could enhance

accuracy and broaden understanding of osmotic behavior in biological systems.