Osmosis in potato cells

1.0 Abstract
This experiment’s ultimate goal is to find the water potential of the potato cell. This was achieved through placing potato cores in different concentrations of sucrose (0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 2.0%, 3.0% and 4.0%) solution and to observe how much water was gained or lost through osmosis to reach a prediction of the concentration within the potato cell. The results displayed that the concentration of sucrose within the potato cell is 1.7% and that as the amount of sucrose is increased in the external fluid, the less mass the potato will gain until the concentration is 1.7% – this is when the potato begins to lose weight. It was also shown that the rate of osmosis slows in the second 24 hour it is in the sucrose solution. 3.0 Introduction

3.1 Background information
It is critical to understand how osmosis works through diffusion to reach equilibrium before studying how different concentrations of solutes affect the osmotic rate, and consequently, the mass of the potato – which is the purpose of this experiment. Explaining the osmotic movement of water is essential to understand how plants regulate their total fluid volume (J. Darnell. 2014). According to HyperPhysics, diffusion is the result of particles intermingling due to their random kinetic forces that are absorbed by their surroundings. A distinguishing feature of diffusion is the mixing of particles, rather than mass movement. The particles move from a region of high concentration to an area of low concentration or move down the concentration gradient (BBC, GCSE BiteSize 2014).

Osmosis is a type of diffusion where a spontaneous amount of water moves through a semi-permeable membrane from a region of low solute concentration to an area of high solute concentration in order to reach equilibrium; to become isotonic. To be isotonic means have an equal percentage of solute concentration of either side of the membrane which displays osmotic equilibrium (biologyjunction.com, 2014). If one side of the membrane has a lower amount of water, resulting in a lower osmotic pressure, the movement of water moves into the area. This is called a hypotonic solution where as a hypertonic solution results in a higher osmotic pressure and water will be leaving the solution. Both diffusion and osmosis are forms of passive transports. Passive transport general function is to maintain equilibrium opposed to active transport that transports nutrients through special pumps or channels of the cell membrane.

The experiment applies the principal of osmosis as the water moves from an area of low sugar concentration to an area of high sugar concentration. Whether the water moves from the outside into the potato cells or diffuses through the potatoes semi permeable membrane to the outer area depends on the concentration of the sucrose dissolved in the water. When a sucrose concentration is reached where no water diffuses either in or out of the cell, the potato will neither gain nor lose weight and the concentration of sucrose in the potato has been found (Biology.clemson.edu, 2014). The overall design of this experiment is an extremely simple set up which clearly demonstrates the works of osmosis by measuring the mass of potato cores after being soaked in various concentrations of sucrose solution for two days.

The mass of each will be recorded at 24 hours and then again at 48 hours, to provide data for an approximate curve of when osmosis is fastest to when or if the line plateau’s out, indicating that equilibrium has been reached. These curves between each concentration of solution can be compared to create a visual comparison of osmosis. A control was also included in this experiment to eliminate the independent variable in one group of potato cores so the differences and similarities of the other groups which include an independent variable can be brought into perspective. 3.2 Aim

The aim of this experiment is to demonstrate the effects of different concentrations of sucrose solution during the process of osmosis across potato tissue and to discover the water potential of the potato cells. 3.3 Hypothesis

If the concentration of sucrose (C12H22O11) is increased, the potato will have less mass compared to less concentrated sucrose solutions because the rate of osmosis will decrease as the higher concentration of sucrose molecules will prevent water crossing the cell membrane.

4.0 Method
4.1 Variables
TYPE OF VARIABLE
VARIABLE
SUPPORTING INFORMATION
Independent
Concentration of sucrose
0.2%, 0.4%, 0.6%, 0.8%, 1.0% and 0% concentration of sucrose solution was used making it the independent variable. Dependent
Mass of potato core
The mass of the potato core depends on the concentration of the sucrose solution it is submerged in. Controlled
Time potatoes are in solution
The time the potatoes were in the solution was controlled to 48 hours. Uncontrolled
How much mass each potato will gain/lose
The mass each potato gained or lost was predictable however uncontrollable.

4.2 Materials
X6 washed potatoes
Sucrose (measured in separate cups 0.2g, 0.4g, 0.6g, 0.8g, 1.0g, 2.0g, 3.0g, 4.0g) X6 100mL distilled water
Electronic balance
X7 plastic cups
Measuring cylinder
9mm Cork borer
Cutting board
Marking tape
Tweezers
Stirring rod
4.3 Method
1. 12 potato cores were cut on to the cutting board using a cork borer 9mm in width. Each core was cut to approximately 2 grams. 2. Marking tape was used to label the 6 plastic cups as 0.2, 0.4, 0.6, 0.8, 1.0, 2.0, 3.0, 4.0 and control solution. 3. 0.2g of sucrose was measured by the electronic scales in the appropriate cup. 4. 100mL of water was measured in the measuring cylinder then poured into the cup containing the measured amount of sucrose. This solution was then stirred until completely dissolved. 5. Step three and four was repeated for solutions 0.4, 0.6, 0.8, 1.0, 2.0, 3.0, 4.0 and a separate cup was measured for the control (distilled water). 6. The 12 potato cores were divided into six (6) groups of two (2).

7. Each group’s weight was measured on the electronic balance and the data was recorded. 8. The groups of potatoes were allocated a solution and placed gently with tweezers into its plastic cup. 9. The potato cores were removed with tweezers from the solution and re-weighed in a separate empty plastic cup after 24 hours of sitting in solution. The weight was recorded and the potatoes placed back in its original solution. 10. Step eight was repeated for all 6 groups of potato cores using the same cup to measure. 11. After another 24 hours step 8 was again repeated to determine the final mass of potatoes. These results were recorded. 12. The potato cores were then disposed of in the rubbish bin and the solutions were poured and washed down the drain. 4.4 Risk assessment

There was little risk involved in the substances that are being used in this experiment as sucrose solution has very few harmful properties. The largest risk in using sucrose solution is spillages either on the ground which creates a slip hazard or on the electronic balance which may lead to damage of the scale or low level electrocution. These risks will be reduced if the solutions bottle is kept away from the edge of the table and always has lid tightly fitted to prevent spillage on the floor. Having the lid fitted will also prevent spillage on the electronic balance; however it will be noted to keep the sucrose solution away from the balance or any power points. The only other risk involved in this experiment is in the use of a knife which is a sharp object and may pierce the skin and cause harm. This will be avoided by carrying the knife downwards not pointing towards or away from you, rather to the ground so if it is dropped, will fall on the ground causing no harm. HAZARD

Information
Risk
Management
Waste Disposal Method
Sucrose solution
0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 2.0%, 3.0%, 4.0%
May spill on the floor creating a slip hazard
Keep lid on at ALL times and away from the edge of the bench Down the sink then rinse

Core borer
9mm wide
Sharp edge may cut skin
The borer will always be carried with care and facing the ground

Electronic balance

If exposed to water may cause minor electrocution
Will be kept away from any liquids and liquids will be kept away from power points

From these results, it can be concluded that as the concentration of sucrose solution is increased, the mass that the potato cores gain decreased – proving the hypothesis to be correct. However when observing the rate of osmosis between 24-48 hours, there was a vague pattern of decreased osmotic activity as the concentration of sucrose was increased. The results varied as the 0.2 solution had a gain in mass of 6.22% while the 0.8% solution had a gain of only 1.85%. However in contrast to these results, only 3 of the 5 solutions examined decrease their percentage of change in mass.

These results completely disproved the theory that the change in mass for the second 24 hours measured will mirror the pattern which the first 24 hours showed. One similarity which all the results displayed was that the percentage of mass gained in the second 24 hours recorded decreased, concluding that the rate of osmosis does slow over time. Although this trial of results does disproved the theory that the concentration of sucrose will have a direct impact on how much mass the potato core will gain or lose in the second 24 hours, it does show a clear pattern of change in mass according to the hypothesis in the first 24 hours recorded. This display of random results in the second 24 hours was due to experimental error in uncontrollable variables such as changes in temperature and humidity. This biological theory which the gain or loss of mass in the potato cores can be linked to is osmosis.

Osmosis is the movement of the water from one side of the semi-permeable membrane of the potato cell to the other, caused by the concentration of sucrose. It was hypothesised that as the concentration increased the mass which the potato gained would decrease due to the larger sucrose molecules preventing the water from crossing the membrane. This statement is correct however it contains weak links to the theory of osmosis. The reason the potatoes gain of mass decreased was not due to the sucrose molecules ‘blocking the way’, however because when osmosis occurs, the water moves from an area of low sucrose concentration to an area of high sucrose concentration to level out both sides of the membrane and to reach equilibrium. If the hypothesis was correct, then if the solution the potato was submerged in was as concentrated as to be 50% sucrose solution the potato would still gain a slight amount of mass as a small amount of water could still possibly diffuse through the membrane into the potato.

However the results show differently. They show that when a potato is submerged in a solution of either 2.0%, 3.0% or 4.0% the potato will loss mass rather than gain. From graphing these results, a linear forecast line was drawn to find where, according to these results, the x-intercept was; allowing the concentration of sucrose of the potato cell to be found. The graph indicates a negative gradient and that the approximate concentration of sucrose inside the potatoes cells was 1.7%. From this discovery it can be concluded that the concentration of sucrose in which the potato would not gain nor lose any mass would be at 1.7%; or 1.7g sucrose in 100g water. If the concentration of sucrose in the external fluid was any greater, the potato will lose mass as water will be osmosing out of the cell in an effort to reach equilibrium with the surrounding environment.

6.3 Errors and improvements
The first weak link in the design was found when measuring and cutting the potato core manually. It was discovered that it was very difficult to measure the potatoes exactly to the correct millimetre and ensure all cores had the same surface area exposed to the solution. This error was improved as cutting the potatoes manually with a knife was replace with cutting the potatoes with a cork borer to ensure all cores had the same dimensions. Immediately after that issue, it was discovered that 20mL of sucrose solution was not enough to completely cover the three potato cores that were being examined.

It was concluded that it was best to increase the solution level to 100mL and also decrease the amount of potato cores in each solution to two (2) rather than three (3). This ensured that each potatoes surface area was exposed to the same amount of sucrose solution to assure that the most accurate results will be reached. Another point for improvement which could be argued as an error is how the potatoes were measured – based on weight rather than size. Although the diameter and circumference were the same on all potato cores, the density of each individual potato core will vary. This means that when the potatoes were cut to weigh two (2) grams, they could potentially still have different lengths creating a greater surface area. If this was the case, it would create another. 7.0 Conclusion

In conclusion the hypothesis was proven to be incorrect through the results as concluded from the experiment of 2.0g of potato core in solutions varying from 0.2% to 4.0% of sucrose. The hypothesis stated that ‘sucrose molecules will prevent water crossing the cell membrane’. If this statement was true, if the potato core was in any concentration of sucrose, it would always lose weight. However this was disproven as the results were plotted on a scatter graph and a prediction line was added, and displayed that once the concentration was greater than 1.7% sucrose, the potato would lose mass rather than gain it. This shows that the concentration of sucrose inside the potato cell is 1.7%. The concept of osmosis states that the water moves from an area of low concentration of sucrose to an area of high concentration of sucrose. This means that when the concentration of sucrose is higher than 1.7% in the external fluid then the potato will osmose water out in an attempt to reach equilibrium with the outside environment.

8.0 Bibliography
8.1 References
Biology.clemson.edu, (2014). Potato Water Potential. [online] Available at:
[Accessed 2 Aug. 2014]. College-cram.com, (2014). Passive Transport | Biology: Cell Membranes | College-Cram.com. [online] Available at: http://www.college-cram.com/study/biology/cell-membranes/passive-transport/ [Accessed 4 Aug. 2014]. Davis, I., Shachar-Hill, B., Curry, M., Kim, K., Pedley, T. and Hill, A. (2007). Osmosis in semi-permeable pores: an examination of the basic flow equations based on an experimental and molecular dynamics study. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Science, [online] 463(2079), pp.881-896. Available at: http://rspa.royalsocietypublishing.org/content/463/2079/881.short [Accessed 2 Aug. 2014]. Encyclopedia.com, (2014). osmosis Facts, information, pictures | Encyclopedia.com articles about osmosis. [online] Available at: http://www.encyclopedia.com/topic/osmosis.aspx [Accessed 2 Aug. 2014]. Marinelli, J. (2006). Planta. 1st ed. Madrid: Pearson-Alhambra. Potato osmosis. (2014). [online] Available at: http://dpbiologyiszl.wikispaces.com/file/view/Sample+Lab+Report-+Potato+Osmosis.pdf [Accessed 1 Aug. 2014]. Scienceclarified.com, (2014). Osmosis – body, used, water, process, Earth, plants, methods, animals, cells, cause, substance, plant, principle, Osmotic pressure, Osmosis in living organisms. [online] Available at: http://www.scienceclarified.com/Oi-Ph/Osmosis.html [Accessed 1 Aug. 2014]. Searcy, H. (2014). Writing in Science. [online] Monash.edu.au. Available at: http://www.monash.edu.au/lls/llonline/writing/science/7.xml [Accessed 4 Aug. 2014]. The Science Book. (2012). 1st ed. National Geographic, pp.94-110.