Osmosis Water Movement Across Membrane Biology Essay

Published:

Osmosis is the movement of water across a semi-permeable membrane. The reaction only occurs when there is a partially permeable membrane, e.g. a cell membrane. It only occurs with two circumstances:

two solutions with different concentrations

a partially permeable membrane to separate them

When a cell is submerged in water, the water molecules pass through the cell membrane from an area of low solute concentration (outside the cell) to one of high solute concentration (inside the cell); this is called osmosis.

Semi-permeable - thin layers of material which allows some particles to pass through but prevents other particles from passing through it.

When the concentration is the same on both sides of the membrane, the movement of water molecules will be the same in both directions.

Osmosis is important to plants, as they gain water by osmosis through their roots. Water moves around the plants cells, and therefore making them stiff and turgid so the plant can stay upright.

Lady using a tablet
Lady using a tablet

Professional

Essay Writers

Lady Using Tablet

Get your grade
or your money back

using our Essay Writing Service!

Essay Writing Service

The solution with the higher level of solution across the membrane is called hypertonic, whilst the solution with the lesser amount of solution is called hypotonic. If the solution is equal across both sides of the membrane it is called isotonic.

Water from a dilute concentrated solution, diffuses through a partially permeable membrane to a more concentrated solution, in attempt to neutralize more concentrated solution.

Planning

My main aim in this experiment is to find out if osmosis occurs in a potato, and how it affects the potato in different molar solutions of sugar sucrose solution.

Before actually planning the experiment, I will do some preliminary research to find out about osmosis, and matters related to it, such as the range and concentrations of solutions that should lead me to good results at the end of the experiment, and also allows me to form a prediction. I will also need to come up with sensible ways that will make this investigation fair and safe. 

Once the potato chips have been cut from the potato, it will need both light and water in order to survive. With both of these sources, the potato will keep on working, until it dies of either lack of water, or too much water. When the concentration level is lower in the potato, the water will transfer from the solution to the potato, and vice versa. 

In the distilled water, 0m solution, I believe that the water is more concentrated in the potato, and therefore the water should transfer from the water to the potato, making the potato bigger in size, and heavier in mass. The potato cells, being surrounded by a weak solution, will be most likely to swell up and become turgid (see Analysis), taking in all the water possible.

With the potato in 0.2m solutions of sucrose, I don't think there will be much change in the mass of the potato. This is because there is a difference between the two substances. I believe that the mass and the size of the potato will be altered (decreased), but not too much.

The 0.4m and 0.6m molar solutions of sucrose, slightly similar to the 0.2m solution, compared to the potato, both substances have nearly the same concentration levels, which is why I am predicting that there will be no change in the mass of the potato in this experiment.

The 0.8m and 1.0m solution of sucrose, I think, should see a clear difference, based on the fact that there is large difference between the two concentration levels. Consequently, the mass should decrease.

The difference between the water concentration in the potato and the 1.0m solution is clearly substantial and the water in the potato should be transferred from the potato, through the semi permeable membrane, to the solution surrounding the potato. And as a result, I am sure that the mass of the potato will increase considerably. Also, because the potato cells are surrounded by a stronger solution, it will probably become smaller, and even shrink. However, because of such high molars of sucrose, the water is able to completely, throughout the two substances, equaling the concentration levels of the two substances. 

Lady using a tablet
Lady using a tablet

Comprehensive

Writing Services

Lady Using Tablet

Plagiarism-free
Always on Time

Marked to Standard

Order Now

Basically, this means that the potato chips will gain mass when placed in a solution of more water than sucrose, yet lose mass when placed in a concentrated sugar solution, which is the result caused by osmosis.

The single factors I will control are the concentration levels, whilst keeping temperature (room temperature) the same. The measurements I will take are the original mass (of the potato chip), then the new mass, the mass change (+ or -), and finally the percentage of the mass change. I will then find the average of the percentage change. There will be six different concentration levels, giving a wide range of results, with the usage of peer's results to show consistency between my measurements.

To justify my prediction, I looked at the scientific explanation of osmosis. I found that it is a special type of diffusion involving the movement of water molecules only.

Water molecules constantly move. When two solutions are separated by a semi permeable membrane (a cell membrane which allows some substances to pass through whilst preventing others), water passes through the membrane in both directions. The net flow of water is from the more dilute solution to a more concentrated solution. This continues until both concentrations are in dynamic equilibrium that is when the concentration of water is the same on either side of the membrane. Osmosis is the flow of water from a more dilute solution to a more concentrated solution. 

In this case, when the water concentration is lower, the water will go inside the potato, and the potato will gain weight as a result. If there is a higher concentration of water in the potato, the water will go out of the potato.

Possible Variables

- Size of potato

- Amount of solution

- Concentration of sugar sucrose solution

- Time the potatoes are left in the solution

- Ratio of solution

The student will use the ratio of the solution as the variable for this experiment. This will be the only variable in the experiment to ensure a fair test.

Aim

To investigate how higher concentrations of sucrose solution affect the weight of a potato.

Prediction

I predict that the more concentrated the sucrose solution is, the lighter the potato will become in grams.

Fair Test

To make sure my experiment was fair; I had to keep these factors the same:

Surface area, size and shape of potato - these all matter as the potato chips must be alike to enable the diffusion of osmosis in the same parts of the chips.

Volume of sucrose solution used - must be the same amount otherwise too much/little diffusion may occur.

Use of the same type of beaker - this affects the surface area of which the chip lies, and how much solution will be covering at different parts.

Apparatus

I used the following apparatus:

Potato chips (x15) (2g) - part of the experiment

Beakers (x5) - to contain the potato chip

Knife - to chop the potatoes

Cork borer - to cut out potato cylinders

Cutting tile - to cut the potato on

Electronic scale (g) - to weigh the potatoes

Gloves - safety when handling sharp equipment, plus handling solutions

Sugar sucrose solution (0.0m, 0.2m, 0.4m, 0.6m, 0.8m, 1.0m) - molar solutions, part of the experiment

Measuring cylinder - to measure the amount of solution before pouring into the beaker

Pipette - to pour the solutions into measuring cylinders

Plastic - to disallow solution to escape through evaporation

Paper towels - to dry the potatoes after osmosis takes place

Safety

Safety is an important aspect in every experiment, even if the experiment seems to be very harmless, like in this one. There are several ways that you can ensure safety throughout your experiment. This ranges from wearing safety goggles to replacing reagent bottle tops. I will use a safety blade that could still be dangerous if it's treated like a toy and not used in the correct manner. I will also be careful when using the solutions so that don't get into our bodies or on our skin which as a possible consequent, could do damage even though we are not fully aware of it. 

Lady using a tablet
Lady using a tablet

This Essay is

a Student's Work

Lady Using Tablet

This essay has been submitted by a student. This is not an example of the work written by our professional essay writers.

Examples of our work

I will need to make my experiment as safe as possible. It will be safe for me and other students around me. This is what I will need to do:

Care in using glassware as when broken is sharp and can cut the skin

Wear safety goggles as I am using concentrated hydrochloric acid

Care in returning all the equipment at the end of the experiment

Care to eyes and skin plus to be aware of other students around the class

Method

Mass (g)

Start

End

Change

Average Change

0.0m

2

2.1

+0.1

+0.2

 

2

2.3

+0.3

 

2

2.3

+0.3

 

2

2.1

+0.1

0.2m

2

2

+0

+0

 

2

2

+0

 

2

2.1

+0.1

 

2

1.9

-0.1

0.4m

2

1.6

-0.4

-0.45

 

2

1.6

-0.4

 

2

1.5

-0.5

 

2

1.5

-0.5

0.6m

2

1.2

-0.8

-0.75

 

2

1.3

-0.7

 

2

1.3

-0.7

 

2

1.2

-0.8

0.8m

2

1.2

-0.8

-0.825

 

2

1.1

-0.9

 

2

1.2

-0.8

 

2

1.2

-0.8

1.0m

2

1.2

-0.8

-0.875

 

2

1.1

-0.9

 

2

1.2

-0.8

 

2

1

-1

Firstly, we had had to chop up a potato into slices which weigh the same, and are roughly the same size. We had to do this for 15 potato slices and they had to weigh to be exactly 2 grams each. Whilst the potatoes were set aside, we filled in our beakers at 40ml with 6 different liquids. One of the liquids used was water, water was used to provide a bigger insight to our results, and also water is neutral so in our experiment it could be classified as 0.0m concentration strength. The other five liquids were sucrose solution; we had different molecular strengths for each one:

0.2m

0.4m

0.6m

0.8m

1.0m

Including 0.0m (water)

After we filled our beakers with solution, we added 3 potatoes into each beaker. To make our results more accurate we wrapped the top of our beaker with cling film so the liquid couldn't evaporate, this was crucial to my experiment as it would affect my results a lot. The next day which was around 24 hours later I checked up on my potatoes to find out how osmosis had occurred differently from between each potato. I then gained the results of the other peers in my class of 5 people, from these results are discovered which of my results are outliers.

Explanation

The sugar sucrose solution molecules were colliding with other molecules in the potato (e.g. water). As the concentration of the sugar solution was increased, there were more particles in the same volume. Therefore there is a greater chance that the particles will collide, so the rate of reaction increases. Water molecules will then leave the potato making it drier, and lighter, also smaller (to attempt to neutralise the sugar sucrose solution) as the concentrating increased, more water was needed for the neutralization, making the potato lose more water.

Conclusion

My table of results clearly show that if the concentration of the sucrose solution is higher, the potato became lighter in weight as it lost it lost its water and was being dissolved by the sucrose solution. 0.0m accounted for water; therefore it did not react with the potato, although water diffused into the potato through osmosis.

There is a bigger change when the concentration is higher rather than lower, such as at 0.4m it had a change of: -0.4 (1.6-2.0) However at 1.0m it had a change of: -0.8 (1.2-2) meaning that the weight of the potato reduced due to a higher concentration.

This is because water had left the potato, so the potato shrunk is size. Also this is backed up as when the potato was left in water, it became bigger and swelled up and became larger in size and weighed more.

A scientific explanation to this would be that water is a less concentrated solution to the other solutions, so the passed the semi-permeable membrane into a higher concentrated solution.

Other results (Peer)

Start

End

Change

2

2.2

+0.2

2

2.3

+0.3

2

2.3

+0.3

2

2.2

+0.2

2

2

+0

2

2.1

+0.1

2

2.1

+0.1

2

2

+0

2

1.5

-0.5

2

1.4

-0.6

2

1.3

-0.7

2

1.5

-0.5

2

1.3

-0.7

2

1.3

-0.7

2

1.3

-0.7

2

1.3

-0.7

2

1.1

-0.9

2

1.1

-0.9

2

1.2

-0.8

2

1.1

-0.9

2

1

-1

2

1.2

-0.8

2

1.2

-0.8

2

1.1

-0.9The averages prove the decrease in weight.

Graph

The graph shows a negative correlation. It also shows that, there's a large decrease in the weight of the potato at the beginning, but then begins to slow down. The largest decrease is between molecular strengths (0.2m & 0.4m), because between these molecular strengths there was the biggest difference of osmosis.

I could not find any outliers, when comparing with other results. Possibly due to the amount of figures there are (2 figures, e.g. 0.7), therefore I wasn't able to round any results.

Analysis

In the results above, the mass change shows a steady decrease, telling us that as the water concentration decreases, so does the percentage of mass change. This experiment helped me find out that the higher the water concentration, the larger increase in mass (g). Consequently, the percentage will also be higher. The potato cells, working to stay alive, took in, or gave out the water depending on the concentration of the tissue, and the concentration of the solution it is surrounded in. 

- As the molars increased, the average of the weight difference decreased.

Sometimes, cells may be placed in a more concentrated solution, as is the case in the 1m solutions. This causes water to pass out of the vacuole, out of the cytoplasm, out through the cell membrane and cell well, into the solution outside the cell. The pressure of the vacuole on the cytoplasm decreases until the cytoplasm pulls away from the cell wall. Consequently, the cell becomes saggy, and said to be plasmolysis. 

In the 0m sucrose solution, the case was the exact opposite of the 1m sucrose solution. Osmosis now takes place between the cytoplasm and the solution outside the cell. When the potato chip was placed in the less concentrated solution, 0m, water is allowed to pass through the cell wall and cell membrane, as well as the cytoplasm and vacuole. The increased pressure of water in the vacuole, turgor pressure, presses the cytoplasm against the cell wall, the cell is then known to become turgid when it contains as much water as it can hold. 

Evaluation

As a whole I think my experiment went well, although I feel I could have improved the accuracy of some of the results. In some occasions I could provide myself with a wider range of my own results by collecting other student's results and then linking them to mine. I may have been able to concentrate more on my own experiment rather than be distracted by peers. I could have tried to record other aspects of my experiment such as the length, colour, size and other changes to the potato. I could have possibly experimented with other vegetables or maybe even fruits and compare their relativities and differences.

I was very pleased with my results, whilst also believing I had carried out the experiment in a way which deserved good measurements. I can safely say that after comparing my prediction and results, I did get the expected results. This was done too many things, most notable, fair testing. An unfair experiment produces the wrong results which make you jump to the wrong conclusions. Firstly, I had to get the measurements and the weights of the solutions and the potatoes as exact, and as accurate as possible. I tried to get the measurements of the potatoes as accurate as possible for every single potato, evenly cutting the potato pieces, and making a record of the mass to the nearest milligram. To help with this, I used an electronic scale so that we can get the best readings possible.

In this experiment, I believe that I have collected enough results, two trials in fact, all backing up my prediction. I would therefore have to assume that this experiment has been a success in the sense that both my predictions and results run parallel to each other. 

I also felt that to get good results, the potato should be fully covered in the solution, which is why I placed both the potato chip and solution in a test tube. The only problem I came across with this is that because sucrose is denser than water, the solutions with more sucrose than water, i.e. 0.8m and 1.0m, caused the potato chip to float which may prevent the potato chip from being fully covered in the solution. I also wanted to make sure that the potato is fully covered by the 5 different kinds of solutions because, if the potato isn't covered up by the solutions, the effect of osmosis might not occur to the fullest.

It was also vital that I got exact measurements of molars and water because if the volume of one solution in a test tube is higher or lower than another, it will obviously affect the string of results later on. Other minor precautions include making sure that you don't use dirty test tubes or a slightly cracked measuring cylinder because these could still affect the results one way or another which is why these were all taken into account. 

I followed my planning and method correctly, and I should then gain accurate and sufficient enough results to conclude the experiment, and to prove my predictions, which I think I've done because my final results seem to be very reliable which I put down to the precautions I took in an attempt to make this a fair test. 

Using more types of molar sucrose solutions would have helped us obtain better results, and more accurate results; so that we can make sure the results are totally correct. 

Experimenting with one set for a longer period of time, for each set, would lead us to better results, because the osmosis action would reach its maximum capability, and therefore tell us how much water could be transferred for each solution. 

On the subject of time, I felt I made an awful error. I had been given the option to use some hot water from the hot tub, but only realized its potential once I had completed the experiment. Temperature affects the speed of osmosis, and therefore, by placing the test tubes in a beaker of hot water, not only would I speed up the experiment, but I would also maximize the osmosis process. This is the one major change I would take on if I had to option to redo the experiment. 

Repeating the same tasks many other times wouldn't have been very useful, since we had already done the result 3 times, and all my measurements appear to be reliable. 

Even though I didn't use these to improve the accuracy and reliability, I still feel I got results which were not only correct but also backed up my predictions. 

By Klejdi Gjurra