Osmosis and Diffusion Essay

Introduction
Osmosis is the movement of water from a region of higher concentration ( hypertonic ) to a region of lower concentration ( hypotonic solution ) through a cell membrane or other semi-permeable membrane until an equilibrium is reached. It is a special case of diffusion called “ passive transport “ which means no energy is required.

Diffusion is the movement of a substance by which the molecules move from a region of higher concentration to a region of lower concentration.

Aim
Our aim of the experiment was to observe and investigate the process of osmosis, using different levels of salt concentration on potatoes.
Scope
In this investigation three square pieces of potato were placed into individual beakers containing different salt concentrations of 0%, 10% and 20% and observed for 120min.
Hypothesis
The theory behind this experiment was that the piece of potato placed into the 0% salt solution would increase in weight and size as it is a hypertonic solution. The pieces of potato placed into the 10% and 20% salt solution would theoretically decrease in weight and size as they are hypotonic solution.

Materials
1. 3 x 250ml beakers
2. 1 x Stirring rod
3. Table top scale
4. Tap water
5. Knife
6. Paper towel
7. 1 x Potato
8. Maker pen
9. Chopping Board
10.Ballpoint pen and Notepad
11.Stop watch
12.Salt
13.Spoon
14.Empty petri dish

Method
1. Gather all materials needed to perform experiment.
2. Using your marker pen label one beaker with 0%, another with 10% and the other with 20%.
3. Using tape water fill up each beaker up to 100ml line shown on the side of the beaker.
4. Get your table top scale and cancel to 0.00 and then place your empty petri dish on top.
5. Using your spoon scoop out 10grams of salt into your empty petri dish and then pour into your beaker thats labelled 10%.
6. Follow step 4 again, making sure that the petri dish is completely empty of any salt.
7. Using your spoon again, scoop out 20grams of salt into your empty petri dish and then pour into your beaker thats labelled 20%.
8. Using your stirring rod stir both the beakers containing salt until dissolved. Make sure you wipe your stirring rod with paper towel in between, making sure not to transfer solution to the other beaker.

9. Using your knife and chopping board, get your potato and cut your potato into three pieces in similar size.
10.Place each piece of potato one at a time on the table top scale and record the weight of each potato using your ballpoint pen and notepad. Make sure they are all similar weight.
11.Place a piece of potato in each beaker.
12.Set your stop watch at 30 minutes and after the thirty minutes remove the potatoes out of their solution one by one, pat the piece dry on the paper towel, weigh it and record the weight.
13.Repeat step 12, every 30 minutes until you reach 120 minutes in total. 14.Clean up your work bench and ensure that everything is put away in its correct spot.
15.Record data in a table to show your experiment results.
16.Graph Results.

Results
To find the difference in grams (g): Final mass – Initial mass To find the difference in %: Final mass – Initial mass x 100 Initial mass

Table 1. Showing salt solution concentrations and time intervals Treatment Initial
%
mass (g)
Solution 0 minutes

30
minutes

60
minutes

90
minutes

120
minutes

Difference Difference
(g)
%

0.00%

11.18 (g) 11.3 (g)

11.45 (g) 11.52 (g) 11.55 (g) 0.37

10.00%

14.47 (g) 14.63 (g) 14.60 (g) 14.67 (g) 14.62 (g) 0.15

1.03

20.00%

13.12 (g) 13.03 (g) 12.92 (g) 12.89 (g) 12.78 (g) 0.34

2.59

Graph 1. Showing salt solution concentration and time intervals

X axis – grams
Y axis – salt solution %

3.3

Risk Assessment
Before we commenced our experiment our teacher discussed with us the safety precautions we should all take, which involved us wearing protective eye glasses and ensuring that we were chopping directly onto the chopping board and to ensure the knife and beakers were kept at a safe distant away from the edge of the work bench. Variables

There are several possible errors that could have affected the overall outcome of the experiment such as: We were working in an uncontrolled environment ei; the biology classroom. This could affect the varying temperatures humidity with could potentially affect the rate of osmosis, because increased temperature results in increased diffusion, while increased humidity results in an increased number of water molecules. We also have to take into account our human errors like, miscalculations in experiment preparations, such errors could have an effect on the reliability of our results.

Interpretation of results
Table 1 shows the potato piece in the 0% salt solution increased in weight by 3.30%. The potato piece in the 10% salt solution decreased in weight by 1.03% and the potato piece in the 20% salt solution decreased in weight by 2.59%. So our hypothesis was correct in saying that we would predict a decrease in weight the higher the salt concentration was due to osmosis.

Conclusion
As seen from Table 1 and Graph 1, we can ascertain that as salt concentration in the solution decreases, the weight of the potatoes increases after 120 minutes of sitting in the solution and that as the salt concentration increases the weight of the potatoes decreases. This occurrence can be explained through the process of osmosis as mentioned in the introduction.

It is clear from the results that osmosis occurred with all three potato pieces, the results showed that the potato submerged in the 0% salt solution increased in mass due to it being in a hypertonic environment, which means that there is more water in its surrounding environment then there is in the actual potato cells. The results also show that the potato pieces submerged in the 10% & 20% salt solution lost mass due to being in a hypotonic environment, which means that there was more water in the actual potato cells than its surrounding environment. The water moved through a semi-permeable membrane from a higher to lower concentration of salt solution, this is called osmosis. This would explain explain the results shown in Table 1, loss of weight.

Osmosis is important to all living things. Osmosis is the process by which living cells intake and give out water as per their requirement. Without it all biological processes would get ruptured. Without it there will be no plants as water is necessary for them, which they transfer cell to cell through the process of osmosis. In order to improve the accuracy and longevity of the experiment you would have to change some of the ‘ Variables ‘ some of which are listed above. You could do the experiment and then try exposing them to different environmental factors and at different times of the day to gather a wide range of results if you wanted to. References

Type: Website
Reference: dpbiologyiszl, 2013, Potato Osmosis, website, accessed 20 October 2013, http://dpbiologyiszl.wikispaces.com/file/view/Sample+Lab+Report+Potato+Osmosis. pdf
Summary & Evaluation:
This is a similar report on a similar potato osmosis experiment which was performed by another biology student. I believe this is a reliable source, because this is a report on someones actual work and displayed pictures and evidence of their experiment. So you were able to see that it was a true source of information. I found it to be very useful in structuring my report.

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