Last Updated 28 Jan 2021

Osmosis in Different Concentrations

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I am going to investigate osmosis when potato is placed in different  concentrations of sucrose. I am aiming to witness osmosis in 5  different concentrations of sucrose. I will use 5 varying concentrations so that I have a wider spread to compare the results,  and check that I don’t have any anomalies Prediction Osmosis is the process of diffusion of water molecules from a weaker  solution into a stronger solution, through a semi permeable membrane.

The tiny pores in the membrane of the potatoes will allow the water  molecules to go in and out of the potato cell, depending on the  concentration gradient between the potato and the sucrose solution. If  the water concentration is lower in the potato than in the sucrose  solution, then water will pass from the sucrose solution into the  potato, and it will gain weight.

If there is a higher concentration of  water in the potato, then the water will go out of the potato and into  the sucrose solution, as osmosis is the movement of water molecules  from a region of high concentration to a region of low concentration,  through a semi permeable membrane. So, I predict that the higher the  concentration of sucrose, the lower the weight of the potato as water  from the potato diffuses into the sucrose solution. Predicted graph of results: [IMAGE] Apparatus * 6 test tubes * 6 different concentrations of sucrose solutions * Potato Potato cutter/core * Digital measuring scales * Measuring cylinders * Knife * Test tube racks * Tissue paper Method I will need 1 piece of potato in each tube. As there are 15 tubes I  will have to calculate how many pieces I will need altogether. I think  this would be a suitable calculation: 1x15=15. So, I will pierce out  some pieces of a potato using a core, and then cut 15 slices with a  knife. Then I will measure 10ml of each of the 6 sucrose solutions  using a measuring cylinder. I will be given these different  concentrated solutions in the general laboratory.

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I will label the  tubes 1 to 15 and fill each one with 10ml of the solution. Tube 1-3 will have a concentration of 0 Tube 4-6 will have a concentration of 0. 4 Tube 7-9 will have a concentration of 0. 8 Tube 10-12 will have a concentration of 1. 2 Tube 13-15 will have a concentration of 1. 4 I will measure each slice on the measuring scales to identify each  potato slice with its weight before and after immersion in the  sucrose. Having measured each slice on the scale and recorded its  weight, I will then place the slices in the test tube containing the  solution for 24 hours.

Then I will empty the solution from the test  tube by pouring it in the sink and remove the potatoes by hand and  place them one by one on the scale. For accuracy, I will make sure  that I wipe off any excess solution on the scale before placing each  new slice on it. I will record the weight after placing them in the  solution for 24 hours. This process will be repeated for tubes 1 to 15  and the results will be noted in a table and then plotted on a line  graph. I will make this a fair test by only varying the concentration of  sucrose and the size of the potato slices, but keeping everything else  the same.

The same potato must be used for the whole experiment or  otherwise, the results would differ as the age and sizes might be  different, which means one potato might have more water in it than the  other. I will use a 10ml measuring cylinder so that I can accurately  measure the exact amount of sucrose needed. As the cylinder measures  different sucrose solutions, it has to be washed out each time I measure  another 10ml of sucrose for the next tube, because it may be  contaminated with the different sucrose’s.

All the tubes will be kept for  the same time, in the same place, so that the uncontrollable  temperature would not affect the tubes separately. I will not be able to control: * Temperature – because I won’t be in the laboratory for 24 hours,  and the temperature could change in the night, or morning. *Temperature of solution- because I was not able to obtain a thermometer and I was not in the laboratory for 24 hours so it could change. * Weighing scales – because these are digital and therefore, it  produces results by itself. I will be able to control: Concentrations of sucrose – they are already measured * Time – I will do the experiment, and come back the next day at the  same time, and promptly record the results *weight of the potato- I weighed the potato slices before the experiment. For safety in the laboratory, I will be very careful using the sharp  knife which I will be using to cut the potatoes with. I will make sure  that I have an overall so that my clothes don’t get dirty if the  solutions spills. I will remember not to put potatoes or sucrose in my  mouth as they might have been infected by chemicals in the lab, which  are poisonous.

I will measure the weight of the potato in grams, and the concentration of sucrose in percentage. I am expecting everything to work out well as I have a perfectly good  method but if I feel that the results may be wrong, I will repeat my  experiment. Preliminary results These are my results: This experiment supports my plan and prediction. The carrot gains  weight in normal water, and decreases weight in concentrated sugar  solutions. By doing this experiment, I believe that my method is good, and it  will work. I think I should specifically be aware of the scales,  because they alter a lot.

However, this was carried out at home, so  the cooking scales may have not been so accurate, as accuracy is not  very important in cooking. Results these are my first results. They proved to be wrong. This mistake  would have been made my human. I assume that I used two different  scales, and have got all the weights jumbled up. The weight taken at  the beginning is also not correct, so I may have made a mistake right  from the start. Concentration of sucrose. | Weight before| Weight after| 0| 1. 28| | 0| 1. 33| | 0| 1. 29| | 0. 4| 1. 29| | 0. 4| 1. 27| | 0. 4| 1. 2| | 0. 8| 1. 31| | 0. 8| 1. 3| | 0. 8| 1. 3| | 1. 2| 1. 29| | 1. 2| 1. 37| | 1. 2| 1. 27| | 1. 6| 1. 26| | 1. 6| 1. 3| | 1. 6| 1. 31| | Conclusion I found out that as the concentration of sucrose increases, the weight  of the potato decreases. In water it gained 1. 26 grams, but in 1 Sucrose  solution, it lost 0. 16 grams. My prediction supports my conclusion. I have calculated the average change in weight to have a simple, clear  idea where the experiment is leading me to. Instead of having a large  number of weights, I combined them into one by averaging them.

I found  the average by adding the weight gain/loss for each tube and divided  it by three. To find the percentage, I multiplied that decimal by 100. I drew a line graph, and then a line of best fit, which is sloping  downwards, negatively. This proves that the weight is getting lower as  the percentage of the sucrose concentration is getting higher. In my investigation I found a definite relationship between the 2  variables – weight and concentration of sucrose. Any increase in  sucrose concentration led to a decrease in weight. The prediction is supported by the evidence of the graph.

Although  there is one anomaly, all the other results stand out and give a  straight line of best fit – exactly as I predicted. The point of  early plasmolysis is where the concentration of sucrose and potato  are even. There is no osmosis taking place at that point. As I said in  my plan, if the water concentration is lower in the potato than in the  sucrose solution, then water will pass from the sucrose solution into  the potato, and it will gain weight. If there is a higher concentration of water in the potato, then the water will go out of  the potato and into the sucrose solution.

This is because osmosis is  the movement of water molecules from a region of high concentration to  a region of low concentration, through a semi permeable membrane. The up raise of sucrose is the downfall of potato mass. [IMAGE] Osmosis In osmosis, water diffuses through a semi-permeable membrane. This diagram illustrates the concentrated sugar solution, separated  from dilute sucrose solution by a selectively permeable membrane. This  has pores (holes) in it which are very small, and selects what it  wants to let through i. e. small molecules.

Water molecules are very  small. Each one is made of two hydrogen atoms and one oxygen atom. However, sugar molecules are many times larger. In potatoes, the pores  of the membrane only let the water through. There is a higher concentration of sugar molecules on the right-hand  side of the membrane in the diagram, than in the left-hand side. Sugar  molecules would diffuse from the concentrated solution into the dilute  one until they were evenly spread out if there was no membrane, but  they cannot do this as the pores are too small for the sugar to get  through the membrane.

Therefore, the small water molecules diffuse  into the concentrated sugar solution, to make it more dilute. This process is called osmosis. It is the diffusion of water molecules  from a place where they are in a higher concentration, to a place  where they are in a lower concentration, through a selectively  permeable membrane. Potato cells plasmolyse in concentrated solutions. This diagram  illustrates a plant cell[IMAGE] (which is similar to a potato cell) in  a concentrated solution. It will lose water by osmosis. The cytoplasm  and the vacuole will shrink.

The cell membrane is semi-permeable and the vacuole contains a sucrose  solution. So when a cell is placed in distilled water (high  concentration) water will move across the semi-permeable membrane into  the cell (lower water concentration) by osmosis, making the cell  swell. This cell is called ‘turgid’. In potato cells, the cells would  increase in length, volume and weight because of the extra water in  the potato. If the potato was to be placed in a lower concentration, then the  opposite would happen, because water would move out of the cell into  the solution.

If the solution is very concentrated, then a lot of water will diffuse  out of the cell. The cytoplasm and vacuole will keep shrinking, but  the cell wall will not as it is too stiff. As the cytoplasm shrinks  further and further into the centre of the cell, the cell wall gets  left behind. The cell membrane, surrounding the cytoplasm, tears away  from the cell wall. If this happens, the cell is said to be  plasmolysed. The potato will therefore, decrease in length, volume and  weight. Plasmolysis is the point where the membrane is totally detached from  its ell wall, and the potato is killed. Evaluation my experiment shows some accurate results. It concludes the experiment, and proves my prediction. My  final results were quite reliable; due to the precautions I took to make this a fair test. The graph has a straight slope pointing downwards, which is the  clearest way to understand my prediction. All of them are not that  closely together, neither far away, so a line of best fit joins some  tips of the points, and causes it to go straight down.

I have one anomalous result, which falls on 0 on the x axis. This  occurred in tube 5, which contained a concentration of 0. 4. Perhaps I did not  carry out that properly. These were the main problems in carrying out the experiment:- * Scales kept moving * Difficult to get out the potato from the core * Potatoes get stuck in tube. * Solution is still left after wiping the potato and the scales * Different scales * couldn’t control the temperature the point of early plasmolysis would not be valid.

This is because  I have just plotted it on the graph on a line which suits my results. To prove that it is the right point, I would have to do another  experiment to find that out. The other evidence is likely to be valid, because as all the evidence  links to the results. My investigation is fair because I did not  change many things, expect the concentration of sucrose. I think that I have collected quite a lot of evidence to support my  conclusion. The result table is the main source of evidence.

I could  try investigating with more percentages of sucrose concentration, the  size of the potato and have more short intervals between the sucrose’s. This would have a more spread to the results, and therefore, results  can be compared and evaluated more thoroughly. They would be very  accurate as well as reliable. As I have an anomaly, my evidence may not be extremely correct. I  would have to do more research to what I have already done (in the  conclusion) on osmosis, and see what actually happens, and see if it  occurs in plant cells all the time.

If I were to repeat the experiment, I would use a very accurate scale,  so that results would come out accurately and then I would have a accurate  average. The graph will be fairly accurate. I would also make sure  that the scale and the potato slices are properly wiped. This is  because if they are not wiped, the weight would increase, and will not  be accurate. I could use a syringe or a burette to measure the 10ml of  sucrose solution, because those two apparatus are very accurate.

I would do several more experiments with bigger sizes of potatoes to  obtain more evidence to support my conclusion. I will also do some  research on osmosis, and this will make me certain of my evidence if I  have many to compare with. I will agree with the majority. Overall, I am very pleased with these results and with the evidence I  have so far, that osmosis occurs when there is a high concentration  and a low concentration, both aside a semi-permeable membrane. The  lower concentrated substance diffuses through the membrane to where  there is the higher concentrated substance.

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