- If the concentration of the cell and the surroundings are equal, then the cell will neither lose or gain weight and shrivel or swell.
- If a plant cell takes in water by osmosis, it becomes Turgid. This means that the cell is swollen and hard. It doesn’t burst because it has a strong cell wall, which holds the cell together. If the plant cell loses water by osmosis, it becomes Flaccid. This is when the cells shrivel up and pull away from the cell wall. Another term for this is Plasmolysed.
- If an animal cell takes in water by osmosis, it doesn’t become Turgid because they don’t have a cell wall, it bursts. If a cell loses water by osmosis, it doesn’t become Flaccid, the cell shrinks. To stop this from happening, we use our kidneys to control the level water and sugar in our blood steams. This process is called Osmoregulation and involves the part of the brain called Hypothalamus.
Prediction
I predict that it will take about 0.3 to 0.4 Molar Sucrose Solution to equal the concentration of the Potato tuber cell inside. I predicted this by using the research above and matching it with an experiment which we did earlier in the Year. The experiment we did then was to find what happens to a potato tuber cell when in different concentrations of Sucrose Solution. We used three different solutions (1 Molar, 0.5 Molar and 0 Molar) and these were our results.
Before
After
With these results I can predict that the concentration either side of the cell will be the same at about 3.0 to 4.0 Molar Sucrose Solution. This is because 0 Molar gained 0.8 grams of weight, grown 0.1 cm and became Very Firm. The 0.5 Molar lost 0.2 grams of weight, shrivelled 0.1 cm and became quite firm. In my research I have found out that when a cell has gained weight, size and becomes firmer, then the solution surrounding the cell is greater than the concentration inside the cell. Also, if the cell looses weight, shrivels and becomes squashy or less firm, then the concentration inside the cell is greater than the concentration surrounding it. This must mean that the equal amount of Sucrose solution to the cell inside concentration must be in this range.
Plan: -
Apparatus: - 1 x Potato
1 x Potato Cutter
11 x 100 cm³ Beakers
165 cm³ of 1 Molar Sucrose Solution
165 cm³ of Water
2 x 50 cm³ Measuring Cylinders
Knife
Cling Film
Paper Towels
Tweezers
Scales
Timer
Glass rod
Method: -
Take 1 potato and cut up into long thin strips using the potato cutter. Then using the knife cut them into 22 pieces, each 1cm³. Then, using paper towels, wipe off any excess water on the surface of the cube and weigh each cube separately. Record the weights into your results table. Then measure out and fill the beakers with these solutions of Sucrose.
Mix the solutions using a glass rod. Then take 11 of the potato tuber cells (potato cubes) and place 1 into each beaker. Then set the timer on and leave for 24 hours. Repeat this again to get two sets of results. After 24 hours, take each potato tuber cells out of their beakers and wipe off any excess solution. Then weigh each cell again and record this into your results. Then work out how much weight the cell has gained or lost in each solution by subtracting the starting weight by the finishing weight.
Fair Test: -
To make it a fair test you must carry out these precautions: -
- The measuring and the Sucrose and Water are accurate by using a measuring cylinder.
- Don’t use the same measuring cylinder for the Sucrose and the Water because it might contaminate the solutions and make it an un-accurate and un-fair test.
- Make sure that each potato tuber cell is 1cm³ and doesn’t have excess liquids on them.
- Make sure the scales start on 0.00 grams
- The temperature of the room doesn’t increase or decrease.
Safety: -
To make it a fair test you must carry out these precautions: -
- Wear Safety Goggles at all times.
- Bags and Stalls are put on the sides of the room, out of the way of any experiment.
- The normal Science Labs rules must be obeyed.
- Be careful with harmful substances.
- Watch out for Glass objects, which might get broken.
Results: -
Gained or Lost?
Gained or Lost per gram.
Graph
Conclusion
The graph shows a negative correlation on the line of best fit, crossing the x-axis at 0.32 Molar Sucrose Solution. This is when the concentration is the same surrounding the potato tuber cell and inside it. This proves that my prediction was correct because I predicted that the concentration of Sucrose Solution needed to have the same concentration of fluids inside the potato tuber cell would be around 0.3 Molar to 0.4 Molar. When there is more than 0.32 Molar Sucrose Solution surrounding the cell, the potato shrivels and loses weight, and become flaccid, because the concentration outside the cell is lower than the concentration inside the cell so the water molecules move from the potato tuber cell into the surrounding fluids. When the Sucrose Solution is below 0.32 Molar, then the concentration surrounding the cell is higher than the concentration inside the cell. This mean water molecules move into the potato tuber cell and increases it size and weight to make it turgid. But at 0.32 Molar Sucrose Solution, the concentration inside the potato tuber cell and the concentration surrounding it are balanced and no water passes out or into the potato tuber cell. This means that the potato doesn’t lose or gain any weight or size. This supports my prediction because when I did my preliminary work, I was able to work this out with just three different Molar Sucrose Solutions, by looking at the results and my research and working out a range where the concentration could be balanced inside and outside the potato tuber cell.
Evaluation
In the overall experiment, we tested 11 different Molar solutions to cover a great range of concentrations. We repeated each result twice to get an average loss or gain. Then we repeated four results again for a third time because it didn’t look correct on the graph when I pencilled in the line of best fit and then chose the two results that were the closest together.
E.g.
Result 1 - +1.10, Result 2- +2.38, and Result 3- +1.14 - I chose results 1 and 3.
When I re-plotted the results, they all seemed to lie on the line of best fit. I tried to make sure that the temperature in the room stayed the same throughout the experiment. Also, I made sure the surface area and mass were the same to the nearest 1.0-gram. The results that I repeated because they looked wrong might have had excess liquids on them when I weight them before or/and after the experiment and could have affected the results. Also, the temperature, mass or/and surface area of the potato tuber cell could have changed which would affect the results.
I think my method is good because you can get accurate results by using simple apparatus and knowledge. But it could improve my method by controlling the other factors better by making sure that the potato didn’t have any kind of excess liquids on it, the mass was the same weight every time and the surface area was the same size every time. I could only do this with special equipment that wasn’t provided for this experiment. Also, if we put the experiment in a controlled temperature environment, this wouldn’t affect the results either.
I had preliminary work to help me with the investigation, which was very useful in making my prediction. But now I have done the experiment, I could concentrate around the 0.3 - 0.4 Molar Sucrose Solution and go up in hundredths instead of tenths to get a more precise result.
I could do another experiment which the same method but instead of using sucrose, I could use a different mineral to see if it will affect the results in anyway. E.g.: - Starch.
I got my research from the Biology GCSE textbook and from the Internet– http://www.purchon.com/biology/osmosis.htm
