An experiment to find of the isotonic point of root vegetables cells in contents using osmosis

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20603         Candidate number: 1216      Name:  Mohammed Zafran

An experiment to find of the isotonic point of root vegetables cells in contents using osmosis

Aim – I am going to investigate how different concentrations affect root vegetables finding the point of balanced osmosis, as this will be the isotonic point where the amount of water diffusing into the cell is equal to that diffusing out of the cell hence at this point equilibrium will exist and the isotonic point will be obtained.

Therefore when I obtain my results and plot them on a graph the point at which they intercept the x-axis, will be my isotonic point.

As the isotonic point is the point in which the net movement of water is equal therefore as I know that the mass is affected by the water content present in the cell.  Therefore I will plot the values for my % mass increase/ decrease to find the isotonic point for each root vegetable.

The x- axis will have the different concentration values; the y-axis of my graph will have the % change. As the my line of best fit intercepts the x-axis this will mean that my percentage change will be 0% and therefore at this concentration the isotonic point for my root vegetable will be obtained.

Equipment required for the practical investigation.

  • 24 McCartney bottles will be used- These will be used to contain the various concentrations of sucrose solution and the vegetables over the 24 hour period of time. They will be covered with a lid to prevent evaporation. They are used in preference to Petri- dishes as I realised that Petri- dishes lids were not tightly attached to the Petri-dish therefore in my preliminary work my results had a source of error. To increase the reliability and precision of my results McCartney bottles will be used as they have a tight filling lid which will minimize evaporation.

  • Root vegetables- One parsnip, one carrot, one potato and one Swede. These will         be required to take samples for this experiment. They will be used to find the approximate isotonic point for each of the root vegetables. This will be done by measuring the percentage increase/decrease for the mass/length and width of each root vegetable in the varied sucrose solutions. This will therefore enable me to find isotonic point.

  • Electronic balance- In my preliminary work an electronic balance which measured the mass to 1dp was used as this is less accurate the precision and reliability of my preliminary results were low and therefore in my actual experiment an electronic balance will be used which measures to 2 decimal places as this will increase the reliability and precision of my results and reduce the chance of error.

  • 30milimetre Ruler- It will be used to clearly measure the length of the root vegetable. Due to this the same surface area will be exposed to the sucrose solution in each of the Petri dishes.

  • Pen- To mark the labels, which will enable you to know which Petri dish, has which specific root vegetable.

  • 2- 200ml  BEAKERS - Will be used to hold distilled water and the 1M sucrose solution required for the dilutions of the 1 molar sucrose solution to make solution with lower concentrations.

  • 28 labels- These will be required to enable me to know which root vegetable is present in each McCartney bottle. Also will be used label the water and 1Molar sucrose solution beakers. This will prevent my results from becoming mixed up. Will also be used to label the pipettes.

  • Scalpel- This will be used to cut the root vegetable to the accurate and appropriate length, this will minimize the chance of errors and increase the reliability and precision of my results. More accurate than using a knife as it cuts the end edges of the root vegetable to equal lengths. This will enable me to obtain more reliable value for the length.

  • Core Borer (size 4) - This will used to cut an extract cylinder shape from the root vegetable required for this experiment. The diameter of the core borer needs to be the same ensuring that the experiment is fair; this will also ensure that each root vegetable has the same surface area to volume ratio. This will be done by using the same core borer.

  • Distilled Water – Will be used in the dilution of the 1M Sucrose solution where it will be used to dilute 1 mole sucrose solution to different concentration of sucrose. This water used will used rather than tap water as in preliminary work my results were affected by the tap water as it minerals which will contaminate the different sucrose solutions made. As distilled water has no mineral ions present therefore the dilution of sucrose will not be affected. As there will be no mineral or ion content in the sucrose solution except sucrose and water molecules. This will therefore increase the reliability and precision of my results.

  • Paper Towels- These will be used to clean up any spillages of the different solutions also they will be used to dry the root vegetable cylinder once the 24 hour period is up so we could obtain the new mass of the root vegetable.

  • Tile- This will be used to place the root vegetable on a stable place and will be used to cut the root vegetable.

  • 1 molar sucrose solution- This solution will be used to make the other solutions for this experiment via a method known as dilution. I will add water to the 1 molar sucrose solution to dilute it and obtain various other concentrations.

  • Two 10 ml pipettes- one will be used to measure out distilled water and the other will be used to measure the 1 molar sucrose solution. Two different pipettes will be used to prevent cross contamination and this will reduce the chance of getting less reliable results. When measuring the sucrose or water solutions I will always measure from the base of the meniscus that the liquids form, to again ensure that the experiment is kept fair. In my preliminary work I used two 10ml syringes to measure the volumes of sucrose and distilled water. As syringes have a percentage error I will use 10ml pipettes in my actual experiment as this will mean that I get a lower percentage error and therefore the reliability and precision of my results will be high.

PREDICTION

Osmosis is the net movement of water molecules from a region of high concentration to a region of low concentration through a partially permeable membrane. The isotonic point is the point in which equilibrium exists in osmosis and is the point where the outward movement of water molecules of the cell equal the movement of water molecules into the cell. At this point there should be no change in mass/ width and length of the root vegetable.

My prediction for the isotonic point for each root vegetable will be based upon my preliminary work, when I carried out my preliminary work I found that each root vegetable had a different isotonic point. Each root vegetable had a different solute potential and therefore showed a different net movement of water.

What I realised was that the 0.6 and 0.5 drew out the most water I knew my root vegetable cylinder would have a isotonic point below this value. 0.4 and 0.45M sucrose solutions showed the very little intake of water as their mass didn’t increase instead it decreased..

Based upon these preliminary results I expect the isotonic point to lie in the region between 0.4 and 0.3 as this concentration is within the mid range of the hypertonic and isotonic solution. At this concentration I would expect the net movement of water molecules to be equal.

PRELIMINARY WORK

Swede:

Potato:

Carrot:

Parsnip

From my results I can make a prediction that the isotonic point value for the parsnip will be the highest value as it did not show any decrease in mass at the 0.4M sucrose solution.

The Swede showed the second least mass decrease, as this shows that the Swede has a higher solute content than the carrot and potato.

The carrot had a mass % decrease of -18.75% this was the 2nd lowest value which shows that it is sweeter than the potato.

The potato showed the greatest % mass decrease as its mass decreased by -31.25%.

This shows that the potato was the sweetest root vegetable and therefore it should have the lowest isotonic point as the point where the net movement of water is equal will occur quicker hence at this point there will be no change in mass and length.

I predict that in terms of ranking the root vegetable with the highest isotonic point will be:

  1. Parsnip
  2. Swede
  3. Carrot
  4. Potato.

From these results I will change my range for my concentrations used as my results show that a concentration below 0.4 is required as three of my root vegetables showed a mass decrease at the 0.4 molar sucrose solution. Also after tasting each root vegetable I believe that their may be a wider gap for each isotonic point than my preliminary results show. I say this because after tasting each root vegetable, although the sweetness matches the order which I stated for my isotonic point the sweetness of each root vegetable was proportionally different as the Swede was a lot sweeter than the carrot this is why I believe that in my actual practical there will be a wider range of isotonic points for each root vegetable.

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Due to the reasoning above I will use 0.3, 0.4, 0.5, 0.6, 0.7 these new concentrations will enable me to find the precise isotonic point.

When the root vegetable is placed in the 0.3 molar sucrose solution I will expect the root vegetable to become turgid, because at this concentration the root vegetable will have a higher water potential and a lower solute potential. Therefore the water molecules will enter the root vegetable at this concentration by osmosis and will create a pressure potential.

Water potential equation    

This pressure potential will cause the protoplast in the cell ...

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