Experiment to Investigate Osmosis in Potatoes Essay Essay

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The purpose of this experiment is to look into the motion of H2O in and out of works cells. The cells chosen for survey will be taken from murphy tubers. First I will explicate what osmosis is. Osmosis is the transition of H2O from a part of high H2O concentration through a semi permeable membrane to a part of low H2O concentration. This definition contains three of import statements:

a ) It is the transition of H2O through a semi permeable membrane

B ) It is the transition of H2O from a part of high H2O concentration

degree Celsius ) It is the transition of H2O to a part of low H2O concentration.

All the above statements are included in the definition. but define certain facets of it.

Semi-permeable membranes are really thin beds of stuff which allow some things to go through through. but prevent others. A cell membrane is semi permeable. They allow little molecules like O. H2O. amino acids etc. to go through through but will non let larger molecules like saccharose. amylum. protein etc. through. A part of high concentration of H2O is either a really dilute solution of something like saccharose or pure H2O. In each instance there is a batch of H2O: a high concentration of H2O. A part of low H2O concentration is the antonym of the above. i. e. a really high concentration of sucrose solution: a low H2O concentration.

The H2O content of workss varies depending on environmental conditions. In Land workss this H2O plays a critical function in the support of tissues and the conveyance of stuffs around the being. Lack of H2O leads to wilting and finally decease. Water is chiefly absorbed through the roots. which are covered in specially adapted root hair cells. with big surface countries and thin cell walls to help soaking up. It is drawn up the works through xylem vass by a pull resulting from the vaporization of H2O through the pore on the foliages.

This vaporization is called transpiration and the xylem flow resulting is called the transpiration watercourse. Soluble nutrient substances formed during photosynthesis are transported around the works in the bast tubing. This motion of H2O through the works in the xylem vass or bast tubings is similar to the flow of blood in worlds as it transports soluble mineral salts. foods and auxins. ( works endocrines ) . from topographic point to topographic point. The vaporization of H2O from the foliages besides removes heat energy from the works and helps to forestall overheating.

Transpiration pulls H2O up the works root but osmosis is the procedure whereby H2O is drawn into or out of cells and tissues. Osmosis is the flow of H2O by diffusion through a differentially permeable membrane from countries of high H2O concentration to parts of low H2O concentration. The diagram below illustrates this:

Water can freely perforate all membrane. The cellulose cell wall does non move as a semi permeable membrane and will let most substances that are dissolved in H2O to freely go through through it.

Whether H2O enters the cell by osmosis or non will depend on the balance between external and internal solute concentrations and the province of the cell. If the solutions on each side of the differentially permeable membrane are every bit concentrated so there will be no net motion of H2O across the membrane. This is called an equilibrium province and the solutions are referred to as being isosmotic. A solution that contains more solute atoms than another. and is therefore more concentrated. is referred to as being hypertonic. The less concentrated solution is hypotonic. This concentration of solute atoms is normally described as a molar concentration.

Even if the solute concentration external to the cell is hypotonic to the vacuole contents the cell will non go on to take in H2O by osmosis for of all time. The cellulose cell wall provides a stiff barrier to uncontrolled enlargement. A cell that is full of H2O is called bombastic and can non spread out farther as the outward force per unit area on the cell wall is balanced by the inward force of the stretched wall. This wall force per unit area is called turgor force per unit area and the internal outward force on the wall is called osmotic force per unit area.

At the other extreme. a cell placed in a solution that is hypertonic to its contents will lose H2O by osmosis. The cytol will discontinue to exercise a force per unit area on the cellulose cell wall and the cell. described as flaccid. will miss support.

Water loss can go on to such an extent that the cytol. and attached cell membrane. contracts and detaches from the cell wall. A cell in this status is said to hold undergone plasmolysis. This really seldom. if of all time happens in nature.

As osmosis is the diffusion of H2O molecules and as diffusion is the random motion of atoms from countries of high concentration to low concentration it might be expected that any factors that speed up or decelerate down the motion of these atoms would impact the rate of osmosis.

Using cognition of the procedure of osmosis and with a good apprehension of molar concentration I should be able to find the solute concentration of the vacuoles in murphy tuber cells. As it would be impossible to mensurate with any grade of truth the enlargement or contraction of cells on an single footing I have decided to look at addition or loss of H2O in footings of addition or lessening in mass. Mass. I feel. will be a more accurate manner of entering the alteration of the murphies as when mensurating length. it does non take into history the alteration in diameter of the bit. I will besides look at the addition or lessening in length to verify the truth of my consequences and compare the two readings. A cell placed in an isosmotic solution should demo no alteration whereas one placed in a hypertonic solution will lose mass.

For this experiment. I will hold to take a factor to change. These factors are:

?a Molarity of the sucrose solution

?a Surface country of the murphy

?a Type of murphy used

?a Age of the murphy

?a pH of the sucrose solution

?a Temperature

The factor I have chosen to change is the molar concentration of sugar solution as I believe this will be easy to modulate as the concentration can be easy altered utilizing distilled H2O. I will utilize 1 molar solution and change the concentrations as shown below:

Molarity of sugar solutionAmount of waterAmount of sucrose solution

0. 050

0. 241

0. 432

0. 623

0. 814

1. 005

For this experiment I will necessitate:

?a 1 big murphy to bring forth 18 murphy tubers

?a cork bore bit

?a distilled H2O

?a 1 molar sugar solution

?a pipettes

?a 18 trial tubings

?a swayer to mensurate length of murphy tubers

?a electric balance to mensurate the mass

I have selected the above equipment because I feel it will assist me to guarantee accurate consequences. To guarantee a just trial I will take all my murphy samples from the same murphy utilizing the same cork bore bit and maintain all of my setup the same. I will seek and handle each murphy tube the same. I will mensurate each murphy tubing individually to guarantee accurate measurings and carry out the process 3 times for each molar concentration tested. This will intend that I will necessitate to mensurate 18 murphy tubers. Three consequences will enable me to take an mean consequence. doing the consequences. hopefully. more precise and dependable. If one of the consequences seems really different to the others. I shall place it as an anomalous consequence and recapture the reading.

When I carry out this experiment. I will acquire a murphy and take some tubings from it utilizing a cork bore bit I will so cut these tubings into shorter lengths and step the length and mass of each of the 18 lengths. All the lengths will be cut to 25mm. The solutions will be altered harmonizing to the molar concentration required and cm3 of each solution placed in each trial tubing. Each molar concentration will busy three trial tubings. The french friess will so be put into each trial tubing and left over dark. They will so be taken out of their trial tubings. dried lightly with a paper towel and the new mass and lengths recorded. Once the consequences have been collected. they will be tabulated and analysed. A graph will be drawn and any tendencies noticed explained.

Prior to the experiment we carried out a short pilot trial. utilizing potato french friess and solutions of strength 0. 0. 1. 0 and 2. 0 molar solutions. The french friess were 25mm in length each. and each bit was placed in 5 cm3 of either distilled water/1. 0 molar / 2. 0 molar sugar solutions and left for 30 proceedingss. The murphy french friess were so measured and the consequences recorded. They are shown below:



21. 0 grinder

32. 0 grinder

Chip numberOriginal lengthResultant length




These consequences show that a murphy bit placed in H2O will derive in length. a weak sugar solution will lose length and a strong sugar solution will lose length besides. The consequences from this trial will let me to take an appropriate scope of moralities in order to happen out what the concentration is inside the cell vacuole. I am traveling to look into 0. 0. 0. 2. 0. 4. 0. 6. 0. 8 and 1. 0 molar sugar solutions. I have chosen these concentrations to seek and accurately happen when there is no net motion of H2O. hence the concentration of the cell vacuole.

From old work done on osmosis. I predict that molar concentration and mean alteration in mass/ length will be indirectly relative. I think there will be a negative correlativity between the two. I think that there will be both loss and addition in mass discovered. I think the graph will look like this but there will be no plasmolysed on my graph. as I do no anticipate my measurings to travel that far. I hope to be able to place the point when there is no net motion of H2O.

Analysis of Consequences

The Consequences of Osmosis in works cells:

Plant cells ever have a strong cell wall environing them. When the take up H2O by osmosis they start to swell. but the cell wall prevents them from spliting. Plant cells become “turgid” when they are put in dilute solutions. Turgid means swollen and difficult. The force per unit area inside the cell rises. finally the internal force per unit area of the cell is so high that no more H2O can come in the cell. This liquid or hydrostatic force per unit area works against osmosis. Turgidity is really of import to workss because this is what makes the green parts of the works “stand up” into the sunshine.

When works cells are placed in concentrated sugar solutions they lose H2O by osmosis and they become “flaccid” ; this is the exact antonym of “turgid” . If you put works cells into concentrated sugar solutions and expression at them under a microscope you would see that the contents of the cells have shrunk and pulled off from the cell wall: they are said to be plasmolysed.

When works cells are placed in a solution which has precisely the same osmotic strength as the cells they are in a province between turgidness and flabbiness. We call this inchoate plasmolysis. “Incipient” means “about to be” . When I forget to H2O the potted workss in my survey you will see their foliages droop. Although their cells are non plasmolysed. they are non bombastic and so they do non keep the foliages up into the sunshine.

Graph [ 1 ] shows the mean per centum alteration in length of the murphy tubers. It shows that as molar concentration increases the mean alteration in length lessenings. The graph drawn looks accurate as the curve did non hold to be one of best tantrum. but went through all of the points plotted demoing that all the readings were accurate. The murphy tubers gained/ loss length. the molar concentration increases the sugar solution becomes more concentrated. and more concentrated than inside the cell. At 0. 2M solution there is no net motion of H2O. As the strength of the concentration increases the cells shrink and become flaccid.

Graph [ 2 ] shows the mean per centum alteration in mass of the murphy tubers. It shows that as molar concentration increases the mean alteration in length lessenings. This graph is really similar to the graph demoing the length loss or addition. but appears less accurate as there is an anomalous consequence. This is at 0. 4 grinder. it lies off the best-fit curve drawn by 9. 2 % . The curve is one of best tantrum and follows the same tendencies as graph [ 1 ] .

My consequences seem reasonably accurate and although the graph demoing length seems to be more accurate as it is a curve that goes through all of the points. it merely shows the alteration in length. and non in mass. The graph demoing mass alteration [ 2 ] gives a more accurate position of what happened as it takes into history the enlargement of the murphy both ways and has a broader per centum alteration scope. This means that alternatively of merely crossing 30 % in entire ( as does chart [ 1 ] ) it spans 80 % ( as does chart [ 2 ] ) . This gives a broader field of consequences and is hence more accurate. as the mass is a more accurate consequence than length as the murphy bit will acquire wider every bit good as thirster. My consequences do look to be dependable. as the graphs drawn support my anticipation and seem accurate as they all lie on a smooth curve.


From the consequences obtained. I can reason that the mean addition or loss in mass of the murphy bit is indirectly relative to molar concentration. I can besides state that mean addition or loss in length of the murphy bit is indirectly relative to molar concentration. Both of the consequences show a negative correlativity. I can now state that the more concentrated the solution. the more mass/length is lost. This is because the H2O inside the cell moves out. doing the cell to shrivel. When the cells are in a less concentrated solution they gain in length and mass as H2O is taken into the cell and the cell crestless waves. The consequences gave adequate information to back up my original anticipation. Both of the graphs cut the x-axis at 0. 2. demoing that the molar concentration of the internal solute of a cell is 0. 2m. This besides shows that my consequences were really likewise and dependable.


My consequences seem to be really accurate. I can state this because when the points were plotted they all lay on the curve. apart from one anomalous consequence. 0. 4Mon the graph demoing mass. There was nevertheless merely one anomalous consequence and the others were all really dependable. This may hold been because the consequences had an mean taken so it may non hold been accurate. I could increase the truth by taking more repeats which should do the norm more accurate. As the murphies were left over dark. the temperature changed which may hold affected the consequences. but it should non hold made a drastic difference to the graphs as all of the murphies were subjected to precisely the same temperature alterations.

This could be improved by puting the trial tubing into a H2O bath so they were kept at a changeless temperature. The same murphy was used in each of the experiments. which may besides hold contributed to the dependability of my consequences. The mass was more accurate to mensurate for many different grounds. Length does non take into history the alteration in diameter of the french friess. and you can non mensurate fractions of millimeters on a swayer. but the electric balance will enter alteration from 2 denary topographic points.

e. g. mass: 1? 43 “” 1? 34length: 25 “” 23

whilst length can merely be measured to the nearest millimeter. For the mass. we had to be careful that all the murphy french friess were dried in the same manner as this may hold altered the reading. This may hold been what caused the anomalous consequences. as it was lighter that the best fit line i. e. some H2O may hold been lost through harder drying. or squashing during the drying procedure. If some of the H2O evaporated overnight. it would hold incresed the molar concentration of the solutions. therefore doing the consequences innaccurate. This could be combatted by seting a spile in the top of the trial tubing to halt the vaporization and maintaining the sugar slution concentrations the same.

To better the truth of the consequences I would include more concentrations to happen the point of plasmolysis as in my experiment. I did non acquire to the point of plasmolysis in my experiment. so if I was to widen this experiment. I would investigte a wider fury of concentrations to look into furthur and increase truth. I would besides increase the repeats to 5 per molar concentration and increase the molar concentration to seek and happen the point of plasmolysis. I could besides diminish the scope between each molar concentration ( every 0. 05 for illustration ) to seek and happen the exact concentration of the murphy cells where there is non net addition. This probe was succesful but could still be made more accurate by some of the above ways.

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