Probe Into Osmosis, Potato Cylinders Essay, Research Paper

Introduction

Knowing that osmosis ( a diffusion of H2O ) will happen across a semi-permeable membrane whenever there is a difference between the H2O concentrations on the two sides of the membrane, and cognizing that when this happens to cells they will either go bombastic if H2O flows into them, or plasmolysed if H2O flows out of them, and therefore alter their volume, we want to prove the hypothesis that:

If the concentration of a solution into which a cylinder of murphy is placed is greater than a certain degree the cylinder will contract, and if the concentration is less than that degree it will spread out.

We have studied turgidness and plasmolysis in a text edition ( Key Science-Biology, pages 143-144 ) and in a preliminary experiment, where we foremost added 2 % sucrose solution to rhubarb cuticular cells, and saw them go plasmolysed, and so added H2O, and saw them go bombastic. However, we did non utilize different solution concentrations, and did non mensurate the sum of contraction or enlargement that took topographic point. From our consequences in the chief experiment, we should be able to work out non merely the sum of contraction or enlargement caused by each strength of solution, but besides the concentration of the sap inside the cells.

Apparatus

For the experiment we will necessitate:

Either cylinders of murphy with a diameter of 6.5mm and a tallness of 5mm, or a murphy, a bore bit with a diameter of 6.5mm and a scalpel. ( To let us to do our ain ) .

Solutions of changing strengths ( of saccharose and NaCl ) , or a solution of a known strength and distilled H2O. ( To let us to do our ain ) .

Pins ( To guarantee that cylinders remain separate while in the solutions. )

Test-tubes

Calipers ( To mensurate cylinder tallness and diameter. )

Diagram One of the test-tubes during the experiment. Three murphy phonograph record on a pin, non touching.

Method

We take a cylinder of murphy, with a diameter of 6.5mm, from the murphy, and cut it into separate cylinders each with a tallness of 5mm. We so thread at least three of the cylinders, to do the experiment carnival ( in instance one of the cylinders is unnatural or damaged ) , on to a pin, maintaining them apart from each other. We so do up solutions of either saccharose or Na chloride, either by % strength or by molar concentration, and topographic point 4 milliliters of each strength into a separate test-tube. We used a scope of % sucrose solutions, traveling from distilled H2O ( 0 % ) to 2 % ( which we knew from earlier experiments would plasmolyse the cells ) , and a scope of Na chloride solutions from distilled H2O ( 0 ) to 0.4 grinder ( which would once more be plenty to plasmolyse the cells ) . We so place each of the sets of three cylinders on a pin into each of the different solutions, doing certain that the cylinders are covered by the solution, and leave all of the test-tubes stopping point to each other for 24 hours.

We assume that this means that the force per unit area and temperature in each instance is the same, as these are factors which could impact osmosis, and we know that the volume, size and surface country of each cylinder is the same, and as they are all from the same murphy, the lone variable that we are changing is the concentration of the solution. Although ideally the experiment would be repeated several times, we were non able to make this as we did non hold sufficient clip.

After 24 hours we remove the cylinders from solution and, with calipers, which are more accurate than a swayer and would cover the likely scope of sizes ( from 4mm to 7mm ) , measure the new diameter and tallness of the cylinders. The consequences, in table and graph signifier are recorded below in the Results subdivision.

Consequences

ConcentrationCylinder Diameter/mmCylinder Height/mmVolume/mm3 ( 2dp ) Ave. Cylinder Volume/mm3

Pre-immersion6.56.56.5555165.92165.92165.92165.92

Sodium Chloride solution

0.0 Molar6.86.665.56.45.2199.74218.96147.03188.58

0.1 Molar66.56.84.44.94.9124.41162.6177.95154.99

0.2 Molar5.65.95.754.54.5123.15123.03114.83120.34

0.3 Molar66.15.94.94.94.5138.54143.2123.03134.92

0.4 Molar5.9655.65.45153.1152.6898.17134.65

Sucrose Solution

0 % 6.876.85.75.55.3207.01211.66192.48203.72

0.25 % 5.56555.55118.79155.5198.17124.

16

0.50 % 55.255.56.65107.99140.1798.17115.44

1 % 5.554.95.95.15140.17100.1494.29111.53

2 % 4.44.64.44.85.24.472.9986.4266.975.44 Concentration of SolutionAverage % Change in Volume From Original

NaCl solution

0.0 Molar13.66

0.1 Molar-6.59

0.2 Molar-27.47

0.3 Molar-18.68

0.4 Molar-18.84 Concentration of SolutionAverage % Change in Volume from Original

Sucrose Solution

0 % 22.78

0.25 % -25.17

0.50 % -30.42

1 % -32.78

2 % -54.53

Analysis

The consequences show that, in conformity with our hypothesis, the cylinders will spread out when external solute concentration is low ( high H2O concentration ) , and contract in strong solutions ( low H2O concentration ) . This is due to osmosis, where H2O passes from weak solutions to strong solutions across a semi-permeable membrane, such as a cell membrane. The graphs of % alteration against solution strength show that the consequences tend to organize a curve, traversing the ten axis ( where there is no alteration in volume ) , at about 0.07 molar concentration for the Na chloride solution, and at about 0.2 % for the sucrose solution. This concentration is the osmolar concentration ( the sum solute concentration ) of the sap inside the cell. The volume alteration forms a curve when plotted against solute concentration because the cells, which have cellulose cell walls in add-on to a cell membrane, will non spread out or contract indefinitely, and will be held in form within certain bounds. However, the comparatively low figure of solutions tested ( 5 ) means that there is a scope of possible values for the osmolar concentration of sap in the cell, and means that we can non accurately predict values for volume alteration at different concentrations. To reason, hence, the consequences back up our hypothesis, and we were besides able to detect the approximative concentration of the sap in the cell.

Evaluation

Although the consequences of the Na chloride and sucrose experiments back up the hypothesis, there are several anomalous consequences and a big divergence for each consequence. These could be improved by changing the experiment, for illustration by maintaining the test-tubes in a H2O bath at a set temperature, by maintaining them at a changeless force per unit area, and by mensurating the sizes of murphy cylinders before and after with a more accurate method, e.g. accurate weight measuring or volumetric supplanting. The trial might besides be more accurate if the murphy cylinders were left in the solutions for a longer period of clip to let the solution to perforate to the full to the nucleus of the sample. The trial could besides be repeated more times for each concentration of solution, and with a greater figure of concentrations, as this would diminish the mistake & # 8211 ; a disadvantage of our experiment was that one anomalous consequence affected the others significantly ( e.g. NaCl 0.2 molar concentration ) . Another factor is that the murphy from which the cylinders are taken could be unnatural & # 8211 ; this could be prevented by mixing sets of consequences, for illustration of a whole category, where each experimenter used a different murphy.

Consequences that were non as I would hold expected occurred with NaCl solution at 0.2 molar concentration ( see above ) , where the scope of consequences appeared excessively low. However, although this is seemingly an anomalous consequence, it could hold been caused by either experimental mistake & # 8211 ; more important when a little figure of consequences are used, or a difference in the murphy for those cylinders. Either of these would easy be recognised if a larger figure of consequences were collected and used. Another consequence that appeared unusual was the & # 161 ; & # 165 ; measure & # 161 ; & # 166 ; in the graph for the sucrose solution between 0.25 % and 1 % solutions & # 8211 ; here different consequences for each cylinder pulled the mean upwards by a noticeable sum, a job that perchance would non happen if more measurings were taken.

For future experimentation we could reiterate this experiment utilizing a scope of solution strengths really near to the value discovered here of sap osmolarity, to specify more precisely its true value. We could besides widen the experiment to utilize tissue samples from other workss, to detect whether the hypothesis is besides right for other tubers, and even for other works tissues. We would so besides be able to compare osmotic force per unit areas inside different workss.