Determining Osmotic Potential Using Denseness Gradient

A cell, when subjected to an environment where the external water potential is less negative than the inner water probable, will loose drinking water by osmosis down a awareness gradient. Conversely, when exposed to an environment where in fact the internal water potential is less negative than the external water potential the cell will take in water from the encompassing solution. Regarding the former it has the result of the cell loosing its potential to exert pressure on the cell wall and be flaccid. If drinking water loss is consequential the cell will eventually plasmolyse. The point at which the cell is neither turgid nor flaccid and the net movement of water has reached energetic equilibrium is recognized as insipient plasmolysis. It is at this time that the osmotic potential of the cell is add up to the osmotic potential of the surrounding solute. In a more focused solution, plasmolysis will continue, causing the protoplasm to pull away from the cell wall structure leaving a space which steadily fills with the external surrounding substance. As the osmoticum gets into the gap between your protoplasm and the cell wall, the cell thickness increases. Because the osmoticum of sucrose is denser than normal water, the plasmolysed cell is therefore denser than the non plasmolysed cell and can travel further with a quicker rate through the thickness gradient.


To build and utilise a denseness gradient to plot a graph from which the point of insipient plasmolysis can be ascertained, and hence the osmotic probable of a vegetable cell found.


As script - A mean of two ideals was considered as time did not enable for the experiment to be run 3 x.

A graph was then plotted of the mean distance travelled by each stem section against the molar concentration in which it had been equilibrated. The graph was then analysed to see at which point the gradient altered significantly and the point of insipient plasmolysis was found by interpolation this provides you with the osmotic probable of the cell.


Figure 1 shows the stems dropped at a steady rate in a continuous decline before 0. 3m point where the graph dips sharply to the 0. 2m point. Suggesting that the point of insipient plasmolysis is just about 0. 2m as the steep change in direction to the 03. m point means that the cells have increased in density thus travelling further and quicker. The readings at 0. 1m do not fit the general craze of the graph suggesting they are anomalies in the data.

Discussion and Evaluation

The change in the graph occurs because cell membranes in the tissue start to pull away from the cell surfaces, at the 0. 2m concentration. With the 0. 3m solution point, more water has kept the skin cells by osmosis so that they can achieve equilibrium in the surrounding fluid, yet, in doing so the cells have grown to be plasmolysed, allowing the sucrose means to fix enter the space between the cell membrane and cell wall structure, therefore it is here the initial increase in thickness sometimes appears as a sharpened increase in the length travelled by the stem parts. As the skin cells become further plasmolysed scheduled to immersion in increasing extracellular concentrations, more sucrose solution gets into the space in the cells causing them to become denser and hence the stem areas travel further. Insipient plasmolysis was shown to arise when the stems were equilibrated in 0. 2 molar sucrose solution; hence because the solute potential of a solution is proportional to its molarity (Campbell Reece et al. ) the osmotic potential of the solution was 0. 2 moles. At the idea of insipient plasmolysis the osmotic probable of the cell is equal to the osmotic potential of the surrounding fluid and then the osmotic potential of a seed cell is 0. 2moles. The readings taken for the stem in the 0. 1 molar solution show that the stem travelled quite some way, this will not have took place as the cells should not have started to plasmolyse plus they should in simple fact have been turgid at this time as the osmotic probable of the cell is 0. 2m and therefore has a less negative normal water potential than the encompassing fluid, pushing uptake of normal water in to the cell from the encompassing smooth. The stems were well prepared in the group it could have been that the stems weren't uniformly cut and possibly weighed heavier in the first instance. It would have been more wise to perform the experiment a few more times to get a more exact mean for the readings. However, the readings obtained are sufficient to make a graph from which we can identify the point of insipient plasmolysis.


The Osmotic probable of plant cells is add up to that of insipient plasmolysis which is, 0. 2moles


Campbell, R. , Reece, J. , Urry, L. , Cain, M. , Wasserman, A. , Minorsky, P. , and Jackson, R. (2008) Biology, 8th model, Pearson International: Benjamin Cummings


Bioskills Useful book

Enzyme Hydrolysis of Glycogen by Alpha and Beta Amylase


After meals carbohydrates are stored in the liver organ as Glycogen. Glycogen is a branched polymer of sugar where glucose residues are linked by alpha 1-4 glycosidic bonds in linear chains and branched factors are connected by alpha 1-6 glycosidic bonds. When required this Glycogen is released back into the blood vessels but first must divided into smaller 'usable' disaccharides. Alpha amylases catalyse the hydrolysis of glycogen at the 1-4 linkages, producing Maltose and Maltotriose. Beta amylase also serves in the same manner, but only operates at the non lowering end of the polysaccharide as it is an exo-amylase. Once a branch is reached a limit dextrin is produced as hydrolysis halts. Glycogen digestion by enzymes can be ascertained by determining the amount of product produced during hydrolysis. The resulting product being truly a reducing sugar, which reduces yellow DNS dye to produce an orange red colour (3-amino-5 nitrosalicylic acid). The more reducing sugars produced, the darker and denser the color produced during the reduction response. A spectrophotometer is used to be able to measure the thickness of the producing solution as density increases so does indeed absorbance at 540nm.


To determine which if some of two enzymes, Alpha and Beta Amylase digests glygogen most proficiently.

Method - As Script

Maltose concentrations were changed into micromoles per ml and a calibration curve was constructed. A regression collection was added and an formula for the collection found that was used later in order to find concentrations for every enzyme after the assay have been run and absorbance's found. These concentrations were then plotted on a separate graph and the graph analysed to see which enzyme performed most proficiently.


The ends in Body 3 show that alpha amylase produces the most product reaching over 2. 5 micromoles as time passes however the graphs also show an identical curve suggesting that the reaction for both enzymes is progressing at an identical rate.


If a gradient is considered for the original activity for both enzymes it is available that they both produce 0. 1 micromoles of product per ml each and every minute and hence the speed of reaction is apparently the same for both enzymes. However alpha amylase clearly produces more reducing sugar, due to its response within the glycogen chemical substance and the initial rate must therefore be faster than that of Beta amylase which only reacts at the lowering ends of the polysaccharide and it is also inhibited by its product maltose. (www. homedistiller. org/enzymes 11. 4. 10) This shows that t0 is not t0, as advised.

During the test the alpha amylase offered absorbance readings at 540nm at over 1 as did the maltose through the making of the calibration curve, as the absorbance of rays at a specific wavelength by a remedy is 'immediately proportional to the awareness of the absorbing solute' the readings over 1 are highly apt to be inaccurate as the linear romantic relationship only applies up to certain attentiveness, and above this awareness the partnership becomes non linear. As is seen in amount 2 almost all of the absorbances for alpha amylase were over one and therefore should be questioned as to their validity.

On this basis the alpha amylase must have been diluted further to provide absorbances of significantly less than 1 and then this multiplied by the dilution factor to give the absorbance of the original solution.

From the curves in Number 3 it is very visible that t0 is not t0 and the majority of the reactions in both cases took place easily. To uncover t0 further experimentation should be carried out at that time the curve presents a zero order reaction. I. e. where the rate is continuous as time passes. The substrate concentrations ought to be the variable factor with multiple readings used, and the velocity measured for every single one. This data should then be plotted and the two variables which define enzyme kinetics, Km and V potential found. These details can then be applied to the Lineweaver-Burke model and the point at which the collection crosses the y axis is the idea of 1/V0. This amount can then be differentiated to find t0.


It would appear the alpha amylase is the most effective enzyme for digestion of glycogen.

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