Rameia's Cell Diffusion Argumentation

Cell Diffusion Argumentation

Rameia Ramsey

   In this experiment, my partners and I were challenged with how the size of a cell effects the rate of diffusion within it.  We were given two possible explanations and asked to choose one and use our experiment to confirm why the statement we chose was the correct explanation and also use our experiment to refute the other explanation.  Therefore, cells are small because cells that have a larger surface area to volume ratio are more efficient at diffusing essential nutrients.

    In order to prove this explanation, we cut out rectangular prisms of agar to represent our cells.  We cut out two small rectangular prisms and two large rectangular prisms of agar.  The small rectangular prisms had the dimensions of 2cm for the length, 1.5 cm for the width, and 1.5 cm for the height.  The large rectangular prisms had the dimensions of 4cm for the length, 1.5cm for the width, and 2.5cm for the height.  The volume of the small rectangular prisms was 4.5cm³ and the surface area was 16.5cm^2.  The volume of the larger rectangular prisms was 15cm³ and the surface area was 39.5cm^2.  After measuring and calculating all the dimensions of the prisms we then submerged them into a container of weak acid, in this case our weak acid was vinegar.  In the making of the agar to construct the cells a chemical called Phenolphthalein was added.  This chemicals allows us to see the diffusion of the vinegar into the prism as time went on.  The prisms soaked in the vinegar for a total of 27 minutes.  After taking the cells out of the container we measured how much of the blue colored section of the agar remained.  In the small cells what was left was 1cm in length, 0.5cm in height, and 0.5cm in width.  In the larger prisms the blue that remained was a length of 3cm, width of 1cm, and a height of 0.5cm.  The new volume of the small prism would now be 0.25cm³ and the surface area would be 2.5cm^2.  The volume of the large prisms would now be 1.5cm³ and the surface area is now 10cm^2.  By using these volumes of  the cells we see that in the small cell about 5.6% of the cell did not diffuse while about 94.4% of the cell did diffuse.  In the larger cell we see that 10% of the cell did not diffuse and 90% did diffuse.  As shown in the numbers the larger cell diffused less than the smaller cells which supports our explanation.  The smaller cells were able to diffuse more because they have a larger surface area to volume ration which was a ratio of 3.67 while the larger cells had a smaller surface area to volume ratio of 2.63, in turn making the diffusion in smaller cells faster.

    Our evidence refutes explanation two which states that the rate of cell diffusion is related to cell size.  Nutrients diffuse as a faster rate through small cells than they do through large cells.  In order to calculate the rate of diffusion you divide distance of diffusion by the time it took to diffuse.  The large cells and small cells had the same distance of diffusion which was 0.5cm, and when divided by the total time of submergence which is 27 minutes the rate of diffusion for all the cells was 0.019.  If all of the cells have the same rate of diffusion then the size of a cell can not be attributed to how it diffuses materials.  In conclusion,  cells are their small size because having a larger surface area to volume ratio is more beneficial to diffusing nutrients.  

 The cells made of agar placed into the container with weak acid(vinegar)

 Side view of the cells in the container with the weak acid

The cells after being submerged for 27 minutes.  The yellow parts of the cells show where diffusion has occurred. The blue part shows where diffusion has not reached