Sara's Cell Size and Diffuion Argumentation

Sara Bearden

Cell Size and Diffusion

Cells that have a larger surface area to volume ratio are more efficient at diffusing essential nutrients. For this experiment my group and I used five objects that varied in shape and size. We timed how long the shapes took to fully diffuse the weak acid and what we found was that the small cube was the first one to fully diffuse the acid at 15.28 minutes. It's surface area to volume ratio was 6:1 which, was the largest ratio compared to the others. The small rectangle had a 5:1 surface area to volume ratio and it was fully diffused at 16.14 minutes which is only a minute and twenty-six seconds after the small cube was done diffusing the weak acid. With the higher ratio it allowed for the two shapes to diffuse the weak acid easier and allow the acid to reach the center faster. The higher ratio means that there was more membrane for the weak acid or nutrients to enter and be able to move into the cell to the center. That then allows for that acid or another nutrients to be utilized for functions in the cell a lot quicker.  One of the shapes was a plus sign and it also had one of the larger ratios of 4.4:1 however, the diffusion of the weak acid took 33 minutes and that was the last one too finish. This evidence contradicts the claim that a cell with a larger the surface area to volume ratio a cell is more efficient at diffusion essential nutrients.  During the experiment this plus sign was buried under the other four shapes we had which, caused only for a limited amount of membrane to be exposed to the weak acid directly.  The areas that were under the shapes caused the acid to take longer to reach that area, leading to a longer time for the shape to fully diffuse the acid. This also occurred with the bigger cube where it has a surface area to volume ratio of 3:1 but it took 24 minutes to fully diffuse the weak acid.  There was another shape that had a smaller ratio but, it was smaller than the big cube and it finished before the big cube which, shouldn't be according to my claim.  The shape was the big plus sign that had a surface area to volume ratio of 2.2:1. That shape should have been the last one to finish diffusing the weak acid since it had less membrane exposed to it which, only allowed  limited acid to enter the cell and move to the center to be utilized.  But, since it covered the shapes with bigger ratios than itself it caused them to have a slower diffusing time than predicted.  If the shapes were spread out instead of clumped together the time of full diffusion and the ratios would have matched up.  The shapes or "cells" with the larger surface to volume ratios like the small plus sign, rectangle, and the small c would have times closer to each like the rectangle and small cube did. Their larger ratios allow more membrane to be exposed to the nutrients (weak acid) so more can enter and travel to the center of the cell to be utilized for organelle functions.

The rate of diffusion may relate to the size of the cell and sometimes the nutrients diffuse faster through smaller cells than they do in larger cells but, that's not always the case.  For instance, we had a cube with the dimensions of  2cm by 2cm by 2cm and a plus sign that was 2cm all around in the weak acid along with the other three shapes we had.  The cube makes up one part of the cross since, depending on how you cut the cross up you would get five cubes that are all 2cm by 2cm by 2cm so the plus sign ends up bigger than the cube. The cube had a diffusion rate of 1cm per 24 minutes and the plus sign had a diffusion rate of 2.5 com per 21.56 minutes. The distance used in the diffusion rate was the shortest one for the weak acid to take in order to reach the center. The rate of the plus sign is higher than the cube because the weak acid traveled a longer distance in a shorter amount of time than it did in the cube.  What that means is the weak acid reached the center of the plus sooner than it did in the cube and that would allow the weak acid to be utilized quicker for the functions of the cell.  Therefore, the rate of diffusion does relate to the size of the cell since that determines how far the nutrients have to travel to the middle of the cell but, it doesn't always means that the smaller cells diffuse the nutrients faster since the plus sign diffused the weak acid which, represented the nutrients faster than the cube which, was smaller than the plus sign.

The shapes after the weak acid was fully diffused.

A bird's eye view of the shapes in the acid and you can see the weak acid starting to diffuse into them.

The shapes in the weak acid as the diffuse it.  With them not spread out it caused for less membrane to be exposed to the acid so the diffusion time was slower for those with larger surface area to volume ratio like the plus sign.

This is the weak acid the shapes were put in.  The acid represent the essential nutrients that cells would have to diffuse. The shapes are the cells.