Biology: Surface area to volume ratio

In Biology, we are currently studying cells.  My students are learning why cells can't keep growing and become giant monster cells that take over the world.  One of the reasons is that the surface area to volume ratio in cells decreases as the cell get larger.  This make nutrient uptake and waste removal slow down to a point where the cell could die.  The only options are to divide or die.  This is leading us into the discussion of mitosis (cell division).  Here, my students are experiencing for themselves, what effect cell size has on diffusion of a material into the cell.  The gel blocks (the cell) have an indicator in them so when the liquid (NaOH) diffuses into the cell, it turns pink.  After making measurements and calculations, they we able to determine that the effectiveness of diffusion does decrease as the cell gets larger.

Cell showing a dark area of diffusion and a light area where diffusion was not able to reach during the 6 min. time period.

Students measuring the area of diffusion of their three cells.

The three cells soaking in the NaOH solution.

Observing all three cells