Introduction: All cells are dependent on a processes called diffusion, which is the movement of a substance from an area of higher concentration to an area of lower concentration. Cells need to obtain certain essential substances, like oxygen, for their survival. The rate of diffusion is said to be dependent upon the various factors: Size of molecules that have to diffuse, concentration gradient, the distance across which diffusion occurs, number of pores/openings, surface area and concentration.
This rate of diffusion is measured by considering the time taken for changes to physical changes to occur. This experiment consists of using agar mixed with an indicator that changes color when places in a basic solution. It will measure the amount of diffusion that occurs in the agar blocks to determine the effect of cell size on the cells ability to obtain substances by diffusion.
Purpose:Determine how surface area and volume relate to one another and how the rate of diffusion varies with the ratio of surface area to volume. In the experiment, we will use the base/acid indicator Phenolphthalein in three different sized agar cubes dipped in a sodium hydroxide solution. This will make it possible to measure the depth to which the color has penetrated and will demonstrate the relationship between diffusion and volume.
-two large beakers
-Potassium manganate (K2MnO4 )
-Hydrogen chloride (HCl)
-Make two trays of Agar Gelatin. One pure and one dyed pink. -Use the scalpel to cut three agar cubes of each tray: a 3cm cube, a 2cm cube and a 1cm cube (total of six cubes). -Pour the Potassium manganate (K2MnO4 ) into one of the beakers and Hydrogen chloride (HCl) in the other. -Immerse the 3cm clear cube in the pink Potassium manganate (K2MnO4 ) and the pink agar cube in the clear Hydrogen chloride (HCl).
-Set the timer to 10 minutes.
-After the 10 minutes, use the spoon to take the cubes out of the beakers and dry them with a paper towel. -Cut both cubes in half with the scalpel.
-With the ruler, measure how deep the pink penetrated the clear cube and how much the pink cube absorbed the acid. -Repeat the procedure with the smaller cubes, always leaving them in the beaker for 10 minutes.
Its clear to see that the cubes in which most of their volume changed color were the smaller ones. The 1cm Clear cube had 100% of its volume diffused. The smaller agar cubes will be more efï¬cient in diffusion because smaller agar cubes have a bigger surface area to volume ratio. The pink agar cubed immersed in Hydrogen chloride (HCl) had a faster process of diffusion than the clear agar cube immersed in Potassium manganate (K2MnO4 ).
The reason cells are so small is because it facilitates the diffusion. As seen in the experiment, diffusion is more efï¬cient when there is a bigger surface area to volume ratio. This process is essential for every cell to bring nutrients and release wastes and it is only possible due to the fact that cells are very small, making the diffusion a lot faster.