Diffusion: Surface-area-to-volume Ratio and Cube

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An investigation of Factors that Affect Diffusion


The aim of this investigation is to prove the effect of increasing size on the efficiency of diffusion. Diffusion is the process that cells use to obtain oxygen, water and food. Also, how they lose waste substances, for example, urea and carbon dioxide. Basically, Diffusion is when particles move from an area of high concentration to an area of low concentration. The surface area to volume ratio of the cell is an important factor in diffusion. It is the effect of this factor that will be investigated in this practical.

Materials used in the practical consist of blocks of agar jelly containing indicator, a sharp knife, used to cut the agar jelly into the recommended sizes, diluted sulphuric acid (300mL) , ruler, to measure the sizes of the cubes, absorbant paper towel, three 250mL beakers, and a measuring cylinder.

To perform this experiment, the following procedures will need to be follow precisely: Obtain three blocks of agar jelly. Carefully cut three cubes, as close as possible to 1 cm, 2 cm, and 3 cm in size. Try to be exact, as this will help in the calculations later. Record the exact dimensions of the cube, in a table (see back of booklet). Calculate the volume, the surface area, and surface area/volume ratio for each cube. These will be known as the ‘outer’ cube dimensions. Measure 100 mL of sulphuric acid into each of the three beakers. CAUTION: sulphuric acid is dangerous. Handle with care!

Carefully place the largest cube into one of the beakers, in the acid, and begin timing (timing must begin a soon as the cube is placed in the acid). The cube must be left for exactly 10 minutes. After 5 minutes place the middle cube into one of the other beakers of acid and begin timing. After 10 minutes place the smallest cube into the third beaker of acid, remove the first cube and place it on some paper towel. Working quickly and efficiently, blot the excess acid from the...
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