To determine the relationship between Surface Area and Volume Ratio of a phenolphthalein impregnated agar block, and the rate of diffusion into the block.
Diffusion is the passive movement of particles from high concentration to low concentration. It is a very slow process so therefore the smaller the cell it is more efficient and faster.
As the volume of the agar block decreases, the rate of diffusion will increase because the speed of the molecules (movement) is directly associated to the volume.
– Sodium hydroxide () solution
Manipulated Variable (MV): volume of the agar cubes.
Responding Variable (RV): rate of diffusion and percentage of diffusion.
Constant Variable (CV): time, stopwatch, ruler, same bottle of .
– Firstly, cut the agar gel using a knife. Then calculate the surface area and volume of each agar cube. Try to make sure each agar cube is as accurate as possible.
– Take the (2x2x2) agar cube and place it into a beaker.
– After that pour into the beaker and make sure that the agar cube is covered with solution.
– All three cubes of the same volume should be covered with. Then start the stopwatch.
– Leave the agar cubes in the solution for 2 minutes.
– Next, remove the agar cubes from the beakers and place them onto a dry surface.
– Measure the penetrated part of the cube (pink color) with a ruler. Then calculate the percentage.
– Record your results and repeat the procedure for the other agar cubes.
Measuring with a ruler:
Volume of Agar Cube
In conclusion, we tested the Surface Area to Volume ratio in two different ways because we could not decide on which method would be more accurate. As the cell size increases, its volume increases faster than the surface area.
The size of the agar cube played a significant role in this experiment because the larger the cube, the harder it was for the sodium hydroxide to diffuse. When the cells are large, the cell membrane creates a strong barrier against the substance, which makes it difficult for diffusion to take place.
The line of best fit did not pass through the origin because we assumed that the agar and the sodium would be uniformly dense however, they could be heavier. This then caused the systematic error, which is shown on the y-axis of the graph. One point did not suite the graph because of a random error such as the inaccuracy of the cube.
Many errors occurred during this experiment. The agar cubes were difficult to cut and because they were wobbly, it made it even harder to make them the same size and accurate. We were not able to make all the cubes have the same length, height and depth because the agar was only a certain depth. Although three trials were taken for each agar cube, I still believe that the source of error might have been largely affected by this measurement therefore; we used two methods of finding the percentage of present in the agar cube. We did not make sure that the had a constant temperature so this could have been another factor which affected our experiment. This experiment could be improved by having accurately cut agar cubes as well as another possible way of measuring the absorption of sodium hydroxide. One potential method could be using a jelly mould in order to make sure that all the cubes are the same size and this would make the experiment more accurate. Some of our data was collected during another time and mould started growing on the agar so possibly the experiment was affected by this.