Cell Shape and Diffusion Diffusion is a type of passive transport which allows particles to move from a region of high concentration to a region of low concentration. In a living system, diffusion involves a cell membrane. Cells also need to excrete waste which also occurs at the cell membrane. Aim: The aim is to use model cells made from agar which contains phenolphthalein and sodium hydroxide (cut in different sizes) to investigate the effect of shape on the time taken for sulfuric acid to diffuse into the centre of the ‘cells’.

This will be measured by the time it takes for the agar to become colorless. Research Question: How will changing the shape or size of the agar prisms affect the time taken for the sulfuric acid to diffuse into the centre? Hypothesis: If the surface area to volume ratio of the agar prism is large (egg: 1 x 1 CM), then the time taken for the sulfuric acid to diffuse it will be shorter. The smaller the size of the agar block, less time will be needed to diffuse the agar block compared to a larger agar block with a lower AS: V ratio.

Variables: The independent variable was the shapes of the agar prisms and its sizes. The surface area to volume ratio (CM 2 : CM 3). The sizes and shapes used were: Dimensions of each agar block: Table 1 Shape Dimensions (CM) Cube 1 lexeme cube 2 1. MM. Ex.. Corn cube 3 2 x 2 x CM Rectangular prism 1. Essex. Corn The dependent variable was the time in minutes (miss) that it took for the agar prisms to become colorless. The quantitative data that was measured was the time in minutes, that it took the sulfuric acid to diffuse the agar prisms.

All three trials for each shape had similar results. Trial 3 with the rectangular prism took much longer than trial 1 or trial 2 for this shape. Discussion & Conclusion It can be seen through the results that the larger the size of the shapes, the smaller the surface area: volume ratio. Therefore the larger the shapes, the longer it took for the sulfuric acid to diffuse the entire agar block. Changing the shape and the size of the agar prisms affected the time taken for the sulfuric acid to diffuse into the centre, because the smaller the volume of the shapes, the quicker the entire diffusion occurred.

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The outcome of the experiment supported the hypothesis to some extent because the time taken for cube #2, cube #3 and the rectangular prism were estimated according to cube #2 as there was not enough time allocated to complete the rest of the experiment. As the rectangular prism was estimated (The results for Cube 2, 3 and 4 were calculated estimates due to the time limit) to take the longest mime to diffuse does not fit in with the rest of the pattern and can be a result of an error that occurred in the experiment.

However as seen in Figure 2, the values do tend to rise therefore confirming the pattern in the results. Before putting the cubes into the sulfuric acid, they were purple in clear and not clear. After the diffusion had occurred, the cubes changed color and became white and translucent. Evaluation There was a difficulty in this experiment; the time that was allocated to conduct this experiment was not enough and resulted in only a small fraction of the experiment Ewing completed.

Due to this, most of the dependent variable values were estimated and in turn, resulted in inaccurate and insufficient measurements. It is ideal that if this experiment were to be repeated, that the appropriate amount of time (2-3 hours) must be allocated for it to be conducted properly. It will also be best if a stopwatch was used per agar block in order to gain maximum accuracy while measuring the time. Another way to gain more accuracy in the results is to use cutters that are made to specific sizes so that you can use these in order to cut up accurately measured shapes.


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