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To investigate the effect of cell sizes on diffusion by modelling the process of agar blocks and dilute Hydrochloric acid.

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Introduction

To investigate the effect of cell sizes on diffusion by modelling the process of agar blocks and dilute Hydrochloric acid. Introduction Diffusion is defined as the net movement, as a result random motion of its molecules or ions, of a substance from an area of relatively high concentration to an area of relatively low concentration. This enables many biological processes to occur for example one of the most important, supplying the body with sufficient oxygen for respiration. Therefore, in the experiment the aim is to investigate the effect of cell size on diffusion, which will aid the understanding of why our bodies contain different size cells. Preliminary Experiment Aim To investigate the effect of cell sizes on diffusion by modelling the process of agar blocks and dilute hydrochloric acid. Apparatus 1. Agar blocks- made with sodium carbonate solution and stained with phenolphthalein, a pH indicator. 2. 2 M Hydrochloric acid 3. Knife 4. Metric ruler 5. 3 Stop clocks 6. 3 beakers 7. 1 tile 8. Measuring cylinder Method 1. Gather apparatus. 2. Cut agar blocks into cubes of 1cm3, 2cm3 and 3cm3 on a white tile. ...read more.

Middle

Evaluation Overall, I believe that this experiment was completed reasonably well. The results supported the scientific explanation of the effect of cell size on diffusion. However, there are many errors in this experiment, the major one being measuring the end point. In this experiment the stop clocks were stopped when the pink block turned white however, this point could be measured differently depending on people's perception of the colour white. Also, there is the disadvantage of human's reaction time to stop the stop clock, which will inevitably add error to the results. A way to overcome the error of measuring the end point could be to leave the different sized agar blocks in the hydrochloric acid for the same amount of time, then cut them open and measure the distance the acid has diffused. This could gain more accurate results. Another human error is the accuracy of the size of the agar blocks, to overcome this either use a machine to cut them or buy them already cut into shape. Finally to improve this experiment repetitions would be necessary along with more sized cubes in order to gain more accurate and reliable results. ...read more.

Conclusion

Place the blocks on a white tile and cut open. 7. Using a ruler measure the distance that the acid has diffused and record this number. This is the dependent variable as it responds to the independent variable. 8. Repeat steps 2-7 two more times in order to gain three results for each sized cube. This will make the results more accurate and reliable. Prediction I predict that the larger the surface area to volume ratio then the larger the distance, in relationship to the size of the cube, the acid will diffuse. I believe this as small cubes have a larger SA:Vol, therefore they enable more hydrochloric acid to diffuse through them then larger cubes. This relates to cells as, small cells have a large SA:Vol ratio, enabling them to have a good supply of oxygen and glucose and having a small volume means that the demand for oxygen is less, subsequently the cell can use more oxygen and glucose for respiration than bigger cells. As the cell increases in size, the surface area to volume ratio decreases to the point where the supply of oxygen and glucose becomes limited. The cell will die if it gets any bigger. This is why in our bodies we are mainly built of loads of small cells. ...read more.

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