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Introduction

MODELLING SURFACE AREA TO VOLUME RATIO IN CELLS Research Question To investigate the effect of increasing the SA:V ratio on the percentage of penetration of HCL, when cubes of bromothymol blue agar are placed in the HCL. (Concentration of the HCL --> 0.1 M) Background Info A cell needs a large surface area in order to carry out metabolic functions (as chemical reactions require a surface). As a cell grows, it needs to carry out more and more reactions. Therefore, since a cell has to maintain a certain surface area to volume ratio, its size is limited. (http://en.wikibooks.org/wiki/IB_Biology/Cells) The surface area to volume ratio in living organisms is very important. Nutrients and oxygen need to diffuse through the cell membrane and into the cells. Most cells are no longer than 1mm in diameter because small cells enable nutrients and oxygen to diffuse into the cell quickly and allow waste to diffuse out of the cell quickly. If the cells were any bigger than this then it would take too long for the nutrients and oxygen to diffuse into the cell so the cell would probably not survive. ...read more.

Middle

Surface Area: Volume Ratio Volume of Bromothymol Blue Agar COLOURED (un-penetrated) (cm3 +/- 1mm) Trial 1 Trial 2 Trial 3 Trial 4 2:1 (3cm) 4.91 3.38 8.00 3.38 3:1 (2cm) 0.51 0.13 1.00 0.34 6:1 (1cm) 0.00 0.00 0.00 0.00 Table 3 The mean penetration percentage (%) and standard deviation of hydrochloric acid (HCL-0.1M) when cubes of bromothymol blue agar (side lengths 3cm, 2cm, 1cm) with increasing surface area to volume ratio's (2:1, 3:1, 6:1) are placed into the acid for a period of 6 minutes. Surface Area: Volume Ratio Mean of the percentage of cube uncolored (%) Standard Deviation (3 significant figures) 2:1 (3cm) 81.8 8.06 3:1 (2cm) 93.8 4.64 6:1 (1cm) 100.0 0.00 Qualitative data: table 7 - qualitative data from experiment Surface Area to Volume Ratio Qualitative Observations Trial 1 Trial 2 Trial 3 Trial 4 2:1 (3cm3 cube) * Minimal change observed in first minute. * Appears to be minimally penetrated by hydrochloric acid. * Solution had acidic odour * Remained constant throughout experiment * The cube was pale on the outside with a slight yellow/white tinge * The inside of the cube was a darker blue colour * Whitest on edges- almost transparent * Not much change occurred at first * During the third minute the penetration became more obvious however did not penetrate more that 1/4 of cube. ...read more.

Conclusion

When we were measuring and cutting the cubes, it was hard to be exact because the agar was quite flexible and so when you cut through it, it was hard to cut it straight and to get an exact cube. Also, when we were measuring the cube, not all the edges were straight on the cube and also we were using a regular 30cm ruler with and uncertainty of 1 mm, so it was hard to be exact with our measurements. In the future, we could use set molds to increase the uniformity of the cubes and increase the exactness and straightness of all the sides. The original big block of agar we received was also not consistently blue all the way through to start with which indicated that the bromothymol blue wasn't consistently distributed or maybe a reaction had occurred between the agar and the air. However, when we cut our 3 different sizes of agar cubes, we still had a lot of agar left over so in the future, we would try to choose an area of the agar which was more consistently blue (therefore indicating that the bromothymol blue is more evenly distributed through the agar) and use that area to create our different sized cubes. ...read more.

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