Modelling Surface Area to Volume Ratio in Cells with Agar Cubes

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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. ()

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.

Single celled organisms can survive as they have a large enough surface area to allow all the oxygen and nutrients they need to diffuse through. Larger multi celled organisms need specialist organs to respire such as lungs or gills. ()

A cell is a metabolic compartment where a multitude of chemical reactions occur. The number of reactions increase as the volume of metabolic volume within a cell increases. (The larger the volume the larger the number of reactions) All raw materials necessary for metabolism can enter the cell only through its cell membrane. The greater the surface area the larger the amount of raw materials that can enter at only one time. Each unit of volume requires a specific amount of surface area to supply its metabolism with raw materials. The amount of surface area available to each unit of volume varies with the size of a cell. As a cell grows its SA/V decreases. At some point in its growth its SA/V becomes so small that its surface area is too small to supply its raw materials to its volume. At this point the cell cannot get larger. ()

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Hypothesis

We predicted that as the Surface Area / Volume Ratio increased, the penetration volume of HCL into the agar cubes would increase. This is because a small block has a large amount of surface area compared to its volume so the hydrochloric acid will have a large surface area to diffuse through. A larger block has a smaller amount of surface area in relation to its size so it should take longer for the hydrochloric acid to diffuse into the centre of the cube. The actual rate of the hydrochloric acid diffusing through the agar should be the same ...

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