Surface Area Volume Ratio Experiment
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.
Apparatus Needed For the Experiments:
1. Beakers 2. Gelatin blocks mixed containing universal indicator 3. 0.1M Hydrochloric acid 4. Stop Watch 5. Scalpel 6. Tile 7. Safety glasses
1. A block of gelatin which has been dyed with universal indicator should be cut into blocks of the following sizes (mm).
5 x 5 x 5
10 x 10 x 10
15 x 15 x 15
20 x 20 x 20
10 x 10 x 2
10 x 10 x 10 (Triangle)
10 x 15 x 5
20 x 5 x 5
The triangle is of the following dimensions.
The rest of the blocks are just plain cubes or rectangular blocks.
Universal indicator is a neutral indicator. In the alkali conditions of the gelatin it is blue and when it gets exposed to acid it turns red.
Gelatin is used for these tests as it is permeable and so it acts like a cell. It is easy to cut into the required sizes and the hydrochloric acid can diffuse at an even rate through it.
2. A small beaker was filled with 100cm³ of 0.1 molar Hydrochloric acid. This is to ensure that all the block sizes are fully covered in acid when dropped into the beaker.
3. One of the blocks is dropped into this beaker and the time for the entire universal indicator to disappear is noted in a