Cell Models

• Substances must move into and out of cells for an organism to function.
• Three processes contribute to this movement – diffusion, osmosis and active transport.
• Cells can be modelled using cubes to investigate the effect of increasing size on surface area to volume ratios.
• The surface area to volume ratio of a cube with a length of 6 is 1.
• A stacked bar chart can be drawn to illustrate the proportions of surface area and volume.
• Scientists have estimated the surface area : volume ratios of various organisms.
• Bacterium has a surface area of 6 x 10 -12 m2 and a volume of 1 x 10 -18 m3, resulting in a surface area : volume ratio of 6 000 000 : 1.
• Blow fly has a surface area of 6 x 10 -4 m2 and a volume of 1 x 10 -6 m3, resulting in a surface area : volume ratio of 600 : 1.
• Whale has a surface area of 6 x 10 4 m2 and a volume of 1 x 10 6 m3, resulting in a surface area : volume ratio of 0.06 : 1.
• Large organisms have mechanisms to increase surface area proportionately, such as additional absorbing areas or adaptations of shape.
• Organisms living in harsh environmental conditions may reduce their surface area, for example, cacti, to reduce loss of water.