Here is a link to a brilliant web flash animation showing how cell and organelle sizes compare across the living kingdoms. The animation allows you to slide a cursor to zoom in, slowly revealing smaller and smaller objects. From coffee bean to ameoba to skin cell to X chromosome to lysosome to HIV virus to carbon atom. An excellent animation suitable for all age groups. Click on the image above or here to see the animation. There is also a great flash animation looking inside plant and animal cells. Click here to see. Thanks to Piero for the links!