Aphid fish are the smallest type of fish that can be seen by the naked eye (bare eye-no glasses or microscope).
The whole surface of a human body can be seen if it is naked.
By definition, a microorganism cannot be seen by the unaided human eye.
the Oocyte is the largest human cell and can be seen by the naked eye. more information on the Oocyte: http://en.wikipedia.org/wiki/Oocyte
The smallest particle that can be seen with a light microscope is about 0. 2 microns. If an object is smaller than that, the light's wavelength cannot traverse it causing it to fall out of the visible spectrum.
A particle is an atom which cant be seen by the naked human eye, everything is made up of: in solids; gasses and liquids. Each atom contains electrons, protons and neutrons, which is what gives each particle its properties. Solids tend to have more compact particles where as gasses have less.
the human heart can be seen with the naked eye if chest is open