The unit of measurement that scientists use to determine the diameter of an animal cell is the

Meter (http://en.wikipedia.org/wiki/Meter), inch (http://en.wikipedia.org/wiki/Inch), mile (http://en.wikipedia.org/wiki/Mile), yard (http://en.wikipedia.org/wiki/Yard), Astronomical Unit (http://en.wikipedia.org/wiki/Astronomical_unit), lightyear (http://en.wikipedia.org/wiki/Lightyear), parsec (http://en.wikipedia.org/wiki/Parsec), planck length (http://en.wikipedia.org/wiki/Planck_length), sheppey (http://en.wikipedia.org/wiki/List_of_humorous_units_of_measurement#Distance:_Sh eppey).

We can use all of these and many more to determine the diameter of a cell. We can use them all easily because of scientific notation (http://en.wikipedia.org/wiki/Scientific_notation).

Take your pick! You teacher cannot mark you wrong as long as it's a unit of length (http://en.wikipedia.org/wiki/Category:Units_of_length). (Sheppey might be stretching it a little too far!).