Your body is made up of trillions of cells—but what do you really know about them? Take our lab quiz and determine your CIQ (cell identification quotient).
October 1, 2011|
Life on Earth is mind-bogglingly diverse with estimates of the number of existing species in the tens of millions. Over the last 4 billion years, many species have gone extinct; and because of the actions of humans, many existing species are now endangered.