Introduction: Cellular Structure and Function
All organisms are made of cells. Complex organisms (such as humans) are made up of collections of highly specialized cells, each with its own specific function. Different types of cells have evolved specific shapes and properties which help them do their jobs inside the organism.
Still Image:
Sea urchin egg and sperm
Hundreds of sperm surround an already-fertilized sea urchin (Lytechinus pictus) egg. The first sperm to penetrate the egg triggers formation of the fertilization membrane (most easily seen on the lower right side of the egg), which forms a barrier to other sperm.
Sea urchin eggs were fertilized, then immediately mounted in seawater between a slide and coverslip (using a silicon spacer). Images were taken at room temperature on a compound inverted microscope using a 40x DIC objectiveand digital camera.