The Franklin Institute
Franklin Institute: White Blood Cells
This site contains a brief description of what white blood cells are and how they work.
Science Bob Pflugfelder
Science Bob: Body Zone: The Skeleton
An introduction to the function of the skeletal system, including blood cell production and the importance of calcium.
Treehut
Suzy's World: Blood
Use this site to find out why your body needs blood with this quick fact sheet. You can also try an experiment with your pulse.
Cells Alive
Cells Alive!: Cell Gallery
This gallery shows pictures of a variety of cell types with hyperlinks to additional information about cells. Very interesting pictures.