American Chemical Society
Middle School Chemistry: Chapter 3: Density
Six interactive chemistry lessons about density complete with handouts and animations.
Other
Food and Water Watch: Factory Farm Map
A United States map showing density levels of animals raised for food, accompanied by effects of factory farming and latest news on farming, animal welfare and food safety.
My Science Site
Life Systems: Cells, Tissues, Organs
Extensive site for teachers provides some helpful resources that pertain to plant and animal cells. Includes a microscope diagram as well as plant, animal and pond labs. Also contains links to structures and mechanisms, matter and...