What do you have in common with a shark, a zebra, and a pine tree? All four of you are alive - and so all four of you are made up of cells. Cells perform amazing functions. An animal's muscle cells contract and expand in response to signals they receive from nerve cells, allowing the animal to run or jump. Plants' leaves contain cells that collect sunlight, which in turn provides energy for photosynthesis, the process by which plants create their own food. Well-known science authors Alvin and Virginia Silverstein and Laura Silverstein Nunn explore these and other cellular functions, from the simplest prokaryotes to the ten-foot-long neurons in a giraffe's neck. The authors also discuss how advances in cell research have led to artificial cloning, and how they are bringing scientists closer than ever to finding cures for serious diseases.