Illustrations by Amy Blandford
Cells are small, but numerous
Although cell size doesn’t necessarily scale up with body size, the total number of cells does scale to body size. An adult human body contains approximately 30-40 trillion cells (not counting bacteria)—this is more than 100 times the estimated number of stars in the Milky Way galaxy! Meanwhile, the body of an adult African savanna elephant is estimated to contain over one quadrillion cells.
Egg
The egg, or oocyte, is one of the largest cells by volume in the mammalian body. On average, a human oocyte is 0.11 mm in diameter.
Blood
Mammalian red blood cells (RBC) are round, don’t contain a nucleus, and are similar in size across species (a blue whale’s RBC are 0.008 mm in diameter; a brown rat’s RBC are 0.007 mm in diameter). Amphibian, reptile, and bird RBC are elliptical, contain a nucleus, and vary greatly in size across species. The three-toed amphiuma, a salamander native to the US, has the largest measured RBC of any animal on Earth (0.06 mm long).
Feather
A cell’s size and shape can change throughout its life cycle. During the growth phase, cells from a whooping crane’s emerging feathers measure about 0.09 mm long. During mitosis (cell division), these cells shrink to about 0.03 mm.
Plant
Plant and animal cells are alike, but not identical, in structure. In contrast to animals, cells from plants like king protea (0.05 mm long) are surrounded by a cell wall, use chloroplasts to synthesize energy (photosynthesis), and contain a fluid-filled central vacuole that provides nutrient storage and maintains the cell’s inner pressure.
Skin
Fibroblasts are found in connective tissues such as bone, cartilage, and ligaments. These cells lend structure to organs and other tissues throughout the body. Manatee skin fibroblasts (0.08 mm long) help repair damage to their tough, one-inch-thick skin.
