Although humans have studied thousands of them, there are many more for aspiring biologists to describe. They are interesting to study because each species is unique, and many are beautiful or have interesting adaptations. Let's look at some of these. We have already looked at factors that limit cell size and shape. These tiny organisms also have the power of movement.
Some cells have tiny hair-like fibers that are called flagella.
These fibers thrash in the water and drive the cell forward. Although this is a feature of some self-sufficient little organisms, we also see this same feature in sperm cells, which propel themselves with flagella. Cillia Some cells have groups or rows of tiny fibers that move together like oars in a sort of rippling pattern. Cillia are also found in the oviducts of some multicellular animals. Their beating causes a gentle current that moves an egg cell from the ovary towards the womb.