C is for Cilia

Cilium (pl. cilia) – a short microscopic hairlike vibrating structure; important for movement of micro-organisms.

Below is a cartoon of the inside of a cilium. This is from a scientific journal, so it’s detailed. What I want you to focus on is part A. This is a slice lengthwise through the cilium. The blue is the inside of the one-celled creature and the red rods are made up of protein called tubulin. Look on the right and the left of the red rods. See the round balls that have little arrows pointing up and down?

Those balls have little motors on them. The motors are stuck to the red rods and the balls are stuck to the “skin”, or membrane, of the micro-organism. The motors move up and down the rods and the blue balls stay stuck to the membrane. When this happens, the whole structure bends to the right. The motors relax and slide back. Now the purple motors move and the whole structure bends left. Repeat and repeat fast. The micro-organism swims.

I’m going to hook you up with some very cool videos. First, you need some vocabulary.

  • proboscis – an elongated sucking mouthpart that is typically tubular and flexible
  • eukaryote (pronounced yoo-karee-ote) – complex organism with organs (or organelles if a micro-organism); most easily distinguished by the presence of a nucleus (the organelle within the cell that holds the chromosomes) in the cell

We are eukaryotes and the single-celled micro-organisms in the videos are eukaryotes. These are not bacteria. They are a different branch of the tree of life.

This is a slow-motion video of a Paramecium moving. The cilia beat one direction and it moves forward. The cilia reverse direction and it moves backwards.

A Paramecium feeding doesn’t look that interesting. This one is trapped in place so that one can see how it feeds. Water and food (mostly bacteria here) are sucked in. There is a vortex created by the cila around the “mouth”. Little sacks, or vesicles, fill with the water and food and expand.
When the vesicles reach a maximum size, they are released within the Paramecium. If you watch closely, you can see some of these vesicles dock with the “skin” of the Paramecium and release the contents to the outside world. The Paramecium has to get rid of the excess water.

Paramecium aren’t the only animalcules with cilia. They are one of the more famous. They eat yeast and bacteria. Swimming fast makes them good hunters. It also keeps them from being eaten. What eats a Paramecium? Didinium. They are even better swimmers than Paramecium. They are more maneuverable because of the two rows of cilia around their circumference.

Drawn by  V. Schewiakoff

I’ll leave you with the video of a Paramecium as lunch for Didinium. If you’re fascinated by these critters, and want to see more, search YouTube for “ciliates”.


The stunning featured image is a photograph taken by Dr. Robert Berdan. More of his work can be found at the Canadian Nature Photographer.

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