Cilia in Cells: Definition, Functions & Structure

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  • 0:01 What Are Cilia?
  • 1:09 How Do Cilia Function?
  • 1:43 Cilia Structure
  • 2:07 Lesson Summary
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Lesson Transcript
Instructor: Danielle Haak

Danielle has a PhD in Natural Resource Sciences and a MSc in Biological Sciences

Cilia have a cool name, but what are they? What do they do? Complete this lesson to find out what your cilia are up to and why you should be impressed with their hard work!

What Are Cilia?

Cilia are little appendages that stick out from eukaryotic cells. They whip back and forth and help cells move around in cellular fluids. They also help particles move past the cell. You might think of them like the paddles on the outside of a canoe; they help to push the boat through the water and also keep seaweed away.

Unlike real paddles, though, cilia are really tiny—only about 0.1 millimeters long. The term 'cilia' refers to a group of these appendages, whereas only one or two of them would be called flagella. Cilia are present on almost all of the cells in your body.

Cilia can be grouped into two categories. First, there are motile cilia, which are always moving in a single direction. They help the cell move around in the cellular fluids and help move fluids past the cell. Motile cilia are found together on cells and coordinate their movements to be most effective, making up for their small size.

The second type of cilia is non-motile cilia, and these are responsible for sensing the surrounding environment. They are also called primary cilia. Whereas motile cilia are found in groups on cells, each cell usually has just one non-motile cilium.

How Do Cilia Function?

Cilia are composed of smaller protein pieces called tubulin and are connected to the cell by the basal body. These tubulin pieces are manufactured in the cell and then transported to the surface. When motile cilia work together to move molecules and liquids past the cells, it is called intraflagellar transport.

If cilia are not functioning properly, this affects intraflagellar transport and is especially problematic in areas like the eyes, which need photoreceptors to work properly. Malfunctioning cilia conditions are called ciliopathies, but underlying causes are still being researched.

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