Cilia are hair-like structures found in unicellular organisms and most cells in the human body. They can move the cell or substances around it. There are two types of cilia: mobile and primary. The structure of a cilium is similar to a tube with microtubules forming doublets. Cilia are used by unicellular eukaryotes to move through liquid. Flagella are longer hairs found in prokaryotes and some eukaryotes. Cilia and flagella were originally used by independent cellular creatures to move around in search of food.
The term cilia is Latin for “eyelashes”. Common in unicellular organisms, these hair-like structures wave to move the cell or to move something around the cell. Cilia are also present on most cells in the human body. Some tissues in the body, such as the fallopian tubes in women and the trachea, also have a special type of cilia that help transport substances along tissue surfaces.
Types of eyelashes in the body
In the body, cilia on the surface of tissue are responsible for protecting a person from germs in the lungs and pushing an egg through the fallopian tube, among other things. These cilia are called mobile cilia and are found in groups and fight in waves. Primary cilia, on the other hand, are usually found only one at a time on cells.
Structure
The structure of a single cilium is very similar to a tube and its long fibers are called microtubules. These microtubules often pair up to form doublets, which in turn form a ring. The cross section of the microtubule doublets looks like a figure 8, because the two microtubules stick together along a line. Nine doublets form the largest ring in what is known as a 9-2 pattern. When kinesin binds to one side of the doublets and not the other, the eyelash flexes and curves, similar to the way a person’s skeletal muscles contract.
functions
Unicellular eukaryotes, which are organisms with cells that have a nucleus, often use cilia to move through liquid. This type of organism is surrounded by a cytoskeleton, made up of protein filaments that allow the cell to maintain its shape. An eyelash attaches to the cell’s cytoskeleton with a basal body, the same way a root attaches hair to human skin.
The rhythm of eyelash waving is controlled by centrioles, which are organelles located within the cell wall. Mitochondria, other units within the cell, supply adenosine triphosphate (ATP), a cellular energy source, for the cilia. ATP directs the chemical kinesin to bind to certain parts of the eyelashes that control their movement. Therefore, the cilia are able to beat or essentially swim through the viscous liquid.
scourges
Similar to cilia, flagella are longer hairs, usually found in one or two, like the tail of a sperm cell. They share many characteristics with cilia, but also occur on prokaryotes, which are organisms with cells that don’t contain a nucleus. Some eukaryotes that use cilia and flagella to move are also found in ferns, algae, bacteria, and within many animals. This adaptation originally allowed independent cellular creatures, such as paramecia, to move around in search of food, rather than waiting for food to arrive at them. Cells that are part of larger systems have continued to use cilia to their advantage.
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