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Skins of the tiny beings,

© Narayan Dattatray Wadadekar

There is a huge big group of creatures called protista. They are difficult to classify. When we find it hard to put an item into a group we make a category, " miscellaneous". The biologists have done the same with several creatures, putting them into the kingdom "protista". The entire kingdom can be regarded as a collection of such sundry organisms which are difficult to fit into any well defined group.

By and large the protists have only one cell that makes their body. If the stuff of the body is cytoplasm then, the cell membrane or plasma membrane is their skin. This is the thinnest skin seen in the living things. Its thickness is about upto 100 angstroms. (1angström = one hundred-millionth i.e.10-8 of a centimeter ). It is made up of lipids, proteins and carbohydrates (containing a few sugar molecules i.e.oligosaccharides). Such branched structures sticking out of cell surfaces allow identification by other cells. The cell membrane encloses the plasma of every cell. It controls what goes into or out of cells. It throws out secretions and excretions, absorbs nutrients, and like kidney of higher animals helps to maintain the internal environment.

Any point on the cell membrane of some protists like amoeba can open up to gobble a bit of food. See an amoeba feeding - http://www.redfish.to/bolivia/amoebas/am...

You can not imagine any higher animals taking in their food into their bodies through any part of their body other than their mouths.

The cell membrane allows diffusion of gases like oxygen and carbon-di-oxide for respiration.

The cell membrane of some protists like euglena is tougher and is called pellicle. You may see it clearly on this site- http://mac2031.fujimi.hosei.ac.jp/PDB/Im...

The cell membrane bears tiny hairlike extensions - cilia and the flagella. These are the organs of locomotion for the unicellular creatures. Flagella are few in numbers and cilia numerous. Flagella are very long and cilia short. Flagella help the cell like sperms to swim. Many protists like Euglena, Trypanosoma, Ceratium are motile on account of their flagella. Over the cell membrane an exoskeleton of a few thecal plates, consisting mainly of cellulose is seen in a group of protista called dinoflagellata. Diatoms is another group of animals in protista. They have beautiful siliceous exoskeletons. The beauty of their shells have earned them the name " Jewels of the Plant world". ( Though possessing chlorophyll now they are not grouped under the plant kingdom.)

There is yet another order of protista called foraminifera ( bearers of windows - apertures) e.g. Arcella. Their shells may have organic or mineral components. Chambers of shell are added as the organism grows.

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