Protists are mainly unicellular organisms that have a complex cellular structure. In this lesson we’ll learn more about the protists’ cell structure, as well as some other unique features.
Definition of a Protist
It is a well-known fact that most bodies of water contain lots of living organisms. Ponds, lakes, and streams are inhabited by a wide variety of animal and plant life.
If one tried to make a list of all the ocean creatures, there would be a lot of pages to fill. But to really identify all living things in water, we’d have to get out a microscope. This allows us to see a whole world of living things that exist at a microscopic level. And what exactly are these creatures? They are microorganisms that we call protists.Members of the kingdom Protista, protists are a highly diverse population of organisms. Have you ever heard of an amoeba or paramecium? If so, you have some knowledge of protists.
Found nearly anywhere there is water, most protists are made up of one single cell. This would explain their microscopic size. What makes protists unique and sets them apart from other unicellular organisms, such as bacteria, is that their cells are eukaryotic. Like a tiny machine with many moving parts, eukaryotic cells have a nucleus and many organelles.
In this lesson we will take a closer look at the cell structure of these microorganisms.
Another Unicellular Organism
We have established that protists are eukaryotic organisms that are mainly unicellular. This means we have something in common with these tiny creatures: We too are made of eukaryotic cells.
This quality also makes them much different, and vastly more complex, than the single-celled organism, bacteria. What is the difference? Let’s compare the two to get a better understanding.Bacteria are prokaryotic, which is a different type of cell altogether. The simplest and most primitive type of cell, prokaryotes, lack the complex organelles that eukaryotes contain. Bacteria are essentially a membrane filled with cytoplasm and genetic information.
You can imagine it this way: A eukaryotic cell is like a working factory with many complex machines and systems running together to perform multiple tasks. A prokaryotic cell, on the other hand, is like a warehouse with a couple of machines that do basic, but important, work.
Interior of a Protist Cell
Let’s take a closer look at how the eukaryotic protist is constructed. In these tiny, complex cells we find a multitude of organelles, including one very important structure, a true nucleus. It should be noted that many features of protists vary greatly depending on the type, and partly on whether a protist is classified as plant-like or animal-like. We’ll start with the common inner cell structures.
As previously mentioned, all protists have a true nucleus. The nucleus is like the central command center of the cell and contains crucial genetic information (DNA and RNA) needed for growth and reproduction. It is enveloped safely in a nuclear membrane and suspended within a jelly-like substance called cytoplasm. Also suspended within the cytoplasm we find such structures as endoplasmic reticulum and Golgi bodies. These organelles play important roles for the protist, such as protein secretion and transport.Protists that are classified as animal-like must gain their nutrition from outside sources, just as we do. An amoeba is one example of a protist that locates, envelopes, and digests its prey.
These protists contain mitochondria, which are organelles that break down food and create usable energy for the organism. Mitochondria are the power generators of the cell.How do the plant-like protists (mainly algae) get nutrition? They use photosynthesis to make their own food. For this process, organelles known as plastids do the hard work.
Plastids have the super power-like ability to harness the sun’s energy and help create sugars for the protists.
Outer Cell Features of Protists
Now, for some of the outer features of protist cells. Everything inside the cell is contained by a cell membrane. A cell membrane can be thought of as a water balloon. The water inside makes up the cell, and the balloon is the cell membrane. This isn’t the only outer covering for many protists. On some we find hard shells made of calcium carbonate.
On others, a glass-like material. This gives protists such as diatoms, foraminifera, and radiolarians a unique, even ornamental appearance. In addition, many forms of algae have a cell wall made of cellulose, just like plants do.Also found on the exterior of some protist cells are organs used for movement. Not all protists can move on their own, but those that can use structures such as cilia or flagella. Cilia are found on protists such as paramecium.
These tiny hair-like structures beat in unison to create movement. Think of them as powerful eyelashes. This helps the paramecium get around in water. A flagellum is a long hair-like structure coming from the end of the protist that provides locomotion. Giardia is an example of a protist that uses this method of transport, and it whips the flagella about in order to move.
Protists are single-celled organisms belonging to the kingdom Protista. They are all eukaryotic, meaning they have a nucleus and many organelles.
Unlike prokaryotic bacteria, which are the simplest and most primitive type of cell, protist cells are enclosed by a cell membrane, which basically is the outer barrier to the cell, and have a true, membrane-bound nucleus, which is the central command center of the cell and contains crucial genetic information (DNA and RNA) needed for growth and reproduction. Other organelles found in the cell are Golgi bodies and endoplasmic reticulum. In animal-like protists such as the amoeba, we find mitochondria, or organelles that break down food and create usable energy for the organism, that convert food into energy.
In plant-like protists (algae), we find plastids used for the process of photosynthesis. All organelles are suspended in a jelly-like substance called cytoplasm. Some protists have hard shells covering them.
Many protists move by means of cilia, which are tiny hair-like structures beat in unison to create movement, or flagella, which are long hair-like structures coming from the end of the protist that provide locomotion.