- A protist is an organism belonging to the Kingdom Protista. The Kingdom Protista includes a diverse array of organisms, numbered in the estimated range of between 65,000 to 200,000. Protists are all eukaryotes, which are complex cells that feature nuclear membranes, as well as organelles like chloroplasts and mitochondria. They can either be unicellular, one-celled, or multicellular, made up of multiple cells. This simple cellular organization distinguishes the protists from other eukaryotes, such as animals, plants and fungi. Aside from their simple makeup, protists do not have much else in common.
- Protists can be classified into three separate groups. The first is protozoa, the animal-like protists, which include such species as Euglenozoa, Ciliates, Sporozoans and Dinoflagellates. Some of these are better known as amoebas and parasites. The second group is algae, the plant-like protists, which include Diatoms, Golden Algae and Brown Algae. The third group is made up of slime molds and water molds, the fungus-like protists.
- Protists are classified in two ways: how they obtain their nutrition and how they move. Protists can be autotrophs, such as algae, which means that they produce their own energy by photosynthesis (use of sunlight) and chemosynthesis (use of hydrogen). Algae use a wide variety of pigments, which enable some of them to possess very unique colors.
- Protists can also be heterotrophs, such as the protozoa and slime molds, which means that they obtain their energy by devouring other organisms. Protists reproduce asexually by binary fission, in which a living cell is divided into two parts, each of which has the potential to grow to the size of the original cell. A few species of protists are capable of sexual reproduction.
- Protists are small enough that they use diffusion, the spread of materials from regions of higher concentration to regions of lower concentration, to move gases and waste material in and out of the cell. They do not need any special organs to facilitate this process.
- Protists eat by a process known as phagocytosis. They swallow their food via their cell membrane and pinch off a piece of membrane to form an open space inside the cell. This open space is called a vacuole. Protists also use vacuoles to store enzymes, water and waste products.
- Locomotion, or movement, is achieved by protists in a number of ways. All protists can move through the water using cilia, flagella or pseudopodia. Cilia are tiny, hair-like protrusions that extend from the surface of a cell or from a unicellular organism. They move together in a rhythm to propel the organism through the water. Flagella are long, thread-like attachments, found in protists singly or in pairs. Pseudopodia, or false feet, are temporary projections, found especially in amoebas.
- Some protists pose significant dangers to both animals and plants. Some examples are Plasmodiumfalciparum, which is carried by mosquitoes and causes malaria in humans, and Phytophthora infestans, which causes potato blight, a catastrophe that led to a massive famine in Ireland. Further studies of protists are underway in an attempt to understand protist biology better; better understanding may enable these diseases, as well as others, to be treated more efficiently.
- Protists are, interestingly, defined by what they are not. They are not bacteria or fungi, nor are they animals or plants. Scientists still do not know how the different groups of protists are related to each other. It is assumed that they evolved from groups of bacteria, but the details of which groups and exactly when this may have happened are still being investigated. Different classifications of protists are so unlike one another that scientists believe that many probably independently evolved from completely diverse groups of bacteria.
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