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Protists Kingdom

The Protists Kingdom or (Protista Kingdom) consists of cells that have a nucleus (eukaryotic cells) but do not fit into the other kingdoms. Protists are typically only made of one cell, or unicellular.  However some protists, such as algae or seaweed, consist of many cells. The protists made of multiple cells only consist of one tissue, rather than many specialized tissues.

Protist in the Protist Kingdom (or Protista Kingdom) under a microscope.

Classifying a Cell into the Protists Kingdom

When scientists discover a new cell, they try to group it into a specific kingdom. If the cell is a prokaryotic cell (it does not have a nucleus), scientists group it into the monera kingdom. Those are very easy cells to group. However, when scientists determine that a cell is a eukaryotic cell (has a nucleus) it gets difficult. It gets difficult because the cell can fall into one of four kingdoms: animal, plant, fungi, or protists.

Many protists appear to be both plant and animal. Like plants, they are green, and can create their own food. However, like animals, they have moving body parts and are able to move around their environments.  You can see why scientists have a hard time classifying these cells.

The best way to think of the protists kingdom, is the kingdom for the misfits or left-overs. This is because when a eukaryotic cell is not an animal, plant, or fungi, the cell is classified a protist. For this reason, protists do not usually have much in common with one another. They have different life cycles, diets, ways to reproduce and ways to move around.  

Biologists believe that the ancestors of plants and animals may have been protists.

Biologists believe that the ancestors of plants and animals may have been protists.

Kinds of Protists

Protozoa:

 These are unicellular organisms that depend on the environment for food. Protozoa are more “animal-like” than the other kinds of protists. Some can be parasitic, which means they damage another organism to survive. 

Protozoa can move around and group into categories based on how they move. They live in water and in soil and are very tolerant to extreme environments. For this reason, you will find protozoa in low and high temperatures. Also, they are generally very small, from 0.01 to 0.5 mm in size. In fact, you would need a microscope to see them.

This is the protozoa Paramecium caudatum. This unicellular organism feeds on bacteria.

This is the protozoa Paramecium caudatum. This unicellular organism feeds on bacteria.

Algae: 

These protists can make their own energy through photosynthesis. They can be single-celled or have multi-celled. Some have the ability to move while others, like seaweed, do not. 

You can find algae in both water and land. They form an important part of phytoplankton, the energy source of most organisms in the sea. 

Image of algae floating on the surface of water.

Algae are a kind of protist that make their own energy through photosynthesis.

Molds: 

These protists include slime molds and water molds.

Water molds generally live in water and wet soil. They are a close relative to plants and are single-celled. Most live off of a host and are usually toxic to their hosts. Molds love to attach to plants, and slowly eat them until they are nothing.

Slime molds can live in many different environments. They live for most of their lives as single-celled organisms. But they have a very unusual lifecycle! When it is time to reproduce, millions of these cells come together and form a giant ball. Some slime molds eat dead plant material in order to survive. They are often found on lawns, forest floors, or in soil. 

A slime mold is a protists that usually lives on forest floor or soil.

A slime mold is a protists that usually lives on forest floor or soil.

Protists and Disease

Malaria is a common and dangerous disease caused by protists. It is caused by Plasmodium Protozoa, a parasite that spreads by mosquitos. When mosquitos bite humans, the protist enters the person’s blood stream from the mosquito’s saliva. It infects red blood cells and causes fatigue, fever, sweating, and vomiting.  

This is a picture of the protist Plasmodium Protozoa, a parasite that is spread by mosquitos and causes malaria.

This is a picture of the protist Plasmodium Protozoa, a parasite that is spread by mosquitos and causes malaria.

Another common disease caused by protists is African Sleeping Sickness. This disease is caused by protists that belong to the genus Trypanosoma. Like malaria, this disease is also spread mostly through insect bites. This illness can be deadly if not treated and leads to trouble sleeping, numbness, confusion

Giardiasis is an infection of the digestive system caused by the protist Giardia Lamblia. This leads to stomach issues such as cramps and diarrhea. Unlike the other diseases, this one spreads through drinking water containing the protist. 

Written by: Pallavi Sai Krishnarao