The protist kingdom It comprises one of the five kingdoms of nature and contains all those eukaryotes (organisms formed by cells in whose cytoplasms a well-defined cell nucleus can be found) that cannot be classified as animals, plants or fungi.
Protists are very diverse organisms from each other. They constitute a large part of the biomass, both in humid terrestrial and aquatic ecosystems, and also live as parasites of other living beings. Although there are some large, multicellular protist organisms, such as algae, most are small and single-celled, such as amoebae.
The term “protist” was coined by the German scientist Ernst Haeckel to include all primitive forms of organisms. As it is not a monophyletic kingdom, that is, the organisms that make it up do not have a common ancestor, understanding the protists and their evolutionary history is a matter of scientific discussion.
Characteristics of the Protista Kingdom
The organisms that make up the protist kingdom do not share significant morphological and physiological characteristics that group them. They have different life cycles and cell structures, varied locomotion mechanisms and occupy different places in the food chain.
The following list accounts for the enormous diversity among protist organisms:
- Cell organization. There are unicellular and multicellular organisms.
- Feeding. Some protist organisms feed autotrophically, through photosynthesis, such as brown algae, and others heterotrophically, such as protozoa.
- Breathing. Their form of respiration is, for the most part, of aerobic origin, they use oxygen to extract energy from organic substances. However, there are some protist species that are anaerobic as they have adapted to oxygen-deprived environments.
- Reproduction. There are protist species that reproduce by clonal (asexual) reproduction, while others reproduce sexually. Some species alternate both types of reproduction.
- Locomotion. Most protists can move and move, either by creeping or by flagella and cilia (structures that help them move in humid environments).
Protista Kingdom Classification
There are various classifications of protist organisms. The most widespread, although not entirely accurate, is the one that differentiates protozoa from algae.
- Protozoa. They are microscopic unicellular organisms that live in humid, aquatic environments or as parasites of other living beings. There are more than 30,000 species, including very diverse taxa with a remote kinship relationship. For instance: the amoebae, ciliates and flagellates or trypanosoma cruzi (the parasite that causes Chagas disease).
- Algae. They almost always live in an aquatic environment, they use water to carry out oxygenated photosynthesis. There are microscopic algae, and species that can measure up to 60 meters. Algae lack roots, stems, and leaves, and their cells have characteristics that are not found in plants or animals. They are the food base for almost all aquatic life. For instance: brown algae, green algae, red algae.
Examples of the protist kingdom