Hobbies And Interests
Definition
Algae are primarily aquatic organisms that are similar to plants in appearance. Initially they were classified as belonging to the group of Thallophytes in the plant kingdom. Thallophytes are plants without roots, stems, leaves or flowers. Algae feed themselves through photosynthesis and the term is used to cover simple organisms that can't be classified as mosses, liverworts or vascular plants. More recently, algae have been reclassified, and transferred from the Plantae kingdom into the Protista and Monera kingdoms.
Protista
The Protista kingdom contains a diverse range of organisms. Protists are the smallest microscopic organisms. Members of this kingdom are not animals, but nor are they plants. They have nucleated cells and live in aquatic environments. Chlorophyta, or green algae, are a division of protists. They are common in fresh water and marine habitats. Sea lettuce is an example of this type of algae. Although this algae is called "green," it is also red and orange. One-celled green algae grows in a polar bear's coat to give it a slightly green tinge. Brown algae, or Phaeophyta, are another division. These include the macroscopic seaweeds and kelps found along seashores.
Monera
Monera is the kingdom of true bacteria. Spherical, rod and spiral-shaped bacteria all belong here, and the bacteria may cause disease or it may boost health. Prokaryotic algae, which is a cyanbacteria, is included in this kingdom. Cyanbacteria is one of the oldest life forms on earth, and has been found in fossils over two million years old. Prokaryotic algae is more commonly referred to as blue-green algae. This algae appears on tree trunks and on plant roots. The thin, black film covering some ancient monuments, such as the Mayan pyramids, is blue-green algae.
Chromista Kingdom
In 2004, biologist Thomas Cavalier-Smith proposed an additional sixth kingdom. The Chromista kingdom contains brown, golden and yellow-green algae. Chromista organisms appear to represent an evolutionary line that diverged from the common ancestor plants, fungi and animals that Cavalier-Smith places in the Eukaryotic Empire. Not all biologists agree with the Cavalier-Smith system, and research into other models of classification is ongoing.