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Algae (UK: / ˈ æ l ɡ iː / AL-ghee, US: / ˈ æ l dʒ iː / AL-jee; [3] sg.: alga / ˈ æ l ɡ ə / AL-gə) is an informal term for any organisms of a large and diverse group of photosynthetic eukaryotes, which include species from multiple distinct clades.
Life originated as marine single-celled prokaryotes (bacteria and archaea) and later evolved into more complex eukaryotes. Eukaryotes are the more developed life forms known as plants, animals, fungi and protists. Protists are the eukaryotes that cannot be classified as plants, fungi or animals. They are mostly single-celled and microscopic.
The name "cyanobacteria" (from Ancient Greek κύανος (kúanos) 'blue') refers to their bluish green color, [5] [6] which forms the basis of cyanobacteria's informal common name, blue-green algae, [7] [8] [9] although as prokaryotes they are not scientifically classified as algae.
The division of life forms between prokaryotes and eukaryotes was firmly established by the microbiologists Roger Stanier and C. B. van Niel in their 1962 paper, The concept of a bacterium. [34] One reason for this classification was so what was then often called blue-green algae (now called cyanobacteria ) would cease to be classified as ...
Eukaryotic cells contain membrane bound organelles. Some examples include mitochondria, a nucleus, or the Golgi apparatus. Prokaryotic cells probably transitioned into eukaryotic cells between 2.0 and 1.4 billion years ago. [31] This was an important step in evolution. In contrast to prokaryotes, eukaryotes reproduce by using mitosis and meiosis.
Later on, some eukaryotes that already contained mitochondria also engulfed cyanobacterial-like organisms. This led to the formation of chloroplasts in algae and plants. There are also some algae that originated from even later endosymbiotic events. Here, eukaryotes engulfed a eukaryotic algae that developed into a "second-generation" plastid.
A protist (/ ˈ p r oʊ t ɪ s t /) is any eukaryotic organism (one with cells containing a nucleus) that is not an animal, plant, or fungus.The protists do not form a natural group, or clade, since they exclude certain eukaryotes with whom they share a common ancestor; [a] but, like algae or invertebrates, the grouping is used for convenience.
In 1937 Édouard Chatton introduced the terms "prokaryote" and "eukaryote" to differentiate these organisms. [9] In 1938, Herbert F. Copeland proposed a four-kingdom classification by creating the novel Kingdom Monera of prokaryotic organisms; as a revised phylum Monera of the Protista, it included organisms now classified as Bacteria and Archaea.