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A variety of algae growing on the sea bed in shallow waters

Algae (/ˈæli, ˈælɡi/; singular alga /ˈælɡə/) is an informal term for a large, diverse group of photosynthetic eukaryotic organisms that are not necessarily closely related, and is thus polyphyletic. Included organisms range from unicellular microalgae genera, such as Chlorella and the diatoms, to multicellular forms, such as the giant kelp, a large brown alga which may grow up to 50 m in length. Most are aquatic and autotrophic and lack many of the distinct cell and tissue types, such as stomata, xylem, and phloem, which are found in land plants. The largest and most complex marine algae are called seaweeds, while the most complex freshwater forms are the Charophyta, a division of green algae which includes, for example, Spirogyra and the stoneworts.

No definition of algae is generally accepted. One definition is that algae "have chlorophyll as their primary photosynthetic pigment and lack a sterile covering of cells around their reproductive cells". Although cyanobacteria are often referred to as "blue-green algae", most authorities exclude all prokaryotes from the definition of algae.

Algae constitute a polyphyletic group since they do not include a common ancestor, and although their plastids seem to have a single origin, from cyanobacteria, they were acquired in different ways. Green algae are examples of algae that have primary chloroplasts derived from endosymbiotic cyanobacteria. Diatoms and brown algae are examples of algae with secondary chloroplasts derived from an endosymbiotic red alga. Read more...

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Phycotechnology refers to the technological applications of algae, both micro- and macroalgae. Algae is extremely useful in various fields. An example for natural phycotechnology is the converting of atmospheric nitrogen into bioaccessible nitrogenous compounds by diazotrophic cyanobacteria (blue-green algae). Species of cyanobacteria like Nostoc, Arthrospira (Spirulina) and Aphanizomenon are used as food and feed due to their easy digestibility and nutrient content. Species of Dunaliella provide products like glycerol, carotenoids, and proteins. Algal-produced proteins can be biofactories for the production of therapeutic substances. Algae is also being used to assist in the remediation of pollution, to create bio-fuels, and as a bio-insecticide. Read more...

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Pink algae is a growth of pink, slimey bacterial matter which can sometimes occur in pools and sometimes in laboratory tubings. The title is a misnomer, because, as noted before, pink algae is actually caused by a bacterium, in the genus methylobacterium. The color of the bacterial growth comes from pigments within its cells. The slime formed around the bacteria provides it with a relatively high level of protection from external threats. Like other species in its genus, pink algae is a methane consuming bacterium. It has an affinity for the matrix of PVC plastics, and will attach itself to both the inside and the outside of PVC materials inside of the pool. Pink algae infestation in a pool often occurs alongside an infestation of white water mold. Read more...

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