Algae are any of a large and diverse group of photosynthetic,eukaryotic organisms. The name is an informal term for a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular microalgae,such as Chlorella,Prototheca and the diatoms,to multicellular forms,such as the giant kelp,a large brown alga which may grow up to 50 metres (160 ft) in length. Most are aquatic and lack many of the distinct cell and tissue types,such as stomata,xylem and phloem that 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 stoneworts. Algae that are carried by water are plankton,specifically phytoplankton.
A chloroplast is a type of membrane-bound organelle known as a plastid that conducts photosynthesis mostly in plant and algal cells. The photosynthetic pigment chlorophyll captures the energy from sunlight,converts it,and stores it in the energy-storage molecules ATP and NADPH while freeing oxygen from water in the cells. The ATP and NADPH is then used to make organic molecules from carbon dioxide in a process known as the Calvin cycle. Chloroplasts carry out a number of other functions,including fatty acid synthesis,amino acid synthesis,and the immune response in plants. The number of chloroplasts per cell varies from one,in unicellular algae,up to 100 in plants like Arabidopsis and wheat.
Photosynthesis is a biological process used by many organisms to convert light energy into chemical energy,which is stored in organic compounds that can later be metabolized through cellular respiration to fuel the organism's activities. The term usually refers to oxygenic photosynthesis,where oxygen is produced as a byproduct and some of the chemical energy produced is stored in carbohydrate molecules such as sugars,starch,glycogen,and cellulose,which are synthesized from an endergonic reaction of carbon dioxide with water. Organisms that perform photosynthesis are called photoautotrophs;most plants,algae,and cyanobacteria are photoautotrophs. Photosynthesis is largely responsible for producing and maintaining the oxygen content of the Earth's atmosphere,and it supplies most of the biological energy necessary for complex life on Earth.
Cyanobacteria,also called Cyanobacteriota or Cyanophyta,are a phylum of autotrophic gram-negative bacteria that can obtain biological energy via photosynthesis. The name 'cyanobacteria' refers to their color,which similarly forms the basis of cyanobacteria's common name,blue-green algae,although they are not scientifically classified as algae. They appear to have originated in a freshwater or terrestrial environment.
A plastid,pl. plastids,is a membrane-bound organelle found in the cells of plants,algae,and some other eukaryotic organisms;. They are considered to be intracellular endosymbiotic cyanobacteria.
Seagrasses are the only flowering plants which grow in marine environments. There are about 60 species of fully marine seagrasses which belong to four families,all in the order Alismatales. Seagrasses evolved from terrestrial plants which recolonised the ocean 70 to 100 million years ago.
Prochlorophyta is a group of photosynthetic bacteria,an important component of picoplankton. These oligotrophic organisms are abundant in nutrient poor tropical waters and use a unique photosynthetic pigment,divinyl-chlorophyll,to absorb light and acquire energy. Prochlorophyta lack red and blue phycobilin pigments and have stacked thylakoids,making them distinctly different from Cyanobacteria,but some authors consider them as part of the Cyanobacteria,as the group Prochlorales.
Photosystems are functional and structural units of protein complexes involved in photosynthesis. Together they carry out the primary photochemistry of photosynthesis:the absorption of light and the transfer of energy and electrons. Photosystems are found in the thylakoid membranes of plants,algae,and cyanobacteria. These membranes are located inside the chloroplasts of plants and algae,and in the cytoplasmic membrane of photosynthetic bacteria. There are two kinds of photosystems:PSI and PSII.
Chlorophyll d is a form of chlorophyll,identified by Harold Strain and Winston Manning in 1943. It was unambiguously identified in Acaryochloris marina in the 1990s. It is present in cyanobacteria which use energy captured from sunlight for photosynthesis. Chl d absorbs far-red light,at 710 nm wavelength,just outside the optical range. An organism that contains Chl d is adapted to an environment such as moderately deep water,where it can use far red light for photosynthesis,although there is not a lot of visible light.
A seagrass meadow or seagrass bed is an underwater ecosystem formed by seagrasses. Seagrasses are marine (saltwater) plants found in shallow coastal waters and in the brackish waters of estuaries. Seagrasses are flowering plants with stems and long green,grass-like leaves. They produce seeds and pollen and have roots and rhizomes which anchor them in seafloor sand.
Photoinhibition is light-induced reduction in the photosynthetic capacity of a plant,alga,or cyanobacterium. Photosystem II (PSII) is more sensitive to light than the rest of the photosynthetic machinery,and most researchers define the term as light-induced damage to PSII. In living organisms,photoinhibited PSII centres are continuously repaired via degradation and synthesis of the D1 protein of the photosynthetic reaction center of PSII. Photoinhibition is also used in a wider sense,as dynamic photoinhibition,to describe all reactions that decrease the efficiency of photosynthesis when plants are exposed to light.
Posidonia is a genus of flowering plants. It contains nine species of marine plants ("seagrass"),found in the seas of the Mediterranean and around the south coast of Australia.
Phyllospadix,commonly known as surfgrass,is a genus of seagrass,a flowering plant in the family Zosteraceae,described as a genus in 1840. Phyllospadix grows in marine waters along the coasts of the temperate North Pacific.
Enhalus is a monotypic genus of marine flowering plants. The sole species is Enhalus acoroides. Enhalus is a large seagrass native to coastal waters of the tropical Indian and Western Pacific Oceans. It is the only species of seagrass that does aerial surface pollination in which the pollen and the styles remain dry. Enhalus is surface pollinated with male flowers that detach from the plant to float on the surface until they reach a female flower where pollination can occur. Enhalus acoroides is considered a slow-growing,"climax" species.
Thalassia is a marine seagrass genus comprising two known species.
Thalassia testudinum,commonly known as turtlegrass,is a species of marine seagrass. It forms meadows in shallow sandy or muddy locations in the Caribbean Sea and the Gulf of Mexico. Turtle grass and other seagrasses form meadows which are important habitats and feeding grounds. The grass is eaten by turtles and herbivorous fish,supports many epiphytes,and provides habitat for juvenile fish and many invertebrate taxa.
Marine botany is the study of flowering vascular plant species and marine algae that live in shallow seawater of the open ocean and the littoral zone,along shorelines of the intertidal zone and coastal wetlands,even in low-salinity brackish water of estuaries.
Prochloron is a genus of unicellular oxygenic photosynthetic prokaryotes commonly found as an extracellular symbiont on coral reefs,particularly in didemnid ascidians. Part of the phylum cyanobacteria,it was theorized that Prochloron is a predecessor of the photosynthetic components,chloroplasts,found in photosynthetic eukaryotic cells. However this theory is largely refuted by phylogenetic studies which indicate Prochloron is not on the same line of descent that lead to chloroplast-containing algae and land plants.
Halodule uninervis is a species of seagrass in the family Cymodoceaceae. It is native to the western Pacific and Indian Oceans. Common names include narrowleaf seagrass in English and a'shab bahriya in Arabic.
Marine primary production is the chemical synthesis in the ocean of organic compounds from atmospheric or dissolved carbon dioxide. It principally occurs through the process of photosynthesis,which uses light as its source of energy,but it also occurs through chemosynthesis,which uses the oxidation or reduction of inorganic chemical compounds as its source of energy. Almost all life on Earth relies directly or indirectly on primary production. The organisms responsible for primary production are called primary producers or autotrophs.
