answers: photosynthesis
context: Cyanobacteria Cyanobacteria , also known as Cyanophyta, are a phylum of bacteria that obtain their energy through photosynthesis, and are the only photosynthetic prokaryotes able to produce oxygen. The name "cyanobacteria" comes from the color of the bacteria (). Cyanobacteria, which are prokaryotes, are also called "blue-green algae", though the term "algae" in modern usage is restricted to eukaryotes. Unlike heterotrophic prokaryotes, cyanobacteria have internal membranes. These are flattened sacs called thylakoids where photosynthesis is performed. Phototrophic eukaryotes perform photosynthesis by plastids that may have their ancestry in cyanobacteria, acquired long ago via a process called endosymbiosis. These endosymbiotic cyanobacteria </s> 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 </s> including modification for grazing, haymaking, reclamation for agriculture, development and ports, evaporation ponds for salt production, modification for aquaculture, insect control, tidal power and flood protection. Marshes are also susceptible to pollution from oil, industrial chemicals, and most commonly, eutrophication. Introduced species, sea-level rise, river damming and decreased sedimentation are additional longterm changes that affect marsh habitat, and in turn, may affect carbon sequestration potential. Both macroalgae and microalgae are being investigated as possible means of carbon sequestration. Because algae lack the complex lignin associated with terrestrial plants, the carbon in algae is released into the atmosphere more rapidly than
question: where do blue-green algae get their energy from