for: algae (programming language) for: Alga, Kyrgyzstan

Algae lack the various structures that characterize land plants, such as phyllids and rhizoids in nonvascular plants, or leaves, roots, and other organs that are found in tracheophytes. They are distinguished from protozoa in that they are photosynthetic. Many are photoautotrophic, although some groups contain members that are mixotrophic, deriving energy both from photosynthesis and uptake of organic carbon either by osmotrophy, myzotrophy, or phagotrophy. Some unicellular species rely entirely on external energy sources and have limited or no photosynthetic apparatus.

All algae have photosynthetic machinery ultimately derived from the cyanobacteria, and so produce oxygen as a by-product of photosynthesis, unlike other photosynthetic bacteria such as purple and green sulfur bacteria.

Ecology

Algae are most prominent in bodies of water but are also common in terrestrial environments. However, terrestrial algae are usually rather inconspicuous and far more common in moist, tropical regions than dry ones, because algae lack vascular tissues and other adaptations to live on land. Algae are also found in other situations, such as on snow and on exposed rocks in symbiosis with a fungus as lichen.

The various sorts of algae play significant roles in aquatic ecology. Microscopic forms that live suspended in the water column (phytoplankton) provide the food base for most marine food chains. In very high densities (so-called algal blooms) these algae may discolor the water and outcompete, poison, or asphyxiate other life forms. Seaweeds grow mostly in shallow marine waters, however some have been recorded to a depth of 300 m.Some are used as human food or harvested for useful substances such as agar, carrageenan, or fertilizer.

Study of algae

The study of marine and freshwater algae is called phycology or algology.

The US Algal Collection is represented by almost 300,000 accessioned and inventoried herbarium specimens.

Classification

While Cyanobacteria have been traditionally included among the algae, referred to as the Cyanophytes or blue-green algae, recent works on algae usually exclude them due to large differences such as the lack of membrane-bound organelles, the presence of a single circular chromosome, the presence of peptidoglycan in the cell walls, and ribosomes different in size and content from eukaryotes Biology 8th ed. Losos, Jonathan B., Mason, Kenneth A., Singer, Susan R., McGraw-Hill. 2007.. Rather than in chloroplasts, they conduct photosynthesis on specialized infolded cytoplasmic membranes called thylakoid membranes. Therefore, they differ significantly from the algae despite occupying similar ecological niches.