page_title: Symbiosis
section_title: Type 2: Partners live as one organism
hierarchical_section_title: Symbiosis / Types of symbiosis / Type 2: Partners live as one organism
caption_attribution_description: English: Dardanus pedunculatus Hermit crab with symbiotic anemones Calliactis sp. attached to its shell. The anemones provide protection with their stinging cells while they benefit from the mobility that the crab provides.
context_page_description: Symbiosis means living together. It describes close and long-term relationships between different species. The term was
  used by Anton de Bary in 1879, as "the living together of unlike organisms".
  A symbiont is an organism living in a relationship with another species in which one or both get benefits. When one species lives inside another species, or a microscopic symbiont lives inside the cells of a host, it is called an endosymbiont.
  The relevance of symbiosis is its frequency and its evolutionary significance. There appear to be no higher plants or animals without symbionts. Those symbionts are of great importance to the larger organisms, who in most cases would be unable to live as they do without their symbionts. Mycorrhiza in higher plants, and gut flora in insects and vertebrates are examples. Humans are no exception.
  Furthermore, most of these associations are between organisms not just from different species, but from different kingdoms. And lastly, the cells of all eukaryotes contain organelles which are descendants of symbiotic relationships which began at least a billion years ago. Mitochondria and plastids are examples.
context_section_description: This kind of symbiosis is called endosymbiosis. Examples are:
  Rhizobia: nitrogen-fixing bacteria which live in root nodules on plants of the pea family.
  Singly-celled forams which include a single-celled alga inside the cell. This is 'facultative', which means they may or may not do it. A more far-reaching version is idioplastic endosymbiosis. Here, the foram consumes the alga, but keeps its chloroplasts in working order.
  Green algae inside marine polychaete worms.
  Single-celled algae inside reef-building corals.
  Bacteria inside the guts of those insects and vertebrates which digest plant cellulose. These are 'obligate' symbionts, which means the host must have them.
  Lichen: fungus+alga or bacterium.
  Mycorrhiza: fungal hyphae and roots of trees.
  Almost for certain, this happened to form the eukaryote cell. That's the type of cell all animals and plants are made of. The organelles inside the cell, such as mitochondria and chloroplasts, contain some DNA. This DNA is the remnant of a once separate bacterium. The theory is that the eukaryote cell evolved by the fusion of several bacteria or archaea organisms.
caption: Dardanus pedunculatus Hermit crab with symbiotic anemones Calliactis sp. attached to its shell. The anemones provide protection with their stinging cells, and they get mobility from the crab.
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