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Passage of an organism from "birth" through birth of equivalent offspring.
"Birth" is in quotes because I am not using the usual, narrow definition of the term, meaning to exit in an immature state from one's mother's womb, but instead in the sense of an organism starting out its life at some immature, semi-independent-from-one's-parent's stage. This thus could be at the point of hatching, or seed dispersal, or even the conclusion of binary fission. A life cycle thus passes from that start through to the next generation's equivalent start.
Note that I use the term "equivalent" because a number of organisms pass through different stages that indeed represent different generations – as most notably seen with alternation of generations in plants – but a life cycle most reasonably starts and ends at the same point in the same stage. Nonetheless, at least so long as different generations retain the same ploidy if not necessarily the same morphology or even environment, then we can describe each generation as progressing through a single life cycle. The term "life history", though, may be employed to take into account such multigenerational complications.
A life cycle, ignoring exceptions as discussed above, generally takes approximately one generation to complete. Similarly, we can speak of a generation time associated with that generation or life cycle. In especially microorganisms one also speaks of a doubling time, reflecting the production of offspring in batches of two.
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