In biology, a spore is a reproductive structure, some of which are adapted for dispersal and surviving for extended periods of time in unfavorable conditions. The spores of seed plants, however, are produced internally, and it is larger structures derived from the spores that disperse (the megaspores are formed within the ovules, and the microspores later give rise to pollen grains).
Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoa. According to scientist Dr. Steinn Sigurdsson, "There are viable bacterial spores that have been found that are 40 million years old on Earth - and we know they're very hardened to radiation."
Spores are usually haploid and unicellular and are produced by meiosis in the sporangium of the sporophyte. Once conditions are favorable, the spore can develop into a new organism using mitotic division, producing a multicellular gametophyte, which eventually goes on to produce gametes. Two gametes fuse to create a new sporophyte. This cycle is known as alternation of generations.
Haploid spores produced by mitosis (known as mitospores) are used by many fungi for asexual reproduction.
Spores are units of asexual reproduction; by contrast, gametes are units of sexual reproduction, as two gametes need to fuse to create a new organism.