Spore
In
biology, a spore is a
reproductive structure that is adapted for
dispersion and surviving for extended periods of time in unfavorable conditions. Spores form part of the
life cycles of many
plants,
algae,
fungi and some protozoans.
Spores are usually haploid and
unicellular and are produced by
meiosis in the sporophyte. Once conditions are favorable, the spore can develop into a new
organism using
mitotic division, producing a multicellular gametophyte, which will eventually go on to produce gametes.
Encyclopedia
- This article is about a biological reproductive structure; for the video game Spore, see Spore . For other uses, see spore .
In
biology, a
spore is a
reproductive structure that is adapted for
dispersion and surviving for extended periods of time in unfavorable conditions. Spores form part of the
life cycles of many
plants,
algae,
fungi and some protozoans.
Spores are usually haploid and
unicellular and are produced by
meiosis in the sporophyte. Once conditions are favorable, the spore can develop into a new
organism using
mitotic division, producing a multicellular gametophyte, which will eventually go 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 are used by many fungi for asexual reproduction.
It is useful to contrast spores with gametes: spores are the units of
asexual reproduction as a single spore develops into a new organism; gametes are the units of
sexual reproduction as two gametes need to fuse to create a new organism.
The term
spore may also refer to the dormant stage of some
bacteria or
archaea, however these are more correctly known as
endospores and are not truly spores in the sense discussed in this article. The term can also be loosely applied to some
animal resting stages. Fungi that produce spores are known as
sporogenous, and those that do not are
asporogenous.
The term derives from the ancient Greek word sp??a, meaning
seed.
Classification of spores
Spores can be classified in several manners.
By function
Diaspores are dispersal units of
fungi,
mosses,
ferns, fern allies, and some other
plants. In fungi,
chlamydospores are thick-walled resting spores, and zygospores are thick-walled resting spores of
zygomycetous fungi which are produced by sexual gametocystogamy and can give rise to a conidiophore with asexual conidiospores.
By spore-producing structure
In fungi and fungus-like organisms, spores are often classified by the structure in which meiosis and spore production takes place, such as a telium,
ascus,
basidium, or oogonium, which produce teliospore, ascospores, basidiospores, and oospores, respectively. Since fungi are often classified according to their spore-producing structures, these spores are often characteristic of a particular taxon of the fungi, such as
Ascomycota or
Basidiomycota.
Meiospores are the product of
meiosis , meaning that they are haploid, and will give rise to a haploid daughter cell or a haploid individual. An example is the parent of gametophytes of the higher vascular plants —the
microspores and
megaspores found in
flowers and
cones; these plants accomplish dispersal by means of
seeds.
A
mitospore is an asexually produced propagule, the result of
mitosis. Most
fungi produce mitospores. Mitosporic fungi are also known as anamophic fungi .
By motility
Spores can be differentiated by whether they can move or not. Zoospore can move by means of one or more
flagellum and can be found in some
algae and
fungi. Aplanospore cannot move, but may potentially grow flagella. Autospore cannot move and do not have the potential to ever develop any flagella. Ballistospore are actively discharged from the body of a fungal fruit . Statismospore are not actively discharged from the fungal fruit body, similarly to a
puffball.
Parlance
In common parlance, the difference between "spore" and "gamete" is that a spore will germinate and develop into a thallus of some sort, while a gamete needs to combine with another gamete before developing further. However, the terms are somewhat interchangeable when referring to gametes.
A chief difference between spores and seeds as
dispersal units is that spores have very little stored food resources compared with seeds, and thus require more favorable conditions in order to successfully germinate. Spores, therefore, are more resistant to harsh conditions and require less
energy to start
mitosis. Spores are usually produced in large numbers to increase the chance of a spore surviving.
The
endospores of certain bacteria are often incorrectly called spores, as seen in the
2001 anthrax attacks where
anthrax endospores were incorrectly called
anthrax spores by the media. Several key differences between bacterial endospores and eukaryotic spores exist: they are primarily a survival mechanism, not a reproductive method, and a bacterium only produces a single endospore.
Diaspores
In the case of spore-shedding vascular plants such as
ferns, wind distribution of very light spores provides great capacity for dispersal. Also, spores are less subject to animal predation than seeds because they contain almost no food reserve, however they are more subject to fungal and bacterial predation. Their chief advantage is that, of all forms of progeny, spores require the least energy and materials to produce.
Vascular plant spores are always haploid and vascular plants are either
homosporous or
heterosporous. Plants that are
homosporous produce spores of the same size and type.
Heterosporous plants, such as
spikemosses,
quillworts, and some aquatic ferns produce spores of two different sizes: the larger spore in effect functioning as a "
female" spore and the smaller functioning as a "
male".
Under high magnification, spores can be categorized as either
monolete spores or
trilete spores. In monolete spores, there is a single line on the spore indicating the axis on which the mother spore was split into four along a vertical axis. In trilete spores, all four spores share a common origin and are in contact with each other, so when they separate each spore shows three lines radiating from a center pole.
See also
