SCIN OUTLINE
11/24/19, 8)16 AMLife cycle | biology | Britannica
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Life cycle BIOLOGY
WRITTEN BY: The Editors of Encyclopaedia Britannica See Article History
Life cycle, in biology, the series of changes
that the members of a species undergo as
they pass from the beginning of a given
developmental stage to the inception of
that same developmental stage in a
subsequent generation.
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Life cycle BIOLOGY !
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The life cycle of a flowering plant.
© Merriam-Webster Inc.
Life cycle QUICK FACTS
KEY PEOPLE
Jan Swammerdam
Pierre-Joseph van Beneden
Francesco Redi
Heinrich Anton de Bary
Charles Joseph Chamberlain
J.C. Arthur
RELATED TOPICS
Life
Prenatal development
Biological development
Aging
Seed
Birth
Fruit
Germination
Phenology
Gestation
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primate: Reproduction and life cycle The stages of the life cycle of primates vary considerably in duration. Among the most primitive members of the group, these stages are…
In many simple organisms, including
bacteria and various protists, the life cycle
11/24/19, 8)16 AMLife cycle | biology | Britannica
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is completed within a single generation:
an organism begins with the fission of an
existing individual; the new organism
grows to maturity; and it then splits into
two new individuals, thus completing the
cycle. In higher animals, the life cycle also
encompasses a single generation: the
individual animal begins with the fusion of
male and female sex cells (gametes); it
grows to reproductive maturity; and it
then produces gametes, at which point
the cycle begins anew (assuming that
fertilization takes place).
The life cycle of the termite.
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In most plants, by contrast, the life cycle is
multigenerational. An individual plant
begins with the germination of a spore,
which grows into a gamete-producing
organism (the gametophyte). The
gametophyte reaches maturity and forms
gametes, which, following fertilization,
grow into a spore-producing organism
(the sporophyte). Upon reaching
reproductive maturity, the sporophyte
produces spores, and the cycle starts
again. This multigenerational life cycle is
called alternation of generations; it occurs
in some protists and fungi as well as in
plants.
The life cycle of the fern.
(
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© Merriam-Webster Inc.
The life cycle characteristic of bacteria is
termed haplontic. This term refers to the
fact that it encompasses a single
generation of organisms whose cells are
haploid (i.e., contain one set of
chromosomes). The one-generational life
cycle of the higher animals is diplontic; it
involves only organisms whose body cells
are diploid (i.e., contain two sets of
chromosomes). Organisms with diplontic
cycles produce sex cells that are haploid,
and each of these gametes must combine
with another gamete in order to obtain
the double set of chromosomes necessary
to grow into a complete organism. The life
cycle typified by plants is known as
diplohaplontic, because it includes both a
diploid generation (the sporophyte) and a
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haploid generation (the gametophyte).
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This article was most recently revised and
updated by Chelsey Parrott-Sheffer, Research
Editor.
LEARN MORE in these related Britannica articles:
primate: Reproduction and life cycle
The stages of the life cycle of primates vary considerably in duration. Among the most…
human nutrition: Nutrition throughout… the life cycleNutritional needs and concerns vary during different stages of life. Selected issues are…
plant development: Life cycles
The life cycle of all tracheophytes (vascular plants), bryophytes
…
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