T. Sagma, Department of Botany, IGGC, Tezu.
Lifecycle pattern in Algae
A life cycle is a series of changes in form that an organism undergoes, returning to the starting state.
Transitions of form may involve growth, asexual reproduction, and/or sexual reproduction. In some
organisms, different "generations" of the species succeed each other during the life cycle. In case of algae,
there are two multicellular stages, and the life cycle is referred to as alternation of generations. The term
life history is often used particularly for organisms such as the red algae (Rhodophyta) which have three
multicellular stages (or more), rather than two.
Life cycles that include sexual reproduction involve alternating haploid (n) and diploid (2n) stages, i.e., a
change of ploidy is involved. To return from a diploid stage to a haploid stage, meiosis must occur.
Lifecycle pattern in Chlorophyceae
1. HaplonticLife Cycle:
The dominant plant body is gametophyte (haploid) and sporophyte (diploid) stage is represented only by
zygote. The gametophytic plant develops haploid gametes in the gametangium.The fusion between
gametes results the formation of zygote, the only diploid stage i.e., sporophytic phase of the life cycle. The
zygote undergoes meiotic division and forms four meiospores. These meiospores develop into haploid
plants. The alternation of generations can be interpreted by chromosome number (ploidy level). This life
cycle is also known as monogenic life cycle. This type of life cycle is found in majority of Chlorophyceae like
Chlamydomonas, Ulothrix, Oedogonium, Spirogyra, Chara etc.eeri ioao
brr biofesd sri sqd
i
biofar srlT toimmt brs 79drm
Spirogyra
302 (0)
Zoospore
gemination
oigtion Gametanga asiyo s lo3ui2i a7armsg
Gamete Gamete
Zoospores (n)
(n)
Lateral orscalarifom
Conjugaltion
Haploid nuclel
Gametophyte Fertilisation
Meiosis Sporophyte
Zygote
(2n)
Fig. 3.19: Haplontic life cycle (Spirogyra)
2. Diplontic Life Cycle:
The dominant plant body is sporophyte and develops sex organs.Sex organs produce gametes by
meiosis. The gamete only represents the gametophytic stage. Thegametes undergo fertilization
immediately and form zygote. The zygote does not undergo meiosis and give rise to new sporophytic
plant body. This type of life cycle is found in some members of Chlorophyceae like Cladophora
glomerata.
Page 1 of 5
, T. Sagma, Department of Botany, IGG
Life
cy
sAiaesq alaoe
Sporophytic
plant
Germination
Gametangla
Zygote
Diploid phase
(2n)
Syngamy Gamctogenic meiosis
Haploid phase
(n)
Gamctes
Gamctes
Diagrammatic outline of a diplontic life cycle
3. Diplohaplontic Life Cycle:
In this type the haploid and diploid phases are equally prominent and are represented by two distinct
vegetative individuals. They differ only in chromosome number and function. The haploid
gametophytic plant reproduces by sexual method, while diploid sporophytic plant by asexual process.
In this life cycle alternation of two vegetative individuals occurs by sporogenic meiosis and fusion of
gametes. This type of life cycle is found in Cladophora, Ulva, Draparnaldiopsis of Chlorophyceae.
Gametes (1n)
Zygote (2n)
-
Gametangia
(Ulva Life Cycle Mature
Gametophytes (1n) sporophyte (2n)
Zoospores (1n) Sporangia
Melosis
39031g 216
in12
Fig: Diplohaplontic life cycle pattern in Ulva
Page 2 of 5
Lifecycle pattern in Algae
A life cycle is a series of changes in form that an organism undergoes, returning to the starting state.
Transitions of form may involve growth, asexual reproduction, and/or sexual reproduction. In some
organisms, different "generations" of the species succeed each other during the life cycle. In case of algae,
there are two multicellular stages, and the life cycle is referred to as alternation of generations. The term
life history is often used particularly for organisms such as the red algae (Rhodophyta) which have three
multicellular stages (or more), rather than two.
Life cycles that include sexual reproduction involve alternating haploid (n) and diploid (2n) stages, i.e., a
change of ploidy is involved. To return from a diploid stage to a haploid stage, meiosis must occur.
Lifecycle pattern in Chlorophyceae
1. HaplonticLife Cycle:
The dominant plant body is gametophyte (haploid) and sporophyte (diploid) stage is represented only by
zygote. The gametophytic plant develops haploid gametes in the gametangium.The fusion between
gametes results the formation of zygote, the only diploid stage i.e., sporophytic phase of the life cycle. The
zygote undergoes meiotic division and forms four meiospores. These meiospores develop into haploid
plants. The alternation of generations can be interpreted by chromosome number (ploidy level). This life
cycle is also known as monogenic life cycle. This type of life cycle is found in majority of Chlorophyceae like
Chlamydomonas, Ulothrix, Oedogonium, Spirogyra, Chara etc.eeri ioao
brr biofesd sri sqd
i
biofar srlT toimmt brs 79drm
Spirogyra
302 (0)
Zoospore
gemination
oigtion Gametanga asiyo s lo3ui2i a7armsg
Gamete Gamete
Zoospores (n)
(n)
Lateral orscalarifom
Conjugaltion
Haploid nuclel
Gametophyte Fertilisation
Meiosis Sporophyte
Zygote
(2n)
Fig. 3.19: Haplontic life cycle (Spirogyra)
2. Diplontic Life Cycle:
The dominant plant body is sporophyte and develops sex organs.Sex organs produce gametes by
meiosis. The gamete only represents the gametophytic stage. Thegametes undergo fertilization
immediately and form zygote. The zygote does not undergo meiosis and give rise to new sporophytic
plant body. This type of life cycle is found in some members of Chlorophyceae like Cladophora
glomerata.
Page 1 of 5
, T. Sagma, Department of Botany, IGG
Life
cy
sAiaesq alaoe
Sporophytic
plant
Germination
Gametangla
Zygote
Diploid phase
(2n)
Syngamy Gamctogenic meiosis
Haploid phase
(n)
Gamctes
Gamctes
Diagrammatic outline of a diplontic life cycle
3. Diplohaplontic Life Cycle:
In this type the haploid and diploid phases are equally prominent and are represented by two distinct
vegetative individuals. They differ only in chromosome number and function. The haploid
gametophytic plant reproduces by sexual method, while diploid sporophytic plant by asexual process.
In this life cycle alternation of two vegetative individuals occurs by sporogenic meiosis and fusion of
gametes. This type of life cycle is found in Cladophora, Ulva, Draparnaldiopsis of Chlorophyceae.
Gametes (1n)
Zygote (2n)
-
Gametangia
(Ulva Life Cycle Mature
Gametophytes (1n) sporophyte (2n)
Zoospores (1n) Sporangia
Melosis
39031g 216
in12
Fig: Diplohaplontic life cycle pattern in Ulva
Page 2 of 5
