Alternation of generation in Bryophytes in brief

1. ALTERNATION OF
GENERATIONS IN
BRYOPHYTES
D R K AV I TA R A M B A L
H . O. D B OTA N Y
M . D. C O L L E G E
PA R E L , M U M B A I - 1 2

2. ALTERNATION OF GENERATION
• Alternation of generations is a life-cycle involving two
phases of life, which regularly alternate with each other.
• Alternation of generations describes a plant's life cycle as it
alternates between a sexual phase, or generation and an
asexual phase.
• The sexual generation produces gametes, or sex cells and is
called the gametophyte generation.
• The asexual phase produces spores and is called the
sporophyte generation.

3. ALTERNATION OF GENERATION
• In Bryophytes, the first phase is
the gametophytic phase, in which
gametes are produced, that contain
half the number of
chromosomes(Haploid).
• This is the dominant phase in the
life of Bryophytes and reproduces
sexually by egg and antherozoid.
• Egg and antherozoid fuse
to produce a zygote, starts the
second phase.
• The zygote germinates to
produce the sporophyte(Diploid). Source: Google Images

4. • This second phase, the sporophytic phase, is the spore
producing phase. The sporophyte cannot exist independently.
• It is either simple or composed of a capsule, a stalk, and a foot
that attaches the sporophyte body to the gametophyte.
• The sporophyte reproduces asexually by means of spores,
which are produced by meiosis and are haploid.
• Each spore germinates to produce a gametophyte, which is
the independent phase.
• This way, the life cycle is completed. This type of life cycle is
called haplodiplontic type of life cycle.

5. ALTERNATION OF GENERATION
IN HEPATICEAE
• Gametophytic generation is prominent and independent.
• Sex organs Antheridia and archegonia develop on it and produce
gametes.(Haploid)
• Fertilization of gametes results in formation of zygote.(Diploid).
• Zygote develops into sporophyte often called
sporogonium(Diploid).
• Sporophyte is completely dependent on gametophyte.

6. ALTERNATION OF GENERATION
IN HEPATICEAE
• Sporophyte very simple in Riccia, some liverworts may show
slightly developed sporogonium.(foot, seta and capsule)
• In primitive capsule entire endothecium forms spores .(Haploid)
• In advanced type some of the endothecium cells form elaters and
elatophores which help in spore dispersal.
• Thus in Hepaticeae there is definite alternation of generations.
• The thalloidal, independent gametophyte alternates with parasitic
sporogonium (Sporophyte).

7. Source :Google Images

8. ALTERNATION OF GENERATION
IN ANTHOCEROTAE
• Prominent generation in Anthocerotae is a gametophytic generation
as in other Bryophytes.
• Like primitive Hepaticeae, thallus or gametophyte is green
,dorsiventrally flattened and lobed.
• The upper surface is smooth and lower side develops number of
unicellular rhizoids.
• Internally thallus is homogenous and consists of Chlorenchymatous
cells.
• Chloroplast with pyrenoid present.

9. ALTERNATION OF GENERATION
IN ANTHOCEROTAE
• Gametophyte gives rise to sex organs (antheridia and archegonia)
bearing male and female gametes(haploid) respectively.
• Gametes fuse to form zygote(diploid) first cell of sporophytic
generation.
• Zygote mitotically divides to give rise to sporophyte.
• Sporophyte better developed than Hepaticeae, partially parasitic on
female gametophyte.
• Sporophyte differentiated into foot, meristematic region an capsule.
• Capsule wall inner to epidermis Chlorenchymatous
(photosynthetic).

10. ALTERNATION OF GENERATION
IN ANTHOCEROTAE
• Some of the sporocytes form pseudoelators.
• Continuous supply of spores is ensured due to meristematic
region.
• Spores germinate to form gametophytes.
• Thus primitive gametophyte of Anthocerotae alternates
with slightly better developed sporophyte.

11. Source :Google Images

12. ALTERNATION OF GENERATION
IN MUSCI
• Comparatively better developed gametophyte of Musci alternates
with better developed sporophyte.
• The gametophyte is erect ,differentiated into rhizoid, stem
like(caulloid) and leaf like structures (phylloids).
• The gametophyte is independent ,autotrophic and free living.
• Gametophyte gives rise to sex organs and gametes (haploid).
• Gametes fuse to form zygote (diploid) in presence of water.
• Sporophyte better developed is semiparasitic, can manufacture its
own food material.
• Thus there is distinct alternation of generations.

13. Source:Google Images

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