Page 4 - 11-Bio-9 Kingdom plantae

9. Kingdom Plantae eLearn.Punjab

The spores germinate and give
rise to gametophyte which is also
haploid. Multicellular male and
female sex organs i.e. antheridia
and archegonia respectively, are
born on gametophyte either on same
or different plants. These sex organs
are multicellular and protected by a
sterile covering of cells (Fig. 9.3).

Gametes are produced by mitosis.
Male gametes produced within
antheridia are called antherozoids;
antherozoids are motile and always
produced in large number. Female
gametes formed within archegonia
are termed as eggs. A single egg
is formed in each archegonium.
Fertilization takes place in water.
Antherozoids (n) are attracted
towards archegonia (n) chemotactically. A single antherozoid fuses with an egg (n) thus accomplishing
fertilization which results in the formation of the diploid zygote (2n). The zygote is retained within the
femalesexorgan(archegonium)forsometime.Afterarestingperiodthezygotedevelopsthroughmitotic
divisionsintoadiploidembryo.Theembryoultimatelydevelopsintoasporophytewhichisalsodiploid.

The entire development of sporophyte thus takes place within the gametophyte plant body. Even
when the sporophyte is fully developed it remains attached to the gametophyte for nourishment
and protection because it does not contain chloroplasts and is unable to perform photosynthesis.
There is an alternation of generations in the life cycle of bryophytes i.e. multicellular haploid
gametophytic (gamete producing) generation alternates with the multicellular diploid sporophytic
(spore producing) generation (Fig. 9.6). It is a very important phenomenon, which provides
continuous genetic variabilities and selection for the best genetic make up for survival and
adaptation in the changing environment(s) (as explained in a later section).

In view of the above mentioned discussion, bryophytes can therefore be defined more precisely as
plants with the distinguishing characters as follows :

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