8/13/2019 Discuss Gametophyte Generation and Sporophyte
Generation in Mosses
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Discuss gametophyte generation and sporophyte generation in
mosses
Mosses are classified in the Division Bryophyta. They are small,
fairly simple
plants, usually found in moist environment and have an erect
shoot bearing tiny leaf like
structures arranged in spirals. They dont have any woody tissue
so they never grow
very large. They have neither xylem nor phloem for the transport
of water and foodthrough the plant. Their life cycle is similar to
all plants characterized in alternation
generation. There are two alternation generation of mosses. The
first is a diploid
generation called sporophyte and the second is haploid
generation called gametophyte.
In the gametophyte generation, the leafy shoot of mosses is
haploid. There are
three type of shoots in mosses; female (develop archegonia at
their tip and have a
single egg forms in each archegonium), male (which develop
antheridia at their tip and
have a multiple swimming sperm form in each antheridium), as
well as sterile (which do
not form sex organs). The gametophyte produces haploid sperm and
egg by mitosis.
Moist environment is very important to perform sexual production
of mosses. This isbecause water is transportation agent of sperm to
egg cells. The sperm from male plant
will transferred to female plant and fertilized to produce
zygote, 2n.
The zygote begins the sporophyte generation. Then, the zygote
undergoes
mitosis to produce an embryo that grows to become mature
sporophyte generation. It
consists of a foot (which absorbs water, minerals, and probably
some food from the
parent gametophyte) and a stalk (at the tip of which is formed a
sporangium). However,
in the sporophyte generation, it is still depends on the
gametophyte for water and
nutrient. The sporangium consists of spore mother cells, sealed
by an operculum and
covered with a calyptra (remaining hoodlike tissue at the tip).
The sporophyte continuesto grow and elongate, the surrounding
gametophyte tissue keeps pace, but eventually
cracks at its middle. Underneath the calyptra grows a capsule
filled with many haploid
spores. During the summer, each spore mother cell undergoes
meiosis, producing four
haploid spores the start of the new gametophyte generation. Late
in the summer, the
calyptra and operculum become detached from the sporangium
allowing the spores to
be released. These tiny spores are dispersed so effectively by
the wind that many
mosses are worldwide in their distribution. When the spore
reaches a moist
environment, it develops to form a filamentous, elongating
structure of cells called a
protonema. This protonema gives rise to buds and develops into
the mature leafy
shoots into the next haploid gametophyte generation. The
gametophyte in this
generation will mate and continue the alternation of
generations.
In conclusion, the gametophyte generation is responsible for
sexual reproduction
and the sporophyte generation is responsible for dispersal. The
green leafy, mosses of
the bank of streams are all haploid gametophyte. The diploid
generation of a plant
arises when a male and female gametophyte fuses their haploid
gametes resulting
