Biology Questions and Answers
- How are the male gametes
of gymnosperms formed?
What is the relationship
between the pollen grains and
the concept of alternation of
generations?
In the male strobiles (cones) there are
microspostrobile) that contain microsprophylls (fertile leaves oorangia.f the
Within the microsporagium spore
mother cells undergo meiosis andgenerate haploid microspores. The (^)
microspoprojectionsre wall d (to facilitateevelops into winglike its aerial
propagation) and mitosis occurs
producing and the tube cell. Thtwo cells, the generative celle final structure
containing these elements is the pollen
grain.
The pollen grain relates to the
alternation omale gametophyte (thf generations since it is the haploid stage oef (^)
the life cycle).
- How are the female
gametes of gymnosperms
formed? What is the
relationship between this
process and the concept of
alternation of generations?
In the female strobiles (comegasporophylls (fertile leaves ones) thf theere are
strobile) that contain megasporangia. In
the megaspocell undergoes meiosisrangium the spore mother generating four
haploid cells of which three regress and
one gives bmegaspore. The functional mirth to the functionalegaspor (^) e
by several mitosis forms the female
gametophyte that contains the
oospheres (female gametes) oplant. The female gametophyte isf the
located within the megasporangium that
has a small opening, the micropylthrough which the pollen tube enters.e,
The process is related life cycle (alternation of generations)to the diplobiontic
since the functional megaspore
generates th(the female gametophytee haploid stage o). f the plant
- How do fecundation and
zygote formation occur in
these plants? Do these
processes depend on water?
The microsporanrupture at the right period of the yeargia in the male strobile
releasing thousands of pollen grains.
Since their pollen grains arthey can be transported by the winde “winged”
over distances. When the pollen grains
fall into the female strobilthe micropyle and enter the pollenes they pass
chamber. This process is calledpollination.
Within the pollen chambgenerative cell nucleus divides forminger the (^)
two gametic nuclei and the tube cell
elongates forming the pollen tube. Thepollen tube penetrates the female
gametophyte and the gametic nuclei
(also kthrough the tube; one of them unitesnown as sperm nuclei) pass (^)
with an oosphere (the female gamete)
and forms thfecundation occue zygote (2rs one year n). Generallyafter
pollination and during this time interval
the maturation female gametes takes place.of the male and of the
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