Transcript Gymnosperms

Kristin Stuck
Maggie Quamme
 Adapted
for water conservation.
 Gametophytes reduced in size, often staying
within the parent sporophyte plant.
 Swimming sperm replaced by dispersal of the
whole male gametophyte (pollen) by wind or
insects.
 Seeds came into being.
 The seeds develop on the surface of the
reproductive structures (thus also called the
“naked-seed plants”) such as the cones in
pine.
Sporophyte is underground network of roots
supporting a stem, the trunk, branches.
 Sporophyte has two types of reproductive
structures referred to as male and female cones.
 Each cone is considered to be a branch with a
number of leaves, called sporophylls.
 Each sporophyll has a sporangium where spores
are produced.
 Spores and gametes come in two sizes:
microspores and megaspores are produced in
separate sporangia and develop into male and
female gametophytes, respectively.

Male cones typically found in clusters at the tips
of lower, side branches, and take several years
to develop.
 Leaves are called microsporophylls.
 Each microsporophyll has a microsporangium
where the microspores are produced.
 Inside the microsporangium, each microspore
divides and forms a four-celled male
gametophyte, also known as pollen, which
contains two sperm nuclei.
 Pollination is the transfer of the whole male
gametophyte to the female plant. Not
fertilization.

 Female
cones form higher up and take years
to develop.
 Leaves/scales are called megasporophylls
and produce megaspores.
 Each scale (megasporophyll) has two areas
(megasporangia or ovules) where megaspores
can develop.
 Each ovule has a micropyle, a small hole in
the near end of the ovule wall so the sperm
can enter.


Pollination: When a pollen grain goes between the
“stem” of the female cone and a megasporophyll.
Fertilization: a tube from the pollen (called a pollen
tube) grows into the micropyle, then into the female
structures. Causes production of megaspore by the
female. The megaspore develops into a female
gametophyte and produces a few archegonia, each
with an egg in it. The pollen forms two sperm nuclei
that go up pollen tube toward the archegonia. A
sperm nuclei fertilizes one of the eggs in one of the
archegonia in each of the ovules. The other sperm
nucleus and all other eggs and archegonia in that
female gametophyte disintegrate so one zygote per
ovule is left.
From the zygote, cells divide and grow into an
embryo sporophyte (2n). This forms in the
female gametophyte (1n). Typically, parts of the
old megasporophyll from the parent pinecone
(2n) form a protective seed coat and the “wing”
for dispersal.
 When the seed is mature or ripe, it separates
from the female cone and is carried by the wind
to a new location. When the seed germinates,
the embryo continues to grow into a new pine
tree. Initially, it uses the nutrients provided by
the female gametophyte until its first leaves are
above ground and large enough to do
photosynthesis.

Cycads have leaves
that look like palms,
but the plant gets a
big cone in the center
for reproduction.
Ginkgoes are
dioecious (di =
two; oecious, eco
= house), they
come in male and
female plants.
A valuable street tree
because of its
unusual foliage and
tolerance of
pollution.
Examples: pines, firs, spruces,
yews, junipers, cedars,
cypress, and redwoods. Many
are evergreen. The leaves are
needle-shaped to conserve
moisture. Some kinds can be
very old and/or large: in
California, a number of
redwoods are over 100 m tall,
there is a sequoia with a trunk
diameter of 26 m, and there is
a bristlecone pine which is
over 4600 years old.