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The
Diversity of The World of Life
Green
Plants (Viridaeplantae)
Ginkgos
(Ginkgophyta, or
Ginkgoales)
Representatives
Ginkgo,
The Maidenhair Tree (Ginkgo
biloba)
Biology
ENVIRONMENTS
Ginkgos live on land, in Temperate climates.
Surviving horticultural
specimens of ginkgos are descended from trees planted centuries ago around
Chinese Buddhist
temples -- the ginkgo rarely grows in the wild anymore.
OVERALL STRUCTURE
Cell walls, composed primarily of cellulose, give shape to individual cells.
The ginkgo is a large tree with woody roots, woody trunk
and branches, and fan-shaped "deciduous" leaves (shed in the
winter and re-grown in the spring).
ENERGY CAPTURE
Light-energy is captured, for photosynthesis, by chloroplasts
within the cells in the leaves.
EXCHANGE OF MATERIALS WITH THE ENVIRONMENT
Water vapor and gases flow especially through
"stomata" pores (each regulated by a pair of "guard
cells") in leaves. A
waxy "cuticle" helps prevent water loss from the leaves, and bark
helps prevent water loss from the woody stems.
Water with dissolved substances is absorbed especially by the root
"hairs", at the tips of young "primary" roots.
INTERNAL TRANSPORT
Similar
to conifers.
DEVELOPMENTAL CONTROL
The growth and development of ginkgos is under genetic and
undoubtedly hormonal control.
ASEXUAL REPRODUCTION
Ginkgos can reproduce asexually, via vegetative body parts.
SEXUAL REPRODUCTION
In
ginkgos, as in other plants, there is an "alternation of
generations" in the life cycle, between "diploid" forms
(with both sets of chromosomes) and "haploid" forms (with just
one set of chromosomes). As in other higher plants, the haploid
"gametophytes" (producing the "gametes", sperms and
eggs) are dependent upon the dominant, diploid "sporophytes" (the
typical plant bodies).
Ginkgos
are "dioecious" (with separate sexes -- that is,
with male and female plants).
Borne on twigs on female trees are "ovules".
An ovule is composed of "integuments" covering a "megasporangium" (the
"nucellus" tissue), in which is embedded the female gametophyte.
The female gametophyte bears reduced "archegonia", in each of
which forms an egg. On
male trees, "strobili" cones bear haploid
"microspores", which upon release are carried by the wind, some to the female trees.
After being drawn
into the "micropyle" entrance to the ovule, a microspore
develops into the mature male gametophyte -- a pollen grain with a forked
pollen tube growing into the nucellus and releasing its flagellated
sperms. The sperms
swim through fluid within a small chamber and into one of the archegonia (Significantly, environmental water is not required for
fertilization, as it is in lower plants). One of the
sperms fertilizes the egg in the archegonium, and the diploid "zygote"
(fertilized egg) develops into the embryo sporophyte.
The integuments (as a seed coat) cover the female gametophyte,
which will be consumed by the embryo within, after a period of dormancy:
A true seed is formed. The
seeds of a ginkgo are fleshy, presumably (like the true fruits of flowering
plants) attracting
hungry animals, which can carry the seeds in their gut to new locations.
Green
Plants (Viridaeplantae)
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