Diverrsity Of Plants
Plants evolved more than 430 million years ago from multicellular green
algae. By 300 million years ago, trees had evolved and formed forests, within
which the diversification of vertebrates, insects, and fungi occurred. Roughly
266,000 species of plants are now living.
The two major groups of plants are the bryophytes and the vascular
plants; the latter group consists of nine divisions that have living members.
Bryophytes and ferns require free water so that sperm can swim between the male
and female sex organs; most other plants do not. Vascular plants have elaborate
water- and food conducting strands of cells, cuticles, and stomata; many of
these plants are much larger that any ...
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evolution of their
conducting tissues, cuticle, stomata, and seeds has made them progressively less
dependent on water. The oldest plant fossils date from the Silurian Period,
some 430 million years ago.
The common ancestor of plants was a green alga. The similarity of the
members of these two groups can be demonstrated by their photosynthetic pigments
(chlorophyll a and b,) carotenoids); chief storage product (starch); cellulose-
rich cell walls (in some green algae only); and cell division by means of a cell
plate (in certain green algae only).
Major Groups
As mentioned earlier, The two major groups of plants are The bryophytes-
-mosses, liverworts, and hornworts--and The vascular plants, which make up nine
other divisions. Vascular plants have two kinds of well-defined conducting
strands: xylem, which is specialized to conduct water and dissolved minerals,
and phloem, which is specialized to conduct The food molecules The plants
manufacture.
Gametophytes and ...
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to the ovule.
The nutritive tissue in gymnosperm seeds is derived from the expanded,
food-rich gametophyte. In angiosperm seeds, the nutritive tissue, endosperm, is
unique and is formed from a cell that results from the fusion of the polar
nuclei of the embryo sac with a sperm cell.
The pollen of gymnosperms is usually blown about by the wind; although
some angiosperms are also wind-pollinated, in many the pollen is carried from
flower to flower by various insects and other animals. The ripened carpels of
angiosperm grow into fruits, structures that are as characteristic of members of
the division as flowers are.
GYMNOSPERMS AND ...
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"Diverrsity Of Plants." Essayworld.com. July 27, 2008. Accessed November 28, 2024. http://www.essayworld.com/essays/Diverrsity-Of-Plants/87378.
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