Plants
Plant, any member of the plant kingdom, comprising about 260,000
known species of mosses, liverworts, ferns, herbaceous and woody ,
bushes, vines, trees, and various other forms that mantle the earth and are
also found in its waters. range in size and complexity from small,
nonvascular mosses, which depend on direct contact with surface water, to
giant redwood trees, the largest living organisms, which can draw water and
minerals through their vascular systems to elevations of more than 100 m
(more than 330 ft).
Only a tiny percentage of plant species are directly used by humans
for food, shelter, fiber, and drugs. At the head of the list are rice,
wheat, corn, legumes, cotton, ...
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tremendous variety of plant species is, in part, a reflection
of the many distinct cell types that make up individual plants. Fundamental
similarities exist among all these cell types, however, and these
similarities indicate the common origin and the interrelationships of the
different plant species. Each individual plant cell is at least partly
self-sufficient, being isolated from its neighbors by a cell membrane, or
plasma membrane, and a cell wall. The membrane and wall allow the
individual cell to carry out its functions.
Tissue Systems
There are many variants of the generalized plant cell and its parts.
Similar kinds of cells are organized into structural and functional units,
or tissues, which make up the plant as a whole, and new cells (and tissues)
are formed at growing points of actively dividing cells. These growing
points, called meristems, are located either at the stem and root tips,
where they are responsible for the primary growth of plants, or ...
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and secondary walls, both types
lack cytoplasm and are dead at maturity. The walls have pits—areas in which
secondary thickening does not occur—through which water moves from cell to
cell. Vessels usually are shorter and broader than tracheids, and in
addition to pits they have perforation.
Phloem
The phloem, or food-conducting tissue, consists of cells that are
living at maturity. The principal cells of phloem, the sieve elements, are
so called because of the clusters of pores in their walls through which the
protoplasts of adjoining cells are connected. Two types of sieve elements
occur: sieve cells, with narrow pores in rather uniform clusters on the
cell walls, and ...
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Plants. (2008, February 23). Retrieved November 23, 2024, from http://www.essayworld.com/essays/Plants/79497
"Plants." Essayworld.com. Essayworld.com, 23 Feb. 2008. Web. 23 Nov. 2024. <http://www.essayworld.com/essays/Plants/79497>
"Plants." Essayworld.com. February 23, 2008. Accessed November 23, 2024. http://www.essayworld.com/essays/Plants/79497.
"Plants." Essayworld.com. February 23, 2008. Accessed November 23, 2024. http://www.essayworld.com/essays/Plants/79497.
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