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division of labor
A multicellular organism is characterized by a --- --- --- among cell types specialized for different functions.
Mature --- cells have primary walls that are relatively thin and flexible, and most lack secondary walls.
The protoplasts of neighboring cells are generally connected by ---, cytoplasmic channels that pass through pores in the walls.
(Plant cells) The endoplasmic reticulum is continuous through the plasmodesmata in the form of structures called ---.
An adhesive layer called the --- --- cements together the cell walls of adjacent cells.
(Plant cells) The secondary cell wall is closer to the --- than the primary wall, because it forms later, usually after the cell has stopped growing.
The highly specialized cells that function in the transport of sugar sap in the phloem (the sieve-tube members) are thin-walled and living and are examples of --- cells.
Parenchyma cells perform most of the --- functions of the plant, synthesizing and storing various organic products.
Developing plant cells of all types are --- cells before specializing further in structure and function.
Plant cells that retain the less specialized condition and become mature --- cells do not generally undergo cell ---.
Most --- cells retain the ability to divide and --- into other types of plant cells under special conditions... during the repair and replacement of organs after injury to the plant, for example.
In the laboratory, it is possible to regenerate an entire plant from a single --- cell.
Cell recognition: Relatively unspecialized, with thin, flexible primary walls. These cells carry on most of the plant's metabolic functions.
Cell recognition: Unevenly thickened primary walls; provide support to parts of the plant that are still growing.
Cell recognition: Specialized for support, have secondary walls hardened with lignin and may be dead (lacking protoplasts) at functional maturity.
--- cells have thicker primary walls than parenchyma cells, though the walls are unevenly thickened.
Grouped in strands or cylinders, --- cells help --- the young parts of the plant shoot.
Young stems and petioles often have a cylinder of --- just below their surface (the strings of a celery stalk, for example).
Because they lack secondary walls and the hardening agent lignin is absent in their primary walls, --- cells provide support without restraining growth.
Unlike sclerenchyma cells, mature, functioning --- cells are living and flexible and --- with the stems and leaves they support.
Also functioning as supporting elements in the plant, but with thick secondary walls usually strengthened by lignin, --- cells are much more rigid than collenchyma cells.
Mature --- cells cannot elongate, and they occur in regions of the plant that have stopped growing in length.
So specialized are --- cells for support that many are dead at functional maturity, but they produce secondary walls before the --- dies.
In parts of the plant that are still elongating, the --- walls of --- are deposited unevenly in spiral or ring patterns like the wire helix that reinforces the wall of a vaccuum hose.
The spiral helix form of --- cell wall thickening enable the cell wall to stretch like a spring as the cell grows.
The water-conducting vessel elements and tracheids in the --- are --- cells with dual functions: support and transport.
Aside from vessel elements and tracheids, there are also two types of sclerenchyma cells called -- and --- that specialize entirely in support.
(Sclerenchyma) --- which are shorter than fibers and irregular in shape, impart the hardness to nutshells and seed coats and gritty texture to pear fruits.
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