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lenka90 lenka90
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12 years ago
also:

How does the diference in structure between palisade and spongy cells heop them carry out their different functions?

What is the purpose of the pericycle?

Which stem tissue is the oldest band of xylem found closest to?

How is the shape and function of the central cylinder of a root similar to a water pipe or blood vessel?
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12 years ago
The stomata are pore-like openings that function in respiration, they also are a major source of water loss (though some of this is desirable for transpiration) so one strategy for water-restricted species is to place the stomata on the undersid eof the leafe where they are less exposed to the sun, therefore reducing water loss during the day. Other plants prefer to only open the stomata at night, for the same reason.
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12 years ago
Dicotyledons usually have more stomata on the lower epidermis than the upper epidermis. As these leaves are held horizontally, upper epidermis is directly illuminated. Locating fewer stomata on the upper epidermis can then prevent excess water loss.

Monocotyledons are different. Because their leaves are held vertically, they will have the same number of stomata on the two epidermes.

If the plant has floating leaves, there will be no stomata on the lower epidermis and they absorb gases directly from water through the cuticle. If it is a submerged leaf, no stomata will be present on either side.

In botany, a stoma (also stomate; plural stomata) is a tiny opening or pore, found mostly on the under-surface (epidermis) of a plant leaf, and used for gas exchange. The pore is formed by a pair of specialized parenchyma cells known as guard cells which are responsible for regulating the size of the opening. Air containing carbon dioxide enters the plant through these openings where it gets used in photosynthesis and respiration. Oxygen produced by photosynthesis in the chlorenchyma cells (parenchyma cells with chloroplasts) of the leaf interior exits through these same openings. Also, water vapor is released into the atmosphere through these pores in a process called transpiration.

Palisade layer. This consists of one or more layers of cylindrical cells oriented with their long axis perpendicular to the plane of the leaf. The cells are filled with chloroplasts (usually several dozen of them) and carry on most of the photosynthesis in the leaf.
 
Spongy layer. Lying beneath the palisade layer, its cells are irregular in shape and loosely packed. Although they contain a few chloroplasts, their main function seems to be the temporary storage of sugars and amino acids synthesized in the palisade layer. They also aid in the exchange of gases between the leaf and the environment. During the day, these cells give off oxygen and water vapor to the air spaces that surround them. They also pick up carbon dioxide from the air spaces. The air spaces are interconnected and eventually open to the outside through pores called stomata (sing., stoma).
PERICYCLE
Found in the stele of plants, the pericycle is a cylinder of cells that lies just inside the endodermis. It conducts water and nutrients inward to the vascular tissue. In dicots, it is also has the capacity to produce lateral roots. Branch roots arise from this primary meristem tissue.

A plant tissue characteristic of the roots, located between the endodermis and phloem.
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