Roots

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  • Topic: Root, Plant anatomy, Phloem
  • Pages : 5 (1006 words )
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  • Published : January 14, 2013
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ROOTS
* is an organ of a plant that typically lies below the surface of the soil. * a part of a plant body that bears no leaves, and therefore also lacks of nodes. * is the beginning of the vascular system pipeline that moves water and minerals from the soil up to the leaves and fruits. FUNCTIONS OF ROOTS:

* Underground (usually)
* Anchor the plant in the soil
* Absorb water and nutrients
* Conduct water and nutrients
* Food Storage
ROOT SYSTEM:
1. Tap root system
* A root system consisting of one prominent main root with smaller lateral roots branching from it. * Ex: carrots, beets, sugar beets, parsnips, turnips, rutabagas, radishes 2. Fibrous Root System

* A root system consisting of several adventitious roots of approximately equal size that arise from the base of the stem. * These roots are adventitious which means they can grow from plant organs other than roots e.g. stems. * Ex: sweet potatoes, cassava

STRUCTURE OF ROOTS:
1. Epidermis – The outer layer of cells
* Root Hair
* An extension of an epidermal cell of a root that increases absorptive capacity of the root. * Absorptive unicellular extensions of epidermal cells of a root that functions as the major site of water and mineral uptake. * Increase surface area of root in contact with moist soil, increasing root’s absorptive capacity. 2. Cortex

* Primary tissues of a root bound on the outside by the epidermis and on the inside by the endodermis. 3. Endodermis
* a single layer of cells in a root that separates the cortex tissues from the pericycle. * Casparian Strip
* A band of waterproof material around the radial and transverse cells of the endodermis * Ensures that water and minerals enter the xylem only by passing through the endodermal cells 4. Pericycle

* a layer of cells immediately inside the endodermis. Branch roots arise from the pericycle. 5. Vascular system
Xylem
* Involved in conduct of water and ions in the plant.
* Typically composed of non-living conductive cells and living parenchyma cells * Conductive cells have thick secondary cell walls, often deposited unevenly in a coil-like pattern so that they may stretch * Dead at functional maturity

* Two types of conductive cells- tracheids and vessels * Tracheids - long, slender cells connected to each other by pits.  Found in all vascular plants * Vessels - shorter, larger diameter cells with completely perforated cell wall ends.  Found only in Angiosperms * Xylem Parenchyma arranged in rays

* Xylem parenchyma are also distributed throughout the tracheids and vessel elements 

Phloem
* Involved in transport of sucrose, other organic compounds, and some ions * Conductive cells living at functional maturity
* Protoplast may lack organelles and nucleus, though
* Endwalls connect to each other via sieve-plates
* Two types of conductive cells in the phloem - sieve-tube members and companion cells * Sieve-tube members - actual conduit for sucrose transport * Companion cells - has a nucleus that may also control the sieve-tube element and may aid in sucrose loading * Sclerenchyma tissue is often associated with phloem

6. Pith
* center most region of the root.
7. Stele
* a cylinder of vascular tissues at the center of a primary eudicot root. 8. Symplast
* a continuum consisting of the cytoplasm of many plant cells, connected from one cell to the next by plasmodesmata. 9. Apoplast
* a continuum consisting of the interconnected, porous plant cell walls, along which water moves freely. FOUR REGIONS:
10. Root Cap
* Thimble-like covering which protects the delicate meristem tissues. * Produced from cells derived from the root apical meristem. * Secretes polysaccharide slime that lubricates the soil. * Constantly sloughed off and replaced.

* May...
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