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Flashcards in PLANT ROOT Deck (12):
1

Cortex

Ring of the root outside of the endodermis composed of many parenchyma cells, that store food (especially in the form of starch).

2

Epidermis

Very outer edge of the root (outer skin).

This area covers the entire root, except for the area immediately around the root cap.

3

Three root zones

1.) Zone of maturation
2.)Zone of elongation
3.)Zone of cell division

4

Zone of Maturation
(Zone of differentiation)

Where meristematic root cells differentiate into a mature form and function.

It is here that they specialize into of the following plant tissues~dermal,ground, or vascular tissues.

5

Zone of Elongation

In this region, cells grow by elongation.

Cells work like bio-hydraulic pumps (empty vacuoles fill with water, creating hydraulic pressure inside the cells making the root tip move downward) to force the roots through the soil.

6

Zone of Cell Division
(Meristematic Zone)

Named after the root apical meristem, cells undergo rapid mitotic division and are either pushed up to the zone of elongation or down toward the root tip.

Those cells that get squashed down, line up with cells in front whilst new cells are produced behind.
This phenomena creates columella cells (rectangular cells that line up in columns), which in turn make up the root cap.

7

Root Cap

Protects the root apical meristem while the root moves through the soil.

One way it protects is through the production of lubricating mucilage

Cells here contain, Statoliths: Heavy specialized organelles that sink to the bottom of the cell (in essence act as weights) helping roots detect gravity. This phenomenon also triggers the cellular membranes of this area to produce auxin and therefore, Statoliths, are partially responsible for the downward direction of root growth

Outer cells of root tips are eventually sloughed off and replaced by new ones. Sloughed cells supplement the plants' amino acid/sugar exudate content attracting microbes necessary for nutrient uptake into the rhizosphere.

8

Root Mucilage

With a texture such as gel, the mucilage is particularly apt. at seeping into minuscule soil particles/crevices and softening them before actual contact with the root tips.

Has a great influence on the uptake of metal nutrients. Phosphorus, zinc, iron, and magnesium all diffuse in through the mucilage.

Nutrient uptake is dictated by the concoction of chemicals that a plant gives off into the rhizosphere through mucilage.

9

Vascular Cylinder
(Stele)

Area inside of the endodermis.

Important to note that different plant species have different kinds of vascular bundles.

Xylem,
Phloem,
Pericyle,
Vascular Cambium
Pith

10

Pericycle

A thin layer of cells,just inside the endodermis (outermost layer of the stele), that retains the ability to grow.

Generally dedicated toward lateral growth (widening) sometimes new roots or branches can develop from this region.

This growth is responsible for lateral roots, that grow out through the casparian strip, through the cortex, and into the soil. (Usually developing root hairs as well)

As a whole new (3 part) root tangent is made, the pericycle will go back to increasing girth.

11

Vascular Cambium

A plant tissue located between the xylem and the phloem in the stems and roots of plants.

It is the source of both secondary xylem growth inwards towards the pith, and secondary phloem growth outwards to the bark.

Responsible for creating new xylem or phloem cells, as directed from intercellular messages.

Also works with the pericycle in the creation of new roots and shoots.

12

Root Hairs

Specialized epidermal cells on roots that are extremely important to the uptake of nutrients. They dramatically increase the surface area of the for the root that is exposed to the soil.

Each root hair is a single cell and can grow to amazing lengths. Only a small zone located between the root cap and zone of cell division contains the meristematic code to become root cells.

Plants can grow tens of thousands in area no bigger than several inches, though only very few stay long enough to develop into roots (life expectancy day-a couple weeks)

Root hairs will exude chemicals in order to prevent all epidermal cells from becoming root hairs. (Avoid a tangled mess of root hairs).

Root hairs contain a special relationship with calcium.