Chapter 7
Roots
External Structures of Roots
Literal roots (branch roots)
initiated by cell division in the pericycle
Radicle
taproot present in seed, becomes largest root.
Adventitious roots
roots that are not pre-existing.
Fibrous root system
similarly sized roots.
Mucigel
lubricates passage of the root through the soil.
Zone of elongation
where cells undergo division and expansion.
Root Hair Zone
located behind Zone of elongation. Region in which many of the epidermal cells extend as trichomes.
Root Hairs
Part of the root that is not elongating.
Internal Structure of Roots
Root Caps
thick
layer of cells that protect
apical meristem.
Root Apical meristem
produces root tissue, files of cells can be seen.
Quiescent center
Where healthy cells are stored and protected.
Zone
of Elongation
located behind root apical meristem. Where cells expand.
Zone of Maturation
Maturation zone of cells.
Root Hairs
grow outward, increase water and
mineral absorption.
Endodermis
innermost layer of cortical cells.
Casparian Strips
control the types of minerals that enter the xylem water stream.
:
Mature Portions of the Root
Passage Cells
cells that only have Casparian strips. Once thought to represent passageways for the mineral absorption.
Root Pressure
Root hair zone causes powerful absorption of water and water pressure.
Differs from bud formation in roots.
Other Types of Roots and Root Modifications.
Storage Roots
Carbs are stored here, to produce new shoots come spring.
Prop Roots
Do not make contact with soil. They transfer additional nutrients and water to the stem.
Buttress Roots
upper side of root grows more rapidly than other parts of the root.
Aerial Roots of Orchids
Root epidermis- velamen. this specimen is adapted to little rainfall
Contractile Roots
roots undergo more contraction than prop roots.
Mycorrhizae
relationship in which organisms benefit.
Mycorrhiza
Singular of Mycorrhizae
Ectomycorrhizal relationship
fungi penetrate between outermost root cortex cells.
Endomycorrhizal association
hyphae penetrate the root cortex as far as the endodermis. penetrate through cortex walls but cannot get through Casparian strip.
*Root Nodules and Nitrogen fixationn.
chemical conversion of atmospheric nitrogen into useable compounds.
**Infection thread.
tube where bacteria sits.
Root Nodlue
supplied bysugars, this procedure adjusts cortical mitosis.
Haustoria
Roots of parasitic plants.