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Roots (Other Types of Roots and Root Modifications (Root Nodules and…
Roots
External Structure of Roots
Taproots
carrots, beets, and radishes
carbohydrate storage during winter
Organization of Root System
Branch Roots
Lateral Roots
coming out of larger main root
Radicle
embryonic root
grows into a larger root in the system
Figure 7-2
Fibrous Root System
radical dies after germination
Adventitious Roots
as plants age, more root primordial are in stem tissue
not radicals
dot come from preexisting roots
Figure 7-5
Figure 7-6
Structure of Individual Roots
Root Cap
protects root apical meristem
Figure 7-7
Figure 7-8
Mucigel
lubricates passage of the root through the soil
makes soil release nutrient ions
dictyosomes of root cap cells secrete a complex polysaccharide
Zone of Elongation
behind the root cap and root apical meristem
cells undergo division and expansion
Root Hair Zone
many of the epidermal cells extend out as narrow trichomes
Root Hairs
form only in the part of the root that's not elongated
Internal Structure of Roots
Root Cap
Figure 7-10
Root Apical Meristem
Quiescent Center
mitotically inactive central region
Figure 7-11
Zone of Elongation
Zone of Maturation/Root Hair-Zone
Figure 7-12
Endodermis
in the zone of maturation, minerals don't have free access to vascular tissues
the innermost layer of the cortical cells differentiates into a cylinder
Casparian Strips
controls the type of minerals that enter the xylem water stream
Figure 7-13
Firgure 7-14
Figure 7-15
Pericyle
between the vascular tissue ad the endodermis are parenchyma cells
when lateral roots are produced
Mature Portions of the Root
Passage Cells
slow to develop
Root Pressure
absorption of minerals in the root hair zone
powerful absorption of water and water pressure
Origin and Development of Lateral Roots
Figure 7-16
Other Types of Roots and Root Modifications
Storage Roots
carrots
carbohydrate storage
Prop Roots
palms
Figure 7-17
Buttress Roots
Figure 7-18
Aerial Roots of Orchids
Figure 7-19
Contractie Roots
Figure 7-20
Mycorrhizae
Ectomycorrhizal Relationship
fungal hyphae penetrate between the outermost root cortex
Endomycorrhizal Association
hyphae penetrate the root cortex as far as the endodermis
"Mycorrhiza"
roots of most species of seed plants have a symbiotic relationship with soil fungi
both organisms benefit
Root Nodules and Nitrogen Fixation
Nitrogen Fixation
the chemical conversion of atmosphere nitrogen into usable compounds
Infection Thread
the tube
bacterium sits on it
Root Nodule
where adjacent cortical cells undergo mitosis
Figure 7-21
Haustorial Roots of Parasitic Flowering Plants
Haustoria
roots of parasitic plants
Figure 7-23
