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Ch. 7; Roots (Other Types of Modification (Root of Strangler Figs…
Ch. 7; Roots
Other Types of Modification
Storage Roots
long term storage of carbohydrats
produce new shoot in spring
Prop Roots
Provide support and stability
Secondary growth
Woody
Buttress Roots
brace against wind
Mangroves
intertidal marshes
brace-like
aerial
Covered in air chambers . (lenticles)
Cortex
Wide aerenchyma
Subteranean
respire through diffusion
Aerial Roots of Orchids
Epiphytic
Epidermis (velamen)
Waterproof barrier
Contractile Roots
firmly fixed to soil
contractiion
Mycorrhizae
Ectomycorrhizal relationship
fungal hyphae and outer cortex cells,
No invasion of cells
Ecotomycorrhizal association
invade cortex cells
Root Nodules and Nitrogen Fixation
Nitrogen Fixation
conversion of nitrogen into usable compounds
Infection thread
tube where bacterium sits
mitosis
Nodules form
Root Nodule
simple or complex
Haustorial Roots of Parasitic Flowering Plants
Little root structure
Adheres tightly to host
Root of Strangler Figs
Epiphytes
cling to bark host
absorbs nutrients through water running down branche
become woody
Encircle host trunk
eventually killing host
Internal structure of Roots
Root Cap
Constantly regenerating itself
Protects root apical meristem
Root Apical Meristem
Quiescent center
Inactive central region
resistent to harmful agents
become active when root apical meristem or root cap are damaged.
No disruption due to primordia, leaf traces or axillary buds.
Zone of Maturation/Root Hair Zone
Root hairs grow
increased water and mineral absorbption
Cortex cells
Transfer minerals
Diffusion
Absorption
Cortical intracellular spaces
oxygen diffuses through root
No free access to vascular tissues
Endodermis
waterproof radial walls
Mature Portions of the Root
only function for a few days
Endodermis
watertight sheath form around vascular tissue
Suberin over radial surfaces, and tangential face
irregular
Passage cells
Cells with Casparian strips
Root Pressure
Powerful water absorption and pressue
Cortex and Epidermis
Superfluous
Zone of Elongation
cell expansion
outer cells are protoderm
Epidermis
Provascular cells
Primary Xylem and phloem
Ground tissue
root cortex
Origin and Development of Lateral Roots
Initiate by cell division
Small Root primordium
Root apical meristem
Swell into cortex
New lateral root destroys and break down epideris
rot cap formed
External Structures of Roots
Organization of Root Systems
Lateral and Branch root
numerous, small
Taproot
Develope in embryonic root (radicle)
Fibrous root system
Mass of similarly sized roots
Adventitious Roots
Increase absorption and transport capacities of root system.
Structure of Individual Root
Root Tip
where Growth and length occur.
Root Cap
Thick layer of cells protecting root apical meristem
Zone of Elongation
Cells undergo division and expansion
Root Hair Zone
Epidermal cells extend out.
Root Hair
form where root is not elongating
