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Chapter 7 Roots - Coggle Diagram
Chapter 7 Roots
Other Types of Roots & Root Modifications
Storage roots
Prop Roots
Transport additional nutrients and water
Buttress roots
Certain tropical trees
tall
platelike
upper side grows more rapidly
Aerial Roots of Orchids
Many are epiphytic
living attached to the branches of trees
adapted to drought conditions
Water from orchids can be used for the tree
Contractile roots
may be more common than generally appreciated
Mycorrhizae
Two main types of relationships
Ectomycorrhizal relationship
Nearly all wood forest plants
fungal hyphae
between outermost root cortex cells
never invade
Endomycorrhizal association
Herbaceous plants
hyphaee penetrate the rot cortex
cant pass the Casparian strip
Symbiotic relationship
with soil fungi
Root Nodules & Nitrogen Fixation
Nitrogen fixation
chemical conversion
atmospheric nitrogen into usable compounds
Infection thread
Bacterium sits in this tube
Root nodule
adjacent cortical cells undergo mitosis
Haustorial Roots of Parasitic Flowering Plants
Haustoria
parasitic plants
highly modified
Roots of Strangler Figs
Grow as epiphytes
perched on branch of host tree
birds eat the fruit
deposit the seed on another tree
Eventually encases tree
Causes tree to die
most likely due to it not being able to photosynthesize
Internal Structure of Roots
Root cap
Root apical meristem
Root apical meristem
Quiescent center
Mitotically inactive central region
Zone of Elongation
Behind root apical meristem
where cells expand
Zone of Maturation/Root Hair Zone
Root hair grows outward
greatly increasing absorption of water
Endodermis
cylinder
Casparian strips
band of altered walls
controls the types of minerals
that enter the xylem water stream
Pericycle
Irregular region
of parenchyma cells
Between
Vascular tissue
And endodermis
Mature Portions of the Root
Passage cells
Thought to be passageways for minerals
Just slow to develop
Root pressure
Due to absorption of minerals
External Structure of Roots
Organization of Root System
Fibrous root system
Most monocots
Some eudicots
mass of many similarly sized roots
Radicle
Taproot develops
From embryonic root
Lateral roots
Branch roots
Adventitious roots
Do not arise on pre-existing roots
not radicles
Increase the absorptive/transport capacities
Structure of Individual Roots
Root Cap
thick layer of cells
protects root apical meristem
Mucigel
Complex polysaccharide
Secreted by dictyosomes of root cap cells
Zone of elongation
behind root cap
and root apical meristem
cells undergo division
cells undergo expansion
Root hair zone
Narrow trichomes
Root hairs
on the root that doesnt elongate
Origin & Development of Lateral Roots
Lateral roots
initiated by cell division
in pericycle
Endogenous origin
initiated deep within the root