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Roots (Other types of Roots and Root Modifications (Root Nodules and…
Roots
Other types of Roots and Root Modifications
Mycorrhizae
Ectomycorrhizal and endomycorrhizal
Ectomycorrhizal doesn't invade, endomycorrhizal does
Root Nodules and Nitrogen Fixation
Only some prokaryotes can use N2
Infection thread penetrates cells and allows nitrogenous compounds to form
Plant gives sugars to bacterium
Contractile Roots
Become anchored and pull bulb deeper
Caused by changes in cortex cells
Aerial Roots of Orchids
Epiphytic, living attached to branches of trees
Velamen acts as waterproof barrier
Haustorial Roots of Parasitic Flowering Plants
Secrete adhesive or grow around small branch or roots
Penetration occurs through force or expansion
Prop Roots
Grow above ground
Secondary growth makes roots woody
Roots of Strangler Figs
Roots cling to tree and grow downward
"Strangles host"
Reach soil and branch out
Storage Roots
Long term storage for carbohydrates
Carbohydrates stored in root to produce shoot in spring
Annual plants can survive without storage
Origin and Development of Lateral Roots
Crushes endodermis
Destroys cortex and epidermis and emerges with root cap
Root primordium swells into cortex
Initiated by cell divisions in pericycle
Endogenous origin
Internal Structure of Roots
Zone of Elongation
Minerals penetrate root
Protoderm, epidermis, and vascular tissues
Cells enlarge
Zone of Maturation/ Root Hair Zone
Cortex cells transfer minerals from the epidermis to the vascular tissues
Plasmodesmata
Root hairs increase absorption of water and minerals
Casparian strips
Lateral roots are initiated in the pericycle
Root Apical Meristem
Quiescent center is inactive until it's damaged
No disruptions because leaf primordia, leaf traces, axillary buds
Mature Portions of the Root
Root hairs die and degenerate
Absorption of water and minerals greatly reduced
Endodermis helps keep water in against the root pressure
Root Cap
Protection for the root apical meristem
Starch grains are digested, dictyosomes secrete mucus
Regeneration
External Structures of Roots
Organization of Root Systems
Seed plants have singular prominent taproot
Fibrous root system
Most Monocots can't undergo secondary growth
Adventitious roots increase the absorptive and transport capacities
Lateral roots branch out
Structure of Individual Roots
Dictyosomes of root cap cells secrete mucigel for roots to ease through the soil
Root hairs increase surface area
Growth and length occur in the shoot
Respiration of root hairs + soil water = ions for the roots to absorb