lecture 14, Roots Flashcards
what is pando?
the heaviest and oldest living organism on earth, known as the trembling giant and contains a massive underground root system
where did roots evolve from?
subterranean portion of ancient vascular plants. evolved from rhizoids which are protuberances that extend from the lower epidermal cells of bryophytes and algae
what is stele?
primary tissues in a vascular plant. vasculature developed from solid cylinder in protostele
what is the siphonostele?
central pith surrounded by vascular tissue
over evolutionary time, what did the protostele evolve into
siphonostele and then the eustele
what does the stele contain?
pith, leaf gap, and phloem
the pith evolves in the middle of the stele, so no vasculature surrounds this ground tissue. the leaf gap is where vascular tissue goes off to leaves; gap is where parenchymal cells of leaf develop. the phloem is on the outside always
how did microphylls evolve?
evolved as outgrowths, enations
-single strand of vasculature
-protosteles
-no leaf gap
how did megaphylls evolve?
by fusion of branch systems
-siphonostele
-pith and leaf gap
-common to all vascular plants
how did roots evolve?
as part of the apical-basal meristem; primary tissue extensions into the soil- not as lateral appendages like the leaves
characteristics of a monocot:
-contain a single cotyledon
- long narrow leaf, parallel veins
-vascular bundles scattered
-floral parts in multiples of 3
characteristics of a dicot:
- two cotyledon
- broad leaf, network of veins
-vascular bundles in a ring
-floral parts in multiples of 4 or 5
what is the dicot root structure?
vascular bundle is in the center, xylem matures from proto to meta, phloem is on the outside, surrounded by pericycle
primary growth in dicot roots comes from and gives rise to …
comes from the procambium, which give rise to:
1. vascular tissues, phloem and xylem
2. non-vascular, pericycle, one/more layers that surrounds the bundle
what is secondary growth composed of in dicot roots?
vascular cambium –> secondary vascular tissue
cork cambium –> periderm- cork tissue
what happens during secondary growth?
- growth of secondary xylem and phloem crushes primary phloem forming fibers
- secondary phloem and xylem form rings separated by the vascular cambium
- periderm in most woody roots provides protective layer - replacing epidermis
what happens after 1 year of secondary growth?
- epidermis sloughing off
- periderm developing
- primary phloem crushed into fibers
- secondary vasculature growing
what is the monocot root structure
xylem and phloem both in ring shape, xylem is in the inner ring and phloem the outer.
contains a center of vasculature that has parenchymal cells (pith)
primary and secondary single layer in a root?
primary: epidermis
secondary: periderm
what are the specialized structures in the roots:
root cap, mucigel sheath, root hairs
what is the specialized dermal root structures?
- root cap:
- detection of gravity
- lubricates passage of cells through soil
- secretes mucilage - mucigel sheath:
- mucilage secretion - Root hairs:
- single cell wide
- water acquisition
what are the components of root ground tissues?
cortex, endodermis, casparian strip
what does the casparian strip contain?
suberin, lignin, and a waterproof layer that protects interior
how does lateral root development occur?
arises from pericycle, occurs some distance behind region of elongation, new lateral root primordium pushes through the cortex
what are the main functions of the root
- absorption and conductance
- anchoring
- storage
- symbiosis
