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Chapter 8 Mind Map, Fleshy Taproots, Adventitious Roots, Root Tip, Lateral…
Chapter 8 Mind Map
Concepts
functions of roots
anchoring the plant firmly to the substrate
absorbing water and minerals
producing hormones
root anchoring is necessary for the plant to remain upright
roots have an absorptive function but are adapted to its underground environment
cytokinin and gibberellin are important hormones for plant growth
fleshy taproots
examples include: carrots, beets, radishes
plant's main site of carbohydrate storage during winter
roots can specialize for particular tasks
division of labor is crucial in root development
characteristics of structure should be analyzed by function
Other Types of Roots and Root Modifications
storage roots
roots provide long-term storage for carbohydrates
roots are only permanent organs in biennial species
annual plants can survive without this storage capacity
are less available as food than shoots
have a much more stable environment
subject to less extreme changes in temperature and humidity
prop roots
roots grow through the air before reaching the soil
can be between 20 centimeters and 4 meters
transport additional nutrients and water to stem
act as stabilizers for stem
buttress roots
upper-side grows more rapidly than rest of root
brace the trunk from being blow away
aerial roots of orchids
roots spread along bark or dangle freely in the air
root epidermis
velamen is composed of several layers of dead cells
velamen acts as a waterproof barrier
contractile roots
roots contract once in contact with the soil
stem is pulled downward
base of shoot is kept at, or below, soil level
can be important in keeping stem at proper depth
mycorrhizae
soil fungi which have a symbiotic relationship with roots
ectomycorrhizal relationship
with nearly all woody forest plants
fungal hyphae penetrate between cortex cells
fungi do not invade cells themselves
endomycorrhizal association
with nearly all herbaceous plants
hyphae penetrate cortex to endodermis
cannot penetrate Casparian strips
fungi does invade cells
root nodules and nitrogen fixation
nitrogen fixation
chemical conversion of atmospheric nitrogen into usable compounds
nitrogen-fixing bacteria help immensely with this task
infection thread
tube created by nitrogen-fixing bacteria
pushes through cells until it gets to the inner cortex
forces cells to undergo mitosis
mitosis forms a root nodule
root nodule is able to fix nitrogen due to bacterium inside cells
haustorial roots of parasitic flowering plants
haustoria
highly modified roots of parasitic plants
very little root-like structures remain
able to penetrate host and absorb materials
roots of strangler figs
strangler fig germinates where it lands
roots cling to host tree and grow rapidly down
once roots reach soil, upper roots become woody
roots eventually encompass the host tree's trunk
host tree eventually dies by lack of light
Origin and Development of Lateral Roots
lateral roots are initiated by cell divisions in the pericycle
some cells resume mitotic division in the pericycle
small root primordium
root apical meristem is formed and begins to push outward
endodermis is broken for outward growth
vascular tissues connect to parent root
Internal Structure of Roots
root cap
cells at tip of root are constantly undergoing cell division
cells in layers closest to the meristem are meristematic
cells are small and meristematic before moving to tip of root
structure and metabolism change dramatically as cells move
root cap needs to be replaced every 4-5 days
root apical meristem
regular files of cells originate in the meristem
experiences no disruptions from
leaf primordia
leaf traces
auxiliary buds
quiescent center
mitotically inactive central region
cells are more resistant to harmful agents
act primarily as a reserve of healthy cells
when needed, can help replace root cap
zone of elongation
located just behind root apical meristem
cells begin to differentiate but are not mature
tissues are extremely permeable
very short
absorbed minerals are used for root growth
zone of maturation / root hair zone
several processes occur at once
root hairs begin to grow outward
increased absorption of water and minerals
thin cuticle (or layer of fats) appears
cortex cells continue to enlarge
cells transfer minerals from the epidermis to the vascular tissues
oxygen diffuses throughout root from soil or stem
endodermis
made of lignin and suberin
radial walls of cortex
creates an impenetrable, waterproof wall that minerals cannot pass through
Casparian strips
bands of altered walls
involved in controlling the types of minerals that enter xylem
prevent secretory products from glands to seep out
impermeable
mature portions of the root
root hairs only function for a few days before dying
passage cells
cells that only have Casparian strips
once thought to represent passageways for material absorption
cells may only be slow to develop
root pressure
water pressure cause by the absorption of minerals
occurs around root hairs
External Structure of Roots
organization of root systems
lateral roots
also called branch roots
single prominent taproot
much larger than all the other roots
taproot develops the embryonic root (radicle)
radicle becomes the largest root in the system
may also produce further lateral roots
fibrous root system
mass or similarly sized roots
occurs in most monocots and some eudocots
arises because radicle dies during or immediately after germination
adventitious roots
increase absorptive and transport capabilities
these roots do not arise on preexisting roots
these roots are not radicals
eudicot roots
many under secondary growth
increased quantity of healthy, functional wood
monocot roots
most cannot undergo secondary growth
once stem is formed, conducting capacity cannot be increased
adventitious roots are extremely advantageous
structure of individual roots
roots grow by localized growth at the apical meristem
root cap protects root apical meristem
mucigel
secreted by root cap
lubricates the passage of the root through the soil
causes soil to release nutrients
permits ions to diffuse more rapidly towards the root
rich in carbohydrates and amino acids
zones of root
zone of elongation
few millimeters long
here, cells undergo division and expansion
root hair zone
many epidermal cells extend out as narrow trichomes
root hairs only form on a part of the root that is not elongating
Root Function - Anchoring Plant
Zone of Elongation
Lateral Roots
Roots Undergo Secondary Growth
Roots can Specialize for Particular Tasks
