Bio Ch 36
What do roots usually lack?
'supporting collenchyma cells
xylem often has
234 or more extensions called xylem arms
what are transcription factors
DNA binding proteins that regulate the synhesis of RNA from a DNA template
what is a fibrous root system
it has several to many roots of similar size developing from the end of the stem with lateral roots branching off these roots
what is the pericylce
it is just inside the endodermis
what does the pericylce make up
it is made up of a single layer of parenchyma cells that give rise to multicellular lateral roots also called branch roots
the pericycle is involved in forming the
lateral meristems that are responsible for secondary growth in woody plants
what is the path of water up until now
look at pg 765 last paragraph
the cortex is made of primarily
loosely packed parenchyma cells
taproots are characteristic of
many eudicots and gymnosperms-a few trees retain their taproots which become massive as they grow
the root hairs are a ______of the root epidermis that enables it to absorb more water from the soil
modification
prop roots are more common in
monocots than eudicots
because no monocots have secondary growth
no vascular cambium exists in monocot roots
a taproot system consists of
one main root that formed from the seedling's enlarging radicle. Many lateral roots of various sizes branch out from a taproot
water moves through aquaporins only along the
osmotic gradient from a region of higher to lower
the root increases in girth and the vascular cambium continues to move
outward
minerals enter endordermal cells by
passing through carrier proteins in their plasma membranes
phloem is located in
patches between the xylem arms
the cork cambium in the root initially arises from regions in teh
pericycle
the outermost layer of the stele is the
pericycle
the root epidermis is replaced by what
periderm
because it has an inner core of vascular tissue, the primary eudicot root lacks
pitch
in most herbaceous eudicot roots, the central core of vascular tissue lacks what
pith
The main roots of the fibrous root system don't arise from
pre existing roots but from the stem-such roots are called adventitious roots
what does the endodermis do
regulates the movement of water and minerals that enter the xylem in the roots center
What structures do roots have that shoots lack
root caps and root hairs
pathway of water to this point
root hair/epidermis--> cortex--> endodermis-->pericycle-> root xylem
from the endrodermis water and mineral ions enter the
root xylem and water is conducted to the rest of the plant
once water enters the xylem, it is transported upward through
root xylem into stem xylem and from there to the rest of the plant
after passing through the endodermal cells, water enters the
root xylem often at one the xylem arms
the vascular cambium is
sandwhiched between the xylem and phloem
before secondary growth starts in a root, the vascular cambium is
sandwiched between the primary xylem and the primary phloem
woody plants have roots with
secondary growth
the vascular cambium gives rise to what
secondary tissues in woody plants
the root epidermis does NOT
secrete a thick, waxy cuticle in the region of root hairs because this layer would impede the absorption of water form the soil
instead the phloem and xylem are in
separate alternating bundles arranged around the central pitch which consists of parenchyma cells
the roots of many tropical rainforest trees are
shallow and concentrated near the surface in a mat only a few centimeters thick
each root hair is
short but quite numerous
Fibrous roots form in plants with a
short lived embryonic root-the roots originate first from the base of the embryonic root and later from the stem tissue
Root hairs are
short lived tubular extensions of epidermal cells located just behind the growing root top
dissolved sugar (sucrose) is conducted in
sieve tube elements of phloem
xylem does NOT form the central tissue in what
some monocot roots
What is the most common form of stored energy in plants
starch
at the center of a eudicot primary root is the
stele or vascular cylinder
What is the primary function of the root cortex
storage
What does the casparian strips contain
suberin
What are the two kinds of root systems found in plants
taproot and fibrous
How do taproots obtain water
taproot systems extend down into the soil to obtain water located deep underground(TREE)
Many trees have _____roots when they are young and later develop large shallow_____ roots
taproots;lateral roots
Root hairs continually form in
the area of cell maturation closest to the root tip to replaces those that are dying off at the more mature end of the root hair zone
what distinguishes the roots of herbaceous eudicots and monocots
the arrangement of vascular tissues
the symplast is what
the continuum of living cytoplasm, which is connected from one cell to the next by cytoplasmic bridges called plasmodesmata
what is the inner layer of the cortex
the endodermis
what happens as the root increases in girth
the epidermis cortex endodermis and primary phloem are gradually torn apart
the apoplast consists of
the internconnected porous cell walls of a plant along which water and minerals dissolve mineral ions move freely
What increases absorption
the lack of a cuticle and the presence of root hairs
what is carrier mediated transport
the minerals ions are pumped against their concentration gradients-requires energy in the form of ATP
what orients the root to grow downward
the root cap
What happens as the root grows?
the root pushes it way through the soil, cells of the root cap are sloughed off by the frictional resistance of the soil particles and replaced by new cells formed by the root apical meristem. The root cap cells secrete lubricating polysaccharides that reduce friction as the root passes through the soil. The root cap also appears to be involved in orienting the root so that it grows downward. when root cap removed, the root apical meristem grows a new one
What make up the entire plant body
the symplast and apoplast
The water and dissolved minerals that enter the root cortex from the epidermis move in solution along two pathways:
the sypmplast and apoplast
what is the stele called
the vascular cylinder
How do the water and dissolved mineral ions move?
the water and mineral ions can diffuse across the cortex without ever crossing a plasma membrane to enter a living cell
How do fibrous root systems obtain water
they are located relatively close to the surface-are adapted to obtain rain water from a larger area as it drains into the soil
What is the shape of the enderdermal cells
they fit snygly against one another and each has a special bandlike region called a casparian strip on it's radial (side) and transverse (upper and lower) walls
What do root hairs do
they greatly increase the absorptive capacity of roots by increasing their surface area in contact with moist soil(microvilli). Soil particles are coated with microscopically thin layer of water in which minerals are dissolved. The root hairs establish an intimate contact with soil particles which allows efficient absorption of water and minerals
what do buttress roots do
they hold the trees upright and aid in the extensive distribution of the shallow roots
at the onset of secondary growth, the vascular cambium extends out
to the pericycle which develops into vascular cambium opposite the xylem arms
water and dissolve minerals are conducted in
tracheids and vessel elements
the development of root hairs is under the control of two regulatory genes that code for
transcription factors
in swampy or tidal environments where the soil is flooded or waterlogged, some roots grow
upward until they are above the tide level
what is the centermost tissue of the stele
xylem
the root mat does what
catches and absorbs almost all minerals released from leaves by decomposition
lateral roots originate when
cells in a portion of the pericycle start dividing, as it grows, the lateral root pushes through several layers of root tissue before entering the soil
one of the major componenets of cells walls is
cellulose
what is periderm
composed of cork cells and cork parenchyma
what composes the bulk of a herbaceous eudicot
cork
as the vascular cambium divides to produce secondary tissue, it eventually forms a
cylinder of vascular cambium that continues to divide producing secondary xylem (wood) tot he inside and secondary phloem(inner bark) to the outside
what is a radicle
embryonic root
in a herbaceous eudicot, a single layer of protective tissue called the what covers its rotos
epidermis
the layers of monocots starting from the outside are
epidermis cortex endodermis and pericycle
pith is what
ground tissue found in the centers of many stems and roots
what are aquaporins
integral membrane proteins that facilitate the rapid transport of water across the membrane
The oxygen that root cells need for aerobic respiration diffuses from air spaces in the soil into the
intracellular spaces of the cortex and from there into the cells of the root
what is the stele or vascular cylinder
a central cylinder of vascular tissues
as a result, the pericycle links the separate sections of vascular cambium so that the vascular cambium becomes
a continuous loop of cells in cross section
what is suberin
a fatty material that is waterproof
How do we know this
a microscopic examination of the parenchyma cells that form the cortex often reveals numerous amyloplasts which store starch
each lateral root has all the structures of
a normal root that it came from
What do the large intracellular spaces provide?
a pathway for water uptake and allow for aeration of the root
what is a root cap
a protective thimblelike layer many cells thick that covers the delicate apical meristem
each root tip is covered by
a root cap
the xylem in monocot roots doesnt form
a solid cylinder in the center
cellulose does what
absorb water like a sponge
prop roots are
adventitious roots that develop from branches r a vertical stem and grow downward into the soil to help support the plant in an upright position
these plants have primary growth at
apical meristems and secondary growth at lateral meristems
water enters by osmosis both directly across the lipid bilayer of the endodermal plasma membrane and through
aquaporins
Why do roots lack that?
because the soil supports the root although roots as they age may develop some sclerenchyma cells
Trace the path of water
beginning with root hairs, most of the water enters the root moves along the cell walls rather than enter the cells
swollen bases or braces called
buttress roots