Plant Organ - Root and Stem

Roots

generallly grow downward, in the direction of gravity.

Soil Conditions

greatly affect the extent of root growth.

Plant's Underground Root System

branches out into the soil from the plant's central axis, is often more extensive than its aerial parts.

a.) Taproot System

b.) fibrous system

Two types of root systems.

Root Systems

may develop from the embryonic root in the seed.

Embryonic root

" The Radicle"

Taproot Systems

develops from the embryonic root in the seed.

Taproot

consists of one main root formed from the enlarging radicle with many smaller lateral branch roots.

Lateral Roots

often occur initially in regular rows along the length of the main root.

Dandelion; Herbaceous Eudicot; Taproot System

a ________ is a good example of a common __________ with a __________.

true

true or false: few trees such as hickory, retain their taproots, which become quuite massive as the plants age.

False (downward)

true or false: most trees, have taproots when young and later develop large, shallow lateral roots from which other root branch off and grow upwards.

Gymnosperms

are seed-bearing plants that do not produce flowers.

Pines, Hemlock, and Firs

examples of gymnosperms

Eudicots

are angiosperms that are flowering plants.

Oak, Cherry, Bean, and Daisy

examples of Eudicots

Bundle Scars

Forms within the leaf scars when the vascular tissue that extends from the stem out into the leaf

Terminal bud scale scars

Residue on the stem when the bud resumes growth and the bud scales fall off

Fibrous Root System

the roots of these are adventitious and develop from stem tissue.

Fibrous

several to many roots of the same size that develop from the end of the stem, which smaller lateral roots branching off these roots.

Fibrous

they form in plants in which the embryonic root is short-lived.

Adventitious

do not arise from pre-existing roots but from the stem.

Adventitious Organs

occur in unusual locatinos, such as roots that develop on a stem or buds that develop on roots.

Monocots

are grass or grass-like flowering plants.

Onion, Crabgrass

examples of monocots

Anchorage

roots anchor a plant securely in the soil.

Absorbtion

roots absorb water and dissolved minerals (inorganic nutrients), such as Nitrates, Phosphates, and Sulfates from the soil.

Firm Anchorage

is essential to a plant's survival so that the stem remains upright, enabling leaves to absorb sunlight efficiently.

Conduction

The water and minerals absorbed are conducted by the various parts of the root and shoot systems.

Storage Taproots

Are usually biennials that, as part of the strategy to survive winter, store their food reserves in the root during the first year's growth and use these reserves to reproduce during the second year's growth.

Taproot and Fibrous roots

May be modified for storing food.

Beets, Carrots, Radishes, and Turnips

examples of taproots

Sweet Potatoes

example of fibrous

True

true or false: although roots use some phtosynnthetic products for their own respiratory needs, most are stored and later transported out of the roots when the plant needs it.

Carrot roots

have an extensive phloem for storage.

Leaves; Photosynthesis; Phloem; Storage

surplus carbohydrates produced in the _____ leaves by ______ are transported in the ______, as sugar, to the roots for ______, usually as sugar or starch, until needed.

Root Cap

a protective thimble like that layers many cells thick, covers the delicate root apical meristem.

False (Parenchyma cells)

true or false: as the root grows, pushing its way through the soil, sclerenchyma cells of the root cap slough off by the frictional resistance of the soil partices and replaced by new cells formed by the root apical meristem toward its outer side.

Root cap cells

secrate lubricating polysaccharides that reduce friction as the root passes through the soil.

root cap

involved in orienting the root so that it grows downward.

root hairs

short-lived, unicellular extentions of epideral cells near the growing root tip.

root hairs

typically less than 1cm or 0.4in in length, but are quite numerous.

root hairs

form continually in the area of cell maturation closest to the root tip tp replace those that are dying off at the more mature end of the root hair zone.

root hairs

they greatly raise the absorptive capacity of the root by increasing the surface are in contact with the moist soil.

root epidermis

does not secrete a thick, waxy cuticle.

Absorption

the lack of a cuticle and the presence of root hairs increase _______.

Epidermis

lacks pith, a ground tissue in the centers of many stems and roots.

Cellulose

one of the major components of cell walls. it absorbs water as sponge does.

True

true or false: most of the water that enters the root moves along the path of least resistance along the cell walls rather than entering the cells.

cortex

ground tissue which is composed of primarily and loosely arranged parenchyma cells with large intercellular spaces, makes up the bulk of the root.

cortex

lacks supporting collenchyma cells, although it may develop some supporting sclerenchyma cells as it ages.

storage

primary function of the root cortex.

endodermis

inner layer of cortex which controls the amounts and kinds of water and dissolved materials that enter the xylem in the roots center.

endodermal cells

fits snugly against one another and each cell has a special bandlike region called a casparian strip on its radial and transverse walls.

radial

side

transverse

upper and lower

casperian strip

is a band of waterproof material that ensure water and minerals enter the xylem only by passing through the endodermal cells.

casperian strip

contains suberin.

Osmosis

water enters endodermal cells by _____.

inorganic minerals

enter endodermis by passing through carrier proteins in their plasma membranes.

endodermis

controls what kinds of dissolved minerals and how mcuh of each kind move from the soil into the vascular tissue of the root and from there to the rest of the plant body.

symplast and apoplast

the water and dissolved minerals that enter the root cortex from the epidermis move in solution along two pathways, the ___________, until they reach the endodermis.

Plasmadesmata

continuum consisting of the cytoplasm of many plant cells which is connected from one cell to the next by _________.

true

true or false: some dissolved mineral ions move from the epidermis through the cortex.

continuum

consists of the interconnected porous cell walls of a plant, along which water and inorganic mineral ions move freely.

water and mineral ions

the _____ and ______ diffuse across without ever entering a living cell.

pericycle

composed of parenchyma cells that remain meristematic, gives rise to lateral roots.

lateral roots

originate when a portion of the pericycle starts dividing. it pushes through several layers of root tissue before entering the soi.

pericycle

involved in forming the lateral meristems that produce secondary growth in wood roots.

Xylem

centermost tissue of th stele, often has two, threem for, or more extentions, or "xylem arms".

tracheids and vessel elements

conduct water and dissolved minerals.

root xylem

after passing through the endodermal cells, water enters the ______, often at one of the xylem arms.

Phloem

located in patches between the xylem arms.

sieve-tube elements

coducts carbohydrates (sucrose)

sugar

is made in photosynthesis.

sugar

is used for growth and maintenance of root tissues or stored, usually as startch.

starch

sugar is stored as _____.

sugar

is used for growth and maiintenance of tissues.

vascular cambium

this gives rise to secondary tissues in woody plants, and is sandwiched between the xylem and phloem.

primary eudicot root

lacks a pith, a ground tissue found in the centers of many stem and roots.

monocot roots

are considerably more varied in internal structure than eudicot roots are.

xylem in the monocot root

does not form a solid cylinder of vascular tissues in the center.

phloem and xylem

are in separate alternating strands that in cross section are arranged in a circle around the centrally loacted pith, which consists of parenchyma cells.

true

true or false: because monocos do not have true secondary growth, no vascular cambium exists in monocot roots.

secondary growth

plants that produce stems with secondary growth also produce roots with ______.

true

true or false: the production of secondary tissues in the roots of woody plants occurs some distance back from the root tip is the resultof the activity of two latereal meristems, the vascular and cork cambium.

true

true or false: major roots of trees are often massive and have both wood and bark.

temperate climates

in _______, the wood of both roots and stems exhibits annual rings in cross section.

adventintious roots

aften rise from stem nodes.

nodes

regions ofthe stem where leaves are attached.

pandanus

has an elaborate set of aerial prop roots, adventitious roots that arise near the base of the stem and provide additional support.

true

true or false: many aerial advn=entitious roots are adapted for functions other than anchorage, absorption, conduction, or storage.

prop roots

are most common in monocots.

corn and sorghum

both are monocots, are herbaceous plants that produce prop roots.

red mangrove, and banayan

also produce prop roots.

True

true or false: the roots of many tropical rainforest trees are shallow and concentrated near the surface in a mat.

buttress roots

swollen basses and braces. hold the trees upriht and aid in the extensive distribution of the shallow roots.

fig tree, terminalia arjuna, and ficus macrophylla

examples of a buttress roots.

tropical rainforest trees

typically possess elaborate buttresses that support them in the shallow, often wet soil.

Swampy or tidal environments

In _____, some roots grow upward until they are above the high tide level.