BFG Ch 3: stems Flashcards
(23 cards)
6 clearly defined areas of herbaceous stems
epidermis cuticle (made of waxy cutin) cortex pith vascular bundle vascular cambium
epidermis
single layer of outer boundary cells
cuticle
layer of waxy cutin superimposed on and impregnating the outer walls of epidermal cells
stems can be _____ or ______
smooth or hairy
pith
center of the stem
composed of soft, spongy parenchyma cells, which store and transport nutrients throughout the plant.
pith is encircled by a ring of xylem
cortex
outermost layer of the stem or root of a plant, bounded on the outside by the epidermis and on the inside by the endodermis. It is composed mostly of differentiated cells, usually large thin-walled parenchyma cells of the ground tissue system.
The outer cortical cells often acquire irregularly thickened cell walls, and are called collenchyma cells. Some of the outer cortical cells may contain chloroplasts. It is responsible for the transportation of materials into the central cylinder of the root through diffusion and may also be used for food storage in the form of starch.
Vascular bundle
consists of large, water conducting cells of the xylem tissue
toward the outside are food-conducting phloem cells that are smaller.
primary xylem and primary phloem
Vascular cambium
a meristematic tissue whose cells divide laterally and so result in an increase in the stem’s diameter during its secondary growth process
Primary tissues
all cells in an herbaceous stem; established by the apical meristem
secondary phloem, secondary xylem formed by what?
formed by the vascular cambium
What gives the stem its flexibility?
the softness of the pith and cortex cells
what arrangement of xylem/phloem allows them to branch into leaves?
their arrangement into small bundles
How to tree trunks become so thick?
two lateral meristems:
vascular cambium
cork cambium
what side of the vascular cambium becomes secondary xylem?
the inner side; the protoplasm dies and they become wood cells.
The tree trunk is always thicker than what?
its bark
Cork replaces what as a protective tissue in a woody stem?
the epidermis
Vascular cambium expands in ___ directions
three. out, in, and side-to-side
wood is _______, inner bark is _________.
secondary xylem
secondary phloem
What waterproofs cork?
suberin
sapwood vs. heartwood
most recently formed wood, closest to the cambium, conducts water up the tree trunk = sapwood
inner area of the trunk = heartwood; cells of which are plugged with chemical substances and cellular debri
vascular rays
the way that heartwood gets its waste substances from the inner bark
width of annual rings
thicker for more rainfall, thinner for less rainfall
larger at the beginning of each growing season
monocot stems
tons of vascular bundles are scattered throughout the stem
surrounded by uniform masses of thin-walled cells
no secondary growth
trunk thickening in large monocots results from repeated formation of scattered vascular bundles
gives them flexibility in high winds. Sometimes stems are hollow (bamboo) with fibers
