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Ch.5 Tissues and Primary Growth of Stems (External Organization of Stems…
Ch.5 Tissues and Primary Growth of Stems
Basic Types of Cells and Tissues
Parenchyma
primary walls remain thin
mass of parenchyma cells
most common type of cell & tissue
constituting soft part plants
leaves
petals
fruits
seeds
relatively inexpensive to build
Three Sub-types
chlorenchyma
involved in photosynthesis
numerous chloroplasts
thin walls
allow light & C02 to pass through
glandular cells
secrete nectar, fragrances, mycilalage, resigns, and oils
few chloroplasts
elevated dictyosomes & ER
transport sugar & minerals
transform then transport
transfer cells
parenchyma cells
mediate short distance of material
conducts nutrients over long distance over long distances in phloem
Collenchyma
primary walls thin in some areas
thickened in other areas
mostly corners
wall exhibits plasticity
ability to be deformed
present under epidermis or as bands next to vascular bundles
present in elongating shoot tips
long
flexible
unable to hold up stem
thick walls require more glucose
Sclerenchyma
both primary & thick secondary wall
walls elastic
can be deformed
return normal when pressure released
develop from parenchyma cells in mature organs
stop after growth
supported by collenchyma until grown
sclemchyma supports by strength alone
two types
mechanical
sclereids
short
isodiametric
hard
fibers
long
flexiable
many dead, other alive
conducting
tracheids
long, narrow
tapered ends
contain no preforations
dead at maturity
found in all vascular plants
vessel elements
short, wide
perpendicular end walls
1-2 perforations
dead at maturity
exclusively in flowering plants
Internal Organization of Stems: Arrangement of Primary Tissues
Epidermis
outermost surface
single layer parenchyma cells
interchange between plants & environment
prevents loss of water to air
barrier against invasion
outerwall encrusted w/cutin
fatty substance
makes impermeable to water
resist digestive enzymes
provide defense
cuticle
pure layer
smooth
guard cells
stomatal pore
permit CO2 to enter plant
special radical arrangement of cellulose microfibrils
trichomes
protect from animals
shade
creates layer immobile air next to a leaf surface
Cortex
interior to epidermis
composed of photosynthetic parenchyma and sometimes collenchyma
cells fit compactly
in fleshy stems
ex: tubers, corns, succulents
arenchyma
open tissues w/ large intracellular air spaces
Vascular Tissues
xylem
conducts water & minerals
phloem
distributes sugars & minerals
conducting cells
sclerenchyma
tracheids
shape
long/narrow
short/wide
ends pointed
ends usually flat
secondary wall
annular
helical
scalariform
reticulate
circular bordered pits
vessel elements
sclerenchyma
Vascular Bundles
located interior to the cortex
dictots
ring surround pith
monocots
vascular bundles scattered
collateral
both xylem & phloem strands
primary xylem larger
inner trachea elements smaller
Stem Growth and Differentiation
apical meristems
regions where stem grows longer
creates new cells @ tips
cells divide by mitosis & cytokinesis
produces progenitor cells
subapical meristem
cells growing and dividing
below apical meristem
visible differentiation
certain cells stop dividing, starts elongating
protoxylem
first xylem
metaxylem
longest growth time
largest tracherary elements
exterior cells
protophoelm
exterior cells
extremely short lived
metapholem
identical walls
External Organization of Stems
stem, is an axis
shoot, stem plus leaves, flowers, or buds
flowering plants organization
nodes
where leaves attatched
internodes
regions between nodes
leaf axil
stem area just above point where leaf attatches
axillary bud
miniture shoot w/a dormant apical meristem
several young leaves
bud scales
small, corky, waxy
protect delicate organs
terminal buds
extreme tip of each stem
phyllotaxy
alternate
leaves one per node
opposite
leaves two per node
decussate
leaves located in rows of four
whorled
three or more leaves per node
spiral
leaves not aligned with their nearest neighbors
distichous
leaves located in two rows only
types of stems
stolons
runners
ex: grape vines
internodes long & thin
leaves do not expand
bulbs
short shoots
thick fleshy leaves
ex: onions, garlic, daffodils
corms
vertical
thick stems
thin papery leaves
rhizomes
fleshy horizontal stems
plants spread underground
ex: bamboo, irises, canna lilies
tubers
horizontal
grow short perod
mainly for storing nutrients
ex: potatoes
