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Tissues and the Primary Growth of Stems (External organization (shoot…
Tissues and the Primary Growth of Stems
External organization
nodes
internodes between nodes
where leaves are attached
leaf axil
axillary bud within
bud is covered by bud scales
terminal bud
end of stem
phyllotaxy
arrangement of leaves
prevent overshadowing
types
alternate
opposite
whorled
distichous
spiral
decussate
shoot
bulbs
short with thick leaves
corms
thick stem with thin leaves
rhizomes
allow plant to spread underground
tubers
storing nutrients
Internal organization
epidermis
exchange between plant & environment
cutin
cover outer walls
impermeable to water
cuticle formed for water retention
stoma
guard cells
stomatal pore
trichomes (hair)
cortex
vascular tissues
phloem
distributes sugars and minerals
two types of conducting cells (sieve element)
#
sieve tube members
sieve cells
elongate, spindle shaped, sieve areas distributed all over surface
plasmodesmata becomes sieve pores
clusters are called sieve areas
sieve tube
stacked sieve areas
sieve plates
large pores
nuclei degenerate but cells stay alive
xylem
conducts water and minerals
two types of conducting cells (treachery element)
#
vessel elements
tracheids
annular thickenings
helical
scalariform
reticulate
circular border pits
pit membrane
perforations in primary wall
vessel elements->vessel
vascular bundles
xylem and phloem occurring together
primary xylem
primary phloem
arranged in one ring surrounding pith
collateral
Growth and differentiation
shoot apical meristems
new cells at tip of stem
mitosis and cytokinesis
subapical meristem below
protoxylem/protophloem
first to appear
metaxylem/metaphloem
most time to grow; largest
produces primary tissues
results in primary growth
protoderm
in early stages of differentiation
provascular tissues
young cells of xylem and phloem
ground meristem
young cells of pith and cortex
Basic types
parenchyma
#
cells - thin, primary walls
most common type
soft leaves, petals, fruits & seeds
subtypes
chlorenchyma
photosynthesis
numerous chloroplasts
glandular
secrete nectar, fragrances, resins & oils
transfer
transport via pumps
collenchyma
primary wall varies in thickness
plasticity
requires more energy :explode:
protection :lock:
sclerenchyma
primary & thick secondary walls
secondary walls can form pits/pit-pairs
elastic
best in mature plant
rigid/support
two types
mechanical
short sclereids
brittle/inflexible
long fibers
flexible
conducting
