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Tissues & the Primary Growth of Stems (Stem Growth and Differentiation…
Tissues & the Primary Growth of Stems
Basic Type of Cells & Tissues
Collenchyma
primary wall
thin in some areas
thick in other areas
requires glucose for production
exhibits plasticity
layer just under the epidermis
or as bands located next to vascular bundles
can be stretched
Sclerenchyma
two types of walls:
primary walls
thick secondary wall
both are elastic
they can be deformed but return back to normal
develop from Parenchyma cells
in mature organs after they have stopped growing
wind, animals, or snow can be deforming
supports the plant by its strength alone
walls are strong
prevent the protoplast from expanding
two types:
conducting sclarenchyma
tracheids
long and narrow w/ tapered ends
contain no perforations
dead at maturity
found in all vascular plants
vessel elements
short and wide w/ perpendicular end walls
most contain one or two perforations
dead at maturity
almost exclusively in flowering plants
only found in few ferns, horsetails, and gymnosperms
mechanical sclerenchyma
sclereids
more or less isodiametric
often dead at maturity :
fibers
long
many types are dead, other types remain alive
involved in storage
Parenchyma
only primary walls that are thin
most common cell & tissue
all soft parts of plants
active metabolically
Subtypes:
Chlorenchyma
involved in photosynthesis
numerous chloroplast
thin walls to allow light and CO2 in :star:
pigmented cells as well
flower petals and fruit
Glandular
secrete:
mucilage
resins
fragrances
oils
nectar
few cholorplasts
elevated amounts of dicytosomes and endoplasmic reticulum
transport large amounts of sugar and minerals
Transfer cells
plasma membrane capable of holding numerous molecule pumps
mediate short distance transport of materials
increase surface area
alive at maturity
some function by dying at maturity
External Organization of Stems
stem is an axis
corms
vertical thick stems that have thin papery leaves
shoot is the stem plus any leaves, flowers, or buds
bulbs
short shoots that have thick fleshy leaves
nodes
where leaves are attached
internodes
region between nodes
leaf axil
stem area just above the point where a leaf attaches
axillary bud
miniature shoot w/ dormant apical meristem and young leaves
vegetative bud:
grows into a branch
floral bud:
grow into a flower :
bud is covered by bud scales
a small, corky, waxy cover
phyllotaxy
arrangement of leaves on stem
alternate
leaves one per node
whorled
3 or more leaves per node
opposite
leaves 2 per node
decussate
leaves located in 4 rows
spiral
leaves not aligned w/ their nearby neighbors
distichous
leaves located in 2 rows only
Internal Organization of Stems
Arrangement of Primary Tissues
Vascular Tissues
xylem
conducts water and minerals
enter at roots and are conducted upwards
phloem
distributes sugars and minerals
Xylem
2 types of conducting cells
vessel elemetns
tracheids
Cortex
made of photosynthetic parenchyma and collenchyma
Phloem
2 types of conducting cells
sieve cells
sieve tube members
Epidermis
outermost surface
single layer of living parenchyma cells
all interchange of material from environment happens here
barrier against bacteria and fungi, as well as insects
protects the plant form overheating from the sun :
cutin
fatty substance making wall impermeable to water :no_entry:
stomatal pore
hole permitting CO2 to enter plant :check:
guard cells collect water
Vascular Bundles
formed from xylem and phloem
located just interior to the cortex
arranged in one ring surrounding the pith
pith
region of parenchyma similar to the cortex
Stem Growth and Differentiation
stems grow longer by creating new cells
grown in the tips
region known as shoot apical meristems
cells divide by mitosis and cytoinesis
vascular bundles
protophloem
mature exterior cells
metaphloem
cells closest to the metaxylem
protoxylem
part of primary xylem that differentiates early
adjacent cells are still elongating
metaxylem
part of primary xylem that differentiates late
after adjacent cells have completed elongation
protoderm
epidermal cells in early stages of differentiation
protovasculaar tissues
young cells of xylem and phloem
primary tissues
tissues produced by apical meristems
primary growth
growth and tissue formation that results from apical meristem activity
https://youtu.be/Kv_0udatlh8
