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Chapter 5: Tissues and the Primary Growth of Stems (Internal Organization…
Chapter 5: Tissues and the Primary Growth of Stems
Basic Types of Cells and Tissues
Sclerenchyma
primary wall and secondary wall (lignified)
walls are elastic
supports plant by its strength
walls prevent protoplast from expanding
Two cell types
Conducting schlerenchyma
Mechanical schlerenchyma
short sclereids
form hard, brittle walls
long fibers
flexible, strong, elastic
Collenchyma
Primary cell wall is thin but remains thickened in some areas (corners)
exhibits plasticity
ex) shoot tips
Parenchyma
Glandular cells
Clorenchyma cells
involved in photosynthesis
Parenchyma tissue
soft part of plants
most common type of cell/tissue
primary walls, remain thin
Transfer cells
increase surface area
large scale molecular pumping
some parenchyma cells function by dying at maturity
cell walls are 80-100 nm thick
External Organization of Stems
Parts of Stem
Nodes
where leaves attach
Internodes
regions between nodes
Stolons
runners
Leaf axil
just above where leaves attach
Phyllotaxy
Arrangements of leaves on a stem
Alternate phyllotaxy
opposite phyllotaxy
whorled phyllotaxy
Orientation of leaves at a point
distichous phyllotaxy
2 rows
Decussate phyllotaxy
4 rows
Spiral Phyllotaxy
leaves located slightly to the side of the ones above and below it
Most common
Types of stems
Bulbs
Corms
Rhizomes
Tubers
Dormancy
perennial plants survive harsh conditions
Axillary Bud
covered by bud scales
dormant apical meristem
extreme tip is called a terminal bud
Within leaf axil
main axillary bud = trunk
Internal Organization of Stems: Arrangement of Primary Tissues
Epidermis
single layer of living parenchyma cells
Cutin
fatty substance
impermeable to water
protects against pathogens
inhibits CO2 entry
Guard Cells
stomatal pore between guard cells
Stoma
Permits CO2 entry
Trichomes ("hairs")
make it hard for animals
Cortex
Interior to epidermis
Composed of photosynthetic parenchyma and collenchyma
Vascular Tissues
Xylem
Water & minerals
Tracheary Element
Tracheids
absorb water from other tracheids and pass it on
Vessel Elements
Move water with less friction than tracheids
Perforation
each element has at least 2 perforations
Vessel = stack of vessel elements
Thickening
Annular Thickening
Helical Thickening
Scalariform Thickening
Reticulate Thickening
Circular Bordered Pits
Phloem
Sugars & minerals
Sieve Element
sieve cells
spindle shaped
sieve areas all over
Albuminous cells
sieve tube members
wide sieve pores
stacked end to end
companion cells
load sugars in and out sieve tube members
Parenchyma cells
Maturation
Sieve pores
enlarged plasmodesmata
Sieve areas
Nucleus degenerates but cell remains alive
Vascular Bundles
Xylem + phoelem
surround the pith
collateral
Xylem
primary xylem
Phoelem
primary phoelem
Stem Growth and Differentiation
Apical Meristem
Where growth occurs
Subapical Meristem
visible differentiation begins
region below meristem
protoxylem appear
metaxylem
largest tracheary elements
Vascular Bundles
protophloem
exterior maturing cells
short lived
metaphoelem
cells closest to metaxylem
provascular tissues
Concepts
Body of an herb
leaves
stems
roots
never becomes woody
First Plants
basically washed up algae
stems for structure and transport
modern stems
leaves
storage
survival
dispersal
Flowering Plants
angiosperms
297,000 species
largest division in plant kingdom
basal angiosperms
eudicots
monocots
Plant Bodies
herbaceous body (primary plant body)
woody body (secondary plant body)
Both form by cell division!
Newly formed
small, only have primary wall
Parenchyma cells
When final size is reached, cellulose-synthesizing rosettes deposit secondary wall
secondary wall thickens
lignin is added to walls
plasmodesmata
narrow pits at first
"pit-pair"
