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Tissues and growth of stems (External Organization of stems (Stem (leaf…
Tissues and growth of stems
Types of Cells and tusues
Parenchyma
Only thin primary walls
Most Common cell type
Active metabolically
Chlorenchyma cells
Involved in photosynthesis
Numerous chloroplasts
Glandular cells
Secrete
nectar
fragrances
mucilage
resins
oils
few chloroplasts
Thin walls
Transfer cells
Mediate short transport
large plasma membrane
large-scale molecular pumping
Some die and maturity
Collenchyma
Primary walls
Thin in some places
Thick in some places
Tips elongate
collenchyma can be streched
wall exhibits plasticity
require more glucose
Produced in shoot tips, young petioles
Sclerenchyma
Primary wall
Elastic
can be deformed
return to original size
secondary wall
almost always lignified
Develop from parenchyma cells
Conducting Sclerenchyma
Mechanical Sclerenchyma
Long fibers
Elastic secondary walls
Flexible
found in wood
Short sclereids
Brittle and inflexible
hard, impenetrable
shells of walmuts
pits of peaches
produced by cell division
External Organization of stems
Stem
axis
leaf axil
area above leaf attachment
auxiliary bud
Miniature shoot
Phyllotaxy
Positions leaves so not shading one another
Stolons "runners"
Internodes long and thin
leaves dont expand
shoot
stem + flowers, leaves, buds
nodes
leaves attached
internodes
region between nodes
Rhizomes
allow plants to spread underground
tubulers
"potatoes"
Stem Growth and Differentiation
Apical meristems
cells divide by mitosis and cytokenisis
subapical meristem
just below apical meristem
cells dividing and growing
protoxylem
constitute 1st xylems
metaxylem
largest tracheary elements of all
protoderm
early cells of differentiation
pro vascular tissues
young xylem and phyloem cells
Internal Organization of stems
Epidermis
Single layer of parenchyma cells
Prevents loss of water to air
outer walls encrusted with cutin
builds up to make cuticle
layer of wax may be present
inhibit CO2 entry
Defense again fungi, bacteria
guard cells
stoma
allow entry of CO2
open during daytime
swell with water
Cortex
photosynthetic parenchyme
sometimes collenchyma
fit compactly
allows for buoyancy
Vacular Tissues
Xylem
Water and minerals enter
tracheids
vessel elements
entire stack is a vessel
must get water from parenchyma
plasmodesmata in walls
secondary wall impermeable to water
Primary wall uncovered
water makes it collapse inward
perforation
each element must have 2
Phloem
sieve cells
sieve tube members
sieve elements
parenchyma cells
nuclie degenerate but cell stays alive
shorter than the plant
Vascular Bundles
pith
parenchyma similar to the cortex
collateral
Xyloem and phloem parallel
Primary phloem
mixed with sieve elements and companion cells
storage parenchyma and mechanical sclerenchyma