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Tissues and the Primary Growth of Stems (internal organization of stems:…
Tissues and the Primary Growth of Stems
Ancient plants
derived from algae that washed up on shore
leaves to capture sunlight more effectively
leaves vary in size depending on [climate]
developed stems and roots
2 mutations occured
stems and leaves conserve more H2O
enhance roots ability to capture CO2 and photosynthesis
body of a herb
secondary plant body
Primary plant body
herb is a plant that never becomes woody
angiosperms
eudicots
monocots
informal classification of flowering plants
basal angiosperms
Basic types of cells and tissues
collenchyma
primary walls thin but thick in some spots (corners)
exhibits plasticity
allows plant to form to increase and decrease in pressure or tension, stays in new shape
present just under epidermis or bands by vascular bundles
by itself unable to support itself. needs parenchyma cells :<3:
require more glucose
usually produces in shoot tips
can absorb water powerful enough to swell
sclerenchyma
has primary wall and thick secondary wall that almost always lignified
elastic, can be deformed and return to shape
different
develop from parenchyma cells in mature organs
can support plant by itself
cannot swell do to absorption of water, very rigid
two types of cells
conducting
tracheids
long and narrow, contain no perforations, dead at maturity
vessel elements
short and wide, 1-2 perforations, dead at maturity
mechanical
sclereids
more or less isodiameter, often dead at maturity
fibers
many dead, those alive used for storage
new cells have primary walls, are parenchyma cells
pit-pair is the meeting of 2 pits in secondary wall :hole:
Parenchyme
mass of these cells= parenchyma tissue
most common is soft parts of plants
relatively inexpensive to make
only good for thin walls
chlorenchyma cells and parenchyma cells involved with photosynthesis
many chloroplasts
Transfer cells
mediate short distance transportation
glandular cells
secrete nectar and fragrances
also parenchyma cells
limited chloroplasts
some function by dying at maturity
phloem conducts nutrients over long distances
external organization of stems
stem is an axis
shoot=stem plus leaves
stem organization
internodes, region between nodes
leaf axil, point just above stem/leaf attachment
within leaf axil is axillary shoot=miniature shoot
leaf scars left when leaves fall in winter :fallen_leaf:
nodes, where leaves are attached :leaves:
bud is covered in waxy bud scales, protects leaves
end of each stem is terminal bud
arrangement of leaves on a stem= phyllotaxy
important so that leaves do not shade each other
one leaf present= alternate phyllotaxy
2 leaves=opposite phyllotaxy
3 or more= whorled
distichous phyllotaxy= 2 rows of leaves
decussate phyllotaxy= 4 rows
spiral phyllotaxy=each leaf is located slightly to the side of ones immediately above and below it, forms a spiral
stolons, also called runners
are able to explore due to long/thin internodes
once it finds suitable microhabitat,
grows shorter and more vertical
new roots established, resembles new plant
types of stems
corms=vertical and thick with thin leaves
rhizomes, fleshy horizontal stems. allows growth underground
all storage roots are subterrainean
bulbs, short and thick/fleshy leaves
tubers, horizontal like rhizomes. grow for short period of time
internal organization of stems: Arrangement of primary tissues
vascular tissue
two types
phloem
sugars and minerals
pick up sugar where it is abundant, takes to where it is needed
leaves
flowers
fruit in summer
storage organ in summer as well
xylem
conducts water and minerals
not a circulatory system
nutrients and wasted carried by xylem either used or evaporated, travel through dead cells
for small organisms that are either unicellular or thin sheet of cells that are separated for nutrients by 5-6 layers
xylem
2 types of conducting cells
tracheids
primary wall of parenchyma cells
secondary wall impermeable to H2O
simple version of secondary wall contains
annular thickenings which are rings that provide surface area for movement
are weak but primary wall free of 2ndary wall
helical thickenings, exists as 1-3 helices interior to primary wall
scalariform thickening, provides strength
tracheary elements with reticulate thickenings, 2nd wall is net shaped
obtain water from other tracheids
contain pit-pairs, aligned set=pit membrane
vessel elements
both are types of sclerenchyma
provide water movement with less friction
must absorb water form parenchyma cells, tracheids, or other vessels
have primary and secondary walls
have region missing form walls called perforation
must be adjacent and each element has 2 perforations
entire stack of vessel elements=vessel
only one perforation
can be meters long
cortex
composed of compacted parenchyma and somtimes collenchyma cells
water based plants have large cortical openings that aid in buoyancy
interior to the epidermis
phloem
2 conducting cells
sieve cells
elongate, spindle-shaped and sieve areas all over surface
evolved first, found in fossils
associated with albuminous cells
help control cell after nuclei dies
sieve tube members
are parenchyma cells, one primary wall
as sieve elements mature, plasmodata in cell develop sieve pores
together form sieve area
small with large ends, stacked end to end
end wall sieve pores form sieve plates
shorter than the plant
evolved same time as the flower
associated with companion cells
load sugars into and out of sieve tubes
sieve elements refer to either
sieve elements nuclei can die but cell lives on
epidermis
outermost surface of plant, one layer of parenchyma cells
exchange of of materials between plant and environment happen here
helps keep water in during uptake or air
protects against bacteria
outer wall encrusted with cutin
builds up a more/less pure layer called cuticle
not enough in severe conditions, extra waxy layer added as well
protects against insects and pathogens
wax and cutin inhibit entry of CO2
contain guard cells with stomatal pore between them
together constitute a stoma
permit entry of CO2
done by
guard cells absorbing H20 and swell, exposing Stoma, allow CO2 to enter
1 more item...
fatty substance that makes wall impermeable to H20 :red_cross:
contain elongated cells that become trichomes or hairs
makes it difficult for animals to land/walk/chew on
vascular bundles
include xylem and phloem
in basal angiosperms, eudicots, arranged in ring called pith
distributed as complex system in moncots
xylem part is called primary xylem, because it is part of primary plant body
phloem is called primary phloem and mixed with
companion cells
or albuminous cells
sieve elements
may be storage for parenchyma and mechanical sclerenchyma as phloem fibers
are collateral, contain phloem and xylem strand parallel to each other
stem growth and differentiation
cells grow longer by creating new cells at tips in region called apical meristems
divide by mitosis
produce progenitor for rest of plant
divide by cytokinesis
region below apical meristems is called subapical meristem
also dividing and growing
visible differentiation visible
some stop growing and start elongating
become first trachieds or vessel elements of vascular bundle
is called protoxylem
contain dead cells at maturity
has to be extensible
young cells of xylem and phloem called provascular cells
largest tracheary element to grow is metaxylem
must have either annular or helical secondary walls
do not have to extensible, feasible secondary wall
size difference (larger) than protoxylem
outer cells of vascular bundle closest to metaxylem called metaphloem
epidermis cells differentiate here
protodem=epidermal cells in early stages of differentiation
ground meristem=equivalent stages of pith and cortex
