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Internal Organization of the Plant Body (Dermal (General Info outer…
Internal Organization
of the Plant Body
Dermal
General Info
outer covering
prevents water loss
protects plants' interior
outermost layer of cells of stems and leaves
Epidermal Pavement Cells
domed, let light through thin primary walls, seal surface of the stem, produce cuticle (cutin and paraffin wax), secrete waterproofing polymers
leukoplasts= produce and store lipids
Dicot
surface layer forms waterproof cover, puzzle piece shaped, tight junctions, randomly dispersed, pairs of guard cells
Monocot
surface layer forms waterproof cover, tapered polygons, pairs of guard cells at regular intervals, aligned parallel arrays
Stomatal Apparatus
subsidiary cells & guard cells
open and close gaps in epidermis that allows exchange of gases to occur
monocot guard cells always found in pairs,
subsidiary cells share cell wall with guard cells
provide water to change shape of guard cells
Trichomes
hairs, glands, and root hairs
hairlike outgrowths of the epidermis
tube extensions from epidermal cells
greatly increase roots surface area for absorption
in most species
reduce water vapor loss
UV shield for photosynthetic cells inside leaf, shade leaf, cut light intensity, slow air movement near stomates, conserves water by preventing vapor to exit leaves
keep leaf surfaces cool
deter herbivores
sharp, scaly, unpalatable, makes difficult for animal to land/walk on and chew leaves, produce secondary metabolites that repel, immobilize and kill
release volatile organic compounds
Vascular
General Info
often at center of plant
conducting cells
distributes/transports materials
Xylem
provide rigid support needed to elevate stems and leaves above the ground
live for a short time, form primary cell wall
Tracheids
long, narrow with slanted end walls
elongate and taper
have pits and pit fields in all walls
end walls fit together to form a long, narrow tube
water moves from one cell to the next through pits or side walls
Vessel Elements
short, barrel shaped
primary walls digested away in end walls
thick ridge around perforation = perforation plate
stacks form hollow columns of water molecules
Phloem
functions:
conduct sucrose from leaves to storage tubers
conduct sucrose from storage tissues to cells that demand more energy
transport amino acids, lipids, micronutrients, hormones, proteins, RNA (long distance signaling molecules)
information super highway
Sieve-tube members
fill with sap that flows through lumen
join end to end to form long tubes of sap
sieve plate with pores in end walls
sieve areas in side walls
two unique proteins: p-protein (cytoplasm) & callose (produced when cell is stressed, around plasmodesmata, makes pores, prevents leakage, plugs end walls if cell is injured)
organelles broken down, degenerate
companion cells
metabolic support cells
connected by plasmodesmata to mature sieve-tube members
contain nucleus & complete set of organelles
resupply proteins needed by sieve tube members
load sucrose into sieve + unload
Ground
General Info
fills space between dermal and vascular tissue
photosynthesis, storage, support
Parenchyma
cells large, thin primary walls
occur throughout the plant body
photosynthesis, storage, secretion
most common cell type, space fillers
metabolic factories - photosynthesis and storage
large volumed cells
isodiametric / octagonal / spherical
thin primary cell walls - 30% cellulose, 30% hemicellulose, 30% pectin
large vacuoles for water and ion storage
functions: wound healing, transfer cells (increase membrane area, increases rate of transport of ions)
Collenchyma
long, flexible cells
occur beneath epidermis of young stems
thick layers of pectin where cells come together
specialized to support young elongated stems and leaf petioles
provide pliant, flexible support
form a solid cylinder under the epidermis or strands of cells under epidermis
unevenly thickened cell walls
primary walls composed of 45% pectin, 35% hemicellulose, 20% cellulose
small diameter, elongated cells
live at maturity
pectin held between walls
Sclerenchyma
thick, lignified secondary cell walls, rigid and waterproof
help support weight of plant
found in roots, stems and leaves
support and protect phloem sieve tube members
add rigid support as non-conducting cells in xylem
made up of fibers and sclereids, which are thick lignified secondary cell walls that die at maturity
fibers
provide rigid support of stems, roots, leaves (hold tissue up, protect nearby cells from pressure)
long, narrow cells with tapered ends
often many cells side by side form bundles
thick secondary cell walls
cell walls contain lignin
sclereids
develop in different shapes
very thick cell walls
form in masses in soft tissues
sometimes occur as sheets
dead at maturity due to rupture of plasmodesmata
can't get water/nutrients to lumen