Plant Structure and Growth
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Roots anchor the plant in the soil, absorb
minerals and water, and store food
Monocots have a fibrous root consisting of a
mat of thin roots that spread out below the
soil surface
Dicots have a taproot consisting of one large,
vertical root that produces many smaller
lateral roots
◦ Often store food
 Carrots, turnips, beats
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Increase the surface area of the root
enormously
Extensions of individual epidermal cells on
the root surface
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Roots that raise above ground from stems or
leaves
Function as props that help support tall
stems
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Shoots consist of stems and leaves
Stems are alternating systems of nodes, the
points at which leaves are attached, and
internodes, the stem segment between nodes
The angle formed by each leaf and the stem
is an axillary bud that has the potential to
form a vegetative branch
◦ Most young plants’ are dormant and growth is
usually concentrated at the tip, called the terminal
bud
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Phenomenon where axillary buds are put into
a state of dormancy so that the terminal bud,
or apical meristem receives all the nutrients
Increases the plant’s exposure to light
Under certain circumstances, it may be
stopped and the axillary buds are allowed to
grow
◦ If top is eaten by an animal
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Stolons: runners of strawberry plants, grow
on the surface of the ground and enable a
plant to colonize large areas asexually when
the single parent plant fragments into many
smaller offspring
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Rhizomes: ginger plants, are horizontal stems
similar to stolons except that they grow
underground
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Tubers: potatoes; swollen ends of rhizomes
specialized for storing food
Bulbs: onions, vertical underground shoots
consisting mostly of the swollen bases of
leaves that store food
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Main photosynthetic organs of most plants
Generally consist of a flattened blade and a
stalk called the petiole which joins the leaf to
the node of the stem
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The dermal tissue, or epidermis, is generally
a single layer of tightly packed cells that
cover and protect all young parts of the plant
◦ Root hairs are extensions of this tissue
◦ Secretes a waxy coating called the cuticle that helps
retain water
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The vascular tissue, in involved in the
transport of materials between roots and
shoots
◦ Xylem and Phloem
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Tracheid and vessel elements are elongated
cells that are dead at functional maturity, and
found in xylem
◦ Their secondary walls are interrupted by pits,
thinner regions where only primary walls are
present
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Sieve-tube members are alive at functional
maturity, lack organelles
◦ Nonconducting companion cells are connected to
the sieve tubes and serves that cell with nutrients
and help load sugar into the tubes
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The tissue that is neither dermal nor vascular
In dicot stems, it is divided into pith, internal
to the vascular tissue, and the cortex,
external to the vascular tissue
Functions in photosynthesis, storage, and
support
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Parenchyma
Collenchyma
Sclerenchyma
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Thin and flexible walls with a large central
vacuole
Transport sap in phloem
Perform most of the metabolic functions,
synthesize and store various organic
products
Fleshy tissue of most fruit is composed of
parenchyma
“Stem Cells” of the plants
◦ Least specialized, but can be turned into other cells
 Can grow an entire plant from one parenchyma cell
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Unevenly thicker cell walls
Grouped in strands or cylinders and help
support young parts of the plant shoot
◦ Strings of celery
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Provide support without restraining growth
◦ Do not have lignin in cell wall to make it strong
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Thick cell walls, cannot grow, function as
support elements
Functionally mature cells are dead
◦ Provide a skeleton that supports the plant
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Vessel elements and tracheids are
sclerenchyma cells
Fibers and sclerids function solely in support
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Primary growth: elongation of the plant,
achieved by apical meristems
Secondary growth: progressive thickening of
roots and shoots, achieved by lateral
meristems
◦ Cork cambium replaces the epidermis with a
secondary tissue, such as bark, that is thicker and
tougher
◦ Vascular Cambium adds layers of vascular tissues
 Wood is the secondary xylem that accumulates over
the years