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Plant Tissues
AP Biology
Typical Plant Structure
• Shoots: above
ground structures
• Roots: below ground
• Structures consist of
three major tissue
systems: ground
tissue, vascular
tissue, and dermal
tissue
Simple vs Complex Tissues
• Simple tissues
consist of only
one cell type
• Complex tissues
consist of more
than one cell
type
Simple tissues
• Parenchyma
• Collenchyma
• Sclerenchyma
parenchyma
Simple Tissues
• Parenchyma: most of
the soft, moist,
primary growth;
pliable, thin, flexible
walls, and many
sided.
• The least specialized
• Generally has a large
vacuole for storage,
secretion
Simple Tissues
• Collenchyma: thicker
walls, but not evenly
thick; provide flexible
support in stalks and
stems. Ex celery strings
• Sclerenchyma: lignin
containing thick walls;
gives strength, retains
moisture—important in
switching to land; stems,
leaf veins, seed and nut
coverings
Complex Tissues
• Xylem
• Phloem
• Epidermis
includes specialized
cells such as guard
cells and sections of
collenchyma and
parenchyma
Xylem: a complex tissue
• Two types of cells:
tracheids and vessels
• Both are dead at
maturity
• The cytoplasm
disappears, leaving
the thick walls
• Water migrates
through these tubes
Phloem: a complex tissue
• Phloem cells
are alive at
maturity
• Sieve cells are
long narrow
cells
• Alongside are
nonconducting
cells called
companion
cells
Vascular Bundles
• Xylem and phloem
are usually together in
vascular bundles
• Arranged differently in
monocots and dicots
in both the root and
the stem
Monocot: distributed
throughout
Dicot: arranged
in a ring in stem
Monocots and Dicots
• One or two
cotyledons
• Classes of
flowering plants
(angiosperms)
• Cotyledon is a seed
leaf, part of the
embryo
Cotyledons
• They look like leaves
and they are the first
plant part you see
when a seedling pokes
its head out of the
ground. Cotyledons
help keep the new
seedling fed until it
can make its own food.
Sometimes cotyledons
are called seed leaves.
Other mono vs dicot
• Monocots: flower
parts in threes or
multiples of three
• Parallel leaf veins
• Dicots: flower parts in
fours, fives, or
multiples of these
• Netlike veins in
leaves
Meristems
• Localized regions of
growth
• Dividing cells (onion root
tip)
• Apical meristem:
lengthens parts in shoots
and roots (primary
growth)
• Lateral meristem:
increases in diameter
(secondary growth)
Vascular cambium adds secondary
xylem and phloem
Cork cambium produces sturdier
periderm that replaces epidermis
Apical meristem
Stem
apical
meristem
Root
apical
meristem
Vascular Cambium
• Produces secondary
xylem and phloem
• Adds diameter
• Wood is the
accumulation of
these secondary
tissues, especially
xylem
Wood
• Is an accumulation of
secondary xylem
• Check pages 516-519
in Chapter 29
• Xylem is added on
the inner surface;
phloem is added on
the outer surface
Vascular Cambium
• Is not active all year
round
• Produces large cells
with thin walls in the
spring (early wood)
• Produces smaller
cells with thick walls
in the dry summer
(late wood)
Growth Rings
• The sections of early
wood and late wood
reflect light differently
• They show up as light
and dark
• These are growth
rings on a tree