PLANT STRUCTURE
CELLS AND TISSUES
External Structure
Morphology
The study or science of the form,
structure, and development of plants
Internal Structure
 Anatomy
A branch of morphology that deals with the
structure of organisms;
The study of body structures
 Histology
The science that deals with the microscopic
structure of plant or animal tissues
Major Plant Classes
Gymnosperms
narrow-leaved, evergreen trees
Angiosperms
broad-leaved, flowering plants
Angiosperm Subclasses
Monocotyledons
embryo has one cotyledon
Dicotyledons
embryo has two cotyledons
Life Cycle of Corn – A Monocot
Germination
“awakening of the embryo”
Water
Radicle – primary root
Plumule – primary shoot
Coleorhiza – protective sheath for radical
Coleoptile – protective sheath for plumule
Maturing Corn Plant
Adventitious roots
a.k.a. anchor, brace, or prop roots
grow from shoot axis (not the radical)
add support
Maturing Corn Plant
Flowers
Reproductive structures
Female – pistillate
form ears of corn
Male – staminate
form tassels
Pollination and Fertilization
Pollen from the mature tassels fall upon
the silks (pistillate filaments)
Fertilization occurs when the mature
pollen grains release sperm that ultimately
fertilize the ovaries
Fruit Formation
Fertilized ovaries develop into fruit
Caryopsis
fruit enclosing true seed
Mature, dry fruit (kernels) harvested,
stored, and planted when conditions are
favorable for growing
CELL FUNCTIONS
o Manufacture, transport, store food
o Uptake and transport water and nutrients
o Structure/support
o Suppress water loss
o Divide/form new cells
Differentiated cells form tissues and
tissues form organs
CELL COMPONENTS
oCell membrane
oCell wall
o3 layers:
oPrimary Cell Wall
oSecondary Cell Wall
oMiddle lamella
CELL COMPONENTS
Protoplast
Living portion of cell
Surrounded by cell plasma membrane
Contains:
cytoplasm
endoplasmic reticulum
ribosomes
plastids
mitochondria
dictyosomes (golgi bodies)
microtubules
glyoxysomes
lysosomes
vacuoles
nucleus
3 major permanent cells:
parenchyma
collenchyma
sclerenchyma
CELL PROCESSES
- Cell division/growth
Specific areas are active:
Root tips, stem tips (apical)
Cambium (dicots)
Intercalary Meristem (monocots)
- Enlargement and Differentiation
forms Tissues
BASIC KINDS OF TISSUES
Meristematic
- actively dividing cells
- differentiate into other tissues and organs
Permanent
- develops from meristematic
- differentiated fully
TISSUES
- Organized groups of cells with common
origin and function
may be:
simple (one cell type)
complex (two or more cell types)
- Simple e.g. – epidermis, parenchyma,
sclerenchyma, collenchyma, and cork
- Complex e.g. – xylem, phloem
4 tissue systems:
meristematic
vascular
dermal
ground (fundamental)
Meristematic Tissue
specialized regions of active cell division
- apical meristems (primary growth)
- axillary buds (shoot’s insurance policy)
- lateral meristems (secondary growth)
- intercalary meristems (grasses)
Vascular Tissue
composed of two types of compound
tissues:
xylem (conducts water/minerals
up from roots)
phloem (conducts food
throughout plant)
Small “groups” of xylem and phloem called:
Vascular Bundles
xylem forms to inside
phloem forms to outside
Fibers (sclerenchyma) often form next to
vascular bundles
Dermal Tissue
outer cell layer in young stems, roots, and
leaves
variations:
root hairs
multiple epidermis
cutin (waxy substances; not on roots)
replaced in older portions of roots/stems by bark
Ground (fundamental) Tissue
all tissues under epidermis not vascular
or meristematic
constitutes most of the primary body of
a plant
three kinds of cells:
parenchyma, collenchyma, sclerenchyma
STEM ANATOMY
Epidermis
- usually single layer
- protects stem
- usually cutinized
- porous
STEM ANATOMY (cont)
Cortex
- surrounds vascular bundles
- surrounded by epidermis
Vascular Cambium
- produces secondary growth in dicots only
- increases stem diameter
Woody Stems (dicots only) – bark formed from
vascular cambium outward
STEM ANATOMY (cont)
Cortex
- beneath epidermis
- encircles inner vascular tissue
- comprised of:
parenchyma
collenchyma
sclerenchyma
STEM ANATOMY (cont)
 Vascular system
*consists of:
- pericycle
- phloem
- vascular cambium
- xylem
- pith rays
- pith
*inclusion and arrangement varies among plant groups
Root Anatomy
Root hairs
- major site of water/nutrient absorption
- located in zone of cell maturation
- extensions of epidermal cells
Lateral (secondary roots)
- form near but behind root hair zone
- from cells of pericycle; meristematic
- forms apex; pushes through endodermis,
cortex, epidermis
LEAVES
Initiated by apical shoot meristem
Monocots vs Dicots
Monocots have strap-shaped leaves with
parallel veins interconnected
Dicots have broader blades with veins arranged
in the shape of a net
LEAVES (cont)
corn (Zea mays) a
monocot leaf showing
parallel venation of
the major veins
LEAVES (cont)
Dicot Leaf from:
yellow poplar
(tulip tree)
(Liriodendron
tulipifera)
LEAVES (cont)
Veins contain sheaths
of vascular bundles
(xylem and phloem
elements)
This is a
photomicrograph of
dicot venation
LEAVES (cont)
Palisade and Spongy
Mesophyll cells
surround these veins
Palisades – major
photosynthesis
Spongy – major
gas exchange
Tepals
 Tepals are elements of the perianth, or outer
part of a flower, which include the petals or
sepals. The term tepal, derived from a
combination of the words 'petal' and 'sepal,' is
usually used when all segments of the perianth
are of similar shape and color, or
undifferentiated. When different types of organs
can be distinguished, they are referred to as
petals and sepals. (source: Wikipedia)
A lilium flower
showing the
tepals: the
inner three
are petals
and the outer
three are
sepals.