Transcript Lecture # 16 Date

NOT ON AP: NEEDED FOR
BACKGROUND
• Plant Structure and
Growth
The Diversity of Angiosperms
• Angiosperms
(flowering plants) can
be divided into 2
major categories:
– Monocots –
• have one seed leaf
(cotyledon)
– Dicots –
• have 2 seed leaves
(cotyledons)
Monocots
• Monocots have only 1 cotyledon (seed leaf)
• Examples of monocots:
– Corn, wheat, lilies, orchids, palms
Dicots
• Dicots have 2 cotyledons (seed leaves)
• Examples of dicots:
– Roses, clover, tomatoes, oaks, daisies
Woody vs. Herbaceous Plants
• Angiosperms can also be subdivided into
the groups of woody and herbaceous plants
– Woody plants are made of cells with
thick cell walls that support the cell body
• Examples: trees, shrubs, vines
– Herbaceous plants do not produce wood
as they grow, and instead have smooth
stems
• Examples: dandelions, sunflowers
Anatomy of an
angiosperm
Angiosperm structure
• Three basic organs:
– Roots (root system)
• fibrous: mat of thin roots
• taproot: one large, vertical root
– Stems (shoot system)
• nodes: leave attachment
• internodes: stem segments
• axillary bud: dormant, vegetative potential
• terminal bud: apex of young shoot
– Leaves (shoot system)
– blade
– petiole
Plant Organ Systems
• Dermal (epidermis): single layer of cells for protection
– Cuticle: a waxy coating on many leaves and stems
• Vascular (material transport)
– xylem: water and dissolved minerals roots to
shoots
– phloem: food from leaves to roots and fruits
• Ground (photosynthesis, storage, support): tissues that
are neither dermal or vascular
– Pith: internal to the vascular tissue
– Cortex: external to the vascular tissue
Plant Growth
• Life Cycles
– annuals: complete their life cycle in
1 year or less (wildflowers; food
crops)
– biennials: complete their life cycle
in 2 years or less (beets; carrots)
– perennials: live many years (trees;
shrubs)
• Meristems: have indeterminate
growth cycles
– apical: tips of roots and buds;
primary growth
– lateral: cylinders of dividing cells
along length of roots and stems;
secondary growth (wood)
The Root System
• What do roots do?
– Anchor the plant in the
soil
– Absorb minerals and
water
– Store food
• Types of root systems
– Fibrous root system
• Found mostly in
monocots
– Taproot system
• Found mostly in dicots
Primary growth
• Roots
• root cap: protection of
meristem and pushes
through soil
• zone of cell division:
primary (apical) meristem
where new root cells are
produced
• zone of elongation: cells
elongate; pushes root tip
into soil
• zone of maturation:
complete maturation and
differentiate to become
tissues
The Shoot System
• The shoot system consists
of:
– vegetative shoots (which
bear leaves)
– floral shoots (which bear
flowers)
• Stems have 3 important
functions:
– Producing leaves, flowers,
branches
– Holding leaves up to the
sunlight
– Transporting substances
between roots and leaves
Primary Tissues of Stems
• Vascular bundles (xylem and phloem)
• Surrounded by ground tissue (xylem faces pith (central
core of plant) and phloem faces cortex (tissue between the
vascular tissue and the dermis). . . See diagram below)
How do stems grow?
• Primary growth
– Increase in length
– Occurs by cell divisions
in apical meristem (at
top of shoot)
• Secondary growth
– Increase in width
– Occurs by cell divisions
in the lateral
meristems (also known
as vascular cambium)
Apical Meristems
The Shoot System: Leaves
• Leaves are
attached to stems
at nodes
• The area between
2 nodes is called
an internode
The Shoot System: Leaves
• Leaves are the primary
photosynthetic organs
of most vascular
plants
• Most leaves have a
flattened blade and a
petiole, which is the
stalk that attaches the
leaf to the stem
Primary Tissues of Leaves
• Epidermis/cuticle (protection; desiccation)
• Stomata (tiny pores for gas exchange and transpiration):
surrounded by guard cells which open and close stomata
• Mesophyll: ground tissue between upper and lower epidermis ; site
where photosynthesis takes place
Secondary Growth
• This type of growth produces thickness in stems
and roots in woody plants
• Two lateral meristems
– vascular cambium: produces secondary xylem
(wood) and secondary phloem (diameter
increase; annual growth rings)
– cork cambium: produces thick covering that
replaces the epidermis; produces cork cells;
cork plus cork cambium make up the periderm
(outer, protective coat)
– Bark: all tissues external to vascular cambium
(phloem plus periderm)
The formation of
“bark”
Tissue Systems in Plants
• All 3 plant organs
(root/stem/leaf) have
dermal, vascular, and
ground tissue systems
• Dermal Tissue System
– Outer protective covering,
similar to our skin 
– Protects the plant from
water loss and disease
– The cuticle is a waxy
coating that helps to
prevent water loss
Tissue Systems in Plants
• Vascular Tissue System
–
Carries out long-distance
transport of materials within
the plant
– Xylem and phloem are
examples of vascular tissues
• Ground Tissue System
–
Pith (inside vascular tissue)
and cortex (outside vascular
tissue) are examples of ground
tissue
– Includes cells specialized for
storage, photosynthesis, and
support
Summary of primary & secondary growth in a woody a stem
PRIMARY
MERISTEMS
Protoderm
Apical
meristem
of stem
PRIMARY
TISSUES
LATERAL
MERISTEM
Epidermis
Primary phloem
Procambium
Secondary
phloem
Vascular
cambium
Primary xylem
Ground
meristem
Ground Pith &
tissue: Cortex
SECONDARY
TISSUES
Secondary
xylem
Periderm
Cork
cambium
Cork
Microscope Activity
• You will be examining various slides of
plants
• In your lab notebooks, I want you to draw
what you see at the 100X and 400X powers
and label as many parts as you can
– You may use your textbooks for aid (look
at the diagrams in Ch. 35)
– pp. 721 - 726