Download Xylem - msdiehlapbiology

Chapter 35
Plant Structure, Growth, and Development
What you must know
The function of xylem and phloem tissue.
 The anatomy of a leaf
 The anatomy of a root

Introduction to Plants
Kingdom: Plantae
 Cell wall
 Autotroph (photosynthesis)
 Multicellular
 Angiosperms (flowering plants)
 ~90% plants
 Produce seeds within a fruit
 Key adaptations: flowers & fruits
Plant Organization
Organs
• Roots
• Stems
• Leaves
Tissues
• Dermal
• Vascular
• Ground
Cell Types
• Xylem
• Phloem
• Parenchyma
I. Plant Organs
Shoot
system
•Above ground
•Stems, leaves
Root
system
•Underground (usually)
•Roots
A. Roots
 Anchors plant, absorbs H2O & minerals, stores
sugars/starches
 Root hairs – tiny extensions of epidermal cells,
increase surface area for H2O and mineral
absorption
 Mycorrhizae: fungus + plant root symbiotic
relationship
Root hairs
Fibrous Roots



Mat of thin roots spread
just below surface
Shallow
Increased surface area
Fibrous Root
(scallion)
Taproots
One thick, vertical root
 Many lateral (branch) roots
 Firmly anchors
 Stores food

Taproot
(carrot)
Modified Roots
Mangrove Forest in Florida
B. Stems
Function: display leaves
 Terminal bud: growth
concentrated at top end of stem
 Secretes hormone to prevent
growth of axillary buds; growth
directed upward, toward light
 Axillary buds – located in V
between leaf and stem; forms
branches (lateral shoots)
 Pinching/pruning – removing
terminal bud
Modified stems

Runner or stolin
◦ Aspen, strawberries, grass
◦ Grow on surface
◦ For asexual reproduction

Rhizome
◦
◦
◦
◦

Iris, ginger, potato, onion
Grow underground
Store food & DNA for new plant
Tuber: end of rhizome
Bulb – underground shoot
◦ Onion
◦ storage leaves
C. Leaves

Function: Photosynthetic organ
blade
petiole
Modified leaves
II. Plant Tissues
A. Dermal Tissue
Single layer, closely packed cells that cover
entire plant
 Protect against water loss & invasion by
pathogens (viruses, bacteria)
 Cuticle: waxy layer

B. Vascular Tissue
Continuous throughout plant
 Transports materials between roots & shoots
◦ Xylem & Phloem

C. Ground Tissue
Anything that isn’t dermal or vascular
 Function: storage, photosynthesis, support
 Pith: inside vascular tissue
 Cortex: outside vascular tissue

III. Cell Types
Xylem
 Conducts H2O and minerals up from root
 Dead, tubular, elongated cells
B. Phloem
 Conducts sugar & organic compounds from
leaves to other parts of plant
 Living cells aid movement of sugar
 2 Cell Types: sieve tubes, companion
cells
A.
Xylem
Phloem
Plant Growth
Types of Flowering Plants:



Annuals – 1 year life cycle
Biennials – 2 years
Perennials – continuous life cycle for many years
Meristem: perpetually embryonic tissues
◦ Cells divide for plant growth
 Apical meristem: growth at tips of roots & buds
of shoots; cause primary growth (increase length)
 Lateral meristem: growth thickens shoots and
roots; secondary growth
Primary and Secondary Growth
Root Anatomy
Root Hairs
Zone of Maturation: primary growth
becomes functionally mature
Zone of Elongation: cells elongate; push root
tip ahead
Zone of Cell Division: apical meristem; new
cells produced (mitosis)
Root cap: protects meristem as it pushes
through soil
Primary Growth
of a Root
Cortex
Epidermis
Key
Root hair
Dermal
Vascular cylinder
Zone of
maturation
Ground
Vascular
Zone of
elongation
Apical
meristem
Root cap
100 µm
Zone of cell
division
Primary Growth of Shoots

Shoot apical meristem:
dome of dividing cells at
tip of terminal bud; divide
and elongate
Leaf Anatomy
◦ Epidermis of underside interrupted by stomata (pores),
flanked by guard cells (open/close stomata)
◦ Mesophyll: ground tissue between upper/lower epidermis
◦ Parenchyma: sites of photosynthesis
Secondary Growth = increase diameter
Involves lateral meristems
◦ Vascular cambium: produces secondary xylem
(wood)
◦ Cork cambium: produces tough covering that
replaces epidermis
 Bark = all tissues outside vascular cambium

Secondary phloem
Vascular cambium
Secondary Late wood
Early wood
xylem
Primary and secondary growth
in a two-year-old stem
Cork
cambium
Periderm
Cork
Epidermis
Cortex
Primary
phloem
Vascular
cambium
Primary
xylem
Pith
Pith
Primary xylem
Vascular cambium
Primary phloem
Cortex
Phloem ray
Xylem
ray
Secondary
xylem
Primary
xylem
Cork
Pith
Secondary
xylem (two
years of
production)
Vascular cambium
Secondary phloem
Bark
Most recent
cork cambium
Cork
0.5 mm
Primary and
Secondary
Growth of a
Stem
Periderm
(mainly cork
cambia
and cork)
Vascular
cambium
Bark
0.5 mm
Primary
xylem
Secondary xylem
Vascular cambium
Secondary phloem
Primary phloem
First cork cambium
Primary
phloem
Secondary
phloem
Xylem ray
Epidermis
Transverse section
of a three-yearold Tilia (linden)
stem (LM)
Layers of
periderm