Transcript PLANT STRUCTURE AND FUNCTION

PLANT
STRUCTURE AND
FUNCTION
THE PHYLOGENY OF
PLANTS…
Charophytes (green algae)
Bryophytes (non vascular)
Trachoephytes (seedless, vascular)
Gymnosperms (“naked seeds”,vascular)
Angiosperms (contained seeds, vascular)
Monocots / Dicots
Double Fertilization
Plant Structure,
Growth and
Differentiation
Flowering Plant Reproduction Review
*sporophyte
*style
*carpel
*seed
*stigma
*ovule
*endosperm
*ovary
*pollen grain
*pollen sac
*petal
*gametophyte
*anther
*sepal
*megaspore
*filament
*carolla
*microspore
*stamen
*calyx
*pollen tube
*pollination
*double fertilization
* seed dispersal
The Seed
Seed structure
Cotyledon
Plumule
Seed coat or
testa
Radicle
Micropyle
© 2008 Paul Billiet ODWS
The Seed


Fertilizationzygoteseed (embryo)
Seed parts:
– Epicotyl : becomes shoot tip
– Plumule: young leaves
– Hypocotyl: food source for cotyledons.
becomes shoot
– Radicle: becomes root
– Coleoptile: protects epicotyl (esp. monocots)
Seed Parts
– Epicotyl
– Plumule
– Hypocotyl

– Radicle
– Coleoptile




Becomes shoot tip
Young leaves
Food source for
cotyledons.
Becomes shoot.
Becomes root
Protects epicotyl
(esp. monocots)
Seed viability
Viability: When a seed is capable of
germinating after all the necessary
environmental conditions are met.
 Average life span of a seed 10 to 15
years.
 Conditions are very important for longevity
 Cold, dry, anaerobic conditions

Germination of Seeds
Dormant Mature seeds
internal / external factors
Increased metabolism
Material synthesis / degredation
Germination: The breaking
of dormancy
The growth of the embryo and its penetration of the
seed coat
Break down of barriers
Abrasion of seed coat (soil
particles)
Decomposition of seed coat
(soil microbes, gut enzymes)
Change in physical state Cracking of seed coat (fire)
rehydration
Destruction and dilution of
inhibitors
Light, temperature, water
Production of growth
promoters
External Factors
Influencing Germination
Imbibition initiates
enzymatic activity
 Oxygen :
Necessary for Aerobic
Respiration
 Temperature: optimal temp =
germination
 Light:
necessary for PS
 Seed coat damage

Water :
Internal Factors
Affecting Germination
Presence / absence of chemical
inhibitors
 Stage of embryonic development

st
1
What is the
part of the
plant to emerge during
germination?
THE RADICLE !!
After Germination…
Growth occurs in Meristematic Regions!
 Growth involves 3 processes:

–Cell Division
–Cell Elongation
–Cell Differentiation
Stages leading to cell
division
Mitchondria
reconstituted
Respiration
Initially anaerobic
Later aerobic
Soluble sugars
ATP
RNA activated
Protein synthesis (0.5h)
Enzymes (proteins)
DNA replication (45h)
http://www.rbgsyd.nsw.gov.au/
Mitosis (70h)
Cell Division



Increase in NUMBER of cells
Indeterminate Growth:
Stems and Roots
Division continues throughout life of
plant!
Determinate Growth:
Leaves and Flowers
Division ceases upon reaching certain
size!
Cell Elongation

Increase in the SIZE of cells
Cell Differentiation
Specialization of cells
 Allows for developmental differences
in structure and function which in turn
allows for distinct plant activities!

Two Types of
Plant Growth
PRIMARY GROWTH:
–Increase in length of plant
–Occurs in ALL plants
SECONDARY GROWTH
increase in width/girth of stems and
roots
Occurs in woody plants only!
Primary Growth

Occurs in apical meristems of plant
– (found at tips of stems and roots)
GROWTH IN ROOTS
FOUR AREAS OF ROOT:

ROOT TIP (ROOT CAP):
protects apical meristem!
secretes lubricating polysaccharide
that aids with progression of root
through soil!
ZONE OF CELL DIVISION
(APICAL MERISTEM REGION):
located closest to root tip
contains actively dividing cells!
ZONE OF ELONGATION
superior to apical meristem!
composed of cells no longer dividing,
but enlarging!
ZONE OF MATURATION
superior to Zone of Elongation
Cells here are completely
differentiated and are fully mature!
•
Growth of Stems:
no root cap
Secondary Growth


Occurs at lateral meristems
(on sides of roots and stems)
Two types of Meristematic Cells:
1. VASCULAR CAMBIUM
2. CORK CAMBIUM
Vascular Cambium
Thin layers of cells
 Form rings around the stem and root
trunk
 Wood forms toward the inside;
 Bark forms toward the outside!

Cork Cambium
Patches of cells
 Located in outer bark region of plant
 Divides to form tissues of outer bark
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In General…
Plants with secondary growth are
PERRENIALS
Plants with primary growth only are
A N N U A L S or
HERBACEOUS
PLANT TISSUES
3 types:
1.
2.
3.
GROUND TISSUE
DERMAL TISSUE
VASCULAR TISSUE
GROUND TISSUE
“FILLER TISSUE”
3 types of GT cells – differing in cell wall
structure
1. Parenchyma
2. Collenchyma
3. Sclerenchyma
Parenchyma cells:
Very thin, flexible cell walls!
 Located throughout plant body
 Function in PS (mesophyll), storage,
secretion of products
 Living at maturity w/ ability to divide
after injury

Collenchyma Cells
Thick , flexible cell walls!
 Provide structural support in
stems/leaves!
 Living at maturity

Sclerenchyma
Thicker 2 cell walls than collenchyma
 Cell wall filled with LIGNIN!
 Provide strength and rigidity to plant
 Dead at maturity!
 2 types of sclerenchyma cells:

 Sclerids:
 Fibers:
short/ irregularly shaped
long, slender, tapered
Parenchyma
Collenchyma
Sclerenchyma
DERMAL TISSUE
Provides protective covering over plant
 2 layers:

– Epidermis
– Periderm
Epidermis
Outermost layer on herbaceous plants
 Secretes cuticle to:

– Prevent water loss (TRANSPIRATION)
PROBLEM!
IF THE CUTICLE BLOCKS WATER, WHAT
ELSE IS PREVENTED FROM
ENTERING/EXITING THE PLANT?
C O
!!
2
Solution?

STOMATA!
– Tiny pores in epidermis surrounded by
two guard cells!
– Open during the day! Why?
 PS
occurs during the day
 Transpiration necessary for cooling
Periderm
Outermost layer of cells on woody
plants
 Replacement of epidermis for plants
with secondary growth
 Continually formed by Cork Cambium

VASCULAR TISSUE

2 MAJOR TYPES:
– XYLEM TISSUE
– PHLOEM TISSUE
– Found together in VASCULAR BUNDLES
– Arise primarily from apical meristem
– Arise secondarily from vascular cambium
XYLEM TISSUE
CONDUCTS WATER
 PROVIDES MECHANICAL SUPPORT
 2 TYPES OF XYLEM CELLS:

– TRACHEIDS:
– VESSEL ELEMENTS:

TRACHEIDS
– LONG, TAPERED CELLS
– Dead at maturity
– CONDUCT WATER FROM ONE
TRACHEID TO ANOTHER VIA PITS
(NO 2 CELL WALL, ONLY THIN 1)

VESSEL MEMBERS/ELEMENTS
shorter/wider than tracheids
dead at maturity
water passes between vessel
members through perforations
(no cell walls at all at perforations!)
PHLOEM TISSUE
CONDUCTS SUGARS
 COMPOSED OF TWO CELL TYPES:

– SIEVE-TUBE MEMBERS
– COMPANION CELLS
Sieve tube members
Form sieve tubes to conduct sugars
throughout plant
 Lack nuclei, ribosomes, vacuoles, etc.

Vascular
bundle

Pores: at ends of sieve tube
members
form sieve plates btwn adjacent cells
Companion Cells
Parenchymal cells
 Connect to sieve tube members via
plasmodesmata
 Support nuclei-lacking STM’s
 Aid in loading sugar into STM’s!

xylem
ROOTS
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Taproots
– Dicots
– Single Primary Root

Fibrous Roots
– Monocots
– Several roots of same size w/ branching

Roots can be adapted for storage of
nutrients:
– Example: Carrot (Taproot)
Sweet Potato (Fibrous Root)