Lecture #4 – Plant Structure,
Growth And Development
Image – the Angel Oak
1
Key Concepts:
•
•
•
•
•
•
•
•
What is a kingdom?
Why study plants?
What makes a plant a plant?
The hierarchy of structure – plant cells,
tissues and organs
Growth
Primary growth – elongation
Secondary growth – diameter expansion
Morphogenesis occurs during growth
2
Carolus
Linnaeus
(1707-1778)
Image – Linnaeus
The founder of
modern taxonomy
defined kingdoms
by morphological
similarity
3
Linnaeus’ Taxonomic Hierarchy
Taxonomic Category
Example (taxon)
Kingdom
Plantae, also Metaphyta = all plants
Division (phylum)
Magnoliophyta = all angiosperms
Class
Liliopsida = all monocots
Order
Asparagales = related families (Orchidaceae,
Iridaceae, etc)
Family
Orchidaceae = related genera (Platanthera,
Spiranthes, etc)
Genus
Platanthera = related species (P. ciliaris, P. integra,
etc)
Specific name/epithet
ciliaris = one species
4
Linnaeus’ Taxonomic Hierarchy
Taxonomic Category
Example (taxon)
Kingdom
Plantae, also Metaphyta = all plants
Division (phylum)
Magnoliophyta = all angiosperms
Class
Liliopsida = all monocots
Order
Asparagales = related families (Orchidaceae,
Iridaceae, etc)
Family
Orchidaceae = related genera (Platanthera,
Spiranthes, etc)
Genus
Platanthera = related species (P. ciliaris, P. integra,
etc)
Specific name/epithet
ciliaris = one species
5
Images – the yellow fringed orchid
6
Platanthera ciliaris
Linnaeus recognized only 2 kingdoms
• If it moved – animal; if it didn’t – plant
• Fungi were lumped with plants
• The microscopic world was largely unknown
Images – the 3 multicellular kingdoms, animals, fungi and plants
7
The 5 kingdom system – developed in the
1960’s and used until recently
Diagram – the 5 kingdom system
8
Molecular data supports 3 domain
classification scheme
Diagram – 3 domain system of classification
Kingdoms are defined by monophyletic lineage
9
Classification is Dynamic!
Diagram – transition from 5 kingdom to 3 domain
system indicating dynamic nature of classification
Multicellular eukaryotes remain fairly well defined –
the plants, fungi and animals. Classification of single
celled organisms is still underway.
10
Current Taxonomic Hierarchy
Taxonomic Category
Example (taxon)
Domain
Eukarya = all eukaryotic organisms
Kingdom
Plantae, also Metaphyta = all plants
Division (phylum)
Magnoliophyta = all angiosperms
Class
Liliopsida = all monocots
Order
Asparagales = related families (Orchidaceae,
Iridaceae, etc)
Family
Orchidaceae = related genera (Platanthera,
Spiranthes, etc)
Genus
Platanthera = related species (P. ciliaris, P. integra,
etc)
Specific name/epithet
ciliaris = one species
11
Why Plants?
12
Why Plants?
Image – shooting stars
13
What makes a plant a plant???
14
Images and diagrams – characteristics that separate
plants from other kingdoms
15
What makes a plant a plant???
• Multicellular, eukaryotic organisms with extensive
specialization
• Almost all are photosynthetic, with chloroplasts (= green)
 Some obtain additional nutrition through parasitism or carnivory
 Some are saprophytic, entirely without chlorophyll (absorb dead
OM)
• Excess carbohydrates stored as starch (coiled, branched
polymer of glucose)
• Cell walls of cellulose = fibrous (not branched)
polysaccharide = accounts for the relative rigidity of the cell
wall
• Cell division by formation of cell plate
• Most extant plant species are terrestrial (many
characteristics that are adapted for terrestrial life)
• Separated from cyanobacteria by chloroplasts
• Separated from green algae by various adaptations to 16
terrestrial life
Read this later….
Plants were the first organisms to
move onto land
• Occurred about 475mya
• Very different conditions from former
marine habitat
• Many new traits emerged in adaptation to
life on dry land
• Extensive adaptive radiation into many
new ecological niches
17
Four major
groups of plants
have emerged
since plants took
to land
Diagram – phylogeny of land plants;
same on next slide
18
We will focus
on
angiosperms
Next semester in
211 you will learn
more about the
transition from
water to land,
and the evolution
of reproductive
strategies in all
plants
19
Angiosperms – the flowering plants:
90% of the Earth’s modern flora
Images – flowering plants
20
Basic Structure of the Plant Cell –
what’s unique???
Diagram – plant cell; same on next slide
21
Basic Structure of the Plant Cell
22
Critical Thinking
• Do all plant cells have chloroplasts???
• How can you tell???
23
Critical Thinking
• Do all plant cells have chloroplasts???
• How can you tell???
24
Critical Thinking
• Do all plant cells have
chloroplasts???
• How can you tell???
Image – chloroplast free white
bracts on white-top sedge
25
More on the cell wall:
• All cell walls are
produced by the cell
membrane, outside
• Primary wall is
produced first
Diagram – primary and secondary
cell walls; same on next slide
 Mostly cellulose
• Secondary walls are
produced later
 Lignified, so ???
• Secondary walls are
interior to primary
walls
26
More on the cell wall:
• All cell walls are
produced by the cell
membrane
• Primary wall is
produced first
 Mostly cellulose
• Secondary walls are
produced later
 Lignified, so
• Secondary walls are
interior to primary
walls
27
Five Major
Plant Cell
Types
Micrographs – plant cell types
• Parenchyma
• Collenchyma
• Sclerenchyma
• Xylem elements
• Phloem elements
28
Parenchyma
•
•
•
•
Thin primary wall
No secondary wall
Many metabolic and storage functions
Bulk of the plant body
Micrographs – parenchyma cells
29
Collenchyma
• Thick primary
wall
• No secondary
wall
Micrograph – collenchyma cells;
same on next slide
Implications???
• Support growing
tissues
30
Collenchyma
• Thick primary
wall
• No secondary
wall
Implications???
• Support growing
tissues
31
Sclerenchyma
• Thick secondary wall
• Secondary walls are
lignified
Micrograph – sclerenchma
cells; same on next slide
Implications???
• Support mature plant
parts
• Often dead at maturity
32
Sclerenchyma
• Thick secondary wall
• Secondary walls are
lignified
Implications???
• Support mature plant
parts
• Often dead at maturity
33
Collenchyma vs. Sclerenchyma
•
•
•
•
Both provide structural support
Both have thick walls
Collenchyma = thick primary wall, no lignin
Sclerenchyma = thick secondary wall, lignified
Micrographs – collenchyma and sclerenchyma cell comparison
34
Xylem Elements
• Lignified secondary
walls
• Always dead at
maturity (open)
• Function to transport
water and dissolved
nutrients, and to
support the plant
• Tracheids and vessel
elements
Diagrams and
micrograph – tracheids
and vessel elements
35
Critical Thinking
• Vessel elements and
the convergent
evolution of rings
• What else looks like
this????
• What is the
function????
Micrograph – rings of lignin in
developing vessel element; same
on next slide
36
Critical Thinking
• Vessel elements
and the convergent
evolution of rings
• What else looks
like this????
• What is the
function????
37
Phloem Elements
• Sieve tube members +
companion cells
• STM lack nucleus,
ribosomes – their
metabolism is controlled
by the companion cells
Micrograph – phloem elements
• Function to transport the
products of metabolism
• Non-angiosperms have
more primitive phloem
elements
38
Critical Thinking
• What might be the functional advantage of
a cell with no nucleus???
Diagram – phloem elements
39
Critical Thinking
• What might be the functional advantage of
a cell with no nucleus???
40
Plants are
Simple 
Only Five Major
Cell Types
Micrographs – plant cell types
• Parenchyma
• Collenchyma
• Sclerenchyma
• Xylem elements
• Phloem elements
41
Tissue
Systems
•
•
•
•
Diagram – plant tissue types
Epidermis
Vascular
Ground
Meristem
42
Epidermis Tissue:
• Covers the outer surface of all
plant parts
• Shoot surfaces covered with
waxy cuticle
Micrograph
and diagram –
epidermis
Helps to protect the plant and
prevent desiccation
• Usually a single, transparent
cell layer
• Tight joints; stomata allow for
gas exchange
43
Critical Thinking
• Do roots have a waxy cuticle???
• Why or why not???
44
Critical Thinking
• Do roots have a waxy cuticle???
• Why or why not???
Never forget the importance of
natural selection!!!!!
45
Vascular Tissue:
• Transports water, solutes,
and metabolic products
throughout the plant
• Confers structural support
• Includes xylem elements,
phloem elements,
parenchyma and
sclerenchyma fibers
Micrograph – vascular
bundle in cross section
46
Critical Thinking
• Why does vascular tissue give structural
support to a plant???
47
Critical Thinking
• Why does vascular tissue give structural
support to a plant???
48
Ground Tissue:
• Bulk of the plant
body – pith, cortex
and mesophyll
• Mostly parenchyma
• Most metabolic,
structural and
storage functions
Micrograph and diagram – ground
tissues in stems and leaves
49
Critical Thinking
• Is this what the inside of a tree looks
like???
Micrograph – herbaceous dicot stem
50
Critical Thinking
• Is this what the inside of a tree looks
like???
Micrograph of herbaceous eudicot stem; image of woody
stem; diagram of woody stem tissue organization
51
Meristem Tissue:
• How the plant grows
• Cells divide constantly during the growing
season to make new tissues
• More details later
Image – new growth at tip of stem
52
Plants are
Simple 
Only Four Major
Tissue Types
•
•
•
•
Diagram – plant tissue systems
Epidermis
Vascular
Ground
Meristem
53
Tissues Make Organs:
• Roots – anchor the plant, absorb water and
nutrients
• Stems – support the leaves
• Leaves – main site of photosynthesis
• Reproductive organs (flowers, cones, etc –
more later)
All organs have additional functions –
hormone synthesis, transport, etc…
54
Plant Organ Systems
Diagram – root and shoot systems
55
Modern molecular evidence indicates
four classes of angiosperms
paleoherbs
magnoliids
eudicots
monocots
ancestral
56
Paleoherbs and Magnoliids comprise
about 3% of angiosperms
Paleoherbs
• Aristolochiaceae,
Nymphaeaceae, etc
Magnoliids
• Magnoliaceae,
Lauraceae, nutmeg,
black pepper, etc
Images – water lily and magnolia
57
Modern evidence indicates 4 classes of
angiosperms
paleoherbs
magnoliids
eudicots
monocots
~ 97% of
angiosperms
ancestral
58
Monocots include grasses, sedges,
iris, orchids, lilies, palms, etc…..
Images – monocots
59
Eudicots include 70+% of all
angiosperms:
• Most broadleaf trees and shrubs
• Most fruit and vegetable crops
• Most herbaceous flowering plants
Images – eudicots
60
Monocots vs. Eudicots
Monocots
• Flower parts in multiples
of 3
• Parallel leaf venation
• Single cotyledon
• Vascular bundles in
complex arrangement
• ~90,000 species
Eudicots
• Flower parts in multiples
of 4 or 5
• Netted leaf venation
• Two cotyledons
• Vascular bundles in a
ring around the stem
• Modern classification
indicates 2 small primitive
groups + eudicots
• 200,000+ species
61
Root System Tissue Organization
Eudicots
Monocots
Micrographs – cross sections of eudicot and moncot
roots; same on next 3 slides
Epidermis, ground, endodermis, pericycle, vascular tissues
62
Eudicot root – closeup
Epidermis
Cortex
Endodermis
Pericycle
Vascular
tissues – in
solid core
63
Monocot root – closeup
Epidermis
Cortex
Endodermis
Pericycle
Vascular tissues – in
ring
Pith in the very center
64
Critical Thinking
• Where do branch roots form???
65
Critical Thinking
• Where do branch roots form???
Micrograph – root emerging from pericycle
66
Stem System Tissue Organization
Eudicots
Monocots
Micrograph – eudicot and monocot stem tissue
organization; same on next 4 slides
Epidermis, ground, vascular tissues
67
Eudicot stem – closeup
Epidermis
Cortex
Vascular
tissues –
bundles in
a ring
Pith
68
Monocot stem – closeup
Epidermis
Cortex
Vascular
tissues –
bundles are
scattered
69
Wood forms from a meristem that
links the vascular bundles:
70
Stem System Tissue Organization
Eudicots
Monocots
Monocots cannot make wood
More on wood formation later
71
Leaf Tissue Arrangement
Micrograph – cross-section of leaf tissue arrangement
Epidermis, ground, vascular tissues
72
Leaf closeup
Epidermis
Diagram – leaf tissue arrangement
Cortex –
palisade
mesophyll
Cortex – spongy
mesophyll
Vascular tissues
73
Stomata – pores to allow for gas
exchange and transpiration
Micrograph – epidermis tissue
showing stomata
74
See, plants really are simple 
• 5 cell types
• 4 tissue types
• 4 organ types
Diagram – shoot and root systems
75
Plant Growth
• Remember, most plants are anchored by
roots
• They can’t move to escape or take
advantage of changes in their environment
• Plants adjust to their environment
• Simple structure + lots of developmental
flexibility allow plants to alter when and
how they grow
Developmental flexibility comes from
meristems
76
Meristem Tissues
• Actively dividing cells that generate all
other cells in the plant body
• Cause indeterminate growth
Stems and roots elongate throughout the
plant’s life (indeterminate primary growth)
Trees continually expand in diameter
(indeterminate secondary growth)
Branches form in roots and stems
77
Not all plant parts have
indeterminate growth patterns
Indeterminate:
Roots
and
Stems
Determinate:
Leaves
Flowers
Fruits
These parts grow
throughout the life of
the plant, exploring
new environments or
responding to
damage
These parts grow to a
genetically +/predetermined size
and shape and then
stop – cannot repair
78
damage
Some mature cells can
de-differentiate to become
meristematic once more!!!
• Primarily occurs in the indeterminate parts
Stems and roots
• A process that very seldom occurs in other
kingdoms
• Allows stems and roots to repair damage
and form branches and sprouts
79
Critical Thinking
• Can all plant cells de-differentiate???
• What would control this???
80
Critical Thinking
• Can all plant cells de-differentiate???
• What would control this???
81
Critical Thinking
• Can all plant cells de-differentiate???
• What would control this???
82
Growth in Plants:
an irreversible increase in size due to
metabolic processes
(processes that use ATP energy)
• Cell division produces new cells = function
of meristem
• Cell expansion increases the size of the
new cells = up to 80% of size increase
• Cell differentiation occurs during and after
expansion
83
The plane of cell division contributes to morphogenesis
Diagram – planes of cell division and the effect on morphogenesis
Division in 2 planes forms sheets of cells
84
Critical Thinking
• What tissues are files of cells???
• What tissues are sheets of cells???
• What tissues are 3-D bulky???
85
Critical Thinking
• What tissues are files of cells???
• What tissues are sheets of cells???
• What tissues are 3-D bulky???
86
Growth in Plants:
an irreversible increase in size due to
metabolic processes
(processes that use ATP energy)
• Cell division produces new cells = function
of meristem
• Cell expansion increases the size of the
new cells = up to 80% of size increase
• Cell differentiation occurs during and after
expansion
87
Auxin-mediated cell expansion
Diagram – how auxin works to promote cell expansion
ATP is used
88
The direction of cell expansion depends on cellulose
orientation, and contributes to morphogenesis
Diagram – cellulose orientation in primary
wall and the effects on morphogenesis
89
Growth in Plants:
an irreversible increase in size due to
metabolic processes
(processes that use ATP energy)
• Cell division produces new cells = function
of meristem
• Cell expansion increases the size of the
new cells = up to 80% of size increase
• Cell differentiation occurs during and after
expansion
90
Expansion and
differentiation
occur in an
overlapping
zone in all plant
parts
Diagram – patterns of
growth in roots
91
REVIEW: Growth in Plants:
an irreversible increase in size due to
metabolic processes
(processes that use ATP energy)
• Cell division produces new cells = function
of meristem
• Cell expansion increases the size of the
new cells = up to 80% of size increase
• Cell differentiation occurs during and after
expansion
92
Location of the
meristems
determines the
pattern of plant
growth
Diagram – location of
meristems on the plant
body; next slide also
Most common
meristems:
apical, axillary
and lateral
93
Apical
meristems
cause
elongation of
roots and
stems
94
Micrograph – longitudinal section showing distribution of tissues in root
95
Images – root cap and mucigel
96
Root Cap
• Protects the meristem
• Secretes mucigel
Eases movement of roots through soil
Secretes chemicals that enhance nutrient
uptake
• Constantly shedding cells
Mechanical abrasion as roots grow through
soil
• Constantly being replenished by meristem
97
Primary Growth in Roots
Diagram – longitudinal section of root showing
zones of growth; same on next 2 slides
98
Primary Growth in Roots
99
Primary Growth in Roots
100
Root Hairs
• Form as the epidermis
fully differentiates
• Extensions off epidermal
cells
 NOT files of cells
 Part of an epidermal cell
Micrograph – root hairs
extending from epidermis;
same on next few slides
• Hugely increase the
surface area of the
epidermis
• 10 cubic cm (double
handful) of soil might
contain 1 m of plant roots
 Mostly root hairs
101
Critical Thinking
• What is the selective advantage of root
hairs???
102
Critical Thinking
• What is the selective advantage of root
hairs???
103
Root Hairs
• By contrast, 10 cc of soil
may contain up to 1000 m
of fungal hyphae (1km!)
 These serve a similar
function for the fungus
 Ramify throughout the
substrate for maximum
absorption
 Some fungi form symbiotic
associations with plant
roots and both organisms
benefit from this huge
absorptive surface area!
 More in 211…..
104
Apical
meristems
cause
elongation of
roots and
stems
Diagram – location of apical meristems
105
Apical Meristems in Shoots
Micrograph – longitudinal
section of stem showing
apical and axillary meristems
106
Critical Thinking
• There is no “shoot cap” – why not???
107
Critical Thinking
• There is no “shoot cap” – why not???
108
Axillary
meristems
allow for
branching –
similar in
structure and
function to
apical
meristems
Diagram – meristem locations
Remember, pericycle in
roots has same function
109
Axillary Meristems in Shoots
Micrograph – longitudinal
section of stem showing
apical and axillary meristems;
same on next two slides
110
Primary Growth in Shoots
• Apical meristem
• Leaf primordia
• Axillary buds
111
As with roots – cell
division occurs first;
zones of expansion
and differentiation
overlap
Axillary buds may
activate to make
branches, or may
remain dormant
112
Primary growth of a shoot – elongation from the tip
Diagram – how stems elongate during primary growth
113
Lateral
meristems
cause
diameter
expansion
Diagram – meristem locations
Roots also expand
in diameter, but it’s
more complicated –
we’ll save that for
BIOL 300
114
Lateral Meristems = Cambiums
Diagram – lateral meristems
115
Remember:
Diagram – primary vs. secondary growth
Elongation is
primary growth
Diameter
expansion is
secondary growth
116
Secondary
growth –
diameter
expansion
Images – cross section of wood and whole tree
117
Eudicot Stem – recall the
arrangement of vascular bundles
Micrograph – cross section of a
eudicot stem; same on next 2 slides
118
Eudicot Stem – recall the
arrangement of vascular bundles
Vascular
cambium
forms here:
119
Eudicot Stem – recall the
arrangement of vascular bundles
Vascular
cambium
forms here:
a cylinder of
meristem
tissue between
the xylem to
the interior and
the phloem to
the exterior
120
Secondary xylem and phloem form through
cell division by the vascular cambium
Diagram – location of the vascular
cambium relative to other tree tissues
121
During primary growth
the vascular tissues
form in bundles from
the apical meristem
Diagram – transition from primary
growth to secondary growth;
same on next slide
During secondary
growth the vascular
tissues form in
cylinders from the
vascular cambium
2o xylem to the
inside
2o phloem to the
outside
122
Secondary
xylem
accumulates
123
Secondary Xylem = Wood!
Micrograph – cross section of woody plant
showing secondary tissues; same on next slide
124
Annual growth rings are accumulating
rings of secondary xylem
125
Critical Thinking
• Why do eudicot trees taper???
Diagram –
pattern of
accumulation of
secondary xylem
as a tree grows;
same on next
slide
126
Critical Thinking
• Why do eudicot trees taper???
127
Bark
• All tissues external to the vascular
cambium
• Diameter expansion splits original
epidermis
Bark structurally and functionally replaces
epidermis
• Inner bark
Functional secondary phloem
• Outer bark
Composition varies as tree matures
128
Bark Formation
Micrograph – cross section of a tree showing bark formation
129
Cork Cambium
• Meristematic tissue
• Forms in a cylinder during 2o growth
• Divides to produce cork cells
Cells filled with waxy, waterproof suberin
• Eventually cork cambium becomes cork
itself
130
More on cork cambium
• First layer develops from cortex
De-differentiation!!!
• Second layer forms from cortex – same
process
• Third layer forms from cortex…..
• Cortex eventually runs out
• Then what???
131
More on cork cambium
• First layer develops from cortex
De-differentiation!!!
• Second layer forms from cortex – same
process
• Third layer forms from cortex…..
• Cortex eventually runs out
• Then what???
132
More on cork cambium
• First layer develops from cortex
De-differentiation!!!
• Second layer forms from cortex – same
process
• Third layer forms from cortex…..
• Cortex eventually runs out
• Then what???
133
More on cork cambium
• First layer develops from cortex
De-differentiation!!!
• Second layer forms from cortex – same
process
• Third layer forms from cortex…..
• Cortex eventually runs out
• Then what???
134
Critical Thinking
• What is the next available layer of
tissue???
Diagram – lateral meristems and
the secondary tissues in a tree;
same on next slide
135
Critical Thinking
• What is the next available layer of
tissue???
136
More on cork cambium
• First layer develops from cortex
De-differentiation!!!
• Second layer forms from cortex – same
process
• Third layer forms from cortex…..
• Cortex eventually runs out
• Then what???
137
More on cork cambium
• First layer develops from cortex
De-differentiation!!!
• Second layer forms from cortex – same
process
• Third layer forms from cortex…..
• Cortex eventually runs out
• Then what???
138
Stem Tissue Derivations and Fates:
Diagram – how undifferentiated cells develop into the tissues of the plant body
Cells divide, expand and differentiate
139
Review: Key Concepts:
•
•
•
•
•
•
•
•
What is a kingdom?
Why study plants?
What makes a plant a plant?
The hierarchy of structure – plant cells,
tissues and organs
Growth
Primary growth – elongation
Secondary growth – diameter expansion
Morphogenesis occurs during growth
140
Monocots, Palmetto Trees,
Ft. Moultrie and the SC State Flag
Various images and a micrograph of a monocot stem – an
example of one influence of plants on American history
141