Plant Structure, Growth

1
Plant Structure, Growth Development

• Chapter 35

2
Flowering plants 2 main groups
Monocots
Eudicots
See Fig. 30.12
3
Monocot (e.g., corn) seedlings each have 1
cotyledon (seed leaf) in monocots the cotyledon
often remains within the confines of the seed
4
Eudicot (e.g., bean peanut) seedlings each have
2 cotyledons (seed leaves)
5
Organ systemsof flowering plants
See Fig. 35.2
6
Organs of flowering plants
Primary root first to appear
Eudicot Taproot system
Monocot Fibrous root system
7
Organs of flowering plants
Root hairs are extensions of epidermal cells
8
Organs of flowering plants
Root hairs dramatically increase a roots surface
area for absorbing water and nutrients
9
Organs of flowering plants

• Food storage is a function of all roots, but some
  (e.g., carrot taproots) are highly modified for
  storage

10
Organs of flowering plants

• Aboveground (aerial or prop) roots give extra
  support

11
Organs of flowering plants

• Breathing roots conduct oxygen to waterlogged
  roots

12
Organs of flowering plants

• The roots of many orchids are photosynthetic

13
Organ systemsof flowering plants
See Fig. 35.2
14
Organs of flowering plants
Some plants have specialized water-storage stems
Baobab trees
Saguaro cacti
15
Organs of flowering plants
Stolons (runners) are horizontal, wandering,
aboveground stems
16
Organs of flowering plants
Rhizomes (e.g., edible base of a ginger plant)
are horizontal, belowground stems
17
Organs of flowering plants
Tubers (e.g., potatoes, yams) are the swollen
ends of rhizomes, specialized for food storage
18
Organs of flowering plants
Bulbs are vertical, underground stems consisting
mostly of the swollen bases of leaves specialized
to store food
19
Organs of flowering plants
Thorns are rigid, sharp branches that deter
potential herbivores (especially mammalian
browsers)
20
Organ systemsof flowering plants
Terminal buds generally exercise apical dominance
over axillary buds
See Fig. 35.2
21
Organs of flowering plants
See Fig. 35.6
22
Organs of flowering plants
Some arid-adapted plants have succulent leaves
Aloe vera
23
Organs of flowering plants
Leaves specialized into spines help defend
against herbivores
24
Organs of flowering plants
Tendrils are specialized leaves or stems that
twist around structures to lend support
25
Organs of flowering plants
Leaves specialized to trap animals occur in
carnivorous plants
26
Organs of flowering plants
Leaves specialized to trap animals occur in
carnivorous plants
27
Organs of flowering plants
Leaves specialized to trap animals occur in
carnivorous plants
28
Organs of flowering plants
Leaf hairs (trichomes) help reduce water lossand
provide some protection against herbivores
29
Organ systemsof flowering plants
Undifferentiated meristematic cells occur in buds
Whole plant growth is indeterminate
,but growth of some organs
is determinate
See Fig. 35.2
30
Organ systemsof flowering plants
When a cell divides, the daughter cells grow
and they may differentiate (specialize),
depending especiallyon where they are located
during development
See Fig. 35.2
31
Differentiated cells contribute to 3 tissue
systems
Dermal tissue (epidermis)
Generally a single cell layer that covers the
plant
Absorption in root system
Water retention in shoot system, aided by waxy
cuticle
See Fig. 35.8
32
Differentiated cells contribute to 3 tissue
systems
Vascular tissue
Xylem transports water and dissolved minerals
Phloem transports sugars dissolved in water
See Fig. 35.8
33
Differentiated cells contribute to 3 tissue
systems
Vascular tissue
Xylem
Cells are dead at functional maturity
See Fig. 35.9
34
Differentiated cells contribute to 3 tissue
systems
Vascular tissue
Phloem
Cells are alive at functional maturity
See Fig. 35.9
35
Differentiated cells contribute to 3 tissue
systems
Ground tissue
All non-epidermal, non-vascular tissue
Three principal cell types Parenchyma
Collenchyma Sclerenchyma
See Fig. 35.8
36
Differentiated cells contribute to 3 tissue
systems
Ground tissue
Parenchyma

• Thin-walled, live cells
• Perform most metabolic functions of plant
• photosynthesis
• food storage
• synthesis and secretion

37
Differentiated cells contribute to 3 tissue
systems
Ground tissue
Collenchyma

• Cells with unevenly thickened walls that lack
  lignin
• Alive at maturity
• Grouped into strands or cylinders to aid support
  without constricting growth

38
Differentiated cells contribute to 3 tissue
systems
Ground tissue
Sclerenchyma

• Very thick walls, hardened with lignin
• Dead at maturity
• Give strength and support to fully grown parts of
  the plant
• Fibers occur in groups
• Sclereids impart hardness to nutshells and the
  gritty texture to pears

39
Primary growth in roots
Primary growth in roots lengthens roots from the
tips
The root cap continually sloughs off
See Fig. 35.12
40
Primary growth in roots
The apical meristem produces three primary
meristems
See Fig. 35.12
41
Primary growth in roots
The cells are produced
See Fig. 35.12
42
Primary growth in roots
The cells are produced then elongate
See Fig. 35.12
43
Primary growth in roots
The cells are produced then elongate and
finally mature differentiate
See Fig. 35.12
44
Primary growth in roots
The cells are produced then elongate and
finally mature differentiate
Protoderm cells become the epidermis
See Fig. 35.12
45
Primary growth in roots
The cells are produced then elongate
Protoderm cells become the epidermis
Ground meristem cells become the cortex
See Fig. 35.12
46
Primary growth in roots
The cells are produced then elongate and
finally mature differentiate
Protoderm cells become the epidermis
Ground meristem cells become the cortex
Procambium cells become the vascular stele
See Fig. 35.12
47
Primary growth in roots
Pericycle
Outermost layer of stele
These cells retain meristematic capabilities, and
can produce lateral roots
See Fig. 35.12
48
Primary growth in roots
Endodermis
Innermost layer of cortex
These cells regulate the flow of substances into
the vascular tissues of the stele
See Fig. 35.12
49
Primary growth in roots
Endodermis
Innermost layer of cortex
These cells regulate the flow of substances into
the vascular tissues of the stele
Casparian strip disallows flow of substances
except through the endodermal cells themselves
50
Primary growth in shoots
Primary growth in shoots lengthens shoots from
the tips
The apical meristem produces the same three
primary meristems as in the roots
Protoderm Ground meristem Procambium
See Fig. 35.15
51
Primary growth in shoots
Primary growth in shoots lengthens shoots from
the tips
Leaves arise from leaf primordia on the flanks of
the apical meristem
See Fig. 35.15
52
Primary growth in shoots
Primary growth in shoots lengthens shoots from
the tips
Axillary buds (that could produce lateral
branches) develop from islands of meristematic
cells left at the bases of leaf primordia
See Fig. 35.15
53
Primary growth in shoots
Procambium cells develop into vascular bundles
See Fig. 35.16
54
Primary growth in shoots
Procambium cells develop into vascular bundles
See Fig. 35.17
55
Primary growth in shoots
Procambium cells develop into vascular bundles
The veins in leaves
56
Primary growth in shoots
Protoderm cells develop into epidermis
See Fig. 35.17
57
Primary growth in shoots
Protoderm cells develop into epidermis
Some epidermal cells are guard cells surrounding
stomata
See Fig. 35.17
58
Primary growth in shoots
Protoderm cells develop into epidermis
Some epidermal cells are guard cells surrounding
stomata
See Fig. 35.17
59
Primary growth in shoots
Ground meristem cells develop into ground tissues
See Fig. 35.17
60
Primary growth in shoots
Ground meristem cells develop into ground tissues
In dicot stems these are the pith and cortex
See Fig. 35.16
61
Secondary growth in stems
Girth growth
See Fig. 35.18
62
Secondary growth in stems
Primary growth at a branch tip lays down apical
and axillary meristems for further lengthening,
as well as a lateral meristem the vascular
cambium
See Fig. 35.18
63
Secondary growth in stems
The vascular cambium produces secondary xylem to
the inside and secondary phloem to the outside
See Fig. 35.18
64
Secondary growth in stems
A second lateral meristem develops from the
cortex the cork cambium
Cork cambium produces cork cells that replace the
epidermis
See Fig. 35.18
65
Secondary growth in stems
As the stem continues to expand its girth, the
tissues outside the cork cambium rupture and
slough off
See Fig. 35.18
66
Secondary growth in stems
As the stem continues to expand its girth, the
cork cambium reforms in deeper layers of cortex
tissue, and then in secondary phloem when the
primary cortex is gone
See Fig. 35.18
67
Secondary growth in stems
Periderm Cork cambium and cork
Bark All tissue outside vascular cambium
See Fig. 35.18
68
What is wood?

• wood secondary xylem

69
Heartwood No longer conducts water, but
strengthens stem
Sapwood Conducts water and minerals
See Fig. 35.20
70
Why do trees have rings?
71
Seasonal differences in the rate of xylem
production produce annual rings
72
Summary of 1o and 2o growth in a woody stem
73
Growth increase in mass by cell division and
cell expansion
Differentiation specialization
Morphogenesis the development of body form and
organization
Development all the changes that progressively
produce an organisms body (growth,
differentiation, etc.)
74
If all cells of a body contain the same set of
genes, how do they differentiate, and how does
morphogenesis occur?
Differential expression of genes owing to
differences in the environment each cell
experiences
75
If all cells of a body contain the same set of
genes, how do they differentiate, and how does
morphogenesis occur?
For example, positional information determines
whether the cells produced by an apical meristem
become protoderm, ground meristem, or procambium
76
If all cells of a body contain the same set of
genes, how do they differentiate, and how does
morphogenesis occur?
Every step in development requires input from
both genes and the environment!