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Chapter 25
Plant Structure
and Organization
Plant Structure and
Organization
Outline
Plant Organs
Roots
Stems
Leaves
Monocots vs. Eudicots
Epidermal Tissue
Vascular Tissue
Roots
Organization
Diversity
Stems
Organization
Diversity
Leaves
Organization
Diversity
2
Plant Organs
Plant Structure and
Organization
3
Roots
Generally, the root system is at least equivalent in
size and extent to the shoot system
- Anchors plant in soil
- Absorbs water and minerals
- Produces hormones
Root hairs:
- Projections from epidermal root hair cells
- Greatly increase absorptive capacity of root
Organization of Plant Body
4
Vegetative Organs of Several Eudicots
5
Stems
Plant Structure and
Organization
6
Shoot system of a plant is composed of the stem,
branches, and leaves
Stem is the main axis of a plant that elongates
and produces leaves
- Nodes occur where leaves are attached to the stem
- Internode is region between nodes
Stem also has vascular tissue that transports
water and minerals
Leaves
Plant Structure and
Organization
7
Leaves are the major part of the plant that carries
on photosynthesis
Foliage leaves are usually broad and thin
- Blade - Wide portion of foliage leaf
- Petiole - Stalk attaches blade to stem
- Leaf Axil - Axillary bud originates
Tendrils - Leaves that attach to objects
Bulbs - Leaves that store food
Monocot vs. Eudicot
Plant Structure and
Organization
Monocots (Single cotyledon)
Cotyledons act as transfer tissue
Root vascular tissue occurs in ring
Parallel leaf venation
Eudicots (Two cotyledons)
Cotyledons supply nutrients to seedlings
Root phloem located between xylem arms
Netted leaf venation
8
Flowering Plants:
Monocots or Eudicots
9
Plant Tissues
Plant Structure and
Organization
Epidermal Tissues
Contain closely packed epidermal cells
- Covered with waxy cuticle
Roots contain root hairs
Lower leaf surface contain stomata
Woody plants covered by cork
10
Modifications of Epidermal Tissue
11
Ground Tissue
Plant Structure and
Organization
12
Ground tissue forms bulk of a plant
Parenchyma cells:
- Least specialized and are found in all organs of
plant
- Can divide and give rise to more specialized cells
Collenchyma cells:
- Have thicker primary walls
- Form bundles underneath epidermis
- Flexible support to immature regions of the plant
Ground Tissue Cells
13
Ground Tissue
Plant Structure and
Organization
Sclerenchyma cells:
Have thick secondary walls impregnated with
lignin
Most are nonliving
Primary function is to support mature regions of
the plant
- Fibers
- Sclereids
14
Vascular Tissue
Plant Structure and
Organization
Xylem transports water and minerals from the
roots to the leaves
Tracheids
- Long, with tapered ends
 Pits
in end walls
 Vascular
rays
 Fibers
Vessel Elements
- Larger, with perforated plates in their end walls
15
Xylem Structure
16
Ground Tissue
Plant Structure and
Organization
Sclerenchyma cells:
Have thick secondary walls impregnated with
lignin
Most are nonliving
Primary function is to support mature regions of
the plant
- Fibers
- Sclereids
17
Vascular Tissue
Plant Structure and
Organization
Phloem transports sucrose and other organic
compounds from the leaves to the roots
Sieve-tube members are conducting cells
- Contain cytoplasm but no nuclei
- Channels in end walls
- Plasmodesmata extend from one cell to another
through sieve plate
18
Phloem Structure
19
Organization of Roots
Plant Structure and
Organization
20
Root apical meristem
Located in the root tip
Protected by root cap
Primary meristems are in the zone of cell division
Zone of maturation contains fully differentiated
cells
Tissues of Eudicot Root
Epidermis
Cortex
Endodermis
Casparian Strip
Vascular Tissue
Pericycle
Plant Structure and
Organization
21
Eudicot Roots
22
Branching of Eudicot Root
23
Plant Structure and
Organization
Organization of Monocots Roots
Monocot roots:
Ground tissue of root’s pith is surrounded by
vascular ring
Have the same growth zones as eudicot roots,
but do not undergo secondary growth
24
Monocot Root
25
Root Diversity
Plant Structure and
Organization
26
Primary root (taproot) - Fleshy, long single root,
that grows straight down
Stores food
Fibrous root system - Slender roots and lateral
branches
Anchors plant to soil
Adventitous roots - Roots develop from organs of
the shoot system
Prop roots
Root Diversity
Plant Structure and
Organization
Haustoria:
Rootlike projections that grow into host plant
Make contact with vascular tissue and extract
water and nutrients
Mycorrhizas:
Associations between roots and fungi
Assist in water and mineral extraction
Root nodules - Contain nitrogen-fixing bacteria
27
Root Diversity
28
Organization of Stems
Plant Structure and
Organization
Shoot apical meristem
Produces new cells that elongate and increase
stem length
Protected by terminal bud
- Enveloped by leaf primordia
- Specialized primary meristems
 Protoderm
 Ground
Meristem
 Procambium
29
Woody Twig
30
Shoot tip and Primary Meristems
31
Herbaceous Stems
Plant Structure and
Organization
32
Mature nonwoody stems exhibit only primary
growth
Outermost tissue covered with waxy cuticle
Stems have distinctive vascular bundles
- Herbaceous eudicots - Vascular bundles arranged
in distinct ring
- Monocots - Vascular bundles scattered throughout
stem
Herbaceous Eudicot Stem
33
Monocot Stem
34
Woody Stems
Plant Structure and
Organization
35
Woody plants have both primary and secondary
tissues
Primary tissues formed each year from primary
meristems
Secondary tissues develop during first and
subsequent years from lateral meristems
Woody Stems
Plant Structure and
Organization
Woody stems have no vascular tissue, and
instead have three distinct regions
Bark
Wood
Pith
36
Secondary Growth of Stems
37
Bark
Plant Structure and
Organization
38
Bark of a tree contains cork, cork cambium, and
phloem
Bark can be removed, but it is harmful to the
plant due to lack of organic nutrient transport
Cork cells are impregnated with suberin
Gas exchange is impeded except at lenticels
Wood
Plant Structure and
Organization
39
Wood is secondary xylem that builds up year
after year
Vascular cambium dormant during winter
Annual ring is made up of spring wood and
summer wood
In older trees, inner annual rings, heartwood, no
longer function in water transport
Three-year-old Woody Twig
40
Tree Trunk
41
Stem Diversity
Plant Structure and
Organization
Stolons:
Above-ground horizontal stems
Produce new plants when nodes touch the
ground
Rhizomes:
Underground horizontal stems
Contribute to asexual reproduction
Variations:
- Tubers - Enlarged portions functioning in food
storage
- Corms - Underground stems that produce new
plants during the next season
42
Stem Diversity
43
Leaf Diversity
Plant Structure and
Organization
44
Blade of a leaf can be simple or compound
Leaves are adapted to environmental conditions.
Shade leaves
Spines
Climbing leaves
Leaf Structure
45
Classification of Leaves
46
Leaf Diversity
47
Plant Structure and
Organization
Review
Plant Organs
Roots
Stems
Leaves
Monocots vs. Eudicots
Epidermal Tissue
Vascular Tissue
Roots
Organization
Diversity
Stems
Organization
Diversity
Leaves
Organization
Diversity
48
Ending Slide Chapter 25
Plant Structure
and Organization