Chapter 35—Plant Structure, Growth, and Development
Concept 35.1: The plant body has a hierarchy of organs,
tissues, and cells.
A. Plant cells—equip plants for specialized functions
1. Parenchyma cells
a. least specialized
b. thin walled
c. storage
2. Collenchyma cells
a. usually lack secondary walls
b. uneven thickness
c. support—elongates to continue support in
young plant parts
3. Sclerenchyma cells
a. functions in support
b. rigid and thick
c. do not elongate—may even be dead
d. 2 types fibers (long) and sclerids (short)
B. Organization
Organs
Systems
Leaves
Dermal
Stems
Vascular
Roots
Ground tissue
1. Dermal—epidermis
a. aids in protection
b. waxy cuticle helps plant retain water
2. Vascular tissue system
a. xylem and phloem
b. function in support and transport
3. Ground tissue system
a. found between dermal and vascular tissue
systems
b. functions in photosynthesis, storage and
support
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4. Water conducting cells of xylem
a. Trachiedslong and thin with parts to allow
water to pass to next cell
b. Vessel elementswider and shorter and
arranged end to end
 Ends perforated to allow water to flow
through vessel.
c. Both dead at maturity
5. Food conducting cells of phloem
a. Sieve tube members
 Alive at maturity
 Transport sucrose, compounds and
minerals
 Arranged end to end with sieve tube
plates
Concept 35.2: Meristems generate cells for new organs
1. Plants have indeterminate growth
2. Parts of the plant have determinate growth (ex:
flowers)
a. apical meristemplant length
 primary growth (1º growth)—elongation
 secondary growth (2º growth)—increased
girth
b. lateral meristemscylinders of dividing cells
extending along the lengths of roots and shoots
 secondary dermal tissue—replaces the
epidermis
 add new layers to vascular tissue
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Concept 35.3: Primary growth lengthens roots and
shoots
I. Angiosperm Body
A. Roots—subterranean
1. Structured to anchor plants, absorb water
and nutrients and store food
2. 2 Types of roots
a. taproot (dicots)
 Large vertical root that produces
smaller secondary roots
 Firm anchorage
 Maybe modified to store large
amounts of food (carrot, turnip, sweet
potato)
b. fiberous root system (monocots)
 Mat of threadlike roots
 Provides extreme exposure to soil
and water
 Prevent soil erosion
Root hairs—help in water absorption—found in both systems
B. Shoots—aerial (vegetative or floral shoots)
1. Stems
a. nodes
b. internodes
c. axillary buds—dormant
d. terminal bud—growth
Axial buds may grow if damage occurs to terminal bud
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II. Primary growth—extends roots and shoots by giving rise
to the primary plant body.
A. Roots
1. Root cap
a. zone of cell division—closest to tip of root
b. zone of elongation
c. zone of maturation—furthest from tip
2. Tissues of roots
a. protodermoutermost part of meristem
 contains root hairs
b. procambiuma stele (central cylinder)
 phloem develops in stele
c. ground meristemground tissue system
 stores food
B. Shoots
1. Apical meristem is a dome-shaped mass of
dividing cells at the tip of the terminal bud
2. Most shoot elongation occurs due to the growth of
slightly older internodes
3. Axillary buds may form branches later in life
4. Tissue of stems
a. Vascular bundles run length of stem
 Xylem and phloem
5. Modified stems
a. stolonshorizontal stems (strawberries)
“runners”
b. rhizomehorizontal stems underground
(irises)
c. bulbsunderground shoots with modified
leaves for food storage
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C. Leaves
1. Main photosynthetic organ of plant
2. Monocotsveins run parallel to leaf
3. Dicotsveins can be pinnate or palmate
4. Leaves can be used to classify plants
5. Tissue organization of leaves
a. epidermistightly locked cells
 protect
 prevents water loss
b. specialized cells—stomata
 contained in epidermis
 are surrounded by guard cells
 control gas exchange for photosynthesis
 control transpiration—water loss
c. ground tissue of leaf is mesophyll
 mainly parenchyma cells equipped with
chloroplast
d. leaf vascular tissue is continuous with stem
vascular tissue and continuous from roots
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Concept 35.4: Secondary growth adds girth to stems
and roots in woody plants
A. Lateral meristems create girth
1. Secondary vascular tissue
a. vascular cambiumxylem and phloem
b. fasicular cambiumwithin the vascular bundle
c. interfasicular cambiumin the rays between
vascular bundles
d. ray initialsradial files of cells which permit lateral
transport of water and nutrients as well as storage
of starch and other reserves
e. fusiform initialsproduce new vascular tissues;
secondary xylem to the inside of the vascular
cambium and secondary phloem to the outside
2. Periderm
a. cork cambiumtough thick cover that replaces
epidermis
 protects the plant body
 cylinder of fixed size and does not grow in
diameter—creates rings in stems
 becomes woody
B. Secondary growth of roots
1. Vascular cambium
2. Cork cambium
 Older roots become woody
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Concept 35.5: Growth, morphogenesis and
differentiation produce the plant body
 Development is the sum of all changes that
progressively elaborate an organism’s body
 Growth is an irreversible increase in size resulting from
cell division and cell enlargement
 Morphogenesis is the development of body shape and
organization
 Cellular differentiation is the divergence in structure and
function of cells as they become specialized during the
plant’s development
 The cytoskeleton guides cell division and expansion by:
1. Orienting the plane of cell division
2. Orienting the direction of cell expansion—elongation
is the primary direction of cell expansion, very little
plant cell width occurs.
A. Cell differention depends on gene regulation
All cells in a plant posses a common genome
This has been proven by cloning whole plants from
single somatic cells.
1. All the genes necessary are present since
these cells dedifferentiate in tissue cultures and
then redifferentiate to produce the diversity of
cells found in the plant
2. This ability that cellular differentiation is
controlled by gene expression leading to the
production of specific proteins
3. Different cells types selectively express certain
genes at different developmental pathways that
give rise to the diverse cell types
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B. Pattern formation determines the location and tissue
organization of plant organs
 pattern formation is the development of specific
structures in specific locations
 pattern formation depends on positional
information
 positional information are signals indicating a cell’s
location relative to other cells in an embryonic
mass
C. The genetic basis of pattern formation in flower
development
 The shoot tip in flowering plants shifts from
indeterminate growth to determinate growth when
the flower is produced
-the meristem is consumed during the formation
of primordial for sepals, petals, stamens, and
carpels
D. Positional information commits each primordium to
develop into an organ of specific structure and function
 organ identity genes that function in development
of the floral pattern are regulated by positional
information
 mutations in these organ-identity genes can cause
abnormal floral patterns
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