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Ch. 35: Plant Structure and Growth

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Ch. 35: Plant Structure and Growth. The Plant Body A. Consists mainly of three parts: 1. Roots 2. Stems 3. Leaves B. Comparison of monocots v. dicots. The basic morphology of a plant has two systems: 1. Root System : anchor the plant in the soil,

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slide2

The Plant Body

  • A. Consists mainly of three parts:
  • 1. Roots
  • 2. Stems
  • 3. Leaves
  • B. Comparison of monocots v. dicots
slide3

The basic morphology of a plant has two

  • systems:
  • 1. Root System: anchor the plant in the soil,
  • absorb minerals and water, and store food.
  • a. Monocots – fibrous
  • b. Dicots – taproot
  • c. Root hairs –
  • increase the
  • surface area of
  • roots to
  • maximize the
  • absorption.
slide4

Root hairs are made up of epidermal

cells and are one-cell thick.

slide6

The Shoot System: Stems and Leaves

  • Stems: Alternating system of nodes and
  • internodes.
  • Axillary buds:
  • dormant, but
  • can become
  • a vegetative
  • branch.
  • 2.Terminal bud:
  • where growth
  • of a shoot
  • occurs.

 “Apical dominance”

slide7

Modified Stems:

  • a. Stolons: “Runners”
  • Ex. Strawberries
  • b. Rhizomes:
  • horizontal
  • underground
  • Ex. Ginger
  • c. Tubers:
  • swollen
  • rhizomes for
  • food storage
  • Ex. Potatoes
  • d. Bulbs:
  • vertical
  • underground
  • Ex. Onion
slide9

Stolons allow for asexual reproduction.

Daughter plants are clones of the mother

plant.

slide10

Leaves: Main photosynthetic organs of

  • most plants.
  • 1. Blade
  • 2. Petiole:
  • stalk that
  • joins the
  • leaf to the
  • node of the
  • stem.
slide11

Types of Leaves:

Simple v. Compound: simple leaves

have a single, undivided blade, while

compound leaves have several leaflets

attached to the petiole.

slide12

Modified Leaves:

  • a. Tendrils:
  • b. Spines of cacti:
  • c. Succulents:
  • d. Colored leaves:

Cling to support

Defense

Storing water

To attract pollinators

slide14

Plants are composed of three tissue systems:

  • 1. Dermal/Epidermis:
  • 2. Vascular:
  • 3. Ground:

Covers and protects

  • Transports materials between
  • roots and shoots.
  • Xylem: water and minerals
  • Phloem: food/sugars

“filler tissue”; neither dermal

nor vascular; diverse functions such as

photosynthesis, storage, and support.

-Cortex: external

to vascular tissue

-Pith: internal to

vascular tissue

slide15

The three

tissue system

in a plant body:

-Dermal

-Vascular

-Ground

slide16

Vascular tissue structure:

  • Xylem: made up of two kinds of cells
  • -Tracheids and vessel elements
  • -Both types of cells are nonliving at functional
  • maturity; the secondary cell walls remain
  • behind and leave behind tubes through which
  • water can flow.
  • -Water flows from
  • tracheid to
  • tracheid and
  • vessel element
  • to vessel
  • element through
  • pits.

Wider, short

Thin,

tapered

slide17

Phloem: Made up of two types of cells:

  • -Sieve-tube members and companion cells
  • -Sieve-tube members
  • have no nucleus,
  • ribosomes, a distinct
  • vacuole.
  • -Companion cells have
  • a nucleus and ribo-
  • somes and probably
  • assist sieve-tube cells.
  • -Companion cells also
  • help load sugars into
  • the sieve-tubes for
  • transport.
slide18

The Plant Cell Review

Review:

Vacuole Tonoplast

Chloroplast

Primary

cell wall

Secondary

cell wall

Nucleus

Mitochondria

Peroxisome

(Protoplast: Plant cell minus the cell wall)

slide19

F. THREE TYPES OF PLANT CELLS:

  • Parenchyma cells:
  • -“typical” plant cell because they are the least
  • specialized; developing plant cells are
  • parenchyma cells before becoming specialized.

-thin and flexible; most parenchyma cells lack

a tough secondary cell wall.

-most of the metabolic functions occur in

these cells; photosynthesis takes place in the

parenchyma cells of the leaf.

slide20

Collenchyma cells:

  • -thicker, uneven primary cell walls.

-support young parts of the plant shoot.

-lack secondary cell walls; allows for plant

growth, while providing structural support.

slide21

Sclerenchyma cells:

  • -have secondary cell walls making them rigid
  • and supportive.

-many are dead at functional maturity, but

they produce the

secondary walls before

the protoplast dies;

serves as a “skeleton”

that supports the plant.

-2 types of sclerenchyma

cells:

1.Fibers: tough, long

and slender; in groups

2.Sclereids: irregular

shape; gritty texture in

pears

slide22

Plant Growth and Development

  • How do plants develop their different cell
  • types and how do they mature?

A.Most plants continue to grow: “indeterminate

growth”

B.Flowers and leaves undergo “determinate

growth.”

C.Life cycles of plants:

1.Annuals: Plants that complete their life cycle

in a single year or less; food crop.

2.Biennials: life span 2 years, between

germination, growth, and flowering.

3.Perennials: live many years; trees, shrubs,

and some grasses.

slide23

D. Meristem: perpetual embryonic tissue;

continual growth by cell division.

1. Apical meristem: shoots and roots

 Primary growth

slide24

2. Lateral meristems: Secondary growth

  • In contrast, secondary growth is the

progressive thickening of roots and

shoots in woody plants.

slide25

E. Primary growth in roots:

1. Root cap: protection of meristem

2. Zone of cell division: apical meristem

3. Zone of elongation: cells elongate; push

root tip

4. Zone of maturation: differentiation of cells

(3 tissue systems)

slide26

F. Primary tissues in the roots:

1. Stele: vascular bundle (xylem and phloem)

2. Pith: core; parenchyma cells

3. Cortex: region between stele and epidermis;

innermost layer is called endodermis, which

forms the boundary between cortex and stele.

slide27

4. Lateral roots: arise from the pericycle

(outermost layer of stele).

Pericycle cells become meristematic and

start to divide, pushing through the cortex.

slide28

G. Primary tissue of stems:

1. Vascular bundles (xylem and phloem)

surrounded by ground tissues, pith and cortex.

2. Mostly parenchyma; some collenchyma and

sclerenchyma for support.

slide30

1. Epidermis: cuticle; protection and to

prevent dessication

2. Stomata: tiny pores for gas exchange and

transpiration.

3. Guard cells: specialized epidermal cells

4. Mesophyll cells: ground tissue

(palisade and spongy

parenchyma cells).

slide31

Secondary growth of Stems:

  • 1. Two lateral meristems:
  • -Vascular cambium  secondary xylem
  • (wood) and secondary
  • phloem
  • -Cork cambium  tough, thick covering

 Secondary growth is rare in monocots

slide32

How does the vascular cambrium produce

  • secondary xylem and phloem?

-A cambrium cell divides into a cambrium

cell and a derivative cell, which will

differentiate into xylem or phloem.

-As layers of xylem are added, stems

increase in diameter.

slide33

Secondary xylem forms to

the interior and secondary

phloem to the exterior of

the vascular cambium.

slide34

As secondary

growth continues

over the years,

layer upon layer

of secondary xylem

accumulates,

producing the tissue

we call wood.

 Early wood

 Late wood

These are the

lines you count to

estimate the age

of trees.

slide35

How does cambrium cork produce a tough,

  • thick outer covering?
  • -Cork cambium produces cork cells which
  • contain a waxy, waterproof substance.
  • -The cork plus the cork cambium forms the
  • periderm, a protective layer that replaces
  • the epidermis.
slide36

-Lenticils are splits develop in the periderm

because of higher local activity of the cork

cambium.

slide37

-Bark refers to all tissues external to the

vascular cambium, including secondary

phloem, cork cambium, and cork.

slide38

-Only the youngest secondary phloem,

internal to the cork cambium, functions in

sugar transport.

-Older phloem dies and sloughs off as

bark later.

slide39

-After several years of growth, several

zones are visible in the stem.

a. Two zones of xylem:

-Heartwood (dead; structural purpose)

-Sapwood

b. Vascular cambium

c. Living phloem

d. Cork cambium

e. Cork

slide40

Mechanisms of Plant Growth and Development

  • Arabidopsis thaliana, a weed of the mustard
  • family was the first plant to have its entire
  • genome sequenced.
  • 1. 26,000 genes; many duplicates; 15,000
  • different genes;
  • 45% unknown
slide41

Growth, morphogenesis, and differentiation

  • produce the plant body
  • 1. Morphogenesis: development of body
  • form and organization
  • 2. Differentiation: cellular diversity
  • Plant growth depends on the plane
  • (direction) of cell division.
slide42

Plant growth depends on the symmetry of

  • cell division.
  • Assymetrical cell division, in which one
  • cell receives more cytoplasm than the
  • other, is common in plants cells and
  • usually signals a key developmental event.
  •  Guard cells
slide43

The plane of cell division is determined during

  • late interphase.

-Microtubules

concentrate

into a ring called

the preprophase

band.

-Actin micro-

filaments direct

the formation of

cell plates.

slide44

Morphogenesis depends on pattern formation

  • Pattern formation: development of
  • specific structures in specific locations.
  • Pattern formation depends on positional
  • information - signals that indicate a cell’s
  • location.
  • Homeotic genes: genes that regulate
  • pattern formation.
  • Protein product ofKNOTTED-1 homeotic
  • gene is important
  • for the development
  • of compound leaves.
  •  Over expression
  • of this gene
  • creates
  • “supercompound” leaves.
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