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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Ch. 35: Plant Structure and Growth

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Ch 35 plant structure and growth

Ch. 35: Plant Structure and Growth


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


Ch 35 plant structure and growth

  • 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.


Ch 35 plant structure and growth

Root hairs are made up of epidermal

cells and are one-cell thick.


Ch 35 plant structure and growth

  • 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”


Ch 35 plant structure and growth

  • 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


Ch 35 plant structure and growth

Bermuda Grass


Ch 35 plant structure and growth

Stolons allow for asexual reproduction.

Daughter plants are clones of the mother

plant.


Ch 35 plant structure and growth

  • Leaves: Main photosynthetic organs of

  • most plants.

  • 1. Blade

  • 2. Petiole:

  • stalk that

  • joins the

  • leaf to the

  • node of the

  • stem.


Ch 35 plant structure and growth

  • Types of Leaves:

Simple v. Compound: simple leaves

have a single, undivided blade, while

compound leaves have several leaflets

attached to the petiole.


Ch 35 plant structure and growth

  • Modified Leaves:

  • a. Tendrils:

  • b. Spines of cacti:

  • c. Succulents:

  • d. Colored leaves:

Cling to support

Defense

Storing water

To attract pollinators


Ch 35 plant structure and growth

  • 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


Ch 35 plant structure and growth

The three

tissue system

in a plant body:

-Dermal

-Vascular

-Ground


Ch 35 plant structure and growth

  • 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


Ch 35 plant structure and growth

  • 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.


Ch 35 plant structure and growth

  • The Plant Cell Review

Review:

Vacuole Tonoplast

Chloroplast

Primary

cell wall

Secondary

cell wall

Nucleus

Mitochondria

Peroxisome

(Protoplast: Plant cell minus the cell wall)


Ch 35 plant structure and growth

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.


Ch 35 plant structure and growth

  • 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.


Ch 35 plant structure and growth

  • 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


Ch 35 plant structure and growth

  • 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.


Ch 35 plant structure and growth

D. Meristem: perpetual embryonic tissue;

continual growth by cell division.

1. Apical meristem: shoots and roots

 Primary growth


Ch 35 plant structure and growth

2. Lateral meristems: Secondary growth

  • In contrast, secondary growth is the

    progressive thickening of roots and

    shoots in woody plants.


Ch 35 plant structure and growth

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)


Ch 35 plant structure and growth

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.


Ch 35 plant structure and growth

4. Lateral roots: arise from the pericycle

(outermost layer of stele).

Pericycle cells become meristematic and

start to divide, pushing through the cortex.


Ch 35 plant structure and growth

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.


Ch 35 plant structure and growth

H. Primary tissues in leaves:


Ch 35 plant structure and growth

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).


Ch 35 plant structure and growth

  • 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


Ch 35 plant structure and growth

  • 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.


Ch 35 plant structure and growth

Secondary xylem forms to

the interior and secondary

phloem to the exterior of

the vascular cambium.


Ch 35 plant structure and growth

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.


Ch 35 plant structure and growth

  • 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.


Ch 35 plant structure and growth

-Lenticils are splits develop in the periderm

because of higher local activity of the cork

cambium.


Ch 35 plant structure and growth

-Bark refers to all tissues external to the

vascular cambium, including secondary

phloem, cork cambium, and cork.


Ch 35 plant structure and growth

-Only the youngest secondary phloem,

internal to the cork cambium, functions in

sugar transport.

-Older phloem dies and sloughs off as

bark later.


Ch 35 plant structure and growth

-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


Ch 35 plant structure and growth

  • 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


Ch 35 plant structure and growth

  • 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.


Ch 35 plant structure and growth

  • 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


Ch 35 plant structure and growth

  • 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.


Ch 35 plant structure and growth

  • 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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