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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  • 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,

  • 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.

Root hairs are made up of epidermal

cells and are one-cell thick.

  • 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”

  • 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

Stolons allow for asexual reproduction.

Daughter plants are clones of the mother


Simple v. Compound: simple leaves

have a single, undivided blade, while

compound leaves have several leaflets

attached to the petiole.

  • Modified Leaves:

  • a. Tendrils:

  • b. Spines of cacti:

  • c. Succulents:

  • d. Colored leaves:

Cling to support


Storing water

To attract pollinators

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

The three

tissue system

in a plant body:




  • 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



  • 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.


Vacuole Tonoplast



cell wall


cell wall




(Protoplast: Plant cell minus the cell wall)


  • 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.

-support young parts of the plant shoot.

-lack secondary cell walls; allows for plant

growth, while providing structural support.

-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


1.Fibers: tough, long

and slender; in groups

2.Sclereids: irregular

shape; gritty texture in


A.Most plants continue to grow: “indeterminate


B.Flowers and leaves undergo “determinate


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.

D. Meristem: perpetual embryonic tissue;

continual growth by cell division.

1. Apical meristem: shoots and roots

 Primary growth

2. Lateral meristems: Secondary growth

  • In contrast, secondary growth is the

    progressive thickening of roots and

    shoots in woody plants.

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)

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.

4. Lateral roots: arise from the pericycle

(outermost layer of stele).

Pericycle cells become meristematic and

start to divide, pushing through the cortex.

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.

1. Epidermis: cuticle; protection and to

prevent dessication

2. Stomata: tiny pores for gas exchange and


3. Guard cells: specialized epidermal cells

4. Mesophyll cells: ground tissue

(palisade and spongy

parenchyma cells).

  • 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

-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.

Secondary xylem forms to

the interior and secondary

phloem to the exterior of

the vascular cambium.

As secondary

growth continues

over the years,

layer upon layer

of secondary xylem


producing the tissue

we call wood.

 Early wood

 Late wood

These are the

lines you count to

estimate the age

of trees.

  • 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.

-Lenticils are splits develop in the periderm

because of higher local activity of the cork


-Bark refers to all tissues external to the

vascular cambium, including secondary

phloem, cork cambium, and cork.

-Only the youngest secondary phloem,

internal to the cork cambium, functions in

sugar transport.

-Older phloem dies and sloughs off as

bark later.

-After several years of growth, several

zones are visible in the stem.

a. Two zones of xylem:

-Heartwood (dead; structural purpose)


b. Vascular cambium

c. Living phloem

d. Cork cambium

e. Cork

  • 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

  • Plant growth depends on the plane

  • (direction) 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



into a ring called

the preprophase


-Actin micro-

filaments direct

the formation of

cell plates.

  • 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.