CHAPTER 29

Plant Tissues

MOUNT SAINT HELENS ERUPTION

Volcano is located in southwestern

Washington state

In 1980 it erupted, blowing 500

million metric tons of rock and ash

outward

Ash and lava devastated about

40,500 acres of what had been

forest

RECOVERY

Plants moved into the empty habitat

almost immediately

Fireweed and blackberry were early

colonists

In less than ten years, willow and

alders were on the scene

SUCCESS OF THE ANGIOSPERMS

The angiosperms are seed-bearing vascular plants

In terms of distribution and diversity, they are the most successful plants on Earth

The structure and function of this plant group help explain its success

SHOOTS AND ROOTS

Shoots Produce food by photosynthesis Carry out reproductive functions

Roots Anchor the plant Penetrate the soil and absorb

water and dissolved minerals Store food

Shoot Apical Meristem

primary meristems active

epidermis, ground tissues, primary vascular tissues forming

epidermis, ground tissues,

primary vascular

tissues forming

primary meristems

active

Root Apical Meristem

Fig. 29-3a, p.494

Protoderm

Ground meristem

Procambium

epidermis

ground tissues

primary vascular tissues

a The cellular descendants of apical meristems divide, grow, and differentiate. They form three primary meristems, the activity of which lengthens shoots and roots:

Fig. 29-3a1, p.494

vascular cambium

cork cambium

Lateral Meristems

thickening

Fig. 29-3b, p.494

ANGIOSPERM BODY PLAN

VASCULAR TISSUES

GROUND TISSUES

SHOOT SYSTEM

ROOT SYSTEM

EPIDERMIS

Ground tissue system

Vascular tissue system

Dermal tissue system

Fig. 29-2, p.494

MONOCOTS AND DICOTS:

Parallel veinsNetlike veins

3 pores1 pore

4 or 5 floral parts

3 floral parts

1 cotyledon 2 cotyledons

Vascular bundles dispersed

Vascular bundles in ring

SIMPLE TISSUES

Made up of only one type of cell

ParenchymaCollenchymaSclerenchyma

PARENCHYMA: A SIMPLE TISSUE

Most of a plant’s soft primary growth

Pliable, thin walled, many sided cells

Cells remain alive at maturity and retain capacity to divide

Mesophyll is a type that contains chloroplasts

stem epidermissimple and complex tissues inside the stem

parenchymavessel

of xylem phloem

fibers of sclerenchym

a

Fig. 29-6, p.496

COLLENCHYMA: A SIMPLE TISSUE

Specialized for support for primary tissues

Makes stems strong but pliable Cells are elongated Walls thickened with pectin Alive at maturity

COLLENCHYMA: A SIMPLE TISSUE

Supports mature plant parts Protects many seeds Thick, lignified walls Dead at maturity Two types:

Fibers: Long, tapered cells Sclereids: Stubbier cells

collenchyma parenchyma lignified secondary wall

Fig. 29-7, p.496

COMPLEX TISSUES

Composed of a mix of cell types

Xylem

Phloem

Epidermis

XYLEM

Conducts water

and dissolved minerals

Conducting cells are dead and hollow at maturity vessel

membertracheids

one cell’s wall

pit in wall

sieve plate of

sieve tube cell

companion cell

a bc

Fig. 29-8, p.497

PHLOEM: A COMPLEX VASCULAR TISSUE

Transports sugars

Main conducting cells are sieve-tube members

Companion cells assist in the loading of sugars

sieve plate

sieve-tube

membercompanio

ncell

EPIDERMIS: A COMPLEX PLANT TISSUE

Covers and protects plant

surfaces

Secretes a waxy, waterproof

cuticle

In plants with secondary

growth, periderm replaces

epidermis

leaf surface cuticleepidermal cellphotosynthet

ic cell

Fig. 29-9, p.497

MERISTEMS

Regions where cell divisions produce plant growth

Apical meristems Lengthen stems and roots Responsible for primary growth

Lateral meristems Increase width of stems Responsible for secondary growth

APICAL MERISTEMS

activity atmeristems

new cellselongateand start todifferentiateinto primarytissues

activity atmeristems

new cellselongateand start todifferentiateinto primarytissues

Root apical meristem

Shoot apical meristem

immature leaf

shoot apical meristem

lateral bud forming

vascular tissues

pith

cortex

Fig. 29-10a2, p.498

immature leaf

shoot apical

meristem

descendant meristems (orange)

b Sketch of the shoot tip, corresponding to (a) Fig. 29-10b, p.498

TISSUE DIFFERENTIATION

Protoderm

Ground meristem

Procambium

Epidermis

Ground tissue

Primary vascular

tissue

LATERAL MERISTEMS

Increase girth of older roots and stems

Cylindrical arrays of cells

vascular cambiumcork cambium

thickening

Figure 29.20.aPage 504

SHOOT DEVELOPMENT

immature leaf

ground meristem

primary phloem

primary xylempith

procambium

cortex

procambium

protoderm

shoot apical meristem

procambium

epidermis

Figure 29.10 Page 498

immature leafshoot apical

meristem descendant meristems (orange)

Stepped Art

Fig. 29-10b-d, p.498

primary phloem

primary xylem pith

cortex

TISSUE DIFFERENTIATION

Vascular cambium

Cork cambium

Secondary vascular

tissue

Periderm

INTERNAL STRUCTURE OF A DICOT STEM

Outermost layer is epidermis Cortex lies beneath epidermis Ring of vascular bundles

separates the cortex from the pith

The pith lies in the center of the stem

Figure 29.11.aPage 499

INTERNAL STRUCTURE OF A MONOCOT STEM

• The vascular

bundles are

distributed

throughout the

ground tissue• No division of

ground tissue into

cortex and pithFigure 29.11.b

Page 499

cortex

epidermis

vascular bundle

pith

vessel in

xylem meristem cell

sieve tube in phloem

companion cell in phloem

Fig. 29-11a, p.499

epidermis

vascular bundle

pith

vessel in

xylemcollenchym

a sheath

sieve tube in phloem

companion cell in

phloem

air space

Fig. 29-11b, p.499

COMMON LEAF FORMS

petiole

blade

axillarybud

node

blade

sheath

node

DICOT MONOCOT

Figure 29.12.a,bPage 500

ADAPTED FOR PHOTOSYNTHESIS

Leaves are usually thin High surface area-to-volume ratio Promotes diffusion of carbon dioxide in,

oxygen out Leaves are arranged to capture

sunlight Are held perpendicular to rays of sun Arranged so they don’t shade one

another

POPLAR (Populus)

OAK (Quercus)

MAPLE (Acer)

leaflet

RED BUCKEYE (Aesculus)

BLACK LOCUST (Robina)

HONEY LOCUST (Gleditsia)

Fig. 29-12c,d, p.500

LEAF STRUCTURE

UPPEREPIDERMIS

PALISADEMESOPHYLL

SPONGYMESOPHYLL

LOWEREPIDERMIS

one stoma

cuticle

O2CO2

xylem

phloem

Figure 29.14.bPage 501

leaf blade

leaf vein

stem

Leaf Vein(one vascular bundle) cuticle

Upper Epidermis

Lower Epidermis

Palisade Mesophyll

Spongy Mesophyll

50m

xylem

phloem

cuticle-coated cell of lower epidermis

one stoma (opening across epidermia)

Oxygen and water vapor diffuse out

of leaf at stomata.

Carbon dioxide in outside air enters leaf at stomata.

Water, dissolved mineral ions from roots and stems move into leaf vein (blue arrow)

Photosynthetic products (pink arrow) enter vein, will be transported throughout plant body Fig. 29-14, p.501

MESOPHYLL:PHOTOSYNTHETIC TISSUE

A type of parenchyma

tissue

Cells have chloroplasts

Two layers in dicots Palisade mesophyll

Spongy mesophyll

LEAF VEINS: VASCULAR BUNDLES

Xylem and phloem; often

strengthened with fibers

In dicots, veins are netlike

In monocots, they are

parallel

Fig. 29-15a, p.501

Leaf Veins

Fig. 29-15b, p.501

Leaf Veins

ROOT SYSTEMS

Taproot system of a California poppy

Fibrous root system of a grass plant

Figure 29.19Page 503

ROOT STRUCTURE

Root cap covers tip Apical meristem

produces the cap Cell divisions at the

apical meristem cause the root to lengthen

Farther up, cells differentiate and mature Figure

29.16.aPage 502

INTERNAL STRUCTURE OF A ROOT

Outermost layer is epidermis

Root cortex is beneath the

epidermis

Endodermis, then pericycle

surround the vascular cylinder

In some plants, there is a central

pith

primary xylem

primary phloem

epidermis

VASCULAR

CYLINDER

cortex

pith

Fig. 29-17, p.503

FUNCTION OF ENDODERMIS

Ring of cells surrounds vascular cylinder

Cell walls are waterproof

Water can only enter vascular cylinder by

moving through endodermal cells

Allows plant to control inward flow

ROOT HAIRS AND LATERAL ROOTS

Both increase the surface area of a root system

Root hairs are tiny extensions of epidermal cells

Lateral roots arise from the pericycle and must push through the cortex and epidermis to reach the soil

newlateralroot

SECONDARY GROWTH

Occurs in all gymnosperms,

some monocots, and many

dicots

A ring of vascular cambium

produces secondary xylem and

phloem

Wood is the accumulation of

these secondary tissues,

especially xylem

WHAT HAPPENS AT VASCULAR CAMBIUM?

Fusiform initials give rise to secondary xylem and phloem

Ray initials give rise to horizontal rays of parenchyma

Fig. 29-20, p.504

Fig. 29-22, p.505

Woody Roots

FORMATION OF BARK

All tissues outside vascular cambium

Periderm Cork New parenchyma Cork cambium

Secondary phloem

periderm (includes cork cambium, cork, new parenchyma)

secondary phloem

BARK

vascular cambium

HEARTWOOD SAPWOOD

Fig. 29-24a, p.507

1587–1589 1606–1612

Fig. 29-27c, p.509

Annual RingsNarrow annual rings mark severe

drought years