SC.912.L.14.7Plant Structures and Functions

Plant Structures and Functions 1. Monocots vs. Dicots

- Root structure and vasculature- Stem vasculature- Leaf structure and vasculature

2. Plant tissues - Dermal (epidermis)- Vascular- Ground- Meristematic

3. Plant organs - Roots- Stems- Leaves - Flowers and Cones

4. Plant Growth - Meristems – apical, axillary, lateral- Vascular cambium vs. cork cambium

Plant Classification – Monocots vs. Dicots

Basic categories of plants based on structure and function

Plant “bodies”

Three Basic Plant Organs:

Roots, Stems, and Leaves

Plants, like multicellular animals, have organs composed of different tissues, which in turn are composed of cells

Shootsystem

Leaf

Stem

Rootsystem

• Each plant organ has dermal, vascular, and ground tissues

• Each of these three categories forms a tissue system

Plant Tissues

Dermaltissue

Groundtissue Vascular

tissue

1) Dermal Tissue System

• Outer covering

• Protection

3) Ground Tissue System

• “Body” of plant

• Photosynthesis; storage; support

2) Vascular Tissue System

• “Vessels” throughout plant

• Transport materials

Plant Tissues

Dermal Tissue System (Outer Covering of Plant):

1) Epidermal Tissue (epidermis):

• Forms outermost layer

Cuticle: Waxy covering

• Reduces evaporation

• Inhibits microorganism invasion

Root Hairs: extended root surface

• Increase absorption

2) Peridermal Tissue (periderm):

• Only in woody plants (“bark = dead cells”)

• Protection; support

Plant Tissues - Dermis

Guard cells

Stoma

Epidermal cell

Guard cells

Stomata

Epidermal cell

Guard cells

Stoma

Epidermal cell

Guard cells

Stomata

Epidermal cell

4 µm 200 µm

71 µm

a. c.

b.

Plant Tissues - Dermis

Paired sausage-shaped cells

Flank a stoma – epidermal opening

• Passageway for oxygen, carbon dioxide, and water vapor

Special Dermal Cells – Guard Cells

Plant Tissues - Dermis

Special Dermal Cells – Trichomes & Root hairs

• Trichomes– Hairlike outgrowths of

epidermis – Keep leaf surfaces cool

and reduce evaporation

• Roots hairs– Tube extensions from

epidermal cells– Greatly increase the root’s

surface area for absorption

1) Xylem (dead at maturity):

Plant Tissues - Vascular

A) Tracheids: Narrow, tube-like cells

B) Vessel Elements: Wide, tube-like cells

Vascular Transport System

1) Xylem (dead at maturity):

- Moves water & minerals from roots to shoots

Plant Tissues - Vascular

A) Sieve Tubes: Wide, tube-like cells

B) Companion Cells: support and regulate

sieve tubes

2) Phloem (living at maturity)Plant Tissues - Vascular

Vascular Transport System

- Moves water, sugar, amino acids & hormones2) Phloem (living at maturity)

Plant Tissues - Vascular

Dicots Monocots

Vasculature - Comparisons

Monocots and dicots differ in the arrangement of vessels in the roots and stems

Root

Stem

• Some major types of plant cells:– Parenchyma– Collenchyma– Sclerenchyma

Plant Tissues – Ground Tissue

• Tissues that are neither dermal nor vascular are ground tissue

• Ground tissue internal to the vascular tissue is pith; ground tissue external to the vascular tissue is cortex

• Ground tissue includes cells specialized for storage, photosynthesis, and support

Plant Tissues - Ground

Ground Tissue System (“Body” of Plant):

1) ParenchymaParenchyma (most abundant):

• plant metabolism:

Photosynthesis; hormone secretion; sugar storage

Thin-walled cells; living

Parenchyma cells in Elodea leaf,(w/chloroplasts)

Plant Tissues - Ground

2) CollenchymaCollenchyma:

Thick-walled (uneven);

living

• Offers support (flexible & strong)

Ground Tissue System (“Body” of Plant):

Collenchyma cells sunflower

Plant Tissues - Ground

3) SclerenchymaSclerenchyma:

Thick, hard-walled; Dead

• Offer support (e.g. hemp fibers; nut shells)

Ground Tissue System (“Body” of Plant):

Sclereid cells in pear (LM)

Fiber cells in ash tree

Cell wall

• Roots need sugars from photosynthesis; • Shoots rely on water and minerals

absorbed by the root system

Roots - Overview

• Root Roles:

- Anchoring the plant

- Absorbing minerals and water

- Storing organic nutrients

Taproots: Fibrous roots:

Typical of dicots, primary root forms and small branch roots grow from it

In monocots mostly, primary root dies, replaced by new roots from stem

Roots - Comparisons

Roots – Structure and Development

• Four regions:– Root capProtection, gravity detection

– Zone of cell divisionMitotic divisions

– Zone of elongationCells lengthen, no division

– Zone of maturationCells differentiate, outer layer

becomes dermis

Roots – Structure and Development

In maturation zone, Casparian strip forms – waterproof barrier material surrounding vasculature

Roots – Structure and Development

1250 µm

Epidermis

Primary phloem

Primary xylem

Pith

Endodermis

Cortex

Epidermis

Primary xylem

Pericycle

Primary phloem

48 µm

385 µm

8 µm

EndodermisLocation ofCasparian strip

EndodermisLocation ofCasparian strip

Cortex

Pericycle

Prop roots

“Strangling”aerial roots

Storage roots

Buttress roots

Pneumatophores

Roots – Many Plants Have Modified Roots

Water storage

Stem: an organ made of– An alternating system of

nodes, points at which leaves attach

– Internodes, stem length between nodes

Stems - Overview

• Axillary bud - structure that can form a lateral shoot, or branch

• Apical/terminal bud - located near the shoot tip, lengthens a shoot

• Apical dominance maintains dormancy in most nonapical buds

Apical bud

Node

Internode

Apicalbud

Shootsystem

Vegetativeshoot

Axillarybud

Stem

Stems – Structure and Development

• Stems have all three types of plant tissue

• Grow by division at meristems– Develop into leaves, other

shoots, and even flowers

• Leaves may be arranged in one of three ways

Stems - Comparisons

Monocot

Eudicot

Rhizomes

Bulbs

Storage leaves

Stem

Stolons

Stolon

Tubers

Stems – Many Plants Have Modified Stems

The leaf is the main photosynthetic organ of most vascular plants

Leaves - Overview

Shootsystem

LeafBlade

Petiole

Leaves generally have

a flattened blade

and a stalk called the petiole, which joins the leaf to a node of the stem

Leaves – Structure and Development

• Leaves are several layers thick – each with different cell types

Leaves – Structure and Development

• Most dicots have 2 types of mesophyll– Palisade mesophyllhigh photosynthesis

– Spongy mesophyllair spaces for gas

& water exchange

• Monocot leaves have 1 type of mesophyll

Most dicots have branch-like veins and palmate leaf shape

Monocots have parallel leaf veins and longer, slender blades

Leaves - Comparisons

Monocots and dicots differ in the arrangement of veins, the vascular tissue of leaves

Tendrils

Spines

Storageleaves

Reproductive leaves

Bracts

Leaves – Plants have modified leaves for various functions

Plant Growth:

1) Indeterminate: Grow throughout life

2) Growth at “tips” (length) and at “hips” (girth)

Growth patterns in plant:

1) Meristem Cells: Dividing Cells

2) Differentiated Cells: Cells specialized in structure & role

• Form stable, permanent part of plant

Plant Growth

1) Primary Growth:

1) Increased length

2) Specialized structures (e.g. fruits)

2) Secondary Growth:

Responsible for increases in stem/root diameter

• Apical Meristems: Mitotic cells at “tips” of roots / stems

• Lateral Meristems: Mitotic cells “hips” of plant

Plant Growth

girth

length

Shoot apical meristem Leaf primordia

Youngleaf

Developingvascularstrand

Axillary budmeristems

Plant Growth

Shoot tip (shootapical meristemand young leaves)

Lateral meristems:

Axillary budmeristem

Vascular cambiumCork cambium

Root apicalmeristems

Primary growth in stems

Epidermis

Cortex

Primary phloem

Primary xylem

Pith

Secondary growth in stems

Periderm

Corkcambium

Cortex

Primaryphloem

Secondaryphloem

Pith

Primaryxylem

Secondaryxylem

Vascular cambium

Plant GrowthTwo lateral meristems: vascular cambium and cork cambium

Stem – Secondary Growth:

• thicker, stronger stems

Vascular Cambium: between

primary xylem and phloem

primary phloem

vascular cambium

primary xylem

epidermis

cortexpith

primary xylem

primary phloem

dividingvascularcambium

Plant Growth

Produces inside stem:

A) Secondary xylem - moves H2O, inward

B) Secondary phloem - moves sugars, outward

Plant Growth

primaryphloem

dividingvascularcambium

newsecondaryxylem

newsecondaryphloem

primaryxylem

secondary phloemprimary phloem

vascular cambium

primary xylemsecondary xylem

pithcortex

Secondary growth

Vascular Cambium:

Vascular cambium Growth

Secondaryxylem

After one yearof growth

After two yearsof growth

Secondaryphloem

VascularcambiumX X

X X

X

X

P P

P

P

C

C

C

C

C

C

C C C

C C

CC

Stem – Secondary Growth:

Dead at maturityProtection

Cork Cambium:• Located under outer surface; produces periderm

Plant Growth

Growthring

Vascularray

Secondaryxylem

Heartwood

Sapwood

Bark

Vascular cambium

Secondary phloem

Layers of periderm

annual ring

earlyxylem

latexylem

heartwood(xylem)sapwood(xylem)vascularcambium

phloem

Stem – Secondary Growth:

Sapwood = Young xylem, water

Heartwood = Old xylem, support

Seasonal Growth = annual rings

Secondary phloem = grows outward older phloem crushed

Plant Growth

RESULTS

Rin

g-w

idth

ind

exes

2

1.5

0.5

1

01600 1700 1800 1900 2000

Year

Plant Growth

Using dendrochronology to study climate

Plant Growth

Living tree or dead tree?

Epidermis

Cortex

Endodermis

Vascularcylinder

Pericycle

Core ofparenchymacells

Xylem

Phloem100 µm

Root with xylem and phloem in the center(typical of eudicots)

(a)

Root with parenchyma in the center (typical ofmonocots)

(b)

100 µm

Endodermis

Pericycle

Xylem

Phloem

Keyto labels

Dermal

Ground

Vascular

Plant Growth - Roots

Phloem Xylem

Sclerenchyma(fiber cells)

Ground tissueconnectingpith to cortex

Pith

Cortex

1 mm

EpidermisVascularbundle

Cross section of stem with vascular bundles forminga ring (typical of eudicots)

(a)

Keyto labels

Dermal

Ground

Vascular

Cross section of stem with scattered vascular bundles(typical of monocots)

(b)

1 mm

Epidermis

Vascularbundles

Groundtissue

• In most monocot stems, the vascular bundles are scattered throughout the ground tissue, rather than forming a ring

Plant Growth - Stems

Plant Growth - Leaves• Leaf epidermis contains stomata - allow CO2 exchange

• Stomata flanked by two guard cells, control open vs. closed• The ground tissue in a leaf, called mesophyll, fills the middle

Keyto labels

Dermal

Ground

VascularCuticle Sclerenchyma

fibersStoma

Bundle-sheathcell

Xylem

Phloem

(a) Cutaway drawing of leaf tissues

Guardcells

Vein

Cuticle

Lowerepidermis

Spongymesophyll

Palisademesophyll

Upperepidermis

Guardcells

Stomatalpore

Surface view of a spiderwort(Tradescantia) leaf (LM)

Epidermalcell

(b)

50 µ

m10

0 µ

m

Vein Air spaces Guard cells

Cross section of a lilac(Syringa)) leaf (LM)

(c)

Plant Structures and Functions Summary

1. Monocots vs. Dicots - Root structure and vasculature- Stem vasculature- Leaf structure and vasculature

2. Plant tissues - Dermal (epidermis)- Vascular- Ground

3. Plant organs - Roots- Stems- Leaves

4. Plant Growth - Meristems – apical, axillary, lateral- Vascular cambium vs. cork cambium