Lecture 5 Outline (Ch. 35)

I. Overview – Plant Systems

II. Plant cell types & tissuesCell Types: Parenchyma, Collenchyma, Sclerenchyma

A. Dermal B. Vascular C. Ground

III. Plant organs A. Roots B. Stems C. Leaves

IV. Plant Growth A. Meristems B. Primary vs. secondary

V. Preparation for next lecture

Plant Structure, Growth, Development

Plants are notably different from animals:1. SA:V ratio2. Mobility3. Growth4. Response to environment5. Cell structure

Setting the scene - animal bodies

Cells Tissues Organs Systems

Plant “bodies”

Three Basic Plant Organs:

Roots, Stems, and Leaves(also flowers, branches)

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 system

– Roots– Shoots– Vascular

Plant Tissues

Dermaltissue

Groundtissue Vascular

tissue

1) Dermal Tissues

• Outer covering

• Protection

3) Ground Tissues

• “Body” of plant

• Photosynthesis; storage; support

2) Vascular Tissues

• “Vessels” throughout plant

• Transport materials

Plant Tissues

Three basic cell types:

ParenchymaCollenchymaSclerenchyma

What type of tissue transports fluids in plants?

A. Dermal

B. Roots

C. Vascular

D. Stems

E. Ground

Plant Cell Types

Plant cell structure recap

Cell wall, plasmodesmata

Primary wall (some have secondary wall), middle lamella

Plant Cell Types

1) ParenchymaParenchyma (most abundant):

• plant metabolism:

Photosynthesis; hormone secretion; sugar storage

Flexible, thin-walled cells; living

Parenchyma cells in Elodea leaf,(w/chloroplasts) • thin wall permeable to gasses

• large central vacuole

• able to divide and differentiate

2) CollenchymaCollenchyma:

Thick-walled (uneven); living

• Offers support (flexible & strong)• Able to elongate• Grouped in strands, lack secondary wall

Collenchyma cells sunflower

Plant Cell Types

3) SclerenchymaSclerenchyma: Thick, hard-walled; Dead• Offer support (e.g. hemp fibers; nut shells)• Thick secondary walls with lignin• Rigid (cannot elongate)• Two types – sclereids and fibers

Sclereid cells in pear (LM)

Fiber cells in ash tree

Cell wall

Plant Cell Types

Which is a plant cell type?

A. secondary

B. vascular

C. ground

D. collenchyma

E. leaves

Dermal Tissue System (Covering of Plant):

1) Epidermal Tissue

(epidermis): Outer layer

Cuticle: Waxy covering -

reduces evaporation/ predation

Root Hairs: extended root

surface - Increase absorption

Plant Tissues - Dermis

2) Peridermal Tissue (periderm):

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

• Protection; support

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

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

Vascular tissues made up of multiple cell types:

Plant Tissues - Vascular

Arranged in multiple bundles or central cylinder

Xylem – water and nutrientsPhloem – dissolved sugars and metabolites

1) Xylem (dead at maturity): water and minerals roots to shoots

Plant Tissues - Vascular

A) Tracheids: Narrow, tube-like cells

B) Vessel Elements: Wide, tube-like cells

C) Fibers

1) Xylem:

Plant Tissues - Vascular

Tracheids:- Most vascular plants- Long, thin, tapered ends, lignified secondary walls- Water moves cell to cell through pits

Vessel elements:- Wider and shorter- Perforation plates ends of vessel elements- water flows freely though perforation plates

A) Sieve Tubes: Wide, tube-like cells

B) Companion Cells: support and regulate sieve tubes

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

- Moves water, sugar, amino acids & hormones

2) Phloem (living at maturity)

Plant Tissues - Vascular

Sieve tube elements/members• Living parenchyma• Long narrow cells stack end to end• Pores in end walls (sieve plates)• Lack most cellular structures including:• Distinct vacuole, Some cytoskeletal elements, Nucleus, Ribosomes

Companion Cells:• Adjacent to every sieve tube element• Non-conducting.• Regulate both cells • Connected by numerous plasmodesmata

Dicots Monocots

Vasculature - Comparisons

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

Root

Stem

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

• 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

Mo

no

cot

Eu

dic

ot

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

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

Vasculature - Stems

Dicot Monocot

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

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

Leaves

• Leaf epidermis contains stomata - allow CO2 exchange

• Stomata flanked by two guard cells, control open vs. closed

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)

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 Classification – Monocots vs. Dicots

Basic categories of plants based on structure and function

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

A cross section of what tissue is pictured?

A. Monocot root

B. Dicot root

C. Monocot stem

D. Dicot stem

Things To Do After Lecture 5…Reading and Preparation:

1. Re-read today’s lecture, highlight all vocabulary you do not understand, and look up terms.

2. Ch. 35 Self-Quiz: #1, 3, 6, 7 (correct answers in back of book)

3. Read chapter 35, focus on material covered in lecture (terms, concepts, and figures!)

4. Skim next lecture.

“HOMEWORK” (NOT COLLECTED – but things to think about for studying):

1. Compare and contrast monocots and dicots.

2. List the different types of plant cells and describe which tissues and organs they make up, including roles for each organ.

3. Explain the different between apical and lateral meristems and how growth occurs.

4. Discuss the composition of bark and it’s function for plants (do all plants have this tissue?)