Plant Science Test 2

Where does growth mainly occur?

At shoot and root tips and in special growth zones like buds

How does growth occur?

Size increase often caused by increasing the size of cells by absorbing water into the vacuole

Cell Specialization

Most plant cells can differentiate into different cell types

2 Main Meristems in Early Plant Growth

• Shoot apical

  • Stem, leaves

• Root apical

  • Roots

Shoot Apical Meristem

• Corpus produces tissues that divide and differentiate into 3 new growth zones

  • Protoderm

  • Provascular

  • Ground Tissue

Protoderm

• Produced very early as egg divides

• Produces epidermal cells

Provascular

• Produces xylem, phloem, & vascular cambium

• Xylem = interior

• Phloem = exterior

• Vascular cambium = middle

  • Produces wood later

Ground Meristem

• Produces all other tissues

• Mainly parenchyma

• Pith

• Cortex

1st Vascular Plant Stem

• Protosteles

  • Roots

2nd Vascular Plant Stem

• Siphonosteles

  • 1st seed plants

Protosteles

Xylem cells mature outside to inside (exarch maturation)

Siphonosteles

Xylem cells mature from inside to outside (end arch maturation)

Last Vascular Plant Stem

• Eustele

  • Seed plants

2 Types of Stems

• Woody

• Herbaceous

Woody Plants

• Plants that produce wood as its structural tissue

• Have a strong stem

• Stem is covered with a bark

• Tallest and largest plants on Earth

• Mainly perennials

Herbaceous Plants

• Plants that have no persistent woody stem above ground

• Have a flexible stem

• Stem stays green

• Comparatively short and small

• Annual, biennials, or perennials

Functions of Stems

• Producing leaves

• Places leaves in optimal photosynthetic position

• Long-distance water and food conduction

• Storage (food, water, minerals, etc)

• Perennating organs

• Dispersal agents

• Housing symbiotic organisms

Root underground environment

Stable with little change

Root Functions

• Anchoring

• Storage

• Survival

• Support

• Form networks to catch organic debris

• Haustoria

• Hormone / vitamin sources

Taproots

• Main anchoring root

• Usually weakly woody

• Ex. carrot, turnip

Monocot Roots

• Coleorrhiza grows a day or two, then dies

• Adventitious roots grow from bottom of hypocotyl

• Fibrous

Lateral Roots

• Initiated by hormone auxin from s.a.m.

• Preicycle redifferentiates to produce new r.a.m.

• Link new xylem with old xylem

Adventitious Roots

• Grow from non-root areas

• Add support or increase absorption

Haustoria Roots

• Helps penetrate host plate

• Usually only exterior organ of parasitic plant

• Pulls embryo into host plant

• Ex. mistletoe

Mycorrhizae

• Type of mycorrhizae

• Fungal root

• 2 Types

  • Ectomycorrhizae

  • Endomycorrhizae

Ectomycorrhizae

• Fungi that surround and attach to the root exterior

• Tap into root epidermis / extreme outer cortex

Endomycorrhizae

• Type of mycorrhizae

• Actually penetrate cortex inward to endodermis

  • Don’t pass endodermis

• Set up networks to absorb sugars / proteins

  • Arbuscus

Stem Modifications

• Cladodes

• Rhizomes

• Stolons / Runners

• Thorns

• Corms

• Storage

• Vines

• Tendrils

How many times did leaves evolve?

Twice

Microphylls

• First leaf evolution

• Evolved from stem projections that become vascularized

Megaphylls

• 2nd leaf evolution

• Evolved from photosynthetic branches that became smaller than the main axis over time and expand photosynthetic surfaces

• More complex than microphylls

• Found in more advanced groups

  • Ferns, flowering plants (angiosperms), gynosperms

What do leaves develop from?

S.A.M.

Leaf Veins

• Midrib

• Areoles

• 1st, 2nd… order

Opening in leaves that let CO2 in and O2 out

Stomata

Control size of stomata opening

Guard Cells

Modified Leaves

• Spines

• Bulbs

• Tendrils

• Glands

• Hydathodes

  • Associated with releasing excess water

• Trichomes

  • Leaf hairs

• Insectivorous

  • Pitcher plants, sundews, bladderworts, Venus fly-traps

Environmental Leaves

• Aquatic

• Arid / Xeric

• Windy

• Cold / Dry

How leaves fall off trees in autumn

By using gas ethylene and killing off the cells of the abscission layer

Amount of times vascular cambium has evolved

3 (1 successfully)

Wood formation (secondary xylem)

• Highly coordinated

• Begins in vascular bundle

  • Fascicular

Vascular Cambium Function

To produce cells that become almost any other cell type

2 Types of Vascular Cambial Cells

• Fusiform Initials

• Ray Initials

Fusiform Initials

• Most numerous of vascular cambium cells

• Produce secondary xylem and phloem

• Able to change how they divide in order to produce different sized cells

• “S” plane of division

Ray Initials

• Produce ray parenchyma

• Connect pith to cortex

• Allow slow horizontal conduction

Interconvertibility in Fusiform and Ray Initials

• Fusiform initials can subdivide to produce stack of ray initials

• Ray initials can convert to fusiform initials by lengthening greatly

Growth Rings in Dicots

• 1 year = 1 growth ring

  • Consists of spring and summer wood

    • Springwood: large vascular elements

    • Summerwood: smaller or no vascular elements

Growth Rings in Conifers

• Spring pattern: wider, larger tracheids

  • Earlywood

• Summer pattern: smaller, thicker-walled tracheids

  • Latewood

Heartwood

• Tyloses seal off vessel elements

Climate Data Affecting Growth Rings

• Temperature

• Moisture

• CO2 Levels

• O2 Levels

• Fire Events

• Human Habitation

Secondary Growth in Wood

Bark

Bark

Everything exterior to secondary xylem including vascular cambium

Cork

Hard, airy tissue produced by cork cambium

Why cork is needed

Lenticels

• Bark

• Large fissures in cork that allow gas exchange

Why lenticels are needed

Economic Uses of Bark

• Cork

• Mulch

• Insulation

• Message Boards

• Medicines

• Pre-Industrial clothes, structures, medicines, etc.

Anomalous 2° Growth

• Cambial death

  • Vascular cambium grows, then dies in sections

• Some areas of vascular cambium are more active than others

• Anomalous placement

  • Other vascular cambium arises from cortex, pith, other cells

Sapwood vs Heartwood

• Sapwood = outer 

• Heartwood = inner

Economic Uses of Wood

• Lumber

• Particle Board

• Plywood

• Paper

Reasons to conserve woody plants

• Provide habitats

• Store CO2

• Recycle nutrients

• Climate stability

Root Anatomy

Apical Meristem Cells Diagram

Haustoria are what kind of roots?

Parasitic

Leaf Diagram

Types of Bug-Eating Plants

• Pitcher

• Venus Fly Trap