Chapter 31 and 33

PowerPoint Lectures forBiology: Concepts and Connections, Fifth Edition – Campbell, Reece, Taylor, and Simon

Lectures by Chris Romero

Chapter 31Chapter 31

Plant Structure, Reproduction, and Development (Sections 7 and 8)

A Gentle Giant• Gymnosperms

– Are one of two groups of seed plants

– Bear seeds in cones

• Angiosperms, or flowering plants

– Are the most familiar and diverse group of plants

TALKING ABOUT SCIENCE

31.1 Plant scientist Natasha Raikhel studies the Arabidopsis plant as a model biological system

• Natasha Raikhel

– Is one of America’s most prominent plant biologists

Figure 31.1A

• Dr. Raikhel works with Arabidopsis

– A popular model organism for studying biological systems

Figure 31.1B

PLANT STRUCTURE AND FUNCTION

31.2 The two main groups of angiosperms are the monocots and the dicots

• Monocots and dicots differ in

– The number of seed leaves and in the structure of roots, stems, leaves, and flowers

Figure 31.2

Fibrousroot system

MONOCOTS

Seed leaves Leaf veins Stems Flowers Roots

Onecotyledon Main veins usually parallel

Vascular bundles in complex arrangement

Floral parts usuallyin multiples of three

Twocotyledons Main veins usually branched

Vascular bundles arranged in ring

Floral parts usually inmultiples of four or five

Taprootusually present

DICOTS

31.3 A typical plant body consists of roots and shoots

• A plant’s root system

– Anchors it in the soil

– Absorbs and transports minerals and water and stores food

• The shoot system of a plant

– Is made up of stems, leaves, and adaptations for reproduction, flowers

Terminal bud

PetioleAxillary bud

TaprootRoothairs

Epidermal cell

Root hairInternode

Flower

Shootsystem

Rootsystem

• The body of a dicot

Figure 31.3

31.4 Many plants have modified roots, stems, and leaves

• Some plants have unusually large taproots

– That store food in the form of carbohydrates

Figure 31.4A

Strawberry plant

Potato plant

Stolon (runner)

Taproot

Rhizome

Ginger plant

Rhizome

• Many plants have modified stems

– That store food or function in asexual reproduction

Figure 31.4B

• Other types of plants have modified leaves

– That function in protection or climbing

Figure 31.4C

Figure 31.5A

31.5 Plant cells and tissues are diverse in structure and function

• Most plant cells have three unique structures

– Chloroplasts, the sites of photosynthesis

– A central vacuole containing fluid

– A cell wall that surrounds the plasma membraneChloroplast Central

vacuoleCell walls

Primary cell wall

Middle lamella

Secondary cell wall

Plasmamembrane

Cell walls of adjoining cells

Plasmodesmata

PitPlasma membrane

MicrotubulesRibosomes

Golgiapparatus

Mitochondrion

Endoplasmicreticulum

Nucleus

• Plants have five major types of cells

– Parenchyma, which perform most of the metabolic functions

– Collenchyma, which provide supportPrimary cell wall (thin)

Starch-storing vesicles

Figure 31.5B

Primary cell wall (thick)

Figure 31.5C

– Sclerenchyma, the main component of wood

Figure 31.5D

Secondary cell wall

Fiber cells

Primary cell wall

Secondary cell wall

Primary cell wall Pits

Sclereid cells

Fiber Sclereid

Openings in end wall

Vessel element Tracheids

Colorized SEM 150

• Angiosperms have water-conducting cells

– Tracheids and vessel elements

Figure 31.5E

Figure 31.5F

• Sieve-tube members

– Are food-conducting cellsSieve plate

Companion cell

Primary cell wall

Cytoplasm

• Two kinds of vascular tissue are

– Xylem, which conveys water and minerals

– Phloem, which transports sugars

31.6 Three tissue systems make up the plant body

• Each plant organ is made up of threetissue systems

– The dermal,vascular, and ground tissue systems

Guard cells

Cuticle

Upper epidermis

Mesophyll

Lower epidermis

Phloem

Dicot leaf

Dicot stem

Sheath

Vascular bundle

Cortex

Epidermis

Monocot stemVascular bundle

Epidermis

Vascular cylinder

Phloem

Cortex

Endodermis

Dicot root

Dermal tissue system

Ground tissue system

Vascular tissue system

Figure 31.6

• The dermal tissue system

– Covers and protects the plant

• The vascular tissue system

– Contains xylem and phloem and provides long-distance transport and support

• The ground tissue system

– Consists of parenchyma cells and supportive collenchyma and sclerenchyma cells

PLANT GROWTH

31.7 Primary growth lengthens roots and shoots

• Meristems, areas of unspecialized, dividing cells

– Are where plant growth originates

• Apical meristems

– Are located in the tips of roots and in the terminal and axillary buds of shoots

– Initiate primary (lengthwise) growth by producing new cells

Figure 31.7A

Terminal bud

Axillary buds

Root tips

Arrows = direction of growth

• Roots are covered with a root cap

– That protects the cells of the apical meristem

Figure 31.7B

Vascular cylinder

Root hair

Cortex

Epidermis

Zone of maturation

Zone of elongation

Zone of cell division

Root cap

Apical meristem region

Cellulose fibers

KeyDermal tissue system

• Axillary bud meristems

– Are found near the apical meristems

Figure 31.7C

Apical meristem

Leaves

Axillary bud meristems

31.8 Secondary growth increases the girth of woody plants

• Secondary growth arises from cell division

– In a cylindrical meristem called the vascular cambium

• The vascular cambium thickens a stem

– By adding layers of secondary xylem, or wood, next to its inner surface

Year 1Early Spring

Year 1Late Summer

Year 2Late Summer

GrowthGrowth

Growth

Primary xylem

Vascular cambium

Primary phloem

Cor tex

EpidermisSecondary

xylem (wood)Cork

Corkcambium

Secondary phloem

Shed epidermis

Secondary xylem (2 years’ growth)

Dermal tissue system

Figure 31.8A

• The heartwood and sapwood

– Consist of different layers of xylem

• Outside the vascular cambium, the bark consists mainly of

– Secondary phloem, cork cambium, and protective cork cells

Figure 31.8B

Heartwood

Sapwood

Wood rays

Heartwood

Vascular cambium

Sapwood

Secondary phloem

Cork cambium

PowerPoint Lectures forBiology: Concepts and Connections, Fifth Edition – Campbell, Reece, Taylor, and Simon

Lectures by Chris Romero

Chapter 33Chapter 33

Control Systems in Plants

What Are the Health Benefits of Soy?

• Soy protein

– Is one of the few plant proteins that contains all the essential amino acids

• Phytoestrogens, a class of plant hormones

– Are found in soy

Estrogen (Estradiol) Phytoestrogen (Genistein)

Chemical structures of a humanestrogen and a plant phytoestrogen

• Soy products contain isoflavones

– A type of phytoestrogen that may provide human health benefits

Soybeans

PLANT HORMONES

33.1 Experiments on how plants turn toward light led to the discovery of a plant hormone

• Plants exhibit phototropism

– The growth of shoots in response to light

Figure 33.1A

• Microscopic observations of plants

– Indicate that a cellular mechanism underlies phototropism

Shaded side of shoot

Illuminated side of shoot

Figure 33.1B

Showing That Light Is Detected by the Shoot Tip

• Charles Darwin showed that the tip of a grass seedling detects light

– And transmits a signal down to the growing region of a shoot

Control Tipremoved

Tip covered byopaque cap

Tip coveredby trans-parent cap

Base coveredby opaqueshield

Tip separatedby gelatinblock

Tip separatedby mica

Darwin and Darwin (1880) Boysen-Jensen (1913)

Figure 33.1C

Isolating the Chemical Signal

• The hormone auxin

– Was determined to affect phototropism

– Promotes faster cell elongation on the shaded site of the shoot

Shoot tip placed on agar block.Chemical (later called auxin)diffuses from shoot tipinto agar.

Other controls:Blocks with nochemical haveno effect.

Offset blocks withchemical stimulatecurved growth.Control

Block withchemicalstimulatesgrowth.

No light

Figure 33.1D

33.2 Five major types of hormones regulate plant growth and development

• Even in small amounts, plant hormones

– Trigger signal transduction pathways

– Regulate plant growth and development

• The major types of plant hormones

Table 33.2

33.3 Auxin stimulates the elongation of cells in young shoots

• Plants produce auxin (IAA)

– In the apical meristems at the tips of shoots

• At different concentrations, auxin

– Stimulates or inhibits the elongation of shoots and roots

Figure 33.3A, B

0.9 g/L

10–8 10–6 10–4 10–2 1 102

Increasing auxin concentration (g/L)

• Auxin may act by weakening cell walls

– Allowing them to stretch when cells take up water

Plasmamembrane

Cellwall H+

Vacuole

Cellelongation

Cellulose loosens; cell can elongate

Cellulosemolecule

Cross-linkingmolecule

Enzyme

Cellulosemolecule

Cell wall

Cytoplasm

H+ pump(protein)

Figure 33.3C

• Auxin promotes growth in stem diameter

– By stimulating the development of vascular tissues and cell division in vascular cambium

33.4 Cytokinins stimulated cell division

• Cytokinins

– Are produced by growing roots, embryos, and fruits

– Promote cell division

• Cytokinins from roots may balance the effects of auxin from apical meristems

– Causing lower buds to develop into branches

Figure 33.4

Terminal bud

No terminal bud

33.5 Gibberellins affect stem elongation and have numerous other effects

• Gibberellins

– Stimulate the elongation of stems

Figure 33.5A

• Gibberellins

– Stimulate the development of fruit

– Function in embryos in some of the early events of seed germination

Figure 33.5B

33.6 Abscisic acid inhibits many plant processes

• Abscisic acid (ABA)

– Inhibits the germination of seeds

• The ratio of ABA to gibberellins

– Often determines whether a seed will remain dormant or germinate

• Seeds of many plants remain dormant

– Until their ABA is inactivated or washed away

Figure 33.6

• ABA also acts as a “stress hormone”

– Causing stomata to close when a plant is dehydrated

33.7 Ethylene triggers fruit ripening and other aging processes

• As fruit cells age

– They give off ethylene, which triggers a variety of aging processes

Fruit Ripening

• Ethylene

– Triggers fruit ripening

Figure 33.7A

The Falling of Leaves

• A changing ratio of auxin to ethylene

– Is triggered by shorter days

– Probably causes autumn color changes and the loss of leaves from deciduous trees

Leafstalk

Stem(twig)

Abscissionlayer

Protectivelayer

Stem Leaf stalk

Figure 33.7B

CONNECTION

33.8 Plant hormones have many agricultural uses

• Farmers use auxin

– To delay or promote fruit drop

Figure 33.8

• Auxins and gibberellins

– Are used to produce seedless fruits

• A synthetic auxin called 2,4-D

– Is used to kill weeds

– Has safety questions associated with its use

Chapter 31 and 33

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