Ch. 35: Plant Structure and Growth

I. The Plant BodyA. Consists mainly of three parts:

1. Roots2. Stems3. Leaves

B. Comparison of monocots v. dicots

C.The basic morphology of a plant has twosystems: 1. Root System: anchor the plant in the soil,

absorb minerals and water, and store food.a. Monocots – fibrousb. Dicots – taprootc. Root hairs – increase the surface area of roots to maximize the absorption.

Root hairs are made up of epidermalcells and are one-cell thick.

2.The Shoot System: Stems and Leavesa.Stems: Alternating system of nodes and

internodes.1.Axillary buds:

dormant, butcan becomea vegetativebranch.

2.Terminal bud:where growthof a shootoccurs.

“Apical dominance”

3.Modified Stems: a. Stolons: “Runners”

Ex. Strawberries b. Rhizomes:

horizontalundergroundEx. Ginger

c. Tubers:swollen rhizomes forfood storageEx. Potatoes

d. Bulbs: verticalundergroundEx. Onion

Bermuda Grass

Stolons allow for asexual reproduction. Daughter plants are clones of the motherplant.

b.Leaves: Main photosynthetic organs of most plants.1. Blade2. Petiole:

stalk thatjoins theleaf to thenode of thestem.

3.Types of Leaves:

Simple v. Compound: simple leaves have a single, undivided blade, while compound leaves have several leaflets attached to the petiole.

4.Modified Leaves:a. Tendrils:b. Spines of cacti:c. Succulents: d. Colored leaves:

Cling to supportDefense

Storing waterTo attract pollinators

D.Plants are composed of three tissue systems: 1. Dermal/Epidermis: 2. Vascular:

3. Ground:

Covers and protectsTransports materials betweenroots and shoots.a.Xylem: water and mineralsb.Phloem: food/sugars

“filler tissue”; neither dermalnor vascular; diverse functions such asphotosynthesis, storage, and support.-Cortex: external to vascular tissue-Pith: internal to vascular tissue

The three tissue system in a plant body: -Dermal -Vascular -Ground

Vascular tissue structure:1.Xylem: made up of two kinds of cells

-Tracheids and vessel elements-Both types of cells are nonliving at functional maturity; the secondary cell walls remain behind and leave behind tubes through which water can flow. -Water flows from tracheid to tracheid and vessel element to vessel element through pits.

Thin,tapered

Wider, short

2.Phloem: Made up of two types of cells:-Sieve-tube members and companion cells-Sieve-tube members

have no nucleus, ribosomes, a distinct vacuole. -Companion cells have a nucleus and ribo- somes and probably assist sieve-tube cells.-Companion cells also help load sugars into the sieve-tubes for transport.

Review:

Nucleus

MitochondriaPeroxisome

Vacuole Tonoplast

Chloroplast

Primary cell wall

Secondary cell wall

(Protoplast: Plant cell minus the cell wall)

E.The Plant Cell Review

1.Parenchyma cells:-“typical” plant cell because they are the leastspecialized; developing plant cells are parenchyma cells before becoming specialized.

-thin and flexible; most parenchyma cells lacka tough secondary cell wall.

-most of the metabolic functions occur in these cells; photosynthesis takes place in theparenchyma cells of the leaf.

F. THREE TYPES OF PLANT CELLS:

2.Collenchyma cells:-thicker, uneven primary cell walls.

-support young parts of the plant shoot.-lack secondary cell walls; allows for plantgrowth, while providing structural support.

3.Sclerenchyma cells:-have secondary cell walls making them rigidand supportive.

-many are dead at functional maturity, but they produce thesecondary walls beforethe protoplast dies;serves as a “skeleton”that supports the plant.-2 types of sclerenchyma cells: 1.Fibers: tough, long and slender; in groups 2.Sclereids: irregular shape; gritty texture in pears

II. Plant Growth and Development How do plants develop their different cell types and how do they mature?

A.Most plants continue to grow: “indeterminate growth”B.Flowers and leaves undergo “determinate growth.”C.Life cycles of plants: 1.Annuals: Plants that complete their life cycle in a single year or less; food crop. 2.Biennials: life span 2 years, between germination, growth, and flowering. 3.Perennials: live many years; trees, shrubs, and some grasses.

D. Meristem: perpetual embryonic tissue; continual growth by cell division. 1. Apical meristem: shoots and roots Primary growth

2. Lateral meristems: Secondary growthIn contrast, secondary growth is the progressive thickening of roots and shoots in woody plants.

E. Primary growth in roots:1. Root cap: protection of meristem2. Zone of cell division: apical meristem3. Zone of elongation: cells elongate; push root tip4. Zone of maturation: differentiation of cells (3 tissue systems)

F. Primary tissues in the roots:1. Stele: vascular bundle (xylem and phloem)2. Pith: core; parenchyma cells3. Cortex: region between stele and epidermis; innermost layer is called endodermis, which forms the boundary between cortex and stele.

4. Lateral roots: arise from the pericycle (outermost layer of stele).

Pericycle cells become meristematic and start to divide, pushing through the cortex.

G. Primary tissue of stems:1. Vascular bundles (xylem and phloem) surrounded by ground tissues, pith and cortex.2. Mostly parenchyma; some collenchyma and sclerenchyma for support.

H. Primary tissues in leaves:

1. Epidermis: cuticle; protection and to prevent dessication2. Stomata: tiny pores for gas exchange and transpiration.3. Guard cells: specialized epidermal cells4. Mesophyll cells: ground tissue (palisade and spongy parenchyma cells).

I. Secondary growth of Stems:1. Two lateral meristems:

-Vascular cambium secondary xylem(wood) and secondaryphloem

-Cork cambium tough, thick covering

Secondary growth is rare in monocots

2.How does the vascular cambrium producesecondary xylem and phloem? -A cambrium cell divides into a cambrium cell and a derivative cell, which will differentiate into xylem or phloem.-As layers of xylem are added, stems increase in diameter.

Secondary xylem forms to the interior and secondary phloem to the exterior of the vascular cambium.

As secondary growth continues over the years, layer upon layer of secondary xylem accumulates, producing the tissue we call wood. Early wood Late wood These are the lines you count to estimate the age of trees.

3.How does cambrium cork produce a tough,thick outer covering? -Cork cambium produces cork cells which contain a waxy, waterproof substance.-The cork plus the cork cambium forms the periderm, a protective layer that replaces the epidermis.

-Lenticils are splits develop in the periderm because of higher local activity of the cork cambium.

-Bark refers to all tissues external to the vascular cambium, including secondary phloem, cork cambium, and cork.

-Only the youngest secondary phloem, internal to the cork cambium, functions in sugar transport.-Older phloem dies and sloughs off as bark later.

-After several years of growth, several zones are visible in the stem. a. Two zones of xylem: -Heartwood (dead; structural purpose) -Sapwood b. Vascular cambium c. Living phloem d. Cork cambium e. Cork

III.Mechanisms of Plant Growth and DevelopmentA.Arabidopsis thaliana, a weed of the mustard

family was the first plant to have its entiregenome sequenced.1. 26,000 genes; many duplicates; 15,000 different genes;

45% unknown

B.Growth, morphogenesis, and differentiationproduce the plant body1. Morphogenesis: development of body

form and organization2. Differentiation: cellular diversity

C.Plant growth depends on the plane(direction) of cell division.

D.Plant growth depends on the symmetry of cell division.

1.Assymetrical cell division, in which one cell receives more cytoplasm than the other, is common in plants cells and usually signals a key developmental event. Guard cells

E.The plane of cell division is determined duringlate interphase.

-Microtubules concentrate into a ring called the preprophase band.-Actin micro- filaments direct the formation of cell plates.

F.Morphogenesis depends on pattern formation1.Pattern formation: development of

specific structures in specific locations.2.Pattern formation depends on positional

information - signals that indicate a cell’slocation.

G.Homeotic genes: genes that regulate pattern formation.1.Protein product of KNOTTED-1 homeotic

gene is important for the development of compound leaves. Over expression of this gene creates “supercompound” leaves.