About Plant Biology Chapter 1 Why Study Plant

About Plant Biology Chapter 1 Why Study Plant

About Plant Biology Chapter 1 Why Study Plant Biology? Show interrelationships between plants and other fields of study Prepare for careers in plant biology Gain fundamental knowledge for upper division plant biology courses Share expertise gained with nonbotanists

What is a Plant? An organism that is green and photosynthetic Additional characteristics Cell wall composed of cellulose Multicellular body Can control water loss Have strengthening tissues Can reproduce by means of microscopic, drought-resistant spores

Ecologic Services Sources of food, fabric, shelter, medicine Produce atmospheric oxygen and organic nitrogen Build new land Inhibit erosion Control atmospheric temperature Decompose and cycle essential mineral nutrients Importance of Plants to Human

Civilizations Trees for lumber to make warships Fuel to smelt metals, cure pottery, generate power and heat Sources of wealth spices Sources of industrial products Rubber oil

Natural Plant Losses Plant losses occurring at a faster rate than ever before Factors include Agriculture Urbanization Overgrazing Pollution Extinction Environmental Laws

Described in 1961 by plant biologist Barry Commoner Laws becoming more true every day Four environmental laws Everything is connected to everything else. Everything must go somewhere. Nature knows best. There is no such thing as a free lunch. Scientific Method Codefined and promoted in 17th century by Rene

Decartes and Francis Bacon Steps involved in scientific method Make observations Ask questions

Make educated guesses about possible answers Base predictions on the guesses Devise ways to test predictions Draw conclusions Scientific Method Hypothesis educated guess based on observations and questioning Predicted result occurs hypothesis is most likely correct Individuals using scientific method should

be objective and unbiased Scientific Method Original Hypothesis Results support hypothesis Devise method to test hypothesis

Results support hypothesis but suggest minor refinements Retest using minor refinements of process

Analyze results Results do not support original hypothesis but fall within range that could be expected if original hypothesis is slightly modified

Results are so unexpected that they do not support original hypothesis and require a new hypothesis Test using slightly modified

hypothesis Test new hypotheses Studying Plants From Different Perspectives Plant genetics study of plant heredity Plant systematics study of plant evolution and classification Plant ecology study of how the environment

affects plant organisms Plant anatomy study of a plants internal structure Plant morphology study of how a plant develops from a single cell into its diverse tissues and organs Study Plants from Taxonomic Classification

Microbiology study of bacteria Mycology study of fungi Phycology study of algae Bryology study of mosses Interrelationships Among Several Plant Biology Disciplines Genes

ENVIRONMENT Genetics Evolution Taxonomy & Systematics METABOLISM Ecology

Physiology Paleoecology Biogeography PLANT TAXONOMIC GROUPS

STRUCTURE Phycology Microbiology Mycology Bryology DEVELOPMENT Morphology Anatomy

Plant Classification Taxonomy Linnaean system Easy to use Based on idea that species never changed Grouped organisms according to arbitrary similarities Fails to meet needs of modern biologists Linnaean Taxa

Taxa Ending Kingdom Division -phyta Class

-opsida Order -ales Family -aceae Genus

No standard ending Species No standard ending Plant Classification Whittakers Five Kingdoms Developed in 1969 by Robert Whittaker Each kingdom assumed to be

monophyletic group of species Molecular biology techniques Cladistics Show five kingdom system also does not recognize evolutionary groups Whittakers Five Kingdoms Kingdom Monera Description

Included bacteria Fungi Included molds, mildews, rusts, smuts, and mushrooms Protista Included simple organisms, some were photosynthetic, mostly

aquatic organisms called algae Plantae Included more complex photosynthetic organisms that typically grew on land Animalia Included typically motile,

multicellular, nonphotosynthetic organisms Plant Classification Cladistics Based on evolutionary groups Compare DNA base pair sequences of organisms to determine relatedness Obtain percent similarity between organisms

Plant Classification Clades evolutionary groups Cladogram = phylogenetic tree Branching diagram Emphasizes shared features from common ancestor Future discoveries may require modifications of cladogram Plant Classification Domain

Neutral term Groups of organisms as large or larger than a kingdom Monophyletic Three domains based on cladistics Eukarya Bacteria Archaea Domain Eukarya

Made up of Whittakers plant, animal, and fungal kingdoms Eukaryotic cells Membrane-bounded organelles Linear chromosomes Protists Not monophyletic Controversy over where to place organisms Domain Bacteria

Organisms originally were placed in Whittakers Kingdom Monera Microscopic Prokaryotic cells No membrane-bounded organelles Circular chromosome Sexual reproduction unknown Found in every habitat on Earth Domain Bacteria

Beneficial aspects Decomposers Some carry on photosynthesis Cyanobacteria or blue-green algae Nitrogen fixation Convert inorganic N2 into ammonium for plant use Cyanobacteria Domain Bacteria

Detrimental effects Pathogens cause diseases Human diseases Botulism, bubonic plague, cholera, syphilis, tetanus, tuberculosis Plant diseases Domain Archaea Organisms originally were placed in Whittakers Kingdom Monera

Prokaryotic Different cell structure and chemistry than organisms in Domain Bacteria Domain Archaea Divided into three groups based on habitat Bacteria of sulfur-rich anaerobic hot springs and deep ocean hydrothermal vents Bacteria of anaerobic swamps and termite intestines

Bacteria of extremely saline waters Extreme halophiles Photosynthetic pigment bacteriorhodopsin Three Domains Domain Cell Type Description

Eukaryotic Membrane bounded organelles, linear chromosomes Archaea Prokaryotic Found in extreme environments, cell structure and differ from members of

Domain Bacteria Bacteria Prokaryotic Ordinary bacteria, found in every habitat on earth, play major role as decomposers Eukarya

Kingdom Fungi Eukaryotic cells Typically microscopic and filamentous Rigid cell wall made of chitin Reproduce sexually in a variety of complex life cycles and spores

Widely distributed throughout world mainly terrestrial Kingdom Fungi Economic importance Decomposers Form associations with roots of plants Important foods for animals and humans Mushrooms, morels Decomposing action of yeast

Flavored cheeses, leavened bread, alcoholic beverages Kingdom Fungi Economic importance Production of antibiotics Penicillium Pathogens Invade both plant and animal tissue Cause illnesses

Reduce crop yields Kingdom Protista Eukaryotic cells Reproduce both sexually and asexually Catch-all group Photosynthetic organisms algae Nonphotosynthetic organisms slime molds, foraminiferans, protozoans Kingdom Protista

Algae Arrangements Single cells, clusters, filaments, sheets, threedimensional packets of cells Photosynthetic Float in uppermost layers of all oceans and lakes Kingdom Protista Phytoplankton grasses of the sea

Microscopic algae Form base of natural food chain Produce 50% of all oxygen in atmosphere Kingdom Plantae Included all organisms informally called plants Bodies more complex than bacteria, fungi, or protists Eukaryotic

Kingdom Plantae Unique biochemical traits of plants Cell walls composed of cellulose Accumulate starch as carbohydrate storage product Special types of chlorophylls and other pigments Kingdom Plantae Ecologic and economic importance of plants Form base of terrestrial food chains

Principal human crops Provide building materials, clothing, cordage, medicines, and beverages Challenge for 21 Century st While the human population increases, the major challenge of retaining natural biological diversity and developing a sustainable use of the worlds forests,

grasslands, and cropland remains. As you study plant biology, think of the ways that you can contribute to this challenge. Proteins take on a variety of shapes, which enables specific interactions (function) with other molecules. Fig. 2.22 Stages in the formation of a functioning protein The Plant Cell and the Cell Cycle

Chapter 3 Eucaryotic Cell structure

Rough endoplasmic reticulum-site of secreted protein synthesis Smooth ER-site of fatty acid synthesis Ribosomes-site of protein synthesis Golgi apparatus- site of modification and sorting of secreted proteins Lysosomes-recycling of polymers and organelles Nucleus-double membrane structure confining the chromosomes

Nucleolus-site of ribosomal RNA synthesis and assembly of ribosomes Peroxisome-site of fatty acid and amino acid degradation Flagella/Cilia- involved in motility Mitochondria-site of oxidative phosphorylation Chloroplast-site of photosynthesis Intermediate filaments- involved in cytoskeleton structure Plant vs Animal Cells Plant cells have chloroplasts and perform photosynthesis Outermost barrier in plant cells is the cell

wall Outermost barrier in animal cells is the plasma membrane Cell Basic unit of plant structure and function Robert Hooke Looked at cork tissue under microscope little boxes or cells distinct from one another .that perfectly enclosed air

Nehemiah Grew Recognized leaves as collections of cells filled with fluid and green inclusions Cell Theory Statement All plants and animals are composed of cells. Cells reproduce themselves. All cells arise by reproduction from previous

cells. Year Contributor 1838 Matthias Schleiden and Theodor Schwann

1858 Rudolf Virchow 1858 Rudolf Virchow Basic Similarities of Cells Cells possess basic characteristic of life

Movement Metabolism Ability to reproduce Organelles little organs Carry out specialized functions within cells Light Microscope View cells 20-200 m in diameter Can view living or stained specimens

Resolution (resolving power) Ability to distinguish separate objects Limited by lenses and wavelengths of light used Smallest object that can be resolved is ~ 0.2 m in diameter Confocal Microscope Laser illumination Detecting lens focuses on single point at a time

Scans entire sample to assemble picture No reduction in contrast due to scattered light Can generate 3-D images Transmission Electron Microscope Responsible for discovery of most of smaller organelles in cell Greater resolution Uses beams of electrons rather than light

Magnets for lenses Ultrathin section examined in vacuum View image on fluorescent plate or photographic film Scanning Electron Microscope Collected electrons used to form picture in television picture tube High resolution view of surface structures Requires vacuum Recent refinements

Can operate in low vacuum Can view live plant cells and insects Microscope Comparisons Nature of Source for lenses illumination Light microscope White light Confocal

microscope Transmission electron microscope Scanning electron microscope Laser

Electrons Electrons Glass Glass Magnets

Magnets Condition of specimen Image formation Living or killed stained specimen View directly

through microscope Killed stained specimens Image analyzed on digital computer screen

Ultrathin section of killed specimen contained within vacuum View on fluorescent plate or photographic film

Surface view of killed specimen contained within vacuum, with low vacuum can view living cells Television picture tube Generalized Plant Cell

chloroplast vacuole nucleus cell wall mitochondrion Fig. 3-3 (b & c), p. 33 Boundaries Between Inside and Outside the Cell Plasma Membrane

and Cell Wall Plasma Membrane Surrounds cell Controls transport into and out of cell Selectively permeable Plasma Membrane Composed of approximately half phospholipid and half protein, small amount of sterols

Phospholipid bilayer Separates aqueous solution inside cell from aqueous layer outside cell Prevents water-soluble compounds inside cell from leaking out Prevents water-soluble compounds outside cell from diffusing in Plasma Membrane Proteins in bilayer Perform different functions

Ion pumps Move ions from lower to higher concentration Require ATP energy Proton pump moves H+ ions from inside to outside of cell Ca+2 pump moves Ca2+ to outside of cell Channels allow substances to diffuse across membrane Extracellular environment

PHOSPHOLIPID BILAYER PUMPS AND CHANNELS Cytoplasm SENSORY PROTEINS RECEPTORS

STEROL Fig. 3-4, p. 34 Plasma Membrane Plasmodesmata Connects plasma membranes of adjacent plant cells Extends through cell wall Allows materials to move from cytoplasm of

one cell to cytoplasm of next cell Symplast name for continuous cytoplasm in set of cells E.R. lumen E.R. plasma membrane

Cytoplasm Cell wall plasmodesmal proteins Cytoplasm Fig. 3-5, p. 35 Plasma Membrane

Apoplast Space outside cell Next to plasma membrane within fibrils of cell wall Area of considerable metabolic activity Important space in plant but questionable as to whether it is part of the plants cells Cell Wall Rigid structure made of cellulose microfibrils Helps prevent cell rupture

Process of osmosis allows water to enter cell Inflow of water expands cell Expansion forces cell membrane against cell wall Resistance of cell wall to expansion balances pressure of osmosis Stops flow of water into cell

Keeps cell membrane from further expansion Cell Wall Osmotic forces balanced by pressure exerted by cell wall Creates turgor pressure Causes cells to become stiff and incompressible Able to support large plant organs Loss of turgor pressure plant wilts

Fig. 3-6, p. 35 Cell Wall Place cell in salt solution Water leaves cytoplasm Protoplast (space inside plasma membrane) shrinks Plasma membrane pulls away from cell wall Cell lacks turgor pressure - wilts PROTOPLAST

SOLUTION Concentration 0.3 molar Pressure 0 megapascals Concentration

0.3 molar (Isotonic) Concentration 0.27 molar Pressure 0.66 megapascals Concentration

0.5 molar Pressure 0 megapascals Concentration 0 molar (Hypotonic) Concentration

0.5 molar (Hypertonic) Fig. 3-7 (a-c), p. 36 Fig. 3-7 (d), p. 36 Cell Wall Structure Primary cell wall Cell wall that forms while cell is growing

Secondary cell wall Additional cell wall layer deposited between primary cell wall and plasma membrane Generally contains cellulose microfibrils and water-impermeable lignin Provides strength to wood Cell Wall Structure Specialized types of cell walls cutin covering cell wall or suberin imbedded in cell wall

Waxy substances impermeable to water Cutinized cell walls Found on surfaces of leaves and other organs exposed to air Retard evaporation from cells Barrier to potential pathogens Organelles of Protein Synthesis and Transport Nucleus, Ribosomes, Endoplasmic Reticulum, and Golgi

Apparatus Nucleus Ovoid or irregular in shape Up to 25 m in diameter Easily stained for light or electron microscopy Nucleus Surrounded by double membrane nuclear envelope

Protein filaments of lamin line inner surface of envelope and stabilize it Inner and outer membranes connect to form pores Nucleoplasm Portion of nucleus inside nuclear envelope one pore nuclear envelope

1 m 0.2 m lipid bilayer facing the nucleoplasm nuclear lipid bilayer facing envelope the cytoplasm

pore complex that spans both bilayers Fig. 3-8, p. 37 Nucleus Nucleoli (singular, nucleolus) Densely staining region within nucleus Accumulation of RNA-protein complexes (ribosomes) Site where ribosomes are synthesized

Center of nucleoli DNA templates Guide synthesis of ribosomal RNA Nucleus Chromosomes Found in nucleoplasm Contain DNA and protein Each chromosome composed of long molecule of DNA wound around histone proteins forming a chain of nucleosome

Additional proteins form scaffolds to hold nucleosomes in place Fig. 3-9, p. 37 At times when a chromosome is most condensed, the chromosomal proteins interact, which packages loops of already coiled DNA into a supercoiled array. Fig. 3-9d, p. 37

At a deeper level of structural organization, the chromosomal proteins and DNA are organized as a cylindrical fiber. Fig. 3-9c, p. 37

Immerse a chromosome in saltwater and it loosens up to a beads-on-a-string organization. The string is one DNA molecule. Each bead is a nucleosome.

Fig. 3-9b, p. 37 core of histone molecules A nucleosome consists of part of a DNA molecule looped twice around a core

of histones. Fig. 3-9a, p. 37 Nucleus DNA in chromosomes Stores genetic information in nucleotide sequences Information used to direct protein synthesis Steps in protein synthesis Transcription DNA directs synthesis of RNA

Most RNA stays in nucleus or is quickly broken down Small amount of RNA (mRNA) carries information from nucleus to cytoplasm Nuclear Components Component Structure and Function Nuclear envelope

Double layered membrane, filaments of protein lamin line inner surface and stabilize structure, inner and outer membranes connect to form pores Nucleoplasm Portion inside the nuclear envelope Nucleoli Dark staining bodies within nucleus, site for

ribosome synthesis Chromosomes Store genetic information in nucleotide sequences, each chromosome consists of chain of nucleosomes (long DNA molecule and associated histone proteins) Ribosomes Small dense bodies formed from

ribosomal RNA (rRNA) and proteins Function in protein synthesis Active ribosomes in clusters called polyribosomes Attached to same mRNA All ribosomes in one polyribosome make same type of protein Ribosomes In living cell, ribosomes are not fixed Move rapidly along mRNA

Read base sequence Add amino acids to growing protein chain At end of mRNA, ribosome falls off, releasing completed protein into cytoplasm mRNA ribosomes free polyribosomes

attached polyribosomes Fig. 3-10, p. 38 mRNA ribosomes free polyribosomes

attached polyribosomes Fig. 3-10a, p. 38 Endoplasmic Reticulum

ER Branched, tubular structure Often found near edge of cell Function Site where proteins are synthesized and packaged for transport to other locations in the cell Proteins injected through membrane into lumen

Endoplasmic Reticulum Packaging of proteins by ER Considered to be packaged when separated from cytoplasm by membrane Sphere (vesicle) of membrane-containing proteins may bud off from ER Vesicle carries proteins to other locations in cell Endoplasmic Reticulum Types of ER

rough ER ribosomes attached to surface smooth ER does not have attached ribosomes Carbohydrate transport Often attached to proteins in ER Helps protect carbohydrate from breakdown by destructive enzymes Golgi Apparatus Also called a dictyosome

Consists of stack of membranous, flattened bladders called cisternae 0.25 m vesicles internal spaces cisternae Fig. 3-11, p. 38

Golgi Apparatus Directs movements of proteins and other substances from ER to other parts of cell Cell wall components (proteins, hemicellulose, pectin) pass through cisternae Move to plasma membrane inside membranous sphere Sphere joins with plasma membrane Membrane of sphere becomes part of plasma membrane Protein, hemicellulose, and pectin contents released to outside the cell

Endomembrane System Complex network that transports materials between Golgi apparatus, the ER, and other organelles of the cell Movement Rapid Continuous Organelles of Energy Metabolism

Plastids and Mitochondria Plastids Found in every living plant cell 20-50/cell 2-10 m in diameter Surrounded by double membrane Contain DNA and ribosomes

Protein-synthesizing system similar to but not identical to one in nucleus and cytoplasm two outer membranes thylakoids stroma Fig. 3-12 (a), p. 40

Plastids Proplastids Small plastids always found in dividing plant cells Have short internal membranes and crystalline associations of membranous materials called prolamellar bodies As cell matures, plastids develop Prolamellar bodies reorganized Combined with new lipids and proteins to form more extensive internal membranes

Plastids Types of plastids Chloroplasts Leukoplasts Amyloplasts Chromoplasts Fig. 3-12 (b-f), p. 40 Plastids Chloroplasts

Thylakoids Inner membranes Have proteins that bind to chlorophyll Chlorophyll Green compound that gives green plant tissue its color Stroma Thick solution of enzymes surrounding thylakoids

Plastids Chloroplasts Function Convert light energy into chemical energy (photosynthesis) Accomplished by proteins in thylakoids and stromal enzymes Can store products of photosynthesis (carbohydrates) in form of starch grains Chloroplast

Component Description Thylakoids Inner membranes of chloroplast, contain proteins that bind with chlorophyll Stroma

Thick enzyme solution surrounding thylakoids Chlorophyll Green pigment that gives plant tissue its green color Storage form of carbohydrates produced Starch grains during photosynthesis

Leukoplasts leuko white Found in roots and some nongreen tissues in stems No thylakoids Store carbohydrates in form of starch Microscopically appear as white, refractile, shiny particles Amyloplasts amylo starch

Leukoplast that contains large starch granules Chromoplasts chromo color Found in some colored plant tissues tomato fruits, carrot roots High concentrations of specialized lipids carotenes and xanthophylls Give plant tissues orange-to-red color

Plastids Prefix Meaning Function Chloroplast chloro

yellowgreen Photosynthesis, convert light energy into chemical energy, store carbohydrates as starch grains Leukoplast leuko

white Store carbohydrates in form of starch starch Leukoplasts that contain large granules of starch

color Stores carotenes and xanthophylls, give orangeto-red color to certain plant tissues Amyloplast amylo Chromoplast chromo

Mitochondria Double-membrane structure Contain DNA and ribosomes Inner membrane infolded Folds called cristae Increase surface area available for chemical reactions outer compartment

cristae inner compartment (matrix) inner membrane outer

membrane Fig. 3-13, p. 41 Mitochondria Matrix Viscous solution of enzymes within cristae Function source of most ATP in any cell that is not actively photosynthesizing

Site of oxidative respiration Release of ATP from organic molecules ATP used to power chemical reactions in cell Other Cellular Structures Vacuoles, Vesicles, Peroxisomes, Glyoxysomes, Lysosomes, and Cytoskeleton Vacuoles Large compartment surrounded by single

membrane Takes up large portion of cell volume Tonoplast Membrane surrounding vacuole Has embedded protein pumps and channels that control flow of ions and molecules into and out of vacuole Vacuole Functions May accumulate ions which increase turgor

pressure inside cell Can store nutrients such as sucrose Can store other nutritious chemicals May accumulate compounds that are toxic to herbivores May serve as a dump for wastes that cell cannot keep and cannot excrete Vesicles Small, round bodies surrounded by single membrane

Peroxisomes and glyoxysomes Compartments for enzymatic reactions that need to be separated from cytoplasm Lysosomes Contain enzymes that break down proteins, carbohydrates, and nucleic acids May function in removing wastes within living cell Can release enzymes that dissolve the entire cell Cytoskeleton

Collection of long, filamentous structures within cytoplasm Functions Keeps organelles in specific places Sometimes directs movement of organelles around the cell Cyclosis cytoplasmic streaming Cytoskeleton Structures in cytoskeleton Microtubules

Motor proteins Microfilaments Specialized proteins connect microtubules and microfilaments to other organelles Connections thought to coordinate many cell processes Microtubules Relatively thick (0.024 m in diameter) Assembled from protein subunits called

tubulin Fairly rigid but can lengthen or shorten by adding or removing tubulin molecules Microtubules Functions Guide movement of organelles around cytoplasm Key organelles in cell division Form basis of cilia and flagella Cilia and flagella never found in flowering plants

Important to some algae and to male gametes of lower plants Microfilaments Thinner (0.007 m in diameter) and more flexible than microtubules Made of protein subunits called actin Often found in bundles Function Serve as guides for movement of organelles

Motor Proteins Powered by ATP molecules Microtubule motor proteins Kinesins, dyneins Move along microtubule making and breaking connections between tubulin subunits Microfilament motor proteins myosin Cytoskeleton

Subunits Microtubules Microfilaments Tubulin (protein) Actin (protein)

Motor proteins Kinesins, dyneins Myosin Function

Key organelles in cell division, form basis of cilia and flagella, serve as guides for movement of organelles within cell Serve as guides for movement of organelles within cell The Organization of the Plant Body: Cells, Tissues, and Meristems Chapter 4

Organization of Plant Body Most vascular plants consist of: Above ground part Stems, leaves, buds, flowers, fruit

Below Root System ground part Main roots and branches Shoot System Plant Cells and Tissues

Cell wall surrounds each plant cell Pectin glues plant cells together Meristems Groups of specialized dividing cells Sources of cells and tissues Not tissues themselves Plant organs leaves, stems,roots, flower parts Fig. 4-CO, p. 49

Main Tissues of Plants Ground tissue system Vascular tissue system Dermal tissue system

Most extensive in leaves (mesophyll) and young green stems (pith and cortex) Conducting tissues Xylem distributes water and solutes Phloem distributes sugars Covers and protects plant surfaces

epidermis and periderm Plant Tissues Simple tissues Composed of mostly one cell type Workhorse cells of plant body Functions

Conduct photosynthesis Load materials into and out of vascular system Hold plant upright Store things Help keep plant healthy and functioning Simple Plant Tissues Tissue type Parenchyma tissue

Cell types Parenchyma cells Collenchyma tissue Collenchyma cells Sclerenchyma tissue Fibers, sclereids Table 4-1, p. 50 shoot tip

xylem epidermis mesophyll bud phloem flower node internode

Dermal tissues node pith xylem phloem cortex Vascular tissues

leaf epidermis seeds (inside fruit) Ground tissues Shoot system Root system cortex xylem

primary root lateral root root hairs phloem epidermis root tip root cap Fig. 4-1, p. 51

Parenchyma Usually spherical or elongated Thin primary cell wall Perform basic metabolic functions of cells Respiration Photosynthesis Storage Secretion parenchyma

cells Fig. 4-2a, p. 52 Parenchyma Usually live 1-2 years Crystals of calcium oxalate commonly found in vacuoles May help regulate pH of cells May aggregate to form parenchyma tissue

in Cortex and pith of stems Cortex of roots Mesophyll of leaves Parenchyma Mature cells may be developmentally programmed to form different cell types Wound healing Transfer cells Have numerous cell wall ingrowths

Improve transport of water and minerals over short distances At ends of vascular cells help load and unload sugars and other substances parenchyma cell with lignified wall pit Fig. 4-2b, p. 52 Collenchyma

Specialized to support young stems and leaf petioles Often outermost cells of cortex Elongated cells Often contain chloroplasts Living at maturity collenchyma cell Fig. 4-6, p. 54

Collenchyma Walls composed of alternating layers of pectin and cellulose Can occur as aggregates forming collenchyma tissue Form cylinder surrounding stem Form strands Make up ridges of celery stalk Sclerenchyma Rigid cell walls

Function to support weight of plant organs Two types of cells Fibers Sclereids Both fibers and sclereids have thick, lignified secondary cell walls Both fibers and sclereids are dead at maturity fiber Fig. 4-7a, p. 54

sclereid Fig. 4-7c, p. 54 Sclerenchyma Fibers Long, narrow cells with thick, pitted cell walls and tapered ends Sometimes elastic (can snap back to original length)

Sclerenchyma Fibers Arrangements Aggregates that form continuous cylinder around stems May connect end to end forming multicellular strands May appear as individual cells or small groups of cells in vascular tissues

Sclerenchyma Sclereids Many different shapes Usually occur in small clusters or solitary cells Cell walls often thicker than walls of fibers Sometimes occur as sheets Hard outer layer of some seed coats Complex Tissues Composed of groups of different cell types Complex tissue

Cell types Xylem Vessel member, tracheid, fiber, parenchyma cell Phloem Sieve-tube member, sieve cell,

companion cell, albuminous cell, fiber, sclereid, parenchyma cell Epidermis Guard cell, epidermal cell, subsidiary cell, trichome (hair) Periderm Phellem (cork) cell, phelloderm cell

Secretory structures Trichome, laticifer collenchyma phloem xylem

Fig. 4-8a, p. 56 secondary phloem secondary xylem Fig. 4-8b, p. 56 The Vascular System Xylem

Complex tissue Transports water and dissolved minerals Locations of primary xylem In vascular bundles of leaves and young stems At or near center of young root (vascular cylinder) Xylem Cell Types Cell Type Trachery element

(tracheids and vessel members) Description Water conducting cells Not living at maturity Before cell dies, cell wall becomes thickened with cellulose and lignin Strength and support Fibers

Parenchyma cells Help load minerals in and out of vessel members and tracheids Only living cells found in xylem Xylem Secondary xylem Forms later in development of stems and roots

Water exchanged between cells through tiny openings called pits Simple pits Occur in secondary walls of fibers and lignified parenchyma cells Bordered pits Occur in tracheids, vessel members, and some fibers parenchyma cells annular

spiral reticulate scalariform pitted Fig. 4-9, p. 57 secondary

cell wall nucleus pits primary cell wall cytoplasm secondary cell wall border

primary cell wall Fig. 4-10 (a & b), p. 57 secondary cell wall border primary cell wall

Fig. 4-10 (b), p. 57 Phloem Complex tissue Transports sugar through plant Primary phloem In vascular bundles near primary xylem in young stems In vascular cylinder in roots

Phloem Cell types in angiosperm phloem Sieve-tube members Companion cells Parenchyma Fibers and/or sclereids sieve plate sieve-tube members

parenchyma cells companion cell parenchyma cell sieve-tube plastids plasmodesmata parenchyma plastid

Fig. 4-13, p. 59 Phloem Sieve-tube members Conducting elements of phloem Join end-to-end to form long sieve tubes Mature cell contains mass of dense material called P-protein May help move materials through sieve tubes

Usually live and function from 1 to 3 years parenchyma cell sieve-tube member Fig. 4-14a, p. 59 Phloem Sieve-tube members mature sieve-tube members have aggregates

of small pores called sieve areas One or more sieve areas on end wall of sieve-tube member called a sieve-plate Callose (carbohydrate) surrounds margins of pores Forms rapidly in response to aging, wounding, other stresses May limit loss of cell sap from injured cells Phloem Companion cells Connected by plasmodesmata to mature

sieve-tube member Contain nucleus and organelles Thought to regulate metabolism of adjacent sieve-tube member Play role in mechanism of loading and unloading phloem companion cell sieve-tube member

Fig. 4-14b, p. 59 Phloem Parenchyma Usually living Function in loading and unloading phloem sieve cell sieve area

Fig. 4-14c, p. 59 Phloem Fibers and/or sclereids Long tapered cells Lignified cell walls Phloem Gymnosperms and ferns Sieve cells instead of sieve-tube members Conducting elements in phloem

Long cells with tapered ends Sieve areas but no sieve plates Usually lack nuclei at maturity Albuminous cells Adjacent to sieve cells Short, living cells Act as companion cells to sieve cells The Outer Covering of the Plant

Epidermis Outer covering Usually one cell layer thick Epidermis of succulents may be 5-6 cell layers thick Functions Protects inner tissues from drying and from infection by some pathogens Regulates movement of water and gases out of and into plant

Epidermis Cell types Epidermal cells Guard cells Trichomes (hairs) Epidermis Epidermal cells Main cell type making up epidermis Living, lack chloroplasts

Somewhat elongated shape Cell walls with irregular contours Outer wall coated with cutin to form cuticle Cuticle found on all plant parts except tip of shoot apex and root cap Cuticle often very thin in roots cuticle Fig. 4-17, p. 61

Epidermis Guard cells Found in epidermis of young stems, leaves, flower parts, and some roots Specialized epidermal cells Small opening or pore between each pair of guard cells Allows gases to enter and leave underlying tissue 2 guard cells + pore = 1 stoma (plural, stomata)

guard cell Fig. 4-18a, p. 61 Epidermis Guard cells Differ from epidermal cells Crescent shaped Contain chloroplasts

guard cell pore stoma subsidiary cell stoma apparatus

epidermal cell Fig. 4-18b, p. 61 Epidermis Subsidiary cell Forms in close association with guard cells Functions in stomatal opening and closing Epidermis Trichomes

Epidermal outgrowths Single cell or multicellular Example: root hairs Increase root surface area in contact with soil water Fig. 4-19, p. 62 Periderm Protective layer that forms in older stems and roots

Secondary tissue Several cell layers deep Periderm Composed of Phellem (cork) On outside Cells dead at maturity Suberin embedded in cell walls Phellogen (cork cambium)

Layer of dividing cells Phelloderm Toward inside Parenchyma-like cells Cells live longer than phellem cells Figure 3, p. 63 cuticle

epidermis phellem cork cambium phelloderm cortex Fig. 4-20, p. 63 Periderm

Secretory structures Primarily occur in leaves and stems May be single-celled or complex multicellular structure Examples Trichomes Could secrete materials out of plant to attract insect pollinators Laticifers Secrete latex which discourages herbivores from eating plant

laticifer Fig. 4-21, p. 64 Table 4-2a, p. 65 Table 4-2b, p. 65 Table 4-2c, p. 66 Meristems

Meristems Special region in plant body where new cells form Area where growth and differentiation are initiated Growth Irreversible increase in size that results from cell division and enlargement Cell differentiation

Structural and biochemical changes a cell undergoes in order to perform a specialized function Meristems Categories of meristems Shoot and apical meristems Ultimate source of all cells in a plant Primary meristems Originate in apical meristems Differentiate into primary tissues

Secondary meristems Produce secondary tissues SAM ground meristem Region of primary growth protoderm

procambium Primary meristems cork cambium Secondary vascular meristems cambium

Region of primary growth procambium ground Primary meristem meristems protoderm RAM Root system

Fig. 4-22, p. 66 Root and Apical Meristems RAM root apical meristem SAM shoot apical meristem

New cells produced by cell division Theoretically could divide forever Does not occur Scarcity of nutrients Branch of plant can only carry so much weight Genetic regulation of growth Primary Meristems Functions Form primary tissues Elongate root and shoot

Primary Meristems Types of primary meristems Protoderm Cells differentiate into epidermis Procambium Cells differentiate into primary xylem and primary phloem Ground meristem Differentiates into cells of pith and cortex of stems and roots

Differentiates into mesophyll of leaves young leaf SAM protoderm ground meristem

procambium Fig. 4-23b, p. 67 Fig. 4-23c, p. 67 ground meristem procambium protoderm RAM

root cap Fig. 4-23d, p. 67 Secondary Meristems Functions Cell division Initiation of cell differentiation Lateral growth Increases thickness and circumference of stems and roots

Secondary Meristems Not found in all plants Lacking in plants that grow only one season Leaves usually lack secondary growth Types of secondary meristems Vascular cambium Differentiates into secondary xylem and secondary phloem Cork cambium

Differentiates into periderm Additional Meristems Intercalary meristems In stems Regulates stem elongation Leaf specific meristems Regulates leaf shapes Repair of wounds

Formation of buds and roots in unusual places

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