about plant biology
DESCRIPTION
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?. - PowerPoint PPT PresentationTRANSCRIPT
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About Plant BiologyChapter 1
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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
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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
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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
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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
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Natural Plant Losses
• Plant losses occurring at a faster rate than ever before
• Factors include– Agriculture– Urbanization– Overgrazing– Pollution– Extinction
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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.
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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
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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
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Scientific MethodOriginal Hypothesis Devise method to
test hypothesisAnalyze results
Results support
hypothesis
Results support
hypothesis but suggest minor refinements
Results are so unexpected that
they do not support original hypothesis and require a new
hypothesis
Results do not support original
hypothesis but fall within range that
could be expected if original
hypothesis is slightly modified
Retest using minor
refinements of process
Test using slightly modified
hypothesis
Test new hypotheses
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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 plant’s internal
structure• Plant morphology – study of how a plant
develops from a single cell into its diverse tissues and organs
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Study Plants from Taxonomic Classification
• Microbiology – study of bacteria• Mycology – study of fungi• Phycology – study of algae• Bryology – study of mosses
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Interrelationships Among Several Plant Biology Disciplines
GenesGenetics
Evolution
Taxonomy & Systematics
METABOLISMPhysiology
ENVIRONMENTEcology
Paleoecology
Biogeography
TAXONOMIC GROUPS
DEVELOPMENT
STRUCTUREPhycology
Microbiology
Mycology
Bryology
Morphology
Anatomy
PLANT
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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
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Linnaean Taxa
Taxa EndingKingdomDivision -phytaClass -opsidaOrder -alesFamily -aceaeGenus No standard ending
Species No standard ending
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Plant Classification
Whittaker’s 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
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Whittaker’s Five KingdomsKingdom Description
Monera Included bacteria
Fungi Included molds, mildews, rusts, smuts, and mushrooms
ProtistaIncluded simple organisms, some were photosynthetic, mostly aquatic organisms called algae
PlantaeIncluded more complex photosynthetic organisms that typically grew on land
AnimaliaIncluded typically motile, multicellular, nonphotosynthetic organisms
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Plant Classification
Cladistics• Based on evolutionary groups• Compare DNA base pair sequences of
organisms to determine relatedness• Obtain percent similarity between
organisms
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Plant Classification
• Clades – evolutionary groups• Cladogram = phylogenetic tree
– Branching diagram– Emphasizes shared features from common
ancestor– Future discoveries may require modifications
of cladogram
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Plant Classification
• Domain– Neutral term– Groups of organisms as large or larger than a
kingdom– Monophyletic
• Three domains based on cladistics– Eukarya– Bacteria– Archaea
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Domain Eukarya
• Made up of Whittaker’s plant, animal, and fungal kingdoms
• Eukaryotic cells– Membrane-bounded organelles
• Linear chromosomes• Protists
– Not monophyletic– Controversy over where to place organisms
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Domain Bacteria
• Organisms originally were placed in Whittaker’s Kingdom Monera
• Microscopic• Prokaryotic cells
– No membrane-bounded organelles– Circular chromosome
• Sexual reproduction unknown • Found in every habitat on Earth
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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
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Domain Bacteria
Detrimental effects• Pathogens – cause diseases• Human diseases
– Botulism, bubonic plague, cholera, syphilis, tetanus, tuberculosis
• Plant diseases
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Domain Archaea
• Organisms originally were placed in Whittaker’s Kingdom Monera
• Prokaryotic• Different cell structure and chemistry than
organisms in Domain Bacteria
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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
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Three Domains
Domain Cell Type Description
Eukarya Eukaryotic Membrane bounded organelles, linear chromosomes
Archaea ProkaryoticFound 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
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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
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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
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Economic importance• Production of antibiotics
– Penicillium• Pathogens
– Invade both plant and animal tissue– Cause illnesses– Reduce crop yields
Kingdom Fungi
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Kingdom Protista
• Eukaryotic cells• Reproduce both sexually and asexually• Catch-all group
– Photosynthetic organisms – algae– Nonphotosynthetic organisms – slime molds,
foraminiferans, protozoans
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Kingdom Protista
Algae• Arrangements
– Single cells, clusters, filaments, sheets, three-dimensional packets of cells
• Photosynthetic• Float in uppermost layers of all oceans
and lakes
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Kingdom Protista
• Phytoplankton– “grasses of the sea”– Microscopic algae– Form base of natural food chain– Produce 50% of all oxygen in atmosphere
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Kingdom Plantae
• Included all organisms informally called plants
• Bodies more complex than bacteria, fungi, or protists
• Eukaryotic
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• 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
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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
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Challenge for 21st Century
While the human population increases, the major challenge of retaining natural biological diversity and developing a sustainable use of the world’s forests, grasslands, and cropland remains. As you study plant biology, think of the ways that you can contribute to this challenge.
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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
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The Plant Cell and the Cell Cycle
Chapter 3
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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
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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
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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
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Cell Theory
Statement Year Contributor
All plants and animals are composed of cells. 1838
Matthias Schleiden and Theodor Schwann
Cells reproduce themselves. 1858 Rudolf Virchow
All cells arise by reproduction from previous cells.
1858Rudolf Virchow
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Basic Similarities of Cells
• Cells possess basic characteristic of life– Movement– Metabolism– Ability to reproduce
• Organelles– “little organs”– Carry out specialized functions within cells
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Light Microscope
• View cells 20-200 µm 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
µm in diameter
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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
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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
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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
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Microscope ComparisonsSource for illumination
Nature of lenses
Condition of specimen
Image formation
Light microscopeWhite light Glass
Living or killed stained specimen
View directly through microscope
Confocal microscope Laser Glass
Killed stained specimens
Image analyzed on digital computer screen
Transmission electron microscope Electrons Magnets
Ultrathin section of killed specimen contained within vacuum
View on fluorescent plate or photographic film
Scanning electron microscope Electrons Magnets
Surface view of killed specimen contained within vacuum, with low vacuum can view living cells
Television picture tube
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Generalized Plant Cell
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Fig. 3-3 (b & c), p. 33
chloroplast
cell wall
mitochondrion
nucleusvacuole
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Boundaries Between Inside and Outside the Cell
Plasma Membraneand
Cell Wall
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Plasma Membrane
• Surrounds cell• Controls transport into and out of cell• Selectively permeable
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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
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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
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Fig. 3-4, p. 34
Extracellular environment
PUMPS ANDCHANNELS
SENSORY PROTEINSRECEPTORSCytoplasm
STEROL
PHOSPHOLIPIDBILAYER
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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
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Fig. 3-5, p. 35
E.R. lumenE.R. Cytoplasm
Cell wall
plasmodesmalproteins
plasmamembrane
Cytoplasm
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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 plant’s cells
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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
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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
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Fig. 3-6, p. 35
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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
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Fig. 3-7 (a-c), p. 36
PROTOPLAST SOLUTION
Concentration0.3 molar(Isotonic)
Concentration0 molar(Hypotonic)
Concentration0.27 molar
Pressure0.66 megapascals
Concentration0.5 molar(Hypertonic)
Concentration0.3 molar
Pressure0 megapascals
Concentration0.5 molar
Pressure0 megapascals
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Fig. 3-7 (d), p. 36
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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
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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
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Organelles of Protein Synthesis and Transport
Nucleus, Ribosomes, Endoplasmic Reticulum, and Golgi
Apparatus
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Nucleus
• Ovoid or irregular in shape• Up to 25 µm in diameter• Easily stained for light or electron
microscopy
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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
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Fig. 3-8, p. 37
0.2 µm1 µmnuclear envelope
one pore
lipid bilayer facingthe nucleoplasm
nuclearenvelope
lipid bilayer facingthe cytoplasm
pore complex thatspans both bilayers
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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
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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
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Fig. 3-9, p. 37
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Fig. 3-9d, p. 37
At times when a chromosome is mostcondensed, the chromosomal proteinsinteract, which packages loops of alreadycoiled DNA into a “supercoiled” array.
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Fig. 3-9c, p. 37
At a deeperlevel of structuralorganization, thechromosomalproteins and DNAare organized asa cylindrical fiber.
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Fig. 3-9b, p. 37
Immerse achromosome insaltwater and itloosens up to abeads-on-a-stringorganization. The“string” is oneDNA molecule.Each “bead” isa nucleosome.
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Fig. 3-9a, p. 37
A nucleosomeconsists of part ofa DNA moleculelooped twicearound a coreof histones.core of
histonemolecules
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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
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Nuclear Components
Component Structure and Function
Nuclear envelopeDouble 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
NucleoliDark 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)
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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
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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
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Fig. 3-10, p. 38
mRNAribosomes
freepolyribosomes
attachedpolyribosomes
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Fig. 3-10a, p. 38
mRNA
ribosomes
freepolyribosomes
attachedpolyribosomes
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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
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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
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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
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Golgi Apparatus
• Also called a dictyosome• Consists of stack of membranous,
flattened bladders called cisternae
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Fig. 3-11, p. 38
vesicles internal spaces0.25 µm
cisternae
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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
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Endomembrane System
• Complex network that transports materials between Golgi apparatus, the ER, and other organelles of the cell
• Movement– Rapid – Continuous
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Organelles of Energy Metabolism
Plastids and
Mitochondria
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Plastids
• Found in every living plant cell– 20-50/cell– 2-10 µm in diameter
• Surrounded by double membrane• Contain DNA and ribosomes
– Protein-synthesizing system similar to but not identical to one in nucleus and cytoplasm
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Fig. 3-12 (a), p. 40
two outermembranes
thylakoids
stroma
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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
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Plastids
• Types of plastids– Chloroplasts– Leukoplasts– Amyloplasts– Chromoplasts
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Fig. 3-12 (b-f), p. 40
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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
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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
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Chloroplast
Component Description
ThylakoidsInner membranes of chloroplast, contain proteins that bind with chlorophyll
StromaThick enzyme solution surrounding thylakoids
ChlorophyllGreen pigment that gives plant tissue its green color
Starch grainsStorage form of carbohydrates produced during photosynthesis
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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
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Amyloplasts
• amylo – “starch”• Leukoplast that contains large starch
granules
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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
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PlastidsPrefix Meaning Function
Chloroplast “chloro –” “yellow-green”
Photosynthesis, convert light energy into chemical energy, store carbohydrates as starch grains
Leukoplast “leuko –” “white” Store carbohydrates in form of starch
Amyloplast “amylo –” “starch” Leukoplasts that contain large granules of starch
Chromoplast “chromo –” “color”
Stores carotenes and xanthophylls, give orange-to-red color to certain plant tissues
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Mitochondria
• Double-membrane structure• Contain DNA and ribosomes • Inner membrane infolded
– Folds called cristae– Increase surface area available for chemical
reactions
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Fig. 3-13, p. 41
(matrix)
innercompartment
outermembrane
cristae
outercompartment inner
membrane
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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
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Other Cellular Structures
Vacuoles, Vesicles, Peroxisomes, Glyoxysomes, Lysosomes, and
Cytoskeleton
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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
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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
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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
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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
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Cytoskeleton
• Structures in cytoskeleton– Microtubules– Motor proteins– Microfilaments
• Specialized proteins connect microtubules and microfilaments to other organelles– Connections thought to coordinate many cell
processes
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Microtubules
• Relatively thick (0.024 µm in diameter)• Assembled from protein subunits called
tubulin • Fairly rigid but can lengthen or shorten by
adding or removing tubulin molecules
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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
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Microfilaments
• Thinner (0.007 µm 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
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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
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Cytoskeleton
Subunits Motor proteins Function
Microtubules Tubulin (protein)
Kinesins, dyneins
Key organelles in cell division, form basis of cilia and flagella, serve as guides for movement of organelles within cell
Microfilaments Actin (protein) Myosin
Serve as guides for movement of organelles within cell
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The Organization of the Plant Body: Cells, Tissues, and
MeristemsChapter 4
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Organization of Plant BodyMost vascular plants consist of:
Shoot System
Above ground part
Stems, leaves, buds, flowers, fruit
Root System Below ground part
Main roots and branches
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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
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Fig. 4-CO, p. 49
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Main Tissues of Plants
Ground tissue system
Most extensive in leaves (mesophyll) and young green stems (pith and cortex)
Vascular tissue system
Conducting tissues•Xylem – distributes water and solutes•Phloem – distributes sugars
Dermal tissue system
Covers and protects plant surfaces – epidermis and periderm
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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
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Simple Plant Tissues
Tissue type Cell types
Parenchyma tissue Parenchyma cells
Collenchyma tissue Collenchyma cells
Sclerenchyma tissue Fibers, sclereids
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Table 4-1, p. 50
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Fig. 4-1, p. 51
phloemxylemcortex
cortexphloemxylem
pith
mesophyllepidermis
Shoot systemRoot system
xylem
epidermis
epidermis
phloem
node
node
Vascular tissues
Ground tissues
internode Dermal tissues
root caproot tip
root hairslateral rootprimary root
seeds (inside fruit)
leaf
flowerbud
shoot tip
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Parenchyma
• Usually spherical or elongated• Thin primary cell wall• Perform basic metabolic functions of cells
– Respiration – Photosynthesis– Storage– Secretion
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Fig. 4-2a, p. 52
parenchymacells
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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
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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
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Fig. 4-2b, p. 52
pitparenchyma cell with lignified wall
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Collenchyma
• Specialized to support young stems and leaf petioles
• Often outermost cells of cortex• Elongated cells• Often contain chloroplasts• Living at maturity
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Fig. 4-6, p. 54
collenchyma cell
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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
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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
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Fig. 4-7a, p. 54
fiber
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Fig. 4-7c, p. 54
sclereid
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Sclerenchyma
• Fibers– Long, narrow cells with thick, pitted cell walls
and tapered ends– Sometimes elastic (can snap back to original
length)
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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
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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
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Complex Tissues
Composed of groups of different cell types
Complex tissue Cell types
Xylem Vessel member, tracheid, fiber, parenchyma cell
PhloemSieve-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
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Fig. 4-8a, p. 56
collenchyma
phloem
xylem
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Fig. 4-8b, p. 56
secondary xylem
secondary phloem
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The Vascular System
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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)
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Xylem Cell Types
Cell Type Description
Trachery element (tracheids and vessel members)
•Water conducting cells•Not living at maturity•Before cell dies, cell wall becomes thickened with cellulose and lignin
Fibers•Strength and support
Parenchyma cells•Help load minerals in and out of vessel members and tracheids•Only living cells found in xylem
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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
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Fig. 4-9, p. 57
pitted
parenchyma cells
annularspiral
scalariformreticulate
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Fig. 4-10 (a & b), p. 57
primarycell wall
secondarycell wall
nucleus
pits
primarycell wall
secondarycell wall
cytoplasm
border
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Fig. 4-10 (b), p. 57
primarycell wall
secondarycell wall
border
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Phloem
• Complex tissue• Transports sugar through plant• Primary phloem
– In vascular bundles near primary xylem in young stems
– In vascular cylinder in roots
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Phloem
• Cell types in angiosperm phloem– Sieve-tube members– Companion cells– Parenchyma– Fibers and/or sclereids
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Fig. 4-13, p. 59
plasmodesmata
sieve plate sieve-tube members
parenchyma cell
sieve-tube plastids
parenchyma plastid
parenchyma cells
companion cell
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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
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Fig. 4-14a, p. 59
sieve-tube memberparenchyma cell
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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
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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
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Fig. 4-14b, p. 59
sieve-tube membercompanion cell
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Phloem
• Parenchyma– Usually living– Function in loading and unloading phloem
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Fig. 4-14c, p. 59
sieve areasieve cell
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Phloem
• Fibers and/or sclereids– Long tapered cells– Lignified cell walls
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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
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The Outer Covering of the Plant
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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
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Epidermis
• Cell types– Epidermal cells– Guard cells– Trichomes (hairs)
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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
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Fig. 4-17, p. 61
cuticle
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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)
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Fig. 4-18a, p. 61
guard cell
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Epidermis
• Guard cells– Differ from epidermal cells
• Crescent shaped• Contain chloroplasts
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Fig. 4-18b, p. 61
guard cell
porestoma
stomaapparatus
subsidiarycell
epidermal cell
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Epidermis
• Subsidiary cell– Forms in close association with guard cells– Functions in stomatal opening and closing
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Epidermis
• Trichomes– Epidermal outgrowths– Single cell or multicellular
• Example: root hairs• Increase root surface area in contact with soil
water
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Fig. 4-19, p. 62
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Periderm
• Protective layer that forms in older stems and roots
• Secondary tissue• Several cell layers deep
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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
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Figure 3, p. 63
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Fig. 4-20, p. 63
cuticle
cortex
epidermis
phellem
cork cambiumphelloderm
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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
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Fig. 4-21, p. 64
laticifer
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Table 4-2a, p. 65
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Table 4-2b, p. 65
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Table 4-2c, p. 66
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Meristems
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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
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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
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Fig. 4-22, p. 66
Region ofprimary growth
SAM
Region ofprimary growth
Root system
Primarymeristems
Secondarymeristems
Primarymeristems
RAM
groundmeristem
protodermprocambium
corkcambium
vascularcambium
procambiumgroundmeristemprotoderm
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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
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Primary Meristems
• Functions– Form primary tissues– Elongate root and shoot
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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
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Fig. 4-23b, p. 67
procambium
young leaf SAM
protoderm
groundmeristem
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Fig. 4-23c, p. 67
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Fig. 4-23d, p. 67
ground meristem
procambium protoderm
RAM
root cap
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Secondary Meristems
• Functions– Cell division– Initiation of cell differentiation – Lateral growth
• Increases thickness and circumference of stems and roots
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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
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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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