About Plant Biology

1
About Plant Biology

• Chapter 1

2
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

3
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

4
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

5
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

6
Natural Plant Losses

• Plant losses occurring at a faster rate than ever
  before
• Factors include
• Agriculture
• Urbanization
• Overgrazing
• Pollution
• Extinction

7
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.

8
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

10
Scientific Method
Original Hypothesis
Devise method to test hypothesis
Analyze results
Results support hypothesis
Results support hypothesis but suggest minor
refinements
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
Retest using minor refinements of process
Test new hypotheses
Test using slightly modified hypothesis
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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 plants internal
  structure
• Plant morphology study of how a plant develops
  from a single cell into its diverse tissues and
  organs

12
Study Plants from Taxonomic Classification

• Microbiology study of bacteria
• Mycology study of fungi
• Phycology study of algae
• Bryology study of mosses

13
Interrelationships Among Several Plant Biology
Disciplines
Genes
ENVIRONMENT
Genetics Evolution Taxonomy Systematics
Ecology Paleoecology Biogeography
METABOLISM
Physiology
PLANT
TAXONOMIC GROUPS
STRUCTURE
Phycology Microbiology Mycology Bryology
Anatomy
DEVELOPMENT
Morphology
14
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 Ending
Kingdom
Division -phyta
Class -opsida
Order -ales
Family -aceae
Genus No standard ending
Species No standard ending
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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

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Whittakers Five Kingdoms
Kingdom Description
Monera 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
18
Plant Classification

• Cladistics
• Based on evolutionary groups
• Compare DNA base pair sequences of organisms to
  determine relatedness
• Obtain percent similarity between organisms

19
Plant Classification

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

20
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 Whittakers plant, animal, and fungal
  kingdoms
• Eukaryotic cells
• Membrane-bounded organelles
• Linear chromosomes
• Protists
• Not monophyletic
• Controversy over where to place organisms

22
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

23
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

24
Domain Bacteria

• Detrimental effects
• Pathogens cause diseases
• Human diseases
• Botulism, bubonic plague, cholera, syphilis,
  tetanus, tuberculosis
• Plant diseases

25
Domain Archaea

• Organisms originally were placed in Whittakers
  Kingdom Monera
• Prokaryotic
• Different cell structure and chemistry than
  organisms in Domain Bacteria

26
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

27
Three Domains
Domain Cell Type Description
Eukarya 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
28
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

29
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

30
Kingdom Fungi

• Economic importance
• Production of antibiotics
• Penicillium
• Pathogens
• Invade both plant and animal tissue
• Cause illnesses
• Reduce crop yields

31
Kingdom Protista

• Eukaryotic cells
• Reproduce both sexually and asexually
• Catch-all group
• Photosynthetic organisms algae
• Nonphotosynthetic organisms slime molds,
  foraminiferans, protozoans

32
Kingdom Protista

• Algae
• Arrangements
• Single cells, clusters, filaments, sheets,
  three-dimensional packets of cells
• Photosynthetic
• Float in uppermost layers of all oceans and lakes

33
Kingdom Protista

• Phytoplankton
• grasses of the sea
• Microscopic algae
• Form base of natural food chain
• Produce 50 of all oxygen in atmosphere

34
Kingdom Plantae

• Included all organisms informally called plants
• Bodies more complex than bacteria, fungi, or
  protists
• Eukaryotic

35
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

36
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

37
Challenge for 21st Century

• 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.

38
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
39
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

45
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

51
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. 1858 Rudolf 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

53
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

54
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

55
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

56
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

57
Microscope Comparisons
Source for illumination Nature of lenses Condition of specimen Image formation
Light microscope White 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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chloroplast
vacuole
nucleus
cell wall
mitochondrion
Fig. 3-3 (b c), p. 33
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Boundaries Between Inside and Outside the Cell

• Plasma Membrane
• and
• 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

63
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
• Ca2 pump moves Ca2 to outside of cell
• Channels allow substances to diffuse across
  membrane

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Extracellular environment
PHOSPHOLIPID BILAYER
PUMPS AND CHANNELS
SENSORY PROTEINS RECEPTORS
STEROL
Cytoplasm
Fig. 3-4, p. 34
65
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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E.R. lumen
E.R.
Cytoplasm
plasma membrane
Cell wall
plasmodesmal proteins
Cytoplasm
Fig. 3-5, p. 35
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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 plants 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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PROTOPLAST
SOLUTION
Concentration 0.3 molar
Concentration 0.3 molar (Isotonic)
Pressure 0 megapascals
Concentration 0.27 molar
Concentration 0 molar (Hypotonic)
Pressure 0.66 megapascals
Concentration 0.5 molar
Concentration 0.5 molar (Hypertonic)
Pressure 0 megapascals
Fig. 3-7 (a-c), p. 36
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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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one pore
nuclear envelope
0.2 µm
1 µm
lipid bilayer facing the nucleoplasm
nuclear envelope
lipid bilayer facing the cytoplasm
pore complex that spans both bilayers
Fig. 3-8, p. 37
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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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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
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At a deeper level of structural organization,
the chromosomal proteins and DNA are organized
as a cylindrical fiber.
Fig. 3-9c, p. 37
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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
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A nucleosome consists of part of a DNA
molecule looped twice around a core of histones.
core of histone molecules
Fig. 3-9a, p. 37
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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

88
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)
89
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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mRNA
ribosomes
attached polyribosomes
free polyribosomes
Fig. 3-10, p. 38
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mRNA
ribosomes
attached polyribosomes
free polyribosomes
Fig. 3-10a, p. 38
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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

97
0.25 µm
internal spaces
vesicles
cisternae
Fig. 3-11, p. 38
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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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two outer membranes
thylakoids
stroma
Fig. 3-12 (a), p. 40
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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
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
Starch grains Storage 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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Plastids
Prefix 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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outer compartment
inner membrane
inner compartment
outer membrane
cristae
(matrix)
Fig. 3-13, p. 41
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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

123
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 Meristems

• Chapter 4

128
Organization of Plant Body
Most 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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shoot tip
xylem
epidermis
bud
flower
mesophyll
phloem
node
internode
Dermal tissues
node
pith
xylem
phloem
Vascular tissues
cortex
leaf
epidermis
seeds (inside fruit)
Ground tissues
Shoot system Root system
cortex
primary root
xylem
lateral root
phloem
root hairs
root tip
root cap
epidermis
Fig. 4-1, p. 51
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Parenchyma

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

137
parenchyma cells
Fig. 4-2a, p. 52
138
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

139
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

140
parenchyma cell with lignified wall
pit
Fig. 4-2b, p. 52
141
Collenchyma

• Specialized to support young stems and leaf
  petioles
• Often outermost cells of cortex
• Elongated cells
• Often contain chloroplasts
• Living at maturity

142
collenchyma cell
Fig. 4-6, p. 54
143
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

144
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

145
fiber
Fig. 4-7a, p. 54
146
sclereid
Fig. 4-7c, p. 54
147
Sclerenchyma

• Fibers
• Long, narrow cells with thick, pitted cell walls
  and tapered ends
• Sometimes elastic (can snap back to original
  length)

148
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

149
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

150
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
151
collenchyma
phloem
xylem
Fig. 4-8a, p. 56
152
secondary phloem
secondary xylem
Fig. 4-8b, p. 56
153
The Vascular System
154
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)

155
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
156
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

157
parenchyma cells
spiral
reticulate
annular
pitted
scalariform
Fig. 4-9, p. 57
158
secondary cell wall
nucleus
pits
primary cell wall
cytoplasm
secondary cell wall
border
primary cell wall
Fig. 4-10 (a b), p. 57
159
secondary cell wall
border
primary cell wall
Fig. 4-10 (b), p. 57
160
Phloem

• Complex tissue
• Transports sugar through plant
• Primary phloem
• In vascular bundles near primary xylem in young
  stems
• In vascular cylinder in roots

161
Phloem

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

162
sieve plate
sieve-tube members
parenchyma cells
companion cell
parenchyma cell
sieve-tube plastids
plasmodesmata
parenchyma plastid
Fig. 4-13, p. 59
163
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

164
sieve-tube member
parenchyma cell
Fig. 4-14a, p. 59
165
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

166
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

167
sieve-tube member
companion cell
Fig. 4-14b, p. 59
168
Phloem

• Parenchyma
• Usually living
• Function in loading and unloading phloem

169
sieve area
sieve cell
Fig. 4-14c, p. 59
170
Phloem

• Fibers and/or sclereids
• Long tapered cells
• Lignified cell walls

171
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

172
The Outer Covering of the Plant
173
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

174
Epidermis

• Cell types
• Epidermal cells
• Guard cells
• Trichomes (hairs)

175
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

176
cuticle
Fig. 4-17, p. 61
177
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)

178
guard cell
Fig. 4-18a, p. 61
179
Epidermis

• Guard cells
• Differ from epidermal cells
• Crescent shaped
• Contain chloroplasts

180
guard cell
stoma
pore
stoma apparatus
subsidiary cell
epidermal cell
Fig. 4-18b, p. 61
181
Epidermis

• Subsidiary cell
• Forms in close association with guard cells
• Functions in stomatal opening and closing

182
Epidermis

• Trichomes
• Epidermal outgrowths
• Single cell or multicellular
• Example root hairs
• Increase root surface area in contact with soil
  water

183
Fig. 4-19, p. 62
184
Periderm

• Protective layer that forms in older stems and
  roots
• Secondary tissue
• Several cell layers deep

185
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

186
Figure 3, p. 63
187
cuticle
epidermis
phellem
cork cambium
phelloderm
cortex
Fig. 4-20, p. 63
188
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

189
laticifer
Fig. 4-21, p. 64
190
Table 4-2a, p. 65
191
Table 4-2b, p. 65
192
Table 4-2c, p. 66
193
Meristems
194
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

195
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

196
SAM
ground meristem
Primary meristems
Region of primary growth
protoderm
procambium
cork cambium
Secondary meristems
vascular cambium
procambium
ground meristem
Primary meristems
Region of primary growth
protoderm
RAM
Root system
Fig. 4-22, p. 66
197
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

198
Primary Meristems

• Functions
• Form primary tissues
• Elongate root and shoot

199
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

200
young leaf
SAM
protoderm
ground meristem
procambium
Fig. 4-23b, p. 67
201
Fig. 4-23c, p. 67
202
ground meristem
procambium
protoderm
RAM
root cap
Fig. 4-23d, p. 67
203
Secondary Meristems

• Functions
• Cell division
• Initiation of cell differentiation
• Lateral growth
• Increases thickness and circumference of stems
  and roots

204
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

205
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

206
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