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Created by Julia Hsu Levy – Version 1.5
Chapter 27: Plants
Plant characteristics:
 Eukaryote: nucleus and organelles
 Cellulose cell walls
 Chlorophyll
 Four main groups: bryophytes, pteridophytes, gymnosperms, and angiosperms.
Plants may have evolved from Chara. Evidence includes that these protists
have:
 cellulose rosettes to make cellulose cell walls
 peroxisomes
 flagellated sperm cell morphology
What land plants evolved that did not exist in algae:
 apical meristems
 multicellular embryos
 alternation of generation life cycle in all
 Sporangia (developed 2n structure) that produce spores with cell walls
 Gametangia (developed 1n structure) that produce gametes
 Embryo developed in female tissues that provides nutrients
 Spores covered in sporopollenin (durable organic material)
 adaptations for acquiring, transporting, and conserving water (ex: cuticle,
stomata, vascular tissue)
 adaptations for reducing the harmful effect of UV radiation
 adaptations for repelling terrestrial herbivores and resisting pathogens (ex:
secondary compounds such as termpenes, tannins, phenolics, alkaoids)
Alternation of generation life cycle:
Generic plant sexual life cycle:
1. Sperm and egg fertilize to form zygote.
2. Zygote undergoes mitosis and becomes a
multicellular 2N body (sporophyte).
3. Some of the 2N cells of the sporophyte
undergo meiosis to create spores.
4. 1N spores germinate into a multicellular 1N
body (gametophyte) which can be male or
female.
5. The gametophyte produces gametes by
mitosis.
Sexual reproduction: process of creating offspring
with DNA recombinations different from the parent
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Description
1. Nonvascular
2. Seedless vascular
3. Gymnosperms
Evolutionary History of Plants
Evolutionary Adaptation
Example
from Predecessors
Terrestrial adaptations:
Moss, hornwort, liverwort
cutin
Xylem and phloem  roots, Ferns, lycophytes,
stems, and leaves
horsetails, whisk ferns
Seed-bearing cones, pollen Gingko: ornamental, plant
, sporophyte dominance
only males because female
seed coat decaying
produces foul odor
Cycads: resembles palms
but nonflowering
Gnetum: Welwitchia with
strange meristematic
growth, Ephedra natural
speed
4. Angiosperms
Flowers and seeds within
fruits
Conifers: cone-bearing
plants such as pine,
redwood, etc.
All flowering dicot and
monocot plant
Significant events in plant history:
o The flora and fauna of Earth changed dramatically during the formation of the
supercontinent Pangaea in the Permian.
o This likely led to major environmental changes, including drier and warmer
continental interiors.
o Many groups of organisms disappeared and others emerged as their successors.
(Ex: Reptiles increased, amphibians decreased in diversity)
o Seedless vascular plants that dominated in Carboniferous swamps were largely
replaced by gymnosperms, which were more suited to the drier climate.
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Life cycle of typical moss:
o Antheridia: male gametophyte
o Archegonia: female
gametophyte
o Gametophyte dominant life
cycle (majority of the plant
structure is gametophyte)
o Still requires water for
reproduction
o Rhizoids: root-like structures
that anchor plants to the ground
o Few cells thick because
diffusion required for water
transport
o Ex: peat moss
Life cycle of Pterophyta fern: first formed in “coal forests” of Carboniferous
period
o Sorus: sporangia (spore-bearing structure) found on the underside of the frond
o Characteristic gametophyte stage that looks like a heart (thallus)
o Sporophyte dominant life cycle (megaspores  female, microspore  male)
o Requires some water for reproduction
o Branching possible because of vascular tissue
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Life cycle of Gymnosperm
pine:
o Pine cones: sporangia
o Sporophyte dominant
o Wind pollinated
o Seed: multicellular package of
food and embryo, developed
from ovule
o Seeds exposed to elements
(no fruit for protection or
animal attraction)
o Does NOT require water for
fertilization
o Male gametophyte: pollen
grain with sperm cells inside
o Importance of seed: to
disperse offspring
o Spores retained in parent whereas seeds are released
o Integuments: layers of protective tissue around the female structures such as the
ovule, later develops into the seed coat
o Mostly nonflagellated sperm delivered via pollen tube from pollen grain to ovule
o Male and female cones
o Spores produced on scale-like sporophylls that are the scales of a cone (male and
female)
o Two sperm cells develop in the pollen grain that enters the ovule at the micropyle
o Sperm + egg  embryo
o Mostly evergreen (keeps leaves all year)
Life cycle of Angiosperm:
o “flowering plants”
o most diverse
o Phylum Anthophyta
o divided into monocots and
dicots
o sporophyte dominant
o does not require water for
fertilization
o sperm cells in male
gametophyte (pollen grain)
o seeds may be animal (fleshy) or
wind dispersed (dry)
o DOUBLE FERTILIZATION 
endosperm (sperm+2 polar
bodies) and embryo
(sperm+egg)
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o Ovule undergoes meiosis to make 4 1N cells that go through mitosis to produce 8
1N cells (2 synergids, 2 polar bodies, 3 antipodal cells, 1 egg)
o Produces fruits and flowers
o Flower specialized for reproduction and for attracting animal pollinators
Flower anatomy:
o Sepals: base of the flower, modified
leaves that enclose the flower before it
opens
o Petals: inside the ring of sepals,
brightly colored in plant species that
are pollinated by animals, lack bright
coloration in wind-pollinated plant
species
o Stamens: the male reproductive
organs, produce microspores in anther
 pollen grain (male gametophyte),
filament + anther)
o Carpals: female sporophylls that
produce megaspores and their
products, female gametophytes;
stigma+style+ovary (with ovule
inside)
Flower structure:
o Complete flowers have parts, whereas imcomplete flowers have 1 or more parts
missing.
o Perfect flowers have both male and female organs, whereas imperfect flowers
have only male or female organs.
Fruit: mature ovary, may be dry or fleshy; helps to disperse seeds
o Dry fruits: dandelions and maples with propellers or lightness for wind dispersal,
may be prickly (burrs) for animal dispersal
o Fleshy fruits: eaten, seeds deposited unharmed with fertilizer
Fruit types:
o Simple fruits are derived from a single ovary such as oranges or cherries.
o Aggregate fruit, such as a blackberry, results from a single flower with several
carpals.
o Multiple fruit, such as a pineapple, develops from an inflorescence, a tightly
clustered group of flowers.
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* * * Typical Plant Cell * * *
Protoplasm: everything excluding the cell wall
1. Plasma membrane: membrane that covers the surface of the protoplasm
2. Nucleus: permanent storage place for genetic information (DNA or RNA)
3. Central vacuole: single membrane (tonoplast) organelle that store water and
necessary salts, can
expand rapidly to force
cells to elongate
4. Cytoplasm: all
substances excluding
cell wall, nucleus,
vacuole
5. *Mitochondria: contains
enzymes to carry out
cellular respiration
6. Plastids: organelles that
carry out many functions,
including photosynthesis,
storage, export of
specialized lipid
molecules, pigment
storage
 Chloroplast:
plastids when matured and exposed to light, green due to presence of chlorophyll
 Amyloplast: stores amylose (starch)
 Chromoplast: red, yellow, orange lipids accumulate to give certain fruits/flowers
bright colors
7. Ribosome: particles used during protein synthesis (translation)
 Polysome: cluster of ribosomes, associated with mRNA, to form complexes
8. Endoplasmic reticulum: carries large molecules such as proteins when diffusion is
not possible to transport the molecule around the cell
 rough ER: ribosomes attached to ER, proteins made pass through ER into the
lumen to form vesicles
 smooth ER: lipid synthesis and membrane assembly
9. Dictyosomes (Golgi body, apparatus in animals): stack of thin vesicles that
modifies materials that the cell will secrete, ER vesicles gather to one face of the
dictyosome
 Forming face (cis): vesicles accumulate on this side
 Maturing face (trans): vesicles releasing modified components
10. Endomembrane system: continuation of membrane system in cell, exclusing
mitochondrial and plastid membranes
11. Microbodies: 0.5 - 1.5 m diameter
 Peroxisomes and glyoxysomes: breaks down and builds up hydrogen peroxide
(H2O2) in cell
12. Cytosol: most volume of cytoplasm (mostly water, enzymes, and chemicals)
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14. Microtubules: act as a cytoskeleton, made of two glocular proteins (alpha tubulin
and beta
tubulin)
 Centrioles: 9 sets of 3 short microtubules (9+3 arrangement)
 Cilia: short (2 m) microtubules, arranged in groups
 Flagella: longer microtubules, arranged singly or in sets of 2 or 4
 Basal body: like centrioles, associated with flagella and cilia
15. Microfilmanets: made of flobular protein (actin)
16. Storage bodies: holds nutrient reserves in times of scarcity
 spherosomes: (lipid bodies): large oil droplets (ex: peanut oil, sunflower oil, etc)
 amyloplasts: stores amylose
17. Cell wall: provides structure and protection for all plant cells, except sperm cells
 middle lamella: adhesive layer found between two adjoining plant cells, made of
pectin
 primary cell wall: thin cell wall
 secondary cell wall: protoplast deposits secondary wall between primary cell
wall and plasma membrane, usually full of lignin to make wall stronger than
hemicellulose
 lignin: sugar protein that is fungal , bacterial, chemical, and water resistant
Cells  Tissues  Organs  Systems
Cells
Tissues
Organs
Parenchyma cell:
Dermal: covering,
Roots: anchoring,
thin primary cell wall may have waxy
storage, and
covering (epidermis- absorption
Collenchyma cell:
cuticle, endodermisunevenly thickened Casparian strip)
Stems: support
primary cell wall
Ground: all
Leaves:
Sclerenchyma cell: undifferentiated
photosynthesis,
thickened
cells (pith and
transpirational pull
secondary cell wall
cortex)
Systems
Shoot: aerial for
photosynthesis and
reproduction
Root: subterranean
for water and
mineral absorption
and storage
Meristematic: cell
division (growth);
occurs throughout
lifetime (unlike
animals with growth
limited to juvenile
stage)
Vascular:
conductive
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Vascular tissue: continuous throughout the plant, transport of materials between roots
and shoots
1. Xylem: water and mineral transport by transpiration from root to shoot
o Ex: tracheids (long and thin) and vessel elements (short and wide)
o Functionally dead at maturity (lose protoplasm)
o Perforated ends to allow for water conduction
2. Phloem: food transport by translocation (“source ot sink”) from photosynthetic cells
to storage cells
o Sucrose, other organic compounds, and
some mineral ions move through tubes
formed by chains of cells, sieve-tube
members.
o alive at functional maturity (lack the
nucleus, ribosomes, and a distinct vacuole)
o sieve plates: end walls with pores
o companion cell: nonconducting nucleated companion cell, connected to the
sieve-tube member, may assist the sieve-tube cell.
Plant Organ
Leaf
Stem
Root
Flowers
Comparing Monocots to Dicots
Monocot
Dicot
Parallel veins
Main vein with branched veins
“Scattered” bundles
Ring bundles
Ring bundles within endodermis
Centralized vascular core within
endodermis (“X” xylem pattern)
Fibrous roots
Taproots
3x multiples
4x and 5x multiples
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* * * Stem * * *
Twig:
o
o
o
o
o
node: points where leaves are attached
internodes: points between nodes
axillary bud: potential to form branch
terminal bud: growth of young shoot
Modified stems include stolon, tuber, bulb,
rhizome.
Apical dominance: The presence of a terminal bud
is partly responsible for inhibiting the growth of axillary
buds (auxin induced growth).
o Evolutionary advantage: By concentrating
resources on growing taller, apical dominance
increases the plant’s exposure to light.
In the absence of a terminal bud, the axillary buds
break dominance and gives rise to a vegetative
branch complete with its own terminal bud, leaves,
and axillary buds (cytokinin induced growth).
Dicot stems can form wood because of secondary growth in the vascular bundles.
Monocot stems cannot because the bundles are “scattered.”
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* * * Leaf * * *
Cuticle: waxy covering (cutin) to
prevent against water loss
Epidermis: covering
Palisade parenchyma: primary
photosynthetic cells
Spongy parenchyma: air
pockets to trap moisture, CO2,
and other gases
Stoma(ta): space between two
guard cells, K+ ion pump
regulated with water pressure
Vascular bundle: surrounded by
bundle sheath cells, xylem and phloem for conduction
Leaf structure: blade + petiole (small stalk) that is attached to stem
o Simple: undivided blade
o Compound: divided blade
o Modified leaves: tendrils, spines,
needles, coloration
* * * Roots * * *
Function: water and mineral
absorption
root hairs: increase surface
area, mycorrhizae association
with fungus
root cap: protects apical
meristem
Stele: ring within endodermis
where vascular tissues form
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Zone of cell division: area of rapid mitosis
Zone of elongation: cells growing in length
Zone of maturation: roots hairs and specialized cells
pericycle: outer layer of stele that gives rise (forms) lateral roots (root hairs)
Specialized roots: adventitious above-ground roots for support (aka…prop or aerial
roots)
* * * Plant Growth and Development * * *
Annual plants complete their life cycle - from
germination through flowering and seed production to
death - in a single year or less. Biennial plants span
two years, which may require vernalization (cold
period). Plants that live many years are perennials.
Growth is the irreversible increase in mass that results
from cell division and cell expansion.
 Mitosis
 Cell plate forms between two daughter cells
Development is the sum of all the changes that
progressively elaborate an organism’s body.
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Meristematic
tissue: areas of
indeterminate
growth
1. Apical
meristems: tips of roots and
in the buds of shoots
o primary
growth: elongation
o produces
primary plant body
(initial roots
and shoots)
o Ex: length
2. Lateral
meristems: located within
roots and shoots
o secondary
growth: thickening
(girth)
o Ex: bark, thicker roots, wood
Ways to protect the meristems: root cap, bud scales, hypocotyls while dicots pushing
out of ground, coleoptile while monocots are pushing out of the ground
Secondary plant body: vascular cambium and cork cambium
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* * * Plant Transport * * *
Transpiration: water transport from root to shoot
Endodermis covered with
Casparian strip: a belt of
suberin, a waxy material that is
impervious to water and
dissolved minerals
Ways that material gets into the
root
1. Apoplast: cell walls until the
endodermis
2. Symplast: through cell interior
and between cells via
plasmodesmata
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Guttation: exudation of water droplets from root pressure
Transpiration involves forces
 Cohesion: water molecule attractions
 Adhesion: water molecule attraction to cell walls
Tension force exerted from adhesion LOWERS water potential. Most amount of tension
(negative pressure) in the leaf xylem, where water is pulled towards the air spaces in
the spongy parenchyma.
Cavitation: break in the water column lessened with adhesion to xylem cell walls
 Tracheids are longer, thinner cells with more cell wall. Plants that are very tall
(ex: pine) have tracheid cells that reduce cavitation.
 Vessels are shorter, wider which transports more water but are more prone to
cavitation.
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Changes in turgor pressure that open and close stomata result primarily from the
reversible uptake and loss of potassium ions (K+) by guard cells.
* * * Plant Nutrition * * *
Root system: absorbs water (but 90% lost through transpiration) and minerals
Shoot system: obtains CO2 incorporated into photosynthesis to make the bulk of the
organic matter
A variety of plants parasitize other plants to extract nutrients that supplement or even
replace the production of organic molecules by photosynthesis by the parasitic plant.
 Ex: type of mistletoe which supplements its nutrition by using projections called
haustoria to siphon xylem sap from the vascular tissue of the host tree.
Plant would be unable to obtain adequate nutrition from roots without these two
symbiotic relationships.
1. Mycorrhizae: increases absorptive surface area (sucks in more water)
2. Nitrogen-fixing bacteria: root nodules with pockets of bacteria to convert
atmospheric nitrogen
Bacteria “fix” atmospheric nitrogen to
ammonium which is converted to NO2 (nitrite)
and then nitrate (NO3). Plants use the nitrates
which then consumers eat. Some of the nitrates
are released back into the atmosphere as
nitrogen gas.
Genus: Rhizobium
15-20% of the plant body is dry matter
(non-aqueous).
 95% = organic
 5% = inorganic (not carbonbased)
Types of nutrients
1. Essential nutrient: required to complete life cycle (seed germination to
reproduction) – K
 Hydroponics can determine essential nutrients.
2. Macronutrients: needed in large quantities – C H O N P S K Ca Mg
3. Micronutrients: needed in small quantities – Fe Cl Cu Mb Bo Ni
Nutrient deficiencies are easily diagnosed from characteristic signs.
 Ex: lacking magnesium  chlorosis
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Nitrogen fixation: All plants require nitrogen, which is in the amine-functional group of
the amino acids that makes up proteins. The atmosphere is 80% nitrogen gas (N2)
which plants cannot incorporate. Nitrogen fixing bacteria are required for plants to use
nitrogen.
 N2  NH3  NO2-  NO3-  N2
Humans rely upon plants for nutrition. Plants bred to be “super” varieties have
increased protein because plants naturally do not have much protein. Fixed nitrogen
fertilizers are required in large quantities. Countries that most need the proteinaceous
plants are least able to afford it.
Nodules: legume’s root swellings called, composed of plant cells that contain nitrogenfixing bacteria (Rhizobium).
 Bacteriods: vesicles formed by the root cell to house Rhizobium
 The development of root nodules begins after bacteria enter the root through an
infection thread.
Crop rotation and nitrogen fixation
 Non-legume crop (ex: corn) planted
 Following year legume is planted to restore the concentration of fixed soil
nitrogen.
 Legume crop is not harvested but plowed under to decompose as “green
manure”.
 To ensure the formation of nodules, the legume seeds may be soaked in a
culture of the correct Rhizobium bacteria or dusted with bacterial spores before
sowing.
Signal Transduction Pathway: how external signals are carried into the cell
1. Reception: “getting” signal
2. Transduction: transferring signal with secondary messengers
3. Response: reacting to signal
Greening:
phenomenon of plants
developing chlorophyll
in response to light
Phytochrome:
molecule with receptor
abilities
o Detects light
o Activates Gprotein
o Forces
production of
second
messenger
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(usually Ca2+ or cGMP or cAMP)
o Stimulates activity within the cell
* * * Plant Hormones * * *
Hormones are chemical substances that are produced in one part of the body and
transported to another part to regulate development.
 Hormones are found in very low concentrations.
 Each hormone has more than one function.
Angiosperm life cycle:
Dormancy is the stage when development is suspended in the seed stage. Cells are
not dividing.
There are ways to break dormancy.
o Mechanical abrasion
o Fire: dries the seed , melts waxes in seed coat so water can be absorbed
o Water immersion to leach out inhibiting chemicals (hormones)
o Temperature: vernalization
Germination is the stage when dormancy is broken and the seed begins to develop. .
Flowers are timed to develop according to day-night length. Plants have the ability to
detect the amount of darkness. They are photoperiodic. The mechanisms for light
detection are yet unknown.
 Florigen, even though its not isolated, is believed to be a hormone that travels from
the leaf to where the flowers will begin development.
 Short-day plants: long night plants (require longer than critical night length time for
flowering)
 Long-day plants: short night plants (require less than critical night length time for
flowering)
 Bursts of light alter phytochrome from Pf to Pfr  no flowering but far red light
converts Pfr  Pf.
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Blue-light is found to
be most effective at
inducing plant
responses.
Phytochromes are
responsible for light
absorption.
Senescence is the deterioration of plant tissues
(cells) from aging. Perennial plants do not senesce but instead enter dormancy during
winter months.
Hormone
Gibberellins
Auxin
Cytokinins
Ethylene
Abscisic acid
Major plant hormones
Function
Made in embryo, young leaves, apical meristems
Made in embryo, young leaves, apical meristems
Made in roots
Made in ripening fruit, senescing tissue, stem nodes
Made in root cap, older leaves, stem
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Auxin induced growth: “acid-growth hypothesis”
Auxin transport across two cells deposts proton
ions in the cell wall. The cell wall acidifies (drops
pH) which weakens the cellulose cross-links.
The wall is weaker so that when the cell fills with
water, it elongates.
Auxin and phototropic response: true in monocots
Important: Hormones are produced in very low concentrations. The amplification of
the second messenger is what triggers the significant responses. Hormone effects are
relative to other hormone concentrations and rather than a specific concentration of
that particular hormone.
Ex: Having X amount of auxin will not produce a certain effect, but having X amount of
auxin while there is Y amount of cytokinin present can induce a specific effect.
Plant responses to environmental cues:
1. Phototropism: light
2. Gravitropism: gravity (may not be statolith starch granule settling because they
are NOT in all plants but rather protoplasm pulling on membrane proteins)
3. Thigmotropism: touch
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