2. contents
➢ The third unit of lectures in pharmacognosy will be based on the
following:
➢ Plants in General Aspects
◼ Plant Features
◼ Plant Life Cycles
◼ Plant Evolution
◼ Plant Overview
o Non-vascular plants
o Vascular plants
◼ Coal Forests
o Seedless Vascular Plants
o Seed Vascular Plants
◼ Plant Reproduction
3. PLANT FEATURES
◼ Multicellular
◼ eukaryotic
◼ photoautotrophs
◼ Cellulose-containing cell walls
◼ Store surplus carbohydrates as starch
◼ Some algae also fit the above description
◼ Multicellular eukaryotic photoautotrophs
◼ Chloroplasts contain chlorophylls a & b
◼ All photosynthetic eukaryotes possess chlorophyll a
◼ Green algae also possess chlorophyll b
◼ Generic Plants & Multicellular Green Algae
4. PLANT FEATURES
◼ Plants are mainly terrestrial organisms
◼ Some have returned to the water
◼ Required resources are found in different places
◼ Light and O2 are found in the air
◼ Water and mineral nutrients are found in the soil
◼ Plants display structural specialization
◼ Subterranean organs (e.g., roots)
◼ Aerial organs (e.g., leaf-bearing shoots)
◼ Gas exchange typically regulated by stomata
◼ Water loss typically reduced by cuticle
5. PLANT FEATURES
◼ Life cycles of all plants feature an alternation of
generations
◼ This feature is not unique to plants
◼ Some algae also display an alternation of generations
◼ After fertilization of a female gamete, the zygote
develops into an embryo which is retained and
nourished by the parent
◼ This feature is lacking in algae
◼ Plants are termed embryophytes
6. PLANT LIFE CYCLES
◼ All plant life cycles feature an alternation of
generations
◼ Sporophyte
◼ Multicellular diploid
individual
◼ Produces haploid spores
◼ Gametophyte
◼ Multicellular haploid
individual
◼ Produces haploid gametes
7. MAJOR PLANT GROUPS
◼ Four major periods of plant evolution
◼ New structures evolved, adaptive radiations followed
◼ Origin of plants from
aquatic ancestors
◼ Diversification of
vascular plants
◼ Origin of seeds
◼ Emergence of
flowering plants
8.
9. PLANT EVOLUTION
◼ Plant ancestry can be viewed in terms of a nested
set of monophyletic groups
green
algae
zygophytes,
related
groups
charophytes bryophytes lycophytes horsetails cycads conifers
flowering
plants
seed plants
euphyllophytes
vascular plants
embryophytes (land plants)
(closely related groups)
ferns ginkgos gnetophytes
13. BRYOPHYTES
◼ Nonvascular plants
◼ <19,000 species
◼ Previously grouped together in a single division
◼ Bryophyta
◼ Now separated into three divisions
◼ Bryophyta (mosses)
◼ Hepatophyta (liverworts)
◼ Anthocerophyta (hornworts)
◼ Still, the term “bryophyte” encompasses all three
of these divisions of nonvascular plants
14.
15. BRYOPHYTES
◼ Possess the embryophyte condition
◼ Gametes develop within gametangia
◼ Antheridium (male) and archegonium (female)
◼ Egg is fertilized within the archegonium
◼ Flagellated sperm must swim through film of dew or rainwater from
antheridium to archegonium
◼ Zygote develops into an embryo within this structure
16. BRYOPHYTES
◼ Most bryophytes have no vascular tissue
◼ Water on surface of plant must be imbibed like a
sponge
◼ Distribution through plant is through diffusion,
capillary action, and cytoplasmic streaming
◼ Slow processes
◼ Damp shady places are most common habitats for
bryophytes
◼ Bryophytes lack lignin-fortified support tissues
◼ Low profile, sprawl horizontally
17. BRYOPHYTES
◼ The gametophyte is the dominant generation in
the life cycles of bryophytes
SPOROPHYTE
(2n)
GAMETOPHYTE
(n)
GR ALGA
BRYOPHYTE
FERN GYMNOSPERM ANGIOSPERM
BRYOPHYTE
21. MOSSES
◼ Division Bryophyta
◼ Many plants growing tightly together form a mat
◼ Help to hold one another up
◼ Spongy quality helps to retain water
◼ Substrate gripped with rhizoids
◼ “Root-like” elongated cells or filaments
◼ Analogous to roots of vascular plants
◼ Most photosynthesis occurs in upper part
◼ Stem-like and leaf-like appendages
◼ Analogous to these structures in vascular plants
22. MOSSES
◼ Peat mosses (Sphagnum) cover >3% or Earth’s
terrestrial surface
◼ Probably the most abundant plants on Earth
◼ Greater density in northern
latitudes
◼ Accumulated “peat” (living
and dead) is major reservoir of
organic carbon
◼ Resistant to microbial degradation
◼ Stabilizes atmospheric [CO2]
26. LIVERWORTS
◼ Less conspicuous than mosses
◼ Divided into lobes
◼ Resembles lobed animal liver
◼ Life cycle similar to that of moss
◼ Some sporangia contain coiled cells
◼ Spring out of opened capsule
◼ Aid in dispersal of spores
◼ Also reproduce asexually from small bundles
of cells called gemmae
◼ Dispersed by raindrops
28. HORNWORTS
◼ Resemble liverworts
◼ Sporophytes are elongated capsules resembling
horns
◼ Hornworts are the bryophytes most closely
related to vascular plants
29. ADAPTATIONS
Bryophyte adaptations
◼ Gametangia
◼ Gametangia Embryos
◼ Sporopollenin-walled spores
◼ Stomata
◼ Present in some
◼ Cuticles
◼ Present in some
◼ May or may not be homologous to cuticles in higher
plants
32. SEEDLESS VASCULAR PLANTS
◼ Key changes in early vascular plants
◼ Sporophyte generation is dominant
◼ Sporophyte is branched
◼ More sporangia → more spores
◼ Raw material for evolution of more complex body
parts
◼ e.g., Branches + webs → leaves
33. SEEDLESS VASCULAR PLANTS
◼ Dominated forest landscapes of
Carboniferous period
◼ 360 - 290 million years ago
◼ Three living divisions
◼ Lycophytes
◼ Horsetails
◼ Ferns
35. LYCOPHYTES
◼ Division Lycophata
◼ Evolved in Devonian period
◼ Prevalent in Carboniferous period
◼ Woody tree lineage
◼ Became extinct near end of Carboniferous period
◼ Herbaceous lineage
◼ Represented today by ~1,000 species
◼ e.g., Club mosses & ground pines
◼ (Which, incidentally, are neither mosses nor pines)
◼ Many species are epiphytes
◼ Use another species as substrate (not a parasite)
◼ Many species grow on temperate forest floors
37. LYCOPHYTES
◼ Dominant sporophyte generation
◼ True of all vascular plants
◼ Sporangia borne on sporophylls
◼ Specialized leaves
◼ Discharged spores develop into
inconspicuous gametophytes
◼ Nonphotosynthetic, nurtured by
symbiotic fungi
◼ May live underground for ten years
or more
38. LYCOPHYTES
◼ Some species are homosporous
◼ Single type of spore
◼ Gametophyte with archegonia and antheridia
◼ Gametophyte produces both sperm and eggs
◼ Some species are heterosporous
◼ Megaspore → female gametophyte → eggs
◼ Microspore → male gametophyte → sperm
39. HORSETAILS
◼ Division Sphenophyta
◼ Sometimes considered part of
Division Pterophyta
◼ Ancient lineage of seedless
vascular plants
◼ Dates back to Devonian period
◼ Prevalent during Carboniferous
◼ Modern survivors include ~15
species in the genus Equisetum
◼ Most common in Northern
hemisphere
◼ Generally found in damp
locations, streambanks
40. HORSETAILS
◼ Dominant sporophyte generation
◼ True of all vascular plants
◼ Homosporous
◼ Sporangia within cone-like
structures
◼ Discharged spores develop into
inconspicuous gametophytes
◼ Only a few millimeters long
◼ Photosynthetic, free-living
◼ Outer cell layer silica-embedded
◼ Abrasive, used before scouring pads
41. WHISK FERNS
◼ Division Pterophyta
◼ Formerly Division Psilophyta
◼ Molecular analysis has indicated
its close relatedness with ferns
◼ Simple body structure evolved
secondarily
◼ Ancestors were more complex
◼ Lacks roots present in ancestor
◼ Possess subterranean rhizomes
◼ Small outgrowths of stems are
likely reduced leaves
42. FERNS
◼ Division Pterophyta
◼ Ancient ancestry
◼ Origins in Devonian period
◼ Prevalent in Carboniferous period
◼ Currently most prevalent seedless vascular
plant
◼ >12,000 species exist today
◼ Most diverse in tropics
43. FERNS
◼ Leaves generally larger than those of
lycophytes
◼ Evolved differently
◼ Multiple (not single) strands of vascular tissue
44. FERNS
◼ Leaves (called fronds) are compound
◼ Divided into multiple leaflets
◼ Frond grows as tip (“fiddlehead”) unfurls
◼ Some leaves are specialized sporophylls
◼ Sporangia on underside
◼ Sometimes arranged in clusters termed “sori”
◼ Spring-like devices launch spores several meters
◼ Wind can disseminate widely
49. COAL FORESTS
◼ Seedless vascular plants were widespread
during the Carboniferous period
◼ 360 – 290 million years ago
◼ Formed the fossil fuel coal
◼ Less extensive coal beds were also formed during
other geological periods
◼ Most continents were flooded by shallow swamps
◼ Dead plants did not completely decay
◼ “Peat” formed
◼ Heat and pressure converted peat to coal
50. SEED PLANTS
◼ Swamps began to dry up at the end of the
Carboniferous period
◼ 290 million years ago
◼ Pangea supercontinent formation → hotter and
dryer continental interiors
◼ Flora and fauna changed dramatically
◼ “Punctuated equilibrium”
◼ Seed plants had already existed, but rose to
prominence after this environmental change
◼ Ditto for reptiles, etc.
51. SEED PLANTS
Key adaptations of seed plants
◼ Reduction of the gametophyte
◼ Minute gametophytes retained within and protected
by the sporophyte
◼ Advent of the seed
◼ Seeds replaced spores as a means of dispersing
offspring
◼ Evolution of pollen
◼ Eliminated the liquid H2O fertilization requirement
53. SEED PLANTS
Reduction of the gametophyte
◼ Gametophyte generation becomes even more
reduced in seed plants
◼ Gametophytes of bryophytes are dominant
◼ Gametophytes of seedless vascular plants develop as
an independent generation
◼ Minute gametophytes of seed plants are retained
within sporophyte tissue
◼ Protected from desiccation
◼ Reversal of the gametophyte-sporophyte relationship
found in bryophytes
54. SEED PLANTS
Reduction of the gametophyte
◼ Shift toward diploidy may be response to
damaging effects of ultraviolet radiation
◼ Mutagenic
◼ Light-filtering properties of water afford some
protection to aquatic organisms
◼ Diploid organisms can tolerate some mutations that
would be lethal to haploid individuals
◼ Sporophyte-dominance is an adaptation to terrestrial
conditions
55. SEED PLANTS
Reduction of the gametophyte
◼ Why is the gametophyte reduced, not removed?
◼ Perhaps this haploid generation provides a means of
screening and eliminating deleterious alleles
◼ Gametophyte tissue remains important in nourishing
the embryonic sporophyte
56. SEED PLANTS
Advent of the Seed
◼ Spores are the resistant stage in the life cycle of
bryophytes and seedless vascular plants
◼ Able to withstand harsh environments
◼ Seeds are also able to resist harsh environments
◼ Spores are the means by which bryophytes and
seedless vascular plants disperse offspring
◼ Able to be dispersed over great distances
◼ Seeds became important in dispersing offspring
57. SEED PLANTS
Advent of the Seed
◼ A seed consists of a protective coat housing an
embryonic sporophyte and its food supply
◼ The reduced gametophytes of seed plants
develop within tissues of the parental
sporophyte
58. SEED PLANTS
Advent of the Seed
◼ All seed plants are heterosporous
◼ Megasporangia → megaspores → female
gametophytes → eggs
◼ Microsporangia → Microspores → male
gametophytes → sperm
59. SEED PLANTS
Advent of the Seed
◼ Megasporangium is not simply a chamber
◼ Solid, fleshy structure
◼ “Nucellus”
◼ Additional layers of
sporophyte tissue envelop
the megasporangium
◼ “Integuments”
◼ Provides protection to the megaspore
◼ Integuments + nucellus + megaspore = ovule
60. SEED PLANTS
Advent of the Seed
◼ Female gametophyte contains an egg cell
◼ Egg + sperm → zygote → sporophyte embryo
◼ Entire ovule develops into a seed
◼ Resistant, dispersible, can remain dormant for years
◼ Can germinate under favorable conditions
61. SEED PLANTS
Evolution of Pollen
◼ Microspores develop into pollen grains
◼ Mature to form male gametophytes
◼ Protected by tough sporopollenin-containing
coats
◼ Released from microsporangium
◼ Dispersed by wind or animals
◼ Some pollen grains lands near an ovule
◼ Pollen tube is produced
◼ Sperm discharged into female gametophyte
◼ Sperm lack flagella in conifers, angiosperms, etc.
62. SEED PLANT CLADES
◼ Gymnosperms
◼ Monophyletic group of flower-less seed plants
◼ Angiosperms
◼ Monophyletic group of flowering seed plants
◼ Gymnosperms and angiosperms appear to have
evolved from separate ancestors in the extinct
progymnosperm group
63. GYMNOSPERMS
◼ Probably descended from progymnosperms
◼ Seeds had evolved by end
of Devonian period
◼ Adaptive radiation in
Carboniferous and early
Permian produced the
gymnosperm divisions
◼ Largely replaced seedless
vascular plants
◼ Better adapted to drier
(Pangean) climate
64. AGE OF DINOSAURS
◼ Gymnosperms dominated the Mesozoic era
◼ Terrestrial were supported by gymnosperms
◼ Mainly conifers and great palm-like cycads
◼ The Mesozoic era ends and the Cenozoic era
begins 65 million years ago
◼ Powerful meteorite impact
◼ Climate cooled, mass extinctions ensued
◼ Extinctions of many gymnosperms, some remained
◼ Extinctions of many animal species
◼ Most dinosaurs became extinct
◼ Which ones survived?
65. GYMNOSPERMS
◼ Four divisions currently exist
◼ Ginkgophyta (ginkgo)
◼ Cycadophyta (cycads)
◼ Gnetophyta (gnetophytes)
◼ Coniferophyta (conifers)
67. DIVISION GINKGOPHYTA
◼ Ability to tolerate pollution makes the ginkgo
a popular ornamental tree in cities
◼ Female trees produce fleshy seeds
◼ Seed coat emits repulsive odor
◼ Generally only male trees are planted
69. DIVISION CYCADOPHYTA
◼ Superficially resemble palms
◼ True palms are angiosperms
◼ Seeds develop on the surface of sporophylls
◼ Specialized reproductive leaves
◼ Packed together to form cones
70. DIVISION GNETOPHYTA
◼ Consists of three genera very different in
appearance
◼ Welwitschia
◼ Giant strap-like leaves
◼ Gnetum
◼ Grow in tropics as trees or vines
◼ Ephedra
◼ “Mormon tea”
◼ Shrub of American deserts
71. DIVISION GNETOPHYTA
◼ Consists of three genera very different in
appearance
◼ Welwitschia
◼ Giant strap-like leaves
◼ Gnetum
◼ Grow in tropics as trees or vines
◼ Ephedra
◼ “Mormon tea”
◼ Shrub of American deserts
72. DIVISION GNETOPHYTA
◼ Consists of three genera very different in
appearance
◼ Welwitschia
◼ Giant strap-like leaves
◼ Gnetum
◼ Grow in tropics as trees or vines
◼ Ephedra
◼ “Mormon tea”
◼ Shrub of American deserts
73. DIVISION CONIFEROPHYTA
◼ “Conifers”
◼ Largest of the four gymnosperm genera
◼ ~550 species
◼ e.g., Pines, firs, spruces, larches, yews, junipers,
cedars, cypresses, redwoods, etc.
◼ A few of these species dominate vast forested
regions of the Northern Hemisphere
◼ Reproductive structures are cones
◼ Cluster of scale-like sporophylls
75. DIVISION CONIFEROPHYTA
◼ Most conifers are evergreens
◼ Retain leaves throughout the year
◼ Some conifers have deciduous leaves
◼ Shed in autumn
◼ e.g., Dawn redwood, tamarack
82. WATER TRANSPORT
◼ Tracheids conduct water in
conifers
◼ Elongated, tapered cell
◼ Functions in support and water
movement
◼ Relatively early type of xylem cell
◼ Angiosperms possess more
specialized xylem elements
83. ANGIOSPERMS
◼ Flowering plants
◼ Most diverse and widespread plants
◼ ~300,000 known species of plants currently exist
◼ ~250,000 are angiosperms
◼ All belong to Division Anthophyta
84. ANGIOSPERMS
◼ Division Anthophyta
◼ Contains five major
monophyletic
lineages
◼ Amborella
◼ Water lilies
◼ Other early lineages
◼ Monocots
◼ Eudicots
85. Amborella
◼ Oldest angiosperm lineage
◼ Represented by a single species
◼ Amborella trichopoda
◼ Possesses xylem similar to that of
gymnosperms
◼ Tracheids
◼ Lacks the vessel elements of other angiosperms
86. WATER TRANSPORT
◼ Vessel elements conduct water in angiosperms
◼ Shorter, wider cells
Evolved from tracheids
◼ Arranged end-to-end to form continuous tubes
◼ More specialized for transporting water
◼ Less specialized for support
◼ Xylem reinforced by xylem fibers
◼ Also present in conifers
◼ Evolved from tracheids
◼ Thick, lignified cell walls
◼ Specialized for support
87. WATER LILIES
◼ e.g., Nymphaea carulea
◼ Evolved on land
◼ Secondarily returned to the water
91. FLOWERS
◼ Defining reproductive adaptation of angiosperms
◼ Most produce both male and female
gametophytes
◼ “Perfect flowers”
◼ Pollen is transferred from one flower to the
female sex organs of the same or another flower
◼ Wind may facilitate this transfer
◼ Insects and other animals often facilitate the transfer
◼ Is this always sexual reproduction?
◼ Why might cross-pollination be beneficial?
93. FLOWER STRUCTURE
Sterile Floral Parts
◼ Sepals
◼ Generally green
◼ Enclose flower before it
opens
◼ Petals
◼ Generally brightly colored
◼ Aid in attracting insects and
other pollinators
◼ (Petals of wind-pollinated
flowers are typically drab)
95. FLOWER STRUCTURE
Reproductive Organs: Stamens
◼ “Male” flower parts
◼ Pollen is produced
within anthers,
terminal sacs attached
to stalk-like filaments
96. FLOWER STRUCTURE
Reproductive Organs: Carpels
◼ a.k.a., “Pistil”
◼ “Female” flower parts
◼ One or many per flower
◼ Sticky stigma receives
pollen
◼ Style leads to ovary,
which houses ovules
97. FLOWER ORIGINS
◼ Carpels likely resulted from the rolling of
sporophylls
◼ Megasporangia-containing reproductive leaves
98. FRUITS
◼ Aid in the protection and dispersal of
angiosperm seeds
◼ Mature ovary
◼ Ovary wall thickens to form pericarp
◼ Thickened wall of fruit
◼ Growth triggered by pollination
◼ Fruit surrounds seed(s)
99. FRUITS
◼ Various modifications in fruit assist in seed
dispersal
◼ Some fruits function as kites or propellers,
and are dispersed by the wind
◼ e.g., maple, dandelion
◼ Many fruits promote dispersal by animals
◼ e.g., cockleburs
◼ e.g., edible fruits
100. TYPES OF FRUITS
◼ Simple fruit
◼ Derived from a single ovary
◼ Aggregate fruit
◼ Results from a single flower
with multiple carpels
◼ Multiple ovaries fuse
◼ Multiple fruit
◼ Develops from an
inflorescence, a tightly
packed group of flowers
◼ Multiple ovaries fuse
101. ANGIOSPERM LIFE CYCLE
◼ Heterosporous
◼ Microspores → male gametophyte
◼ Megaspores → female gametophyte
◼ Immature male gametophytes are contained
within pollen grains
◼ Develop within anthers of a stamen
◼ Each pollen grain has two haploid cells
◼ Ovules contain female gametophyte
◼ “Embryo sac”
◼ Consists of a few cells, including one egg
102. POLLINATION
◼ Pollen is released from the anther
◼ Carried to the stigma at tip of carpel
◼ Self-pollination may occur
◼ Many plants have mechanisms making cross-
pollination more likely
◼ e.g., Male and female parts mature at different times
◼ e.g., Male and female parts physically distant
◼ e.g., Self-incompatibility
◼ What is the benefit of cross-pollination?
103. POLLINATION
◼ Pollen grain germinates
◼ Occurs after adhering to the carpel
◼ (Now contains mature gametophyte)
◼ Pollen tube extended down style to ovary
◼ Pollen tube penetrates ovule
◼ Two sperm discharged
◼ “Double fertilization”
104. FERTILIZATION
◼ “Double fertilization”
◼ Sperm + egg → diploid zygote
◼ Mitotic division produces embryo
◼ Rudimentary root
◼ One (monocots) or two (dicots) seed leaves
◼ Sperm + 2 nuclei → 3n nucleus
◼ Mitotic division produces energy-rich endosperm
◼ Ovule matures into a seed
105. FERTILIZATION
◼ Why double fertilization?
◼ Synchronizes development of food storage with seed
development
◼ Without fertilization,
neither will occur
◼ Resources are not wasted
on infertile ovules
106. SEED
◼ Consists of
◼ Embryo
◼ Endosperm
◼ Sporangium
◼ Seed coat
◼ Surrounded by fruit
◼ Developed from ovary
109. ANGIOSPERM RADIATION
◼ Radiation of angiosperms marks the transition
from the Mesozoic era to the Cenozoic era
◼ Earliest angiosperms found are 130 million years old
◼ Adaptive radiation made angiosperms the
dominant plants on Earth by the end of the
Cretaceous 65 million years ago
◼ Adaptive radiation followed a period of
environmental disturbance
110. COEVOLUTION
◼ Plants have influenced the
evolution of animals
◼ Animals have influenced
the evolution of plants
◼ e.g., Plant-herbivore
coevolution
◼ e.g., Plant-pollinator
coevolution
111. COEVOLUTION
◼ Plant-pollinator coevolution is responsible for
the diversity of flowers
◼ What does the pollinator gain?
◼ Nectar, pollen, etc.
◼ What does the plant gain?
◼ Cross-pollination
115. TYPES OF FLOWERS
◼ Many flowers possess all four basic floral
organs
◼ “Complete flowers”
◼ In some flowers, one or more of these basic
organs are absent
◼ “Incomplete flowers”
◼ e.g., Grasses possess flowers lacking petals
116. TYPES OF FLOWERS
◼ Many flowers possess both stamen and
carpels
◼ “Perfect flowers”
◼ “Bisexual flowers”
◼ Some flowers lack either pistils or stamen
◼ “Imperfect flowers”
◼ “Unisexual flowers”
◼ “Staminate” of “carpellate”
117. TYPES OF FLOWERS
◼ Some species possess both staminate and
carpellate flowers on the same plant
◼ “Monoecious”
◼ e.g., Maize
◼ Some species possess staminate and carpellate
flowers on different plants
◼ “Dioecious”
◼ e.g., Sagittaria
118. TYPES OF FLOWERS
◼ Some species possess both staminate and
carpellate flowers on the same plant
◼ “Monoecious”
◼ e.g., Maize
◼ Some species possess staminate and carpellate
flowers on different plants
◼ “Dioecious”
◼ e.g., Sagittaria, date palms, etc.
119. POLLEN GRAIN
◼ Numerous microsporocytes exist within the
sporangia of anthers
◼ Microsporocytes undergo meiosis
◼ Produce four microspores
◼ Each microspore divides once by mitosis
◼ Produce generative cell and tube cell
◼ These cells are encased in a cell wall
◼ Thick, resistant
◼ Sculpted into an elaborate pattern
◼ Unique to each plant species
120. POLLEN GRAIN
◼ Generative cell
◼ Eventually produces sperm
◼ Tube cell
◼ Encloses the generative cell
◼ Will ultimately produce the pollen tube
◼ Pollen grain
◼ Cell wall + tube cell + generative cell
◼ Immature male gametophyte
◼ Becomes a mature male gametophyte when the
generative cell divides to form sperm
121. POLLINATION
◼ The transmission of pollen from an anther to the
stigma of a carpel
◼ This transmission may be mediated by wind or by
animal pollinators
◼ This transmission may occur within a single flower
or between flowers
122. FERTILIZATION
◼ Some flowers normally self-fertilize
◼ “Selfing”
◼ e.g., Mendel’s peas
◼ Self-fertilization does not generate as much
genetic diversity as cross-fertilization
123. FERTILIZATION
◼ The majority of angiosperms possess
mechanisms reducing the likelihood of self-
fertilization
◼ Stamens and carpels of
some bisexual flowers
mature at different times
◼ Physical arrangement of
carpels and stamens may
reduce likelihood of
transmission within a flower
◼ Self-incompatibility
124. SELF-INCOMPATIBILITY
◼ The ability of a plant to reject its own pollen and
that of closely related individuals
◼ Biochemical block prevents pollen from completing
its development
◼ e.g., Suppresses pollen tube formation
◼ Analogous to animal immune systems
◼ Discriminates between self and non-self
125. MAIZE
◼ Most current crop plants were domesticated
approximately 10,000 years ago
◼ Artificial selection gave rise to rapid changes
◼ e.g., Teosinte → maize
126. BIOTECHNOLOGY
◼ Biotechnology is rapidly transforming
agriculture (Details are Yet To be given Later)
◼ Genetic modification of food plants to incorporate
desirable phenotypes
◼ e.g., Insect- or virus-resistant plants
◼ e.g., Increased nutritional value
131. Study Questions
◼ Respond to the following questions:
➢ Give a descriptive account of the plant features with
examples
➢ Illustrate what is involved in what is referred to as plant life
cycle?
➢ Describe in details with examples the group category of
plants that is referred to as vascular plants
➢ Describe in details with examples the group category of
plants that is referred to as nonvascular plants
➢ Explain the differentiating characters of seedless and seed
vascular plants
➢ Give descriptive account of stages involved in pine life cycle
➢ Describe with examples the three major categories of plant
fruits
➢ What are the major factors involved in the plant
reproduction process.
132. Study Questions
◼ Group work discussional questions:
➢ Give a descriptive account of the plant features with
examples
➢ Illustrate what is involved in what is referred to as plant life
cycle?
➢ Describe in details with examples the group category of
plants that is referred to as vascular plants
➢ Describe in details with examples the group category of
plants that is referred to as nonvascular plants
➢ Explain the differentiating characters of seedless and seed
vascular plants
➢ Give descriptive account of stages involved in pine life cycle
➢ Describe with examples the three major categories of plant
fruits
➢ What are the major factors involved in the plant
reproduction process.
