+Chapter 38:
Angiosperm
Reproduction
and
Biotechnology
Mrs. Valdes
AP Biology
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+ Overview: Flowers of Deceit
Angiosperm flowers attract pollinators using
visual cues and volatile chemicals
Many angiosperms reproduce sexually and
asexually
Symbiotic relationships common between
plants and other species
Plant breeders have
genetically
manipulated traits of
wild angiosperm
species by artificial
selection
Concept
38.1:
Flowers,
double
fertilization,
&
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fruits unique features of angiosperm life cycle
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Gametophytes: produce haploid (n) gametes by mitosis;
fertilization of gametes produces sporophyte
Diploid (2n) sporophytes: produce spores by meiosis; grow into
haploid (n) gametophytes
In angiosperms sporophyte is dominant generation AKA large
plant
Gametophytes reduced in size and depend on sporophyte for
nutrients
Angiosperm
life cycle
characterized
by “three Fs”:
• flowers,
• double
fertilization
• fruits
Flower Structure and Function
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• Flowers: reproductive shoots of
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angiosperm sporophyte
• attach to part of stem called the
receptacle
• consist of four floral organs:
sepals, petals, stamens, and
carpels
• Stamen: consists of filament
topped by anther with pollen
sacs that produce pollen
• Carpel: long style with stigma
on which pollen may land
• At base of style is ovary
containing one or more ovules
• Pistil: single carpel or group of
fused carpels
Complete flowers: contain all four
floral organs
Incomplete flowers: lack one or
more floral organs,
Inflorescences: Clusters of
flowers
Development
of
Male
Gametophytes
in
Pollen
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Grains
•
Pollen develops from
microspores within
the microsporangia, or
pollen sacs, of anthers
•
If pollination
succeeds pollen
grain produces pollen
tube that grows down
into ovary and
discharges sperm near
embryo sac
•
Pollen grain: consists
of two-celled male
gametophyte and
spore wall
Development
of
Female
Gametophytes
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(Embryo Sacs)
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Within ovule,
megaspores
produced by
meiosis and
develop into
embryo sacs,
AKA female
gametophytes
Fig. 38-3
Microsporangium
(pollen sac)
Megasporangium (2n)
Microsporocyte (2n)
Ovule
MEIOSIS
Megasporocyte (2n)
Integuments (2n)
Micropyle
4 microspores (n)
Surviving
megaspore (n)
Generative cell (n)
MITOSIS
Male
gametophyte
Ovule
3 antipodal cells (n)
2 polar nuclei (n)
Nucleus of Integuments (2n)
tube cell (n)
1 egg (n)
2 synergids (n)
20 µm
75 µm
Ragweed
pollen
grain
Embryo
sac
Female gametophyte
(embryo sac)
Each of 4
microspores (n)
100 µm
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(b) Development of a female
gametophyte (embryo sac)
(a) Development of a male
gametophyte (in pollen grain)
+ Pollination
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Pollination: transfer of pollen from anther to
stigma
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can be by wind, water, bee, moth and butterfly,
fly, bird, bat, or water
Fig. 38-4a
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Abiotic Pollination by Wind
Hazel staminate flowers
(stamens only)
Hazel carpellate flower
(carpels only)
Fig. 38-4b
+Pollination by Bees
Common dandelion under
normal light
Common dandelion under
ultraviolet light
Fig. 38-4c
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Pollination by Moths and Butterflies
Anther
Stigma
Moth on yucca flower
Fig. 38-4d
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Pollination by Flies
Fly egg
Blowfly on carrion flower
Fig. 38-4e
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Pollination by Birds
Hummingbird drinking nectar of poro flower
Fig. 38-4f
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Pollination by Bats
Long-nosed bat feeding on cactus flower at night
+ Double Fertilization
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After landing on receptive
stigma, pollen grain
produces pollen tube that
extends between cells of
style toward ovary
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Double fertilization:
results from discharge of
two sperm from pollen
tube into embryo sac
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One sperm fertilizes egg,
other combines with polar
nuclei triploid (3n) foodstoring endosperm
Fig. 38-5a
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Stigma
Pollen grain
Pollen tube
2 sperm
Style
Ovary
Ovule
Polar nuclei
Micropyle
Egg
Fig. 38-5b
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Ovule
Polar nuclei
Egg
Synergid
2 sperm
Fig. 38-5c
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Endosperm
nucleus (3n)
(2 polar nuclei
plus sperm)
Zygote (2n)
(egg plus sperm)
Seed
Development,
Form,
and
Function
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After double fertilization,
each ovule develops into
seed
Ovary develops into fruit
enclosing seed(s)
Endosperm development:
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usually precedes embryo
development
endosperm stores nutrients
used by the seedling
OR food reserves of the
endosperm are exported to
the cotyledons
Embryo Development:
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first mitotic division of the
zygote is transverse, splitting
the fertilized egg into a basal
cell and a terminal cell
Structure of the Mature Seed
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• Embryo and food supply are
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enclosed by hard, protective seed
coat
Seed enters a state of dormancy
Embryo consists of embryonic axis
attached to two thick cotyledons
(seed leaves)
Below cotyledons embryonic axis
is called hypocotyl and terminates
in radicle (embryonic root); above
cotyledons called epicotyl
Seeds of some eudicots have thin
cotyledons
Monocot embryo: one cotyledon
Grasses have special cotyledon
called a scutellum
Two sheathes enclose embryo of
grass seed: coleoptile covering
young shoot and coleorhiza
covering young root
Seed
Dormancy:
An
Adaptation
for
Tough
Times
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Seed dormancy increases
chances that germination will
occur at time and place most
advantageous to seedling
• Breaking of seed dormancy often
requires environmental cues, like
temperature or lighting changes
• Germination depends on
imbibition
• uptake of water due to low water
potential of dry seed
1- Radicle (embryonic root)
emerges first
2- Shoot tip breaks through soil
surface
3- Hook forms in hypocotyl, and
growth pushes hook above ground
4- Hook straightens and pulls
cotyledons and shoot tip up
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Fig. 38-9a
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Foliage leaves
Cotyledon
Epicotyl
Hypocotyl
Cotyledon
Cotyledon
Hypocotyl
Hypocotyl
Radicle
Seed coat
(a) Common garden bean
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In maize and other grasses, AKA monocots,
+coleoptile pushes up through soil
Foliage leaves
Coleoptile
Coleoptile
Radicle
(b) Maize
+ Fruit Form and Function
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Fruit: develops from ovary
• Protects enclosed seeds and
aids in seed dispersal by
wind or animals
• may be classified as:
• dry, if ovary dries out at maturity,
• fleshy, if ovary becomes thick, soft, and sweet at maturity
Fruits are also classified by their development:
 Simple: single or several fused carpels
 Aggregate: single flower with multiple separate carpels
 Multiple: group of flowers called an inflorescence
 Accessory fruit: contains other floral parts in addition to
ovaries
Fruit dispersal mechanisms include:
 Water, Wind, Animals
Fig. 38-10
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Carpels
Stamen
Flower
Petal
Stigma
Style
Ovary
Stamen
Stamen
Sepal
Stigma
Pea flower
Ovule
Ovary
(in receptacle)
Ovule
Raspberry flower
Carpel
(fruitlet)
Seed
Stigma
Ovary
Pineapple inflorescence
Each segment
develops
from the
carpel
of one
flower
Apple flower
Remains of
stamens and styles
Sepals
Stamen
Seed
Receptacle
Pea fruit
(a) Simple fruit
Raspberry fruit
(b) Aggregate fruit
Pineapple fruit
(c) Multiple fruit
Apple fruit
(d) Accessory fruit
Fig. 38-11a
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Dispersal by Water
Coconut
Fig. 38-11b
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Dispersal by Wind
Winged seed
of Asian
climbing gourd
Dandelion “parachute”
Winged fruit of maple
Tumbleweed
Fig. 38-11c
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Dispersal by Animals
Barbed fruit
Seeds carried to
ant nest
Seeds in feces
Seeds buried in caches
Concept
38.2:
Plants
reproduce
sexually,
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asexually, or both
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Sexual reproduction results in
offspring genetically different from
parents
Asexual reproduction: results in
clone of genetically identical
organisms
Fragmentation: separation of
parent plant into parts that develop
into whole plants
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very common type of asexual
reproduction
In some species, parent plant’s root
system gives rise to adventitious
shoots that become separate shoot
systems
Apomixis: asexual production of
seeds from diploid cell
Advantages
and
Disadvantages
of
Asexual
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Versus Sexual Reproduction
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Vegetative reproduction:
Asexual reproductio
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beneficial if in stable
environment
clone of plants vulnerable
to local extinction if
environment changes
Sexual reproduction:
generates genetic
variation that makes
evolutionary adaptation
possible
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Only fraction of seedlings
survive
Mechanisms
That
Prevent
Self-Fertilization
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1- Dioecious: species with
staminate and carpellate
flowers on separate plants
2- stamens and carpels mature
at different times OR are
arranged to prevent selfing
3- Self-incompatibility:
MOST COMMON; plant’s
ability to reject own pollen
• Researchers examine
molecular mechanisms
• Some plants reject pollen
that has S-gene matching
allele in stigma cells
• Recognition of self pollen
triggers signal transduction
pathway leading to block in
growth of pollen tube
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+Vegetative Propagation and Agriculture
Clones from cuttings
• Many plants asexually reproduced from plant
fragments called cuttings
• Callus: mass of dividing undifferentiated cells
that forms where stem is cut and produces
adventitious roots
Grafting
• Twig or bud grafted onto plant of closely
related species or variety
• Stock: provides root system
• Scion: grafted onto stock
Test-tube cloning and related techniques
• Plant biologists adopted in vitro methods to
create and clone novel plant varieties
• Transgenic plants: genetically modified (GM)
to express gene from another organism
• Protoplast fusion: used to create hybrid plants
by fusing protoplasts, plant cells with their cell
walls removed
Concept
38.3:
Humans
modify
crops
by
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breeding and genetic engineering
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Humans intervened in reproduction and genetic
makeup of plants for thousands of years
Hybridization: common in nature; used by breeders
to introduce new genes
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Maize, product of artificial selection; staple in many
developing countries
Plant Breeding
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• Mutations arise spontaneously OR can be induced by
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breeders
Plants with beneficial mutations used in breeding
experiments
Desirable traits can be introduced from different species or
genera
Grain triticale derived from successful cross between wheat
and rye
Wheat
Rye
Triticale
Plant
Biotechnology
and
Genetic
Engineering
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• Plant biotechnology
meanings:
General sense: refers to
innovations in use of plants
to make useful products
 Specific sense: refers to use
of GM organisms in
agriculture and industry
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Modern plant
biotechnology NOT
limited to transfer of
genes between
closely related
species or varieties
of same species
Reducing
World
Hunger
and
Malnutrition
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GM plants may increase quality and quantity
of food worldwide
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Transgenic crops have been developed that:
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Produce proteins to defend them against insect pests
Tolerate herbicides
Resist specific diseases
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Nutritional quality of plants being improved
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“Golden Rice”: transgenic variety being
developed to address vitamin A deficiencies
among the world’s poor
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Problem? “Being developed”
Reducing
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Fossil Fuel
Dependency
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Biofuels:
made by
fermentation
and
distillation of
plant
materials like
cellulose
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can be
produced by
rapidly
growing crops
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+ Issues of Human Health
Concerns:
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Genetic engineering may transfer allergens
from gene source to plant used for food
Unforeseen effects on nontarget organisms
Possibility of introduced genes escaping into
related weeds through crop-to-weed
hybridization
• Preventative efforts:
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Male sterility
Apomixis
Transgenes into chloroplast
DNA (not transferred by
pollen)
Strict self-pollination
You
should
now
be
able
to:
+
1.
Describe how the plant life cycle is modified in angiosperms
2.
3.
4.
5.
6.
7.
8.
Identify and describe the function of a sepal, petal, stamen
(filament and anther), carpel (style, ovary, ovule, and stigma),
seed coat, hypocotyl, radicle, epicotyl, endosperm,
cotyledon
Distinguish between complete and incomplete flowers;
bisexual and unisexual flowers; microspores and
megaspores; simple, aggregate, multiple, and accessory fruit
Describe the process of double fertilization
Describe the fate and function of the ovule, ovary, and
endosperm after fertilization
Explain the advantages and disadvantages of reproducing
sexually and asexually
Name and describe several natural and artificial mechanisms
of asexual reproduction
Discuss the risks of transgenic crops and describe four
strategies that may prevent transgene escape