1. © 2017 Pearson Education, Inc.

2. Concept 38.1: Key features of the angiosperm life cycle
The angiosperm life cycle is characterized by “three Fs”: flowers, double fertilization, and fruits
Flowers are the reproductive shoots of angiosperms;
Consist of four floral organs:
Carpels
Stamens
Petals
Sepals
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3. Single carpel Stigma (Simple pistil) Stamen Anther Style Filament
Ovary
Petal
Figure 38.2 The structure of an idealized flower
Sepal
Ovule
Receptacle
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4. Flower Structure and Function
A carpel has a long style with a sticky stigma on top that captures pollen
At the base of the style is an ovary containing one or more ovules
Fertilized ovules produce seeds
A single carpel or group of fused carpels is called a pistil
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5. Flower Structure and Function
A stamen consists of a filament topped by an anther
The anther contains microsporangia (pollen sacs) that produce pollen
Sepals are structures that resemble leaves
They enclose and protect unopened floral buds
Petals are typically brightly colored to attract pollinators
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6. Flower Structure and Function
Complete flowers contain all four floral organs
Incomplete flowers lack one or more floral organs, for example, petals or stamens
Sterile flowers lack both stamens and carpels; unisexual flowers lack one or the other
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7. Methods of Pollination
In angiosperms, pollination is the transfer of pollen from anthers to stigma
Pollination can occur by wind, water, or animals
Wind-pollinated species (e.g., grasses and many trees) release large amounts of pollen
Most angiosperm species depend on animal pollinators to transfer pollen directly between flowers
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8. Pollen Grains
Figure 38.UN03 Test your understanding, question 13 (pollen grains)
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9. Abiotic Pollination by Wind
About 20% of angiosperm species are wind- pollinated
For example, grasses and many trees are wind- pollinated
Wind-pollinated angiosperms tend to produce small, inconspicuous flowers that lack nectar or scent and release large amounts of pollen
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10. Pollination by Bees
About 65% of all angiosperms require insects for pollination; bees are the most important insect pollinators
Bee-pollinated flowers are typically brightly colored and have a sweet fragrance
“Nectar guides” are ultraviolet markings that direct bees and other insects to the nectar-producing glands
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11. Pollination by Moths and Butterflies
Flowers pollinated by moths and butterflies produce sweet fragrances
Butterfly-pollinated flowers are brightly colored; moth-pollinated flowers are usually white or yellow
Pollination by Bats
Bat-pollinated flowers are light-colored and aromatic
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12. Many fly-pollinated flowers look and smell like rotten meat
Pollination by Flies
Many fly-pollinated flowers look and smell like rotten meat
Pollination by Birds
Bird-pollinated flowers are usually large and bright red or yellow, have little odor, and produce large quantities of nectar
The petals of bird-pollinated flowers are often fused into a floral tube
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13. Abiotic pollination by wind Pollination by bees
Common dandelion
under normal light
Common dandelion
under ultraviolet
light
Hazel carpellate
flower (carpels
only)
Figure 38.4a Exploring flower pollination (part 1: wind and bees)
Hazel staminate flowers
(stamens only) releasing
clouds of pollen
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14. Pollination by moths and butterflies Pollination by bats Pollination
by flies
Anther
Moth
Blowfly
Stigma
Moth on yucca flower
Long-nosed bat feeding
on agave flowers at night
Blowfly on carrion
flower
Pollination by birds
Figure 38.4b Exploring flower pollination (part 2: moths, butterflies, bats, flies and birds)
Hummingbird drinking nectar of columbine flower
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15. Coevolution is the joint evolution of interacting species in response to selection imposed by each other
The shapes and sizes of flowers often correspond to the pollen-transporting parts of their animal pollinators
For example, Darwin correctly predicted a moth with a 28-cm-long tongue based on the morphology of a particular flower
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16. Figure 38.5 Coevolution of a flower and an insect pollinator
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17. The Angiosperm Life Cycle: An Overview
The angiosperm life cycle includes
Gametophyte development
Sperm delivery by pollen tubes
Double fertilization
Seed development
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18. Microsporangium (pollen sac)
Carpel
Stamen
Microsporangium (pollen sac)
Mature flower on
sporophyte plant
(2n)
Microsporocytes (2n)
MEIOSIS
Microspore (n)
Generative cell
Tube cell
Male
gametophyte
(in pollen
grain) (n)
Tube nucleus
Germinating
seed
Ovary
Ovule with
megasporangium
(2n)
MEIOSIS
Pollen
grains
Stigma
Megasporangium
(2n)
Pollen tube
Embryo (2n)
Sperm
Endosperm (3n)
Seed
Surviving
megaspore (n)
Tube nucleus
Seed coat (2n)
Integuments
Antipodal cells
Micropyle
Female
gametophyte
(embryo sac)
Polar nuclei
in central cell
Style
Figure 38.6_4 The life cycle of angiosperms (step 4)
Synergids
Egg (n)
Nucleus of
developing
endosperm
(3n)
Zygote (2n)
Egg
nucleus (n)
FERTILIZATION
Haploid (n)
Diploid (2n)
Discharged sperm nuclei (n)
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19. The embryo sac, or female gametophyte, develops within the ovule
One cell undergoes meiosis, producing four megaspores, only one of which survives
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20. Development of Male Gametophytes in Pollen Grains
Pollen develops from microspores within the pollen sacs, of anthers
Each microspore undergoes mitosis to produce two cells: the generative cell and the tube cell
A pollen grain consists of this two-celled male gametophyte and the spore wall
After landing on a receptive stigma, a pollen grain produces a pollen tube that grows down into the ovary and discharges two sperm cells near the embryo sac
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21. Double Fertilization
Fertilization, the fusion of gametes, occurs after the two sperm reach the female gametophyte
One sperm fertilizes the egg, and the other combines with the two polar nuclei, giving rise to the triploid food-storing endosperm (3n)
This double fertilization ensures that endosperm only develops in ovules containing fertilized eggs
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22. Seed Development
After double fertilization, each ovule develops into a seed
The ovary develops into a fruit enclosing the seed
When a seed germinates, the embryo develops into a new sporophyte
A mature seed consists of a dormant embryo surrounded by stored food and protective layers
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23. Endosperm Development
Endosperm development usually precedes embryo development
In most monocots and many eudicots, endosperm stores nutrients that can be used by the seedling
In other eudicots, the food reserves of the endosperm are exported to the cotyledons
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24. Structure of the Mature Seed
The embryo and its food supply are enclosed by a hard, protective seed coat
The seed dehydrates and enters a state of dormancy
A mature seed is only about 5–15% water
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25. Common garden bean, a eudicot with thick cotyledons
Seed coat
Epicotyl
Hypocotyl
Radicle
Cotyledons
Common garden bean, a eudicot with thick cotyledons
Pericarp fused
with seed coat
Scutellum
(cotyledon)
Figure 38.8 Seed structure
Endosperm
Coleoptile
Epicotyl
Hypocotyl
Coleorhiza
Radicle
Maize, a monocot
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26. Seed Dormancy: An Adaptation for Tough Times
Seed dormancy increases the chances that germination will occur at a time and place most advantageous to the seedling
The breaking of seed dormancy often requires a specific environmental cue, such as temperature or lighting changes
Most seeds remain viable after a year or two of dormancy, but some last only days and others can remain viable for centuries
Seed germination is followed by growth of stems, leaves, and roots and eventually by flowering
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27. Seed Germination
Germination depends on imbibition, the uptake of water due to low water potential of the dry seed
The radicle (embryonic root) emerges first; the developing root system anchors the plant and provides water for cell expansion
Next, the shoot tip breaks through the soil surface
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28. Seed Germination
In many eudicots, a hook forms in the hypocotyl, and growth pushes the hook above ground
Light causes the hook to straighten and pull the cotyledons and shoot tip up
In some monocots, the coleoptile pushes up through the soil, creating a tunnel for the shoot tip to grow through
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29. Foliage leaves Cotyledon Hypocotyl Epicotyl Cotyledon Hypocotyl
Radicle
Seed coat
Common garden bean
Foliage leaves
Figure 38.9 Two common types of seed germination
Coleoptile
Coleoptile
Radicle
Maize
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30. Growth and Flowering
The flowers of a given plant species are synchronized to appear at a specific time of the year to promote outbreeding
Flowering is triggered by a combination of environmental cues and internal signals
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31. Fruit Structure and Function
A fruit is the mature ovary of a flower
It protects the enclosed seeds and aids in seed dispersal by wind or animals
In some fruits, such as soybean pods, the ovary wall dries out at maturity, whereas in other fruits, such as grapes, it remains fleshy
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32. Fruits are classified based on their developmental origin
Simple fruits develop from a single or several fused carpels
Aggregate fruits result from a single flower with multiple separate carpels
Multiple fruits develop from a group of flowers called an inflorescence
Accessory fruits contain other floral parts in addition to ovaries
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33. Pineapple inflorescence Apple flower
Stigma
Style
Stigma
Petal
Carpel
Flowers
Style
Carpel
Ovary
Stamen
Stamen
Stigma
Sepal
Ovary (in
receptacle)
Ovary
Ovule
Stamen
Ovule
Pea flower
Raspberry flower
Pineapple inflorescence
Apple flower
Each segment
develops
from the
carpel
of one
flower
Carpel
(fruitlet)
Remains of
stigma and
style
Remains of
stamens and styles
Sepals
Seed
Ovary
Withered
stamen
Figure Developmental origin of different classes of fruits
Seed
Receptacle
Pea fruit
Raspberry fruit
Pineapple fruit
Apple fruit
(a) Simple fruit
(b) Aggregate fruit
(c) Multiple fruit
(d) Accessory fruit
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34. Fruit dispersal by wind, water, or animals ensures that seeds germinate away from the competitive influence of the parent plant
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35. Dispersal by water Dispersal by wind Coconut seed embryo, endosperm,
and endocarp inside
buoyant husk
Dispersal by wind
Giant seed of
the tropical Asian
climbing gourd
Alsomitra macrocarpa
Dandelion fruit
Figure 38.12a Exploring fruit and seed dispersal (part 1: water and wind)
Dandelion ‘‘seeds’’ (actually one-seeded fruits)
Winged fruit of a maple
Tumbleweed
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36. Dispersal by animals Fruit of the puncture vine (Tribulus terrestris)
Squirrel hoarding seeds or fruits
underground
Figure 38.12b Exploring fruit and seed dispersal (part 2: animals)
Ant carrying seed with
attached ‘‘food body’’
Seeds dispersed in black bear feces
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37. Concept 38.2: Flowering plants reproduce sexually, asexually, or both
Asexual reproduction produces offspring without the fusion of egg and sperm
The offspring is a clone, genetically identical to the parent
Asexual reproduction is common in angiosperms and other plants
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38. Advantages and Disadvantages of Asexual and Sexual Reproduction
Asexually reproducing plants do not require pollinators or nearby individuals of the same species to produce offspring
All progeny are genetically identical
This can be beneficial to a successful plant in a stable environment
Asexual reproduction is also called vegetative reproduction because progeny arise from mature vegetative fragments
These progeny are more resilient than the seedlings produced by sexual reproduction
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39. The lack of genetic variation among asexually producing plants makes them vulnerable to local extinction if there is an environmental change
Sexual reproduction generates genetic variation that makes evolutionary adaptation possible
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40. However, “selfing” reduces genetic diversity among offspring
Some flowers can self-fertilize to ensure that every ovule will develop into a seed
However, “selfing” reduces genetic diversity among offspring
Many species have evolved mechanisms to prevent selfing
Asexual reproduction is also called vegetative reproduction because progeny arise from mature vegetative fragments
These progeny are more resilient than the seedlings produced by sexual reproduction
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41. Mechanisms That Prevent Self-Fertilization
Many angiosperms have mechanisms that make it difficult or impossible for a flower to self-fertilize
Dioecious species have staminate flowers (lacking carpels) and carpellate flowers (lacking stamens) on separate plants
Other species have stamens and carpels that mature at different times or are spatially arranged to prevent selfing
The most common mechanism is self- incompatibility, a plant’s ability to reject its own pollen
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