1. Overview: Feeding the World
Seeds changed the course of plant evolution, enabling their bearers to become the dominant producers in most terrestrial ecosystems

2. The reduced gametophytes of seed plants are protected in ovules and pollen grains
In addition to seeds, the following are common to all seed plants:
Reduced gametophytes
The gametophytes of seed plants develop within the walls of spores retained within tissues of the parent sporophyte
Heterospory
Ovules
Pollen

3. Sporophyte
(2n)
Sporophyte
(2n)
Gametophyte
(n)
Gametophyte
(n)
Sporophyte dependent on gametophyte (mosses and other bryophytes)
Large sporophyte and small, independent game-tophyte (ferns and other seedless vascular plants)
Microscopic female
gametophytes (n) in
ovulate cones
(dependent)
Sporophyte (2n),
the flowering plant
(independent)
Microscopic male
gametophytes (n) in
inside these parts
of flowers
(dependent)
Microscopic male
gametophytes (n)
in pollen cones
(dependent)
Microscopic female
gametophytes (n) in
inside these parts
of flowers
(dependent)
Sporophyte (2n),
(independent)
Reduced gametophyte dependent on sporophyte (seed plants: gymnosperms and angiosperms)

4. Heterospory: The Rule Among Seed Plants
Seed plants evolved from plants with megasporangia, which produce megaspores that give rise to female gametophytes
Seed plants evolved from plants with microsporangia, which produce microspores that give rise to male gametophytes

5. Ovules and Production of Eggs
An ovule consists of a megasporangium, megaspore, and one or more protective integuments
Gymnosperm megaspores have one integument
Angiosperm megaspores usually have two integuments

6. Seed coat
(derived from
integument)
Integument
Female
gametophyte (n)
Spore wall
Egg nucleus (n)
Food supply
(female
gametophyte
tissue) (n)
Male gametophyte
(within germinating
pollen grain) (n)
Megasporangium
(2n)
Discharged
sperm nucleus (n)
Embryo (2n)
(new sporophyte)
Megaspore (n)
Pollen grain (n)
Micropyle
Unfertilized ovule
Fertilized ovule
Gymnosperm seed

7. Pollen and Production of Sperm
Microspores develop into pollen grains, which contain the male gametophytes
Pollination is the transfer of pollen to the part of a seed plant containing the ovules
Pollen can be dispersed by air or animals, eliminating the water requirement for fertilization
If a pollen grain germinates, it gives rise to a pollen tube that discharges two sperm into the female gametophyte within the ovule

8. The Evolutionary Advantage of Seeds
A seed develops from the whole ovule
A seed is a sporophyte embryo, along with its food supply, packaged in a protective coat

9. Gymnosperms bear “naked” seeds, typically on cones
The gymnosperms include four phyla:
Cycadophyta (cycads)
Gingkophyta (one living species: Ginkgo biloba)
Gnetophyta (three genera: Gnetum, Ephedra, Welwitschia)
Coniferophyta (conifers, such as pine, fir, and redwood)

10. Cycas revoluta

13. Gnetum. This genus includes about 35 species of tropical trees, shrubs, and vines, mainly native to Africa and Asia. Their leaves look similar to those of flowering plants, and their seeds look somewhat like fruits.

14. Ephedra. This genus includes about 40 species that inhabit arid regions throughout the world. Known in North America as “Mormon tea,” these desert shrubs produce the compound ephedrine, commonly used as a decongestant.

15. Welwitschia. This genus consists of one species Welwitschia mirabilis, a plant that lives only in the deserts of southwestern Africa. Its strap like leaves are among the largest known.

16. Ovulate
cones

17. Douglas fir. “Doug fir” (Pseudotsuga menziesii) provides more timber than any other North American tree species. Some uses include house framing, plywood, pulpwood for paper, railroad ties, and boxes and crates.

18. Pacific yew. The
bark of Pacific yew
(Taxa brevifolia) is a
source of taxol, a
compound used to
treat women with
ovarian cancer. The
leaves of a
European yew
species produce a
similar compound,
which can be
harvested without
destroying the plants. Pharmaceutical companies are now refining techniques for synthesizing drugs with taxol-like properties.

19. Bristlecone pine. This species (Pinus longaeva), which is found in the White Mountains of California, includes some of the oldest living organisms, reaching ages of more than 4,600 years. One tree (not shown here) is called Methuselah because it may be the world’s oldest living tree. In order to protect the tree, scientists keep its location a secret.

20. Sequoia. This giant sequoia (Sequoiadendron giganteum), in California’s Sequoia National Park weighs about 2,500 metric tons, equivalent to about 24 blue whales (the largest animals), or 40,000 people. Giant sequoias are the largest living organisms and also some of the most ancient, with some estimated to be between 1,800 and 2,700 years old. Their cousins, the coast redwoods (Sequoia sempervirens), grow to heights of more than 110 meters (taller than the Statue of Liberty) and are found only in a narrow coastal strip of northern California.

21. Common juniper. The “berries” of the common juniper (Juniperus communis), are actually ovule-producing cones consisting of fleshy sporophylls.

22. Wollemia pine. Survivors of a confer group
once known only from fossils, living Wollemia
pines (Wollemia nobilis), were discovered in
1994 in a national park
only 150 kilometers
from Sydney, Australia.
The species consists of
just 40 known
individuals two small
groves. The inset photo
compares the leaves of
this “living fossil” with
actual fossils.

23. Gymnosperm Evolution
Fossil evidence reveals that by the late Devonian period some plants, called progymnosperms, had begun to acquire some adaptations that characterize seed plants
Gymnosperms appear early in the fossil record and dominated the Mesozoic terrestrial ecosystems
Living seed plants can be divided into two clades: gymnosperms and angiosperms

24. A Closer Look at the Life Cycle of a Pine
Key features of the gymnosperm life cycle:
Dominance of the sporophyte generation
Development of seeds from fertilized ovules
The transfer of sperm to ovules by pollen
The life cycle of a pine is an example

25. Key
Haploid (n)
Diploid (2n)
Ovule
Ovulate
cone
Megasporocyte (2n)
Integument
Longitudinal
section of
ovulate cone
Micropyle
Pollen
cone
Megasporangium
Mature
sporophyte
(2n)
Microsporocytes
(2n)
Germinating
pollen grain
Pollen
grains (n)
(containing male
gametophytes)
MEIOSIS
MEIOSIS
Longitudinal
section of
pollen cone
Surviving
megaspore (n)
Sporophyll
Microsporangium
Seedling
Germinating
pollen grain
Archegonium
Integument
Egg (n)
Seeds on surface
of ovulate scale
Female
gametophyte
Germinating
pollen grain (n)
Food reserves
(gametophyte
tissue) (n)
Seed coat
(derived from
parent
sporophyte) (2n)
Discharged
sperm nucleus (n)
Pollen
tube
Embryo
(new sporophyte)
(2n)
FERTILIZATION
Egg nucleus (n)

26. The reproductive adaptations of angiosperms include flowers and fruits
Angiosperms are flowering plants
These seed plants have reproductive structures called flowers and fruits
They are the most widespread and diverse of all plants

27. Characteristics of Angiosperms
All angiosperms are classified in a single phylum, Anthophyta
The name comes from the Greek anthos, flower

28. Flowers
The flower is an angiosperm structure specialized for sexual reproduction
A flower is a specialized shoot with up to four types of modified leaves:
Sepals, which enclose the flower
Petals, which are brightly colored and attract pollinators
Stamens, which produce pollen
Carpels, which produce ovules

29. Stigma
Carpel
Stamen
Anther
Style
Filament
Ovary
Petal
Sepal
Ovule
Receptacle

30. Fruits
A fruit typically consists of a mature ovary but can also include other flower parts
Fruits protect seeds and aid in their dispersal
Mature fruits can be either fleshy or dry
Various fruit adaptations help disperse seeds
Seeds can be carried by wind, water, or animals to new locations

31. Ruby grapefruit, a fleshy fruit
with a hard outer layer and soft
inner layer of pericarp
Tomato, a fleshy fruit with soft
outer and inner layers of pericarp
Nectarine, a fleshy
fruit with a soft outer
layer and hard inner
layer (pit) of pericarp
Milkweed, a dry fruit that splits
open at maturity
Walnut, a dry fruit that remains
closed at maturity

32. Wings enable maple
fruits to be easily
carried by the wind.
Seeds within berries and other edible fruits are often dispersed in animal feces.
The barbs of cockleburs facilitate seed dispersal by allowing these fruits to hitchhike on animals.

33. The Angiosperm Life Cycle
In the angiosperm life cycle, double fertilization occurs when a pollen tube discharges two sperm into the female gametophyte within an ovule
One sperm fertilizes the egg, while the other combines with two nuclei in the central cell of the female gametophyte and initiates development of food-storing endosperm
The endosperm nourishes the developing embryo

34. Key
Haploid (n)
Diploid (2n)
Microsporangium
Anther
Microsporocytes (2n)
Mature flower on
sporophyte plant
(2n)
MEIOSIS
Microspore (n)
Generative cell
Ovule with
megasporangium (2n)
Male
gametophyte
(in pollen
grain)
Tube cell
Ovary
Pollen
grains
Germinating
seed
MEIOSIS
Stigma
Pollen
tube
Megasporangium
(n)
Embryo (2n)
Sperm
Surviving
megaspore
(n)
Endosperm
(food
supply) (3n)
Seed
Pollen
tube
Seed coat (2n)
Style
Female gametophyte
(embryo sac)
Antipodal cells
Polar nuclei
Pollen
tube
Synergids
Eggs (n)
Zygote (2n)
Sperm
(n)
Nucleus of
developing
endosperm
(3n)
Eggs
nucleus (n)
FERTILIZATION
Discharged
sperm nuclei (n)

35. Angiosperm Evolution
Clarifying the origin and diversification of angiosperms poses fascinating challenges to evolutionary biologists
Angiosperms originated at least 140 million years ago
During the late Mesozoic, the major branches of the clade diverged from their common ancestor

36. Fossil Angiosperms
Primitive fossils of 125-million-year-old angiosperms display derived and primitive traits
Archaefructus sinensis, for example, has anthers and seeds but lacks petals and sepals

37. Carpel
Stamen
5 cm
Archaefructus sinensis, a
125-million-year-old fossil
Artist’s reconstruction of
Archaefructus sinensis

38. An “Evo-Devo” Hypothesis of Flower Origins
Scientist Michael Frohlich hypothesized how pollen-producing and ovule-producing structures were combined into a single flower
He proposed that the ancestor of angiosperms had separate pollen-producing and ovule-producing structures

39. Angiosperm Diversity
The two main groups of angiosperms are monocots and eudicots
Basal angiosperms are less derived and include the flowering plants belonging to the oldest lineages
Magnoliids share some traits with basal angiosperms but are more closely related to monocots and eudicots

40. BASAL ANGIOSPERMS
Amborella trichopoda
Water lily (Nymphaea
“Rene Gerald”)
Star anise (Illicium
floridanum)

41. HYPOTHETICAL TREE OF FLOWERING PLANTS
Star anise
and relatives
Amborella
Water lilies
Magnoliids
Monocots
Eudicots
MAGNOLIIDS
Southern magnolia
(Magnolia
grandiflora)

42. MONOCOTS EUDICOTS Orchid California (Lemboglossum Monocot Eudicot
rossii)
Monocot
Characteristics
Eudicot
Characteristics
California
poppy
(Eschscholzia
california)
Embryos
One cotyledon
Two cotyledons

43. MONOCOTS EUDICOTS Pyrenean oak Leaf (Quercus venation pyrenaica)
Veins usually
netlike
Veins usually
parallel
Stems
Pygmy date palm (Phoenix roebelenii)
Vascular tissue
usually arranged
in ring
Vascular tissue
scattered

44. MONOCOTS EUDICOTS Lily (Lilium “Enchantment”) Roots
Dog rose (Rosa canina), a wild rose
Root system
usually fibrous
(no main root)
Taproot (main root)
usually present

45. MONOCOTS EUDICOTS Barley (Hordeum vulgare), a grass Pea (Lathyrusner
vosus, Lord
Anson’s
blue pea),
a legume
Pollen
Pollen grain with
one opening
Pollen grain with
three openings
Flowers
Anther
Zucchini
(Cucurbita
Pepo), female
(left), and
male flowers
Floral organs
usually in
multiples of three
Stigma
Floral organs usually
in multiples of
four or five
Filament
Ovary

46. Evolutionary Links Between Angiosperms and Animals
Pollination of flowers by animals and transport of seeds by animals are two important relationships in terrestrial ecosystems

47. A flower pollinated by
honeybees.
A flower pollinated by
hummingbirds.
A flower pollinated by nocturnal animals.

48. Human welfare depends greatly on seed plants
No group of plants is more important to human survival than seed plants
Plants are key sources of food, fuel, wood products, and medicine
Our reliance on seed plants makes preservation of plant diversity critical

49. Products from Seed Plants
Most of our food comes from angiosperms
Six crops (wheat, rice, maize, potatoes, cassava, and sweet potatoes) yield 80% of the calories consumed by humans
Modern crops are products of relatively recent genetic change resulting from artificial selection
Many seed plants provide wood
Secondary compounds of seed plants are used in medicines

51. Threats to Plant Diversity
Destruction of habitat is causing extinction of many plant species
Loss of plant habitat is often accompanied by loss of the animal species that plants support

52. Animations and Videos Life Cycle of a Conifer Life Cycle of a Pine
Parts of the Vascular Plant
Parts of a Flower
Double Fertilization
Plant Fertilization
Seed Development
Fruit Development

53. Animations and Videos Life Cycle of an Angiosperm
Life Cycle of a Flowering Plant
Chapter Quiz Questions – 1
Chapter Quiz Questions - 2

54. The reason that two sperm nuclei travel down the pollen tube is that
they both stimulate growth of the pollen tube.
one fertilizes the egg, and the other combines with the two polar nuclei.
one fertilizes the egg, and the other fertilizes the synergid.
one is for fertilizing the egg, and one directs the pollen tube toward the micropyle.
if one fails in fertilization, there is a backup nucleus.
Answer: b

55. The reason that two sperm nuclei travel down the pollen tube is that
they both stimulate growth of the pollen tube.
one fertilizes the egg, and the other combines with the two polar nuclei.
one fertilizes the egg, and the other fertilizes the synergid.
one is for fertilizing the egg, and one directs the pollen tube toward the micropyle.
if one fails in fertilization, there is a backup nucleus.

56. Adaptations that have contributed to the success of plants in terrestrial environments include seeds, vascular tissue, cuticle, and flowers. There are other significant adaptations as well. Which of the following correctly lists the adaptations in the order in which they appeared in the fossil record?
seeds, vascular tissue, flowers, cuticle
cuticle, seeds, flowers, vascular tissue
cuticle, vascular tissue, seeds, flowers
vascular tissue, cuticle, seeds, flowers
Answer: c

57. Adaptations that have contributed to the success of plants in terrestrial environments include seeds, vascular tissue, cuticle, and flowers. There are other significant adaptations as well. Which of the following correctly lists the adaptations in the order in which they appeared in the fossil record?
seeds, vascular tissue, flowers, cuticle
cuticle, seeds, flowers, vascular tissue
cuticle, vascular tissue, seeds, flowers
vascular tissue, cuticle, seeds, flowers

58. These four adaptations (cuticle, vascular tissue, seeds, and flowers) are key characters that define four major modern plant groups. Complete the following table using the key provided.
a) ferns (and relatives) b) bryophytes (mosses) c) flowering plants d) gymnosperms
Answer: a

59. These four adaptations (cuticle, vascular tissue, seeds, and flowers) are key characters that define four major modern plant groups. Complete the following table using the key provided.
a) ferns (and relatives) b) bryophytes (mosses) c) flowering plants d) gymnosperms

60. These four adaptations (cuticle, vascular tissue, seeds, and flowers) are key characters that define four major modern plant groups. Complete the following table using the key provided.
a) ferns (and relatives) b) bryophytes (mosses) c) flowering plants d) gymnosperms
Answer: d

61. These four adaptations (cuticle, vascular tissue, seeds, and flowers) are key characters that define four major modern plant groups. Complete the following table using the key provided.
a) ferns (and relatives) b) bryophytes (mosses) c) flowering plants d) gymnosperms

62. The reason that two sperm nuclei travel down the pollen tube is that
they both stimulate growth of the pollen tube.
one fertilizes the egg, and the other combines with the two polar nuclei.
one fertilizes the egg, and the other fertilizes the synergid.
one is for fertilizing the egg, and one directs the pollen tube toward the micropyle.
if one fails in fertilization, there is a backup nucleus.
Answer: b 62

63. The reason that two sperm nuclei travel down the pollen tube is that
they both stimulate growth of the pollen tube.
one fertilizes the egg, and the other combines with the two polar nuclei.
one fertilizes the egg, and the other fertilizes the synergid.
one is for fertilizing the egg, and one directs the pollen tube toward the micropyle.
if one fails in fertilization, there is a backup nucleus. 63

64. In dicotyledon seed germination, usually the first organ to emerge from the seed is the
shoot tip, as the most important function to get under way is breaking through the soil.
hypocotyl, as the most important function to get under way is breaking through the soil.
cotyledon(s), as the most important function to get under way is photosynthesis.
radicle, as the most important function to get under way is the absorption of water and nutrients.
root, as the most important function to get under way is the anchoring of the plant to the soil.
Answer: d 64

65. In dicotyledon seed germination, usually the first organ to emerge from the seed is the
shoot tip, as the most important function to get under way is breaking through the soil.
hypocotyl, as the most important function to get under way is breaking through the soil.
cotyledon(s), as the most important function to get under way is photosynthesis.
radicle, as the most important function to get under way is the absorption of water and nutrients.
root, as the most important function to get under way is the anchoring of the plant to the soil. 65

66. All of the following statements regarding double fertilization in the angiosperms is true except which one?
The angiosperm embryo is diploid.
The pollen tube reaching the micropyle results in the death of one of the synergids.
The fertilized angiosperm ovule consists of diploid and triploid cells.
The megasporangium gives rise to four haploid eggs through meiosis.
One of the pollen nuclei contributes to the genome of the endosperm.
Answer: d 66

67. All of the following statements regarding double fertilization in the angiosperms is true except which one?
The angiosperm embryo is diploid.
The pollen tube reaching the micropyle results in the death of one of the synergids.
The fertilized angiosperm ovule consists of diploid and triploid cells.
The megasporangium gives rise to four haploid eggs through meiosis.
One of the pollen nuclei contributes to the genome of the endosperm. 67

68. The flowers of wind-pollinated plants
usually have flat blades to direct the wind.
produce sticky pollen.
are usually green and inconspicuous.
are usually white and small.
usually occur on separate male and female plants.
Answer: c 68

69. The flowers of wind-pollinated plants
usually have flat blades to direct the wind.
produce sticky pollen.
are usually green and inconspicuous.
are usually white and small.
usually occur on separate male and female plants. 69

70. An accessory fruit is one that
grows from a lateral meristem.
develops from tissue other than the ovary.
develops from the pericarp.
consists of multiple receptacles.
is not necessary for reproduction.
Answer: b 70

71. An accessory fruit is one that
grows from a lateral meristem.
develops from tissue other than the ovary.
develops from the pericarp.
consists of multiple receptacles.
is not necessary for reproduction. 71

72. Which of the following lists an aggregate fruit, a multiple fruit, and an accessory fruit, in that order?
guava, blackberry, cherry
watermelon, orange, fig
apple, pear, cherry
pineapple, tangerine, cranberry
strawberry, fig, pear
Answer: e 72

73. Which of the following lists an aggregate fruit, a multiple fruit, and an accessory fruit, in that order?
guava, blackberry, cherry
watermelon, orange, fig
apple, pear, cherry
pineapple, tangerine, cranberry
strawberry, fig, pear 73

74. Scientific Skills Exercises
One unusual opportunity to test how long seeds can remain viable occurred when seeds from date palm trees (Phoenix dactylifera) were discovered under the rubble of a 2,000-year-old fortress near the Dead Sea. Scientists measured the fraction of carbon-14 that remained in three of the ancient date palm seeds: two that were not planted and one that was planted and germinated. (For the germinated seed, the scientists used a seed-coat fragment found clinging to a root of the seedling.) The table shows their results.
Data from S. Sallon, et al., Germination, genetics, and growth of an ancient date seed. Science 320:1464 (2008).

75. An ancient date palm seed germinated and grew into a healthy plant
An ancient date palm seed germinated and grew into a healthy plant. What was the source of nutrients for the young sporophyte embryo during germination of the date palm seed?
a) sunlight
b) food stored within the seed
c) water taken up by the germinating seed
d) the surrounding soil
Answer: b

76. An ancient date palm seed germinated and grew into a healthy plant
An ancient date palm seed germinated and grew into a healthy plant. What was the source of nutrients for the young sporophyte embryo during germination of the date palm seed?
a) sunlight
b) food stored within the seed
c) water taken up by the germinating seed
d) the surrounding soil

77. Why is seed dormancy adaptive for many plant species?
a) Seed dormancy increases the longevity of an individual sporophyte plant.
b) Seed dormancy allows seeds to germinate when conditions are favorable for seedling growth.
c) Seed dormancy ensures that a seedling does not compete with its parents.
d) Seed dormancy ensures that a seedling does not germinate when a source of food is not available for the young seedling.
Answer: b

78. Why is seed dormancy adaptive for many plant species?
a) Seed dormancy increases the longevity of an individual sporophyte plant.
b) Seed dormancy allows seeds to germinate when conditions are favorable for seedling growth.
c) Seed dormancy ensures that a seedling does not compete with its parents.
d) Seed dormancy ensures that a seedling does not germinate when a source of food is not available for the young seedling.