Plant Diversity Notes
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19-1
Plants have changed the world
Section 19.1
Figure 19.1
(snow): ©Design Pics/Carson Ganci/Getty Images RF; (prairie): ©Tetra Images/Tetra Images/Corbis RF; (forest): ©Ted Mead/Getty Images RF
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19-2
Plants are essential for life
Section 19.1
On land and in water, plants provide habitats and food to countless species of microbes, fungi, and animals.
Figure 19.1
(snow): ©Design Pics/Carson Ganci/Getty Images RF; (prairie): ©Tetra Images/Tetra Images/Corbis RF; (forest): ©Ted Mead/Getty Images RF
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19-3
Plants share a lineage with protists
Section 19.1
All plants are multicellular, autotrophic eukaryotes that use photosynthesis to obtain energy.
Figure 19.3
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19-4
Green algae are the closest relatives of plants
Section 19.1
Charophytes are a group of modern green algae.
Biologists believe they are similar to the ancestors of plants.
Figure 19.2
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19-5
Green algae share many molecular features with plants
Section 19.1
DNA sequences reveal a close evolutionary relationship.
Chloroplasts contain the same pigments.
Cell walls contain cellulose.
Both use starch as a storage molecule.
Figures 19.2, 19.3
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19-6
Green algae live in water, plants on land
Section 19.1
The different environments select for different body types and reproductive strategies.
Figures 19.2, 19.3
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19-7
Plants are divided into four groups
Section 19.1
Plants arose during the Paleozoic era and diversified into thousands of different species.
Modern-day plants include
Table 19.1
TABLE 19.1 Phyla of Plants
Phylum
Examples
Number of Existing Species
Nonvascular plants
Marchantiophyta
Liverworts
9000
Anthocerotophyta
Hornworts
100
Bryophyta
True mosses
15,000
Seedless vascular plants
Lycopodiophyta
Club mosses, spike mosses
1200
Pteridophyta
Whisk ferns, true ferns, horsetails
11,500
Gymnosperms
Cycadophyta
Cycads
130
Ginkgophyta
Ginkgo
1
Pinophyta
Pines, firs, and other conifers
630
Gnetophyta
Gnetophytes
80
Angiosperms
Magnoliophyta
All flowering plants, including roses, grasses, fruit trees, maples, and oaks
> 260,000
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19-8
Plants evolved key adaptations
Section 19.1
The four plant groups are defined by a series of features that plants developed over time, including having vascular tissue, seeds, and flowers/fruits.
Figure 19.3
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19-9
A leaf is an adaption to life on land
Section 19.1
Figure 19.4
(peas): ©Corbis RF; (leaf micrograph): ©M. I. Walker/Science Source
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19-10
Vascular tissue is an adaption to life on land
Section 19.1
Plant vascular tissue is a bundle of tubes that transports water, minerals, and sugar throughout the plant.
Figure 19.4
(peas): ©Corbis RF; (leaf micrograph): ©M. I. Walker/Science Source
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19-11
A root is an adaption to life on land
Section 19.1
Roots below the ground absorb water and minerals while anchoring the plant in the soil.
Figure 19.4
(peas): ©Corbis RF; (leaf micrograph): ©M.I. Walker/Science Source
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19-12
All plants have similar life cycles
Section 19.1
The similarity among plant life cycles is evidence that all plants share a common ancestor.
Figure 19.5
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19-13
Plant reproduction is complex
Section 19.1
Plant gametes and zygotes can both grow into adult organisms and reproduce.
Figure 19.5
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19-14
Plants alternate generations
Section 19.1
The plant life cycle is called alternation of generations.
A multicellular diploid stage alternates with a multicellular haploid stage.
Figure 19.5
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19-15
Sporophyte generation is diploid
Section 19.1
A fertilized egg forms a diploid zygote, which develops by mitotic cell division into a multicellular, diploid plant called a sporophyte.
Figure 19.5
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19-16
Sporophytes produce spores
Section 19.1
The sporophyte plant produces haploid spores by meiosis.
Figure 19.5
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19-17
Gametophyte generation is haploid
Section 19.1
Spores divide by mitosis into a multicellular, haploid gametophyte.
Figure 19.5
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19-18
Gametophytes produce gametes
Section 19.1
The haploid
gametophyte produces gametes by mitosis.
Figure 19.5
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19-19
Fertilization forms a zygote
Section 19.1
The gametes fuse at fertilization, forming a diploid zygote and starting the cycle again.
Figure 19.5
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19-20
The lifestyle of gametophytes varies through plant phyla
Section 19.1
In simpler plants the gametophyte is larger and less dependent on the sporophyte; in more complex plants the reverse is true.
Figure 19.6
Bryophytes
Seedless Vascular Plants
Gymnosperms
Angiosperms
Gametophyte (haploid generation)
Size relative to sporophyte?
Varies
Small
Microscopic
Microscopic
Depends on sporophyte for nutrition?
No
No
Yes
Yes
Sporophyte (diploid generation)
Size relative to gametophyte?
Varies
Large
Large
Large
Depends on gametophyte for nutrition?
Yes
No
No
No
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19-21
Pollen is an adaption to life on land
Section 19.1
Seed plants produce pollen, which contains the male gametophyte. Pollination can occur without water, and often animals help spread the pollen to new plants.
Figure 19.4
(peas): ©Corbis RF; (leaf micrograph): ©M. I. Walker/Science Source
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19-22
A seed is an adaption to life on land
Section 19.1
Seeds carry dormant plant embryos packaged with a food supply and protected from drying out. They can be dispersed long distances and remain dormant until conditions are favorable.
Figure 19.4
(peas): ©Corbis RF; (leaf micrograph): ©M. I. Walker/Science Source
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19-23
Flowers and fruit are adaptions to life on land
Section 19.1
Flowers produce pollen and egg cells. Fruits develop after fertilization, to protect and disperse the plant offspring.
Figure 19.4
(peas): ©Corbis RF; (leaf micrograph): ©M. I. Walker/Science Source
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19-24
Bryophytes are the simplest plants
Section 19.2
There are about 24,000 existing species of bryophytes, or “nonvascular” plants.
Mosses, hornworts, and liverworts are bryophytes.
Table 19.1
TABLE 19.1 Phyla of Plants
Phylum
Examples
Number of Existing Species
Nonvascular plants
Marchantiophyta
Liverworts
9000
Anthocerotophyta
Hornworts
100
Bryophyta
True mosses
15,000
Seedless vascular plants
Lycopodiophyta
Club mosses, spike mosses
1200
Pteridophyta
Whisk ferns, true ferns, horsetails
11,500
Gymnosperms
Cycadophyta
Cycads
130
Ginkgophyta
Ginkgo
1
Pinophyta
Pines, firs, and other conifers
630
Gnetophyta
Gnetophytes
80
Angiosperms
Magnoliophyta
All flowering plants, including roses, grasses, fruit trees, maples, and oaks
> 260,000
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19-25
Bryophytes are nonvascular and seedless
Section 19.2
The earliest plants probably resembled modern bryophytes. Bryophytes have no vascular tissue, roots, leaves, seeds, or flowers.
Figure 19.3
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19-26
Bryophytes are small, compact plants
Section 19.2
Without vascular tissue and lignin (which strengthens the cell wall), bryophytes lack physical support.
Materials move from cell to cell within the plant by diffusion and osmosis.
They live in moist shady habitats where they will not dry out.
Figure 19.7
(a): ©Dr. Jeremy Burgess/Science Source; (b, c): ©Steven P. Lynch RF
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19-27
Bryophytes have a small sporophyte
Section 19.2
The sporophyte is a stalk attached to the gametophyte.
The sporophyte produces spores that grow into new haploid gametophyte plants.
Figure 19.9
Sporophyte
©Ed Reschke/Photolibrary/Getty Images
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19-28
Bryophyte sexual reproduction requires water
Section 19.2
Gametophytes have male and female structures that produce gametes (eggs and sperm). The sperm swim to the eggs.
Figure 19.9
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19-29
Bryophytes also reproduce asexually
Section 19.2
Mosses and liverworts produce structures called gemmae, which are small pieces of tissue that detach from the gametophyte and grow into new plants.
Table 19.1
Figure 19.8
©M. I. Walker/Science Source
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19-30
Seedless vascular plants have no seeds
Section 19.3
There are about 12,700 existing species of plants with vascular tissue, but no seeds.
This phylum is composed of ferns and their close relatives.
Table 19.1
TABLE 19.1 Phyla of Plants
Phylum
Examples
Number of Existing Species
Nonvascular plants
Marchantiophyta
Liverworts
9000
Anthocerotophyta
Hornworts
100
Bryophyta
True mosses
15,000
Seedless vascular plants
Lycopodiophyta
Club mosses, spike mosses
1200
Pteridophyta
Whisk ferns, true ferns, horsetails
11,500
Gymnosperms
Cycadophyta
Cycads
130
Ginkgophyta
Ginkgo
1
Pinophyta
Pines, firs, and other conifers
630
Gnetophyta
Gnetophytes
80
Angiosperms
Magnoliophyta
All flowering plants, including roses, grasses, fruit trees, maples, and oaks
> 260,000
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19-31
Seedless vascular plants have true roots, stems, and leaves
Section 19.3
Vascular tissue allowed these plants to grow much larger than bryophytes, which gave them an edge in competing for sunlight.
Figure 19.10
(a): ©ImageBROKER/Alamy RF; (b): ©Howard Rice/Garden Picture Library/Getty Images; (c): ©Biosphoto/Superstock; (d): ©Ed Reschke/Photolibrary/Getty Images; (e): ©Rod Planck/Science Source
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19-32
There are four groups of seedless vascular plants
Section 19.3
Seedless vascular plants include:
Figure 19.10
(a): ©ImageBROKER/Alamy RF; (b): ©Howard Rice/Garden Picture Library/Getty Images; (c): ©Biosphoto/Superstock;(d): ©Ed Reschke/Photolibrary/Getty Images; (e): ©Rod Planck/Science Source
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19-33
The earliest seedless vascular plants were probably modern club mosses
Section 19.3
Fossil evidence suggests the first vascular plants originated around 425 million years ago. Club mosses are different from true mosses, which are bryophytes. They are placed in their own phylum.
Figure 19.3
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19-34
Ferns and their relatives evolved later
Section 19.3
Whisk ferns, horsetails, and true ferns make up a second phylum of seedless vascular plants that first appeared around 375 million years ago. Most, but not all, of these species live on land.
Figure 19.3
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19-35
Seedless vascular plants have a conspicuous sporophyte
Section 19.3
The sporophyte develops from a zygote, then grows up and out of the gametophyte.
As it matures, the sporophyte detaches and grows separately from the gametophyte.
Figure 19.11
(spores): ©Ed Reschke/Photolibrary/Getty Images; (gametophyte): ©Les Hickok and Thomas Warne, C-Fern
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19-36
Spores form under the leaves of the sporophyte
Section 19.3
Haploid spores grow on the underside of sporophyte leaves.
The spores form by meiosis and then develop into gametophytes.
Figure 19.11
(spores): ©Ed Reschke/Photolibrary/Getty Images; (gametophyte): ©Les Hickok and Thomas Warne, C-Fern
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19-37
Seedless vascular plants require water for reproduction
Section 19.3
Gametophytes produce male and female gametes. Sperm swim to the eggs in water.
Figure 19.11
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19-38
All plants alternate generations
In bryophytes and seedless vascular plants, the gametophyte is more prominent than the sporophyte.
In gymnosperms and angiosperms, the sporophyte is much more prominent than the gametophyte.
Section 19.1
Figure 19.19
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19-39
Gymnosperms have pollen and seeds
Section 19.4
There are about 850 existing species of gymnosperms.
They evolved about 300 million years ago.
Table 19.1
TABLE 19.1 Phyla of Plants
Phylum
Examples
Number of Existing Species
Nonvascular plants
Marchantiophyta
Liverworts
9000
Anthocerotophyta
Hornworts
100
Bryophyta
True mosses
15,000
Seedless vascular plants
Lycopodiophyta
Club mosses, spike mosses
1200
Pteridophyta
Whisk ferns, true ferns, horsetails
11,500
Gymnosperms
Cycadophyta
Cycads
130
Ginkgophyta
Ginkgo
1
Pinophyta
Pines, firs, and other conifers
630
Gnetophyta
Gnetophytes
80
Angiosperms
Magnoliophyta
All flowering plants, including roses, grasses, fruit trees, maples, and oaks
> 260,000
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19-40
Gymnosperms are “naked seed” plants
Section 19.4
New reproductive adaptations allowed gymnosperms to outcompete seedless vascular plants in many habitats. Gymnosperms produce seeds but do not enclose them in fruit.
Figure 19.3
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19-41
Gymnosperms include cycads
Section 19.4
Cycads were prevalent in the Mesozoic era, but many species are near extinction in the wild today. They have palmlike leaves and produce large cones.
Figure 19.12
Cycads
Ginkgo
Conifers
Gnetophytes
(spores): ©Ed Reschke/Photolibrary/Getty Images; (gametophyte): ©Les Hickok and Thomas Warne, C-Fern(a, cycad): ©Alena Brozova/Alamy;
(a, cycad cone): ©Pat Pendarvis; (b, ginkgo): ©Light of Peace/Flickr/Getty Images RF; (b, ginkgo seed): ©G. R. “Dick” Roberts/Natural Sciences Image Library;
(c, conifer): ©Jack Dykinga/Nature Picture Library; (c, conifer cone): ©Ed Reschke/Peter Arnold/Getty Images;
(d, gnetophyte): ©Jeff Foott/Discovery Channel Images/Getty Images; (d, gnetophyte cone): ©Steven P. Lynch/McGraw-Hill Education
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19-42
Gymnosperms include the ginkgo
Section 19.4
Only one species exists today, and it no longer grows wild in nature. The ginkgo tree has distinctive, fan-shaped leaves.
Figure 19.12
Cycads
Ginkgo
Conifers
Gnetophytes
(spores): ©Ed Reschke/Photolibrary/Getty Images; (gametophyte): ©Les Hickok and Thomas Warne, C-Fern(a, cycad): ©Alena Brozova/Alamy;
(a, cycad cone): ©Pat Pendarvis; (b, ginkgo): ©Light of Peace/Flickr/Getty Images RF; (b, ginkgo seed): ©G. R. “Dick” Roberts/Natural Sciences Image Library; (c, conifer): ©Jack Dykinga/Nature Picture Library; (c, conifer cone): ©Ed Reschke/Peter Arnold/Getty Images;
(d, gnetophyte): ©Jeff Foott/Discovery Channel Images/Getty Images; (d, gnetophyte cone): ©Steven P. Lynch/McGraw-Hill Education
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19-43
Gymnosperms include conifers
Section 19.4
Conifers such as pine trees are familiar gymnosperms. Their leaves are needlelike and they produce egg cells and pollen in cones.
Figure 19.12
Cycads
Ginkgo
Conifers
Gnetophytes
(spores): ©Ed Reschke/Photolibrary/Getty Images; (gametophyte): ©Les Hickok and Thomas Warne, C-Fern(a, cycad): ©Alena Brozova/Alamy;
(a, cycad cone): ©Pat Pendarvis; (b, ginkgo): ©Light of Peace/Flickr/Getty Images RF; (b, ginkgo seed): ©G. R. “Dick” Roberts/Natural Sciences Image Library;
(c, conifer): ©Jack Dykinga/Nature Picture Library; (c, conifer cone): ©Ed Reschke/Peter Arnold/Getty Images;
(d, gnetophyte): ©Jeff Foott/Discovery Channel Images/Getty Images; (d, gnetophyte cone): ©Steven P. Lynch/McGraw-Hill Education
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19-44
Gymnosperms include gnetophytes
Section 19.4
These plants have a mixture of traits that make them difficult to classify. Ephedra, shown here, has cones that resemble tiny flowers.
Figure 19.12
Cycads
Ginkgo
Conifers
Gnetophytes
(spores): ©Ed Reschke/Photolibrary/Getty Images; (gametophyte): ©Les Hickok and Thomas Warne, C-Fern(a, cycad): ©Alena Brozova/Alamy;
(a, cycad cone): ©Pat Pendarvis; (b, ginkgo): ©Light of Peace/Flickr/Getty Images RF; (b, ginkgo seed): ©G. R. “Dick” Roberts/Natural Sciences Image Library;
(c, conifer): ©Jack Dykinga/Nature Picture Library; (c, conifer cone): ©Ed Reschke/Peter Arnold/Getty Images;
(d, gnetophyte): ©Jeff Foott/Discovery Channel Images/Getty Images; (d, gnetophyte cone): ©Steven P. Lynch/McGraw-Hill Education
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19-45
Gymnosperm sporophytes are large and conspicuous
Section 19.4
The sporophytes of most gymnosperms are woody trees or shrubs. Reproductive structures and leaf types are diverse.
Sporophytes produce both male and female cones, where spores form by meiosis.
Figure 19.13
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19-46
Gymnosperm sporophytes produce spores in cones
Section 19.4
Male cones produce microspores on cone scales.
Ovules on female cone scales produce megaspores.
Figure 19.13
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19-47
Gymnosperm gametophytes are microscopic
Section 19.4
Male gametophytes are enclosed inside grains of pollen. Pollen can be dispersed by wind to settle on new plants.
The tiny female gametophytes stay in the cone, enclosed inside the ovule.
Figure 19.13
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19-48
Pollination gets male and female gametophytes together
Section 19.4
The male gametophyte produces a pollen tube that grows through the ovule until it reaches the egg cells inside.
Figure 19.13
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19-49
Fertilization in gymnosperms does not require water
Section 19.4
Sperm do not need to swim through water to eggs for fertilization.
Figure 19.13
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19-50
Gymnosperms zygotes stay inside seeds
Section 19.4
The zygote is the first cell of the sporophyte.
It grows mitotically into an embryo, inside a seed, on a female cone scale.
Figure 19.13
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19-51
Seeds protect sporophyte embryos
Section 19.4
Gymnosperm seeds have a tough outer coat and can be dispersed by wind or animals.
When conditions are favorable they will germinate into seedlings, which develop into mature sporophyte trees.
Figure 19.13
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19-52
Angiosperms have flowers and fruit
Section 19.5
95% of all living plant species are angiosperms.
They evolved about 144 million years ago and rapidly diversified into over 260,000 different species.
Table 19.1
TABLE 19.1 Phyla of Plants
Phylum
Examples
Number of Existing Species
Nonvascular plants
Marchantiophyta
Liverworts
9000
Anthocerotophyta
Hornworts
100
Bryophyta
True mosses
15,000
Seedless vascular plants
Lycopodiophyta
Club mosses, spike mosses
1200
Pteridophyta
Whisk ferns, true ferns, horsetails
11,500
Gymnosperms
Cycadophyta
Cycads
130
Ginkgophyta
Ginkgo
1
Pinophyta
Pines, firs, and other conifers
630
Gnetophyta
Gnetophytes
80
Angiosperms
Magnoliophyta
All flowering plants, including roses, grasses, fruit trees, maples, and oaks
> 260,000
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19-53
Angiosperms produce seeds in fruits
Section 19.5
Angiosperms produce pollen and egg cells in flowers, which develop into fruit after fertilization.
Figure 19.3
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97% of angiosperms are either eudicots or monocots
Section 19.5
Scientists classify the diverse angiosperms into several groups, notably the eudicots and monocots.
The other 3% of angiosperms are a paraphyletic group called basal angiosperms.
Figure 19.14
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Most angiosperms are eudicots
Section 19.5
Eudicots have two cotyledons, which are the first leaves to emerge during germination. Their pollen grains have three pores.
Examples include roses, daisies, sunflowers, oak trees, beans, and the model organism Arabidopsis.
Figure 19.14
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Many angiosperms are monocots
Section 19.5
Monocots have one cotyledon. Their pollen grains have one pore.
Examples include orchids, lilies, grass, bananas, rice, wheat, and corn.
Figure 19.14
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Angiosperm sporophytes are large and conspicuous
Section 19.5
Trees and other familiar angiosperms we see are the sporophytes.
Figure 19.15
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Flowers are sporophyte reproductive structures in angiosperms
Section 19.4
Pollen sacs in flowers produce microspores that develop into male gametophytes.
The ovule in the flower produces megaspores that develop into the female gametophytes.
Figure 19.15
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Microscopic gametophytes get together at pollination
Section 19.5
During pollination, a grain of pollen (male gametophyte) produces a pollen tube to reach the female gametophyte.
Figure 19.15
Female gametophytes consist of one egg and a central cell that contains two polar nuclei.
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Angiosperms have double fertilization
Section 19.5
Two sperm nuclei travel through the pollen tube.
One fertilizes the egg, forming a zygote. This is the first cell of the sporophyte.
The other sperm fertilizes the central cell’s polar nuclei. This will develop into the endosperm, which feeds the embryo inside the seed.
Figure 19.15
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Seeds contain embryo and endosperm
Section 19.5
In angiosperms, the ovule develops into a seed. At the same time, the ovary that surrounds the ovule develops into a fruit.
Figure 19.15
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Angiosperm seeds germinate when conditions are favorable
Section 19.5
Seeds germinate into young sporophytes.
Figure 19.15
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Wind and animals assist angiosperm reproduction
Pollen is transported great distances by wind.
Plants with attractive nectar, petals, or bright colors co-evolved with animals that pollinate them.
Figure 19.16
b. Pollination by animals
(a, maple tree): ©Steven P. Lynch/McGraw-Hill Education; (a, cattails): ©Hans Reinhard/Okapia/Science Source; (b, chamomile): ©McGraw-Hill Education; (b, banana tree): ©Igor Prahin/Flickr Open/Getty Images RF
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