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

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Presentation on theme: "Overview: Feeding the World Seeds changed the course of plant evolution, enabling their bearers to become the dominant producers in most terrestrial ecosystems."— Presentation transcript:

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) Gametophyte (n) Sporophyte dependent on gametophyte (mosses and other bryophytes) Gametophyte (n) Sporophyte (2n) Large sporophyte and small, independent game- tophyte (ferns and other seedless vascular plants) Microscopic female gametophytes (n) in ovulate cones (dependent) Microscopic male gametophytes (n) in inside these parts of flowers (dependent) Sporophyte (2n), the flowering plant (independent) 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 Integument Megasporangium (2n) Megaspore (n) Unfertilized ovule Fertilized ovule Spore wall Male gametophyte (within germinating pollen grain) (n) Micropyle Female gametophyte (n) Egg nucleus (n) Discharged sperm nucleus (n) Pollen grain (n) Seed coat (derived from integument) Embryo (2n) (new sporophyte) Gymnosperm seed Food supply (female gametophyte tissue) (n)

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

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

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

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

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 Archaefructus sinensis, a 125-million-year-old fossil 5 cm 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 Amborella trichopoda Water lily (Nymphaea “Rene Gerald”) Star anise (Illicium floridanum) BASAL ANGIOSPERMS

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

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

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

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

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

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

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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.

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? a)seeds, vascular tissue, flowers, cuticle b)cuticle, seeds, flowers, vascular tissue c)cuticle, vascular tissue, seeds, flowers d)vascular tissue, cuticle, seeds, flowers

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? a)seeds, vascular tissue, flowers, cuticle b)cuticle, seeds, flowers, vascular tissue c)cuticle, vascular tissue, seeds, flowers d)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

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

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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

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

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. 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

76 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.

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.


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