1. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Chapter 30 Plant Diversity II: The Evolution of Seed Plants

2. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Overview: Feeding the World Seeds changed the course of plant evolution, enabling their bearers to become the dominant producers in most terrestrial ecosystems

3. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Seeds and pollen grains are key for life on land In addition to seeds, the following are common to all seed plants: 1.Reduced gametophytes 2.Heterospory 3.Ovules 4.Pollen

4. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 1. Advantages of Reduced Gametophytes Seed plant gametophytes are miniaturized and shielded from UV radiation and desiccation by sporophyte tissue

5. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 2. Heterospory: The Rule Among Seed Plants Seedless plants produce only one type of spore that gives rise to a bisexual gametophyte (homosporous) Seed plants evolved to be heterosporous – Megasporangia produce megaspores that give rise to female gametophytes – Microsporangia produce microspores that give rise to male gametophytes

6. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 3. 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

7. 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)

8. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 4. Pollen and Production of Sperm Microspores develop into pollen grains, which contain the male gametophytes in a pollen wall 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

9. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Evolutionary Advantage of Seeds The whole ovule develops into a seed – The seed contains the embryo, food supply, and protective coat (integument)

10. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Gymnosperms bear “naked” seeds, typically on cones The gymnosperms include four phyla: 1.Cycadophyta (cycads) 2.Gingkophyta (one living species: Ginkgo biloba) 3.Gnetophyta (three genera: Gnetum, Ephedra, Welwitschia) 4.Coniferophyta (conifers, such as pine, fir, and redwood)

11. Cycad Cycas revoluta

12. Gnetophyte 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.

13. Gnetophyte 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.

14. Gnetophyte 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.

15. Confir 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.

16. Conifer 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.

17. Conifer 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.

18. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

19. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A Closer Look at the Life Cycle of a Conifer 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

20. 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)

21. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

22. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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: 1.Sepals: enclose the flower 2.Petals: brightly colored and attract pollinators 3.Stamens: produce pollen 4.Carpels: produce ovules

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

24. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

25. 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

26. 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.

27. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 female nuclei to form the endosperm, which nourishes the developing embryo

28. 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

29. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Angiosperm Diversity The two main groups of angiosperms are monocots and eudicots

30. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Characteristics of Monocots and Eudicots

31. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Evolutionary Links Between Angiosperms and Animals Pollination of flowers by animals and transport of seeds by animals are two important relationships in terrestrial ecosystems A flower pollinated by honeybees. A flower pollinated by hummingbirds. A flower pollinated by nocturnal animals.

32. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

33. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

34. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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