Chapter 12: Diversification of the Eukaryotes: Plants and Fungi

1. Chapter 12: Diversification of the Eukaryotes: Plants and Fungi Where did all the plants and fungi come from?

2. So plants are organisms that are fixed in place, but that's only one aspect of being a plant. A plant is a multicellular eukaryote that produces its own food by photosynthesis and has an embryo that develops within the protected environment of the female parent (Figure 12-1 Defining characteristics of a plant). Plants vary in size from less than 0.04 inches (1 mm) to 380 feet tall (117 m), and most plants live on land. � There are other organisms on earth that are multicellular and photosynthetic eukaryotes. They are the green algae, the closest relatives of plants. They differ from plants, however, in that they live only in the water or on very moist land surfaces. This is in sharp contrast with plants, which can live even in deserts.So plants are organisms that are fixed in place, but that's only one aspect of being a plant. A plant is a multicellular eukaryote that produces its own food by photosynthesis and has an embryo that develops within the protected environment of the female parent (Figure 12-1 Defining characteristics of a plant). Plants vary in size from less than 0.04 inches (1 mm) to 380 feet tall (117 m), and most plants live on land. � There are other organisms on earth that are multicellular and photosynthetic eukaryotes. They are the green algae, the closest relatives of plants. They differ from plants, however, in that they live only in the water or on very moist land surfaces. This is in sharp contrast with plants, which can live even in deserts.

3. Plant Characteristics Multicellular eukaryotes Most Plants Make Their Own Food Photosynthesis (shoots) Some are parasitic Also need Nitrogen, phosphorus, and salts Roots Plants are sessile Food needs to come to them; they need to avoid predators Most plants make their own food. However, a plant can't live on carbohydrates alone. A plant needs nitrogen to build any proteins, phosphorus to make ATP, and salts to create concentration gradients between the inside and outside of cells. Plants use roots, the part of a plant below ground which functions to obtain these needed substances from the soil. Above ground, plants have a shoot that consists of a stem and leaves. The stem is a structure that supports the main photosynthetic organ of a plant: its leaves. Most plants make their own food. However, a plant can't live on carbohydrates alone. A plant needs nitrogen to build any proteins, phosphorus to make ATP, and salts to create concentration gradients between the inside and outside of cells. Plants use roots, the part of a plant below ground which functions to obtain these needed substances from the soil. Above ground, plants have a shoot that consists of a stem and leaves. The stem is a structure that supports the main photosynthetic organ of a plant: its leaves.

4. When we think of plants, we often think of them as �chlorophyll-containing,� but some plants have no chlorophyll. Their ancestors had chlorophyll, but they have lost almost all of their chlorophyll over evolutionary time and can�t carry out photosynthesis. Instead, they live as parasites that steal nutrients from other plants. Dodder is an example of a parasitic plant that almost completely lacks chlorophyll and gets sugar instead from the plant it grows on (Figure 12-2 Dodder: a parasitic, non-photosynthetic plant). When we think of plants, we often think of them as �chlorophyll-containing,� but some plants have no chlorophyll. Their ancestors had chlorophyll, but they have lost almost all of their chlorophyll over evolutionary time and can�t carry out photosynthesis. Instead, they live as parasites that steal nutrients from other plants. Dodder is an example of a parasitic plant that almost completely lacks chlorophyll and gets sugar instead from the plant it grows on (Figure 12-2 Dodder: a parasitic, non-photosynthetic plant).

5. Plants that carry out photosynthesis need sunlight, and that creates a challenge for some plants. If a seed sprouts in the shade, the plant needs to somehow get to the nearest sunny spot. Plants can do that, of course, but not by moving. Instead, they grow toward the light. (Figure 12-3 Plants must overcome the constraint of being immobile). Sex can also be a challenge for an organism that is anchored in place by its roots. Not surprisingly plants have a sex life that is very different from that of animals. Humans and other animals have no haploid stage in their lives (other than the gametes), but many plants do. The haploid stage is the one that allows the male and female plants to reproduce, even though they will never meet because they can't move. Other plants enlist the help of animals to carry the male gamete to the female gamete. Resisting predators is another challenge for organisms that cannot move. Running away is how most animals react to a predator, but plants have found other ways to defend themselves. Thorns are an anatomical defense plants use to avoid predation. Plants also use chemicals to deter predators, as many people experience when they develop an itchy rash from poison ivy. Plants that carry out photosynthesis need sunlight, and that creates a challenge for some plants. If a seed sprouts in the shade, the plant needs to somehow get to the nearest sunny spot. Plants can do that, of course, but not by moving. Instead, they grow toward the light. (Figure 12-3 Plants must overcome the constraint of being immobile). Sex can also be a challenge for an organism that is anchored in place by its roots. Not surprisingly plants have a sex life that is very different from that of animals. Humans and other animals have no haploid stage in their lives (other than the gametes), but many plants do. The haploid stage is the one that allows the male and female plants to reproduce, even though they will never meet because they can't move. Other plants enlist the help of animals to carry the male gamete to the female gamete. Resisting predators is another challenge for organisms that cannot move. Running away is how most animals react to a predator, but plants have found other ways to defend themselves. Thorns are an anatomical defense plants use to avoid predation. Plants also use chemicals to deter predators, as many people experience when they develop an itchy rash from poison ivy.

6. The aquatic ancestors of land plants are green algae. Like plants, green algae are multicellular photosynthetic eukaryotes, but green algae live only in the water or on very moist land surfaces. As water dwellers, green algae do not require specialized structures to obtain water and nutrients; water enters their cells by osmosis and the nutrients they require are in solution in the water that surrounds them. Some green algae, such as sea lettuce and stoneworts, even look like plants, but the closest relatives of plants are some green algae that look like slime on rocks�organisms called coleochaetes (KOH-lee-oh-keets) (Figure 12-5�Plants� closest relatives: a green alga called coleochaete). An individual coleochaete is about the size of a pinhead, is only one cell thick, and can withstand exposure to air, so they survive when the water level in a lake falls and leaves them high and dry. This resistance to drying was the first step that plants took as they moved from water to land.The aquatic ancestors of land plants are green algae. Like plants, green algae are multicellular photosynthetic eukaryotes, but green algae live only in the water or on very moist land surfaces. As water dwellers, green algae do not require specialized structures to obtain water and nutrients; water enters their cells by osmosis and the nutrients they require are in solution in the water that surrounds them. Some green algae, such as sea lettuce and stoneworts, even look like plants, but the closest relatives of plants are some green algae that look like slime on rocks�organisms called coleochaetes (KOH-lee-oh-keets) (Figure 12-5�Plants� closest relatives: a green alga called coleochaete). An individual coleochaete is about the size of a pinhead, is only one cell thick, and can withstand exposure to air, so they survive when the water level in a lake falls and leaves them high and dry. This resistance to drying was the first step that plants took as they moved from water to land.

7. Colonizing land brings challenges... They weren�t impressive looking�just some patches of low-growing green stems at the water�s edge. They did not have any of the structures we associate with plants today�no roots, leaves, flowers. But from an evolutionary perspective, those early plants were enormously important because until terrestrial plants evolved there was nothing on land to eat. Thus, the first land plants not only set the stage for the tremendous diversity of plants we know today, but also paved the way for the evolution and diversification of land animals. � When plants emerged on land they faced the same two challenges that were to confront the first terrestrial animals some 25 million years later�supporting themselves against the pull of gravity and reducing evaporation so that they wouldn�t dry out. The second of these problems was the most urgent�the earliest plants did not have to grow upward, they could creep along the ground, but they did have to avoid drying out (Figure 12-6 Leaving the water). The material that protects land plants from drying is a waxy layer called the cuticle, which covers the entire surface of the plant. The cuticle is what makes leaves shiny; all terrestrial plants have a cuticle. They weren�t impressive looking�just some patches of low-growing green stems at the water�s edge. They did not have any of the structures we associate with plants today�no roots, leaves, flowers. But from an evolutionary perspective, those early plants were enormously important because until terrestrial plants evolved there was nothing on land to eat. Thus, the first land plants not only set the stage for the tremendous diversity of plants we know today, but also paved the way for the evolution and diversification of land animals. � When plants emerged on land they faced the same two challenges that were to confront the first terrestrial animals some 25 million years later�supporting themselves against the pull of gravity and reducing evaporation so that they wouldn�t dry out. The second of these problems was the most urgent�the earliest plants did not have to grow upward, they could creep along the ground, but they did have to avoid drying out (Figure 12-6 Leaving the water). The material that protects land plants from drying is a waxy layer called the cuticle, which covers the entire surface of the plant. The cuticle is what makes leaves shiny; all terrestrial plants have a cuticle.

8. The earliest land plants were the first multicellular organism to live on land; these simple non-vascular plants had no vessels to transport water and nutrients (Figure 12-4�Phylogeny of the plants). The subsequent evolution of land plants was a series of radiations of forms with characteristics that made them increasingly independent of water. The evolutionary tree of plants shows these stages clearly: first the development of vessels to conduct water from the soil through the plant, then seeds that provide nutrients to get new plants off to a good start (Gymnosperms), and finally flowers that allow plants to entice or trick insects and birds to spread the plants� male gametes (Angiosperms). We�ll look at each of these plant adaptations in this chapter. We also explore the ecologically important kingdom of fungi. Although fungi are not plants, they are very closely associated with plants. � �The earliest land plants were the first multicellular organism to live on land; these simple non-vascular plants had no vessels to transport water and nutrients (Figure 12-4�Phylogeny of the plants). The subsequent evolution of land plants was a series of radiations of forms with characteristics that made them increasingly independent of water. The evolutionary tree of plants shows these stages clearly: first the development of vessels to conduct water from the soil through the plant, then seeds that provide nutrients to get new plants off to a good start (Gymnosperms), and finally flowers that allow plants to entice or trick insects and birds to spread the plants� male gametes (Angiosperms). We�ll look at each of these plant adaptations in this chapter. We also explore the ecologically important kingdom of fungi. Although fungi are not plants, they are very closely associated with plants. � �

9. Alternation of Generations A life cycle of alternating haploid and diploid generations in which the diploid embryo is protected by the haploid female Sperm meets egg in the �female�, and develops into a diploid embryo Embryo undergoes meiosis to produce haploid spores Haploid spores grow into haploid gametophytes In order to adapt to land the non-vascular plants had to develop a method of reproduction that protected the plant embryo from drying out and provided it with a source of nutrients. The innovation that made this possible was a life cycle of alternating haploid and diploid generations in which the diploid embryo is protected by the haploid female. This alternation of generations in plants is radically different from the situation in humans and most animals. In animals, a diploid organism (the organism that you see) produces haploid gametes (that are single-celled and they remain that way, never visible to the naked eye), which, at fertilization produce a newly diploid cell that becomes multicellular, growing until we can see it. And then the process all starts again. In order to adapt to land the non-vascular plants had to develop a method of reproduction that protected the plant embryo from drying out and provided it with a source of nutrients. The innovation that made this possible was a life cycle of alternating haploid and diploid generations in which the diploid embryo is protected by the haploid female. This alternation of generations in plants is radically different from the situation in humans and most animals. In animals, a diploid organism (the organism that you see) produces haploid gametes (that are single-celled and they remain that way, never visible to the naked eye), which, at fertilization produce a newly diploid cell that becomes multicellular, growing until we can see it. And then the process all starts again.

10. Despite the limitations of diffusion, three groups of plants known as bryophytes still use diffusion to move substances, rather than having any sort of circulatory system. They are the liverworts, hornworts, and mosses. Liverworts and hornworts are small (less than an inch) simple plants that grow in moist and shady places and resemble flattened moss. Mosses are the plants you are most likely to be familiar with, and there are more than 12,000 species of mosses in habitats extending from Arctic and alpine habitats to the tropics. These bryophyte plants are called non-vascular because they do not have vessels to transport water and food. Water and nutrients are absorbed by projections from the outermost layer of cells that penetrate a few micrometers into the soil. Because these projections are so short, non-vascular plants must either live in places where the soil is always moist or become dormant when the soil surface dries out (Figure 12-7 part 1 Overview of the non-vascular plants. The plants shown here (from left, clockwise) are moss, liverwort, and hornwort). Despite the limitations of diffusion, three groups of plants known as bryophytes still use diffusion to move substances, rather than having any sort of circulatory system. They are the liverworts, hornworts, and mosses. Liverworts and hornworts are small (less than an inch) simple plants that grow in moist and shady places and resemble flattened moss. Mosses are the plants you are most likely to be familiar with, and there are more than 12,000 species of mosses in habitats extending from Arctic and alpine habitats to the tropics. These bryophyte plants are called non-vascular because they do not have vessels to transport water and food. Water and nutrients are absorbed by projections from the outermost layer of cells that penetrate a few micrometers into the soil. Because these projections are so short, non-vascular plants must either live in places where the soil is always moist or become dormant when the soil surface dries out (Figure 12-7 part 1 Overview of the non-vascular plants. The plants shown here (from left, clockwise) are moss, liverwort, and hornwort).

11. Bryophytes �Amphibians� of the plant world Non-vascular, primitive plants Cannot transport water, so need to be close to it Root-like rhizoids for anchoring Marshes, wetlands, bogs, etc. New complications for land-life Gravity Gamete travel UV, temp & wind Mosses, liverworts, hornworts

12. The life cycle of moss provides a useful example: When you look at a spongy mass of moss (or any other non-vascular plant), you see the haploid part of the life cycle (Figure 12-8 Alternation of generations in mosses). The adult moss plants are haploids�that is, they have only one set of chromosomes. There are male and female moss plants that have male and female reproductive structures located among the feathery leaves at the tips of the stems. Water collects here during rainstorms, allowing the sperm to �swim� from the male structure to fertilize eggs in the female structure. Once the egg is fertilized in the female structure, a diploid zygote is formed, and it divides to become an embryo. The embryo is sheltered within the female reproductive structure while it continues to divide by mitosis and mature. The female reproductive structure provides water and nutrients for the growing embryo, and both enlarge. Eventually the female structure elongates to such a degree that it breaks in two and forms a capsule extending over the top of the plant like a raised fist. Inside the capsule haploid spores are formed by meiosis. A spore is a single cell, containing DNA, RNA, and a few proteins. When a capsule ruptures it releases hundreds of spores. The spores that land in moist, sheltered spots grow into new male or female moss plants.The life cycle of moss provides a useful example: When you look at a spongy mass of moss (or any other non-vascular plant), you see the haploid part of the life cycle (Figure 12-8 Alternation of generations in mosses). The adult moss plants are haploids�that is, they have only one set of chromosomes. There are male and female moss plants that have male and female reproductive structures located among the feathery leaves at the tips of the stems. Water collects here during rainstorms, allowing the sperm to �swim� from the male structure to fertilize eggs in the female structure. Once the egg is fertilized in the female structure, a diploid zygote is formed, and it divides to become an embryo. The embryo is sheltered within the female reproductive structure while it continues to divide by mitosis and mature. The female reproductive structure provides water and nutrients for the growing embryo, and both enlarge. Eventually the female structure elongates to such a degree that it breaks in two and forms a capsule extending over the top of the plant like a raised fist. Inside the capsule haploid spores are formed by meiosis. A spore is a single cell, containing DNA, RNA, and a few proteins. When a capsule ruptures it releases hundreds of spores. The spores that land in moist, sheltered spots grow into new male or female moss plants.

13. Some non-vascular plants are economically or ecologically important. Peat moss is the name given to Sphagnum moss when it is harvested and sold as a soil enhancer for gardening. Peat bogs are found in many parts of the world and consist of partly decayed moss. Peat harvested from bogs is dried and burned as fuel in areas where trees are scarce, and peat bogs�such as those on the coast of Malaysia and Indonesia�are important in flood control because they can absorb enormous amounts of water during the monsoon season and release it over a period of months. (Mounds of burning peat are used to dry the barley used to produce Scotch whiskey. This gives Scotch its distinctive smoky taste.) (Figure 12-9 Uses of peat).�Some non-vascular plants are economically or ecologically important. Peat moss is the name given to Sphagnum moss when it is harvested and sold as a soil enhancer for gardening. Peat bogs are found in many parts of the world and consist of partly decayed moss. Peat harvested from bogs is dried and burned as fuel in areas where trees are scarce, and peat bogs�such as those on the coast of Malaysia and Indonesia�are important in flood control because they can absorb enormous amounts of water during the monsoon season and release it over a period of months. (Mounds of burning peat are used to dry the barley used to produce Scotch whiskey. This gives Scotch its distinctive smoky taste.) (Figure 12-9 Uses of peat).�

14. Vascular tissue is a sort of infrastructure of tubes that begins in the roots and extends up the stem of a plant and out to the farthest tips of its leaves. The evolution of vascular tissue allowed early land plants to transport water and nutrients faster and more effectively than relying on diffusion from cell to cell as non-vascular plants do, and their roots penetrate far enough into the soil to reach moisture even when the soil surface is dry. Also, roots that reach deep into the soil provide the support that a plant needs to grow upward without falling over. Vascular plants can grow taller than non-vascular plants and are more successful in areas where the surface of the ground dries out between rainstorms (Figure 12-10 Snapshot of the vascular plants: ferns and horsetails. These are the groups of vascular plants that don�t produce seeds. The plants shown (from left, clockwise) are Christmas fern, horsetails, and ferns in a forest).Vascular tissue is a sort of infrastructure of tubes that begins in the roots and extends up the stem of a plant and out to the farthest tips of its leaves. The evolution of vascular tissue allowed early land plants to transport water and nutrients faster and more effectively than relying on diffusion from cell to cell as non-vascular plants do, and their roots penetrate far enough into the soil to reach moisture even when the soil surface is dry. Also, roots that reach deep into the soil provide the support that a plant needs to grow upward without falling over. Vascular plants can grow taller than non-vascular plants and are more successful in areas where the surface of the ground dries out between rainstorms (Figure 12-10 Snapshot of the vascular plants: ferns and horsetails. These are the groups of vascular plants that don�t produce seeds. The plants shown (from left, clockwise) are Christmas fern, horsetails, and ferns in a forest).

15. Pterophytes Seedless, primitive vascular plants Vascular system allows for vertical & horizontal growth True roots & vascular tissues for liquid transport Gametes STILL NEED WATER to travel Ferns, horsetails, club mosses Taller, but still low lying Still prefer moist environments

16. Like non-vascular plants, ferns and horsetails reproduce with spores. In many ferns, the structures in which haploid spores are produced are called sporangia, and are located on the underside of the leaves, and some species have sporangia that branch from the fronds or grow from the base of the plant. Because horsetails and ferns are taller than non-vascular plants, the spores can be blown by the wind when they are released and they may settle some distance from the parent plant. This increased dispersal ability represented an important adaptation�the non-vascular plants are so low-growing that wind can play little role in moving their spores. A spore that lands on moist soil grows into a tiny heart-shaped structure called a prothallus, which is the free-living haploid life stage of a fern (Figure 12-11 Haploid and diploid life stages in ferns). The prothallus has cells that produce haploid eggs (with one set of chromosomes) and other cells that produce sperm (also with one set of chromosomes). Sperm �swim� through drops of rain water to fertilize an egg, and the fertilized egg (a zygote with two sets of chromosomes) grows into an adult fern.Like non-vascular plants, ferns and horsetails reproduce with spores. In many ferns, the structures in which haploid spores are produced are called sporangia, and are located on the underside of the leaves, and some species have sporangia that branch from the fronds or grow from the base of the plant. Because horsetails and ferns are taller than non-vascular plants, the spores can be blown by the wind when they are released and they may settle some distance from the parent plant. This increased dispersal ability represented an important adaptation�the non-vascular plants are so low-growing that wind can play little role in moving their spores. A spore that lands on moist soil grows into a tiny heart-shaped structure called a prothallus, which is the free-living haploid life stage of a fern (Figure 12-11 Haploid and diploid life stages in ferns). The prothallus has cells that produce haploid eggs (with one set of chromosomes) and other cells that produce sperm (also with one set of chromosomes). Sperm �swim� through drops of rain water to fertilize an egg, and the fertilized egg (a zygote with two sets of chromosomes) grows into an adult fern.

17. 12.5 What is a seed? The evolutionary development of vascular tissue allowed plants to grow large. Suddenly, plants could colonize areas where the soil at the surface of the ground was not always wet because their roots could penetrate the soil to reach water and nutrients. The next big innovation in plant evolution was the seed, an embryonic plant with its own supply of water and nutrients encased within a protective coating (Figure 12-12 What is a seed?). Seeds contain the materials needed to begin a new life. Unlike spores�which are single cells that contain only DNA, RNA, and a few proteins�seeds contain both a multicellular embryo and a store of carbohydrate, called endosperm, that can fuel the seed�s initial growth. A seedling draws energy from the endosperm while it extends its leaves upward to begin photosynthesis and its roots downward into the soil to reach water and nutrients. There are two modern groups of seed producing plants: gymnosperms (including pines, firs, and redwoods) and angiosperms (all of the flowering plants and trees). The evolutionary development of vascular tissue allowed plants to grow large. Suddenly, plants could colonize areas where the soil at the surface of the ground was not always wet because their roots could penetrate the soil to reach water and nutrients. The next big innovation in plant evolution was the seed, an embryonic plant with its own supply of water and nutrients encased within a protective coating (Figure 12-12 What is a seed?). Seeds contain the materials needed to begin a new life. Unlike spores�which are single cells that contain only DNA, RNA, and a few proteins�seeds contain both a multicellular embryo and a store of carbohydrate, called endosperm, that can fuel the seed�s initial growth. A seedling draws energy from the endosperm while it extends its leaves upward to begin photosynthesis and its roots downward into the soil to reach water and nutrients. There are two modern groups of seed producing plants: gymnosperms (including pines, firs, and redwoods) and angiosperms (all of the flowering plants and trees).

18. How are seeds formed? The gametophyte a life stage that produces haploid gametes Pollen grains and ovules Pollen produces a pollen tube that grows into the ovule. The external layer of the ovule forms the seed coat. Seed plants have a life stage that produces haploid gametes (sperm and egg). Botanists call this haploid form the gametophyte. Pollen grains and ovules are the male and female gametophytes of seed plants. A haploid female gamete (egg) forms inside the ovule. When a pollen grain lands near the ovule, it produces a pollen tube that grows into the ovule. Sperm from the pollen grain move through the pollen tube into the ovule and fertilize the egg. The external layer of the ovule forms the seed coat. �Seed plants have a life stage that produces haploid gametes (sperm and egg). Botanists call this haploid form the gametophyte. Pollen grains and ovules are the male and female gametophytes of seed plants. A haploid female gamete (egg) forms inside the ovule. When a pollen grain lands near the ovule, it produces a pollen tube that grows into the ovule. Sperm from the pollen grain move through the pollen tube into the ovule and fertilize the egg. The external layer of the ovule forms the seed coat. �

19. Seed Dispersal Only opportunity most plants have to send their offspring away from home Seeds and seed pods have many ways to do this: forceful send-off of exploding seed pods seeds that hitch rides on passing animals seeds that float in water or almost fly One of the challenges plants face is dispersing their seeds. The seed stage is the only opportunity most plants have to send their offspring away from home, and seeds and seed pods have many ways to do this. These range from the forceful send-off of exploding seed pods, to seeds that hitch rides on passing animals, to those that are so small and light that they can float in water or almost fly (think of dandelions). One of the challenges plants face is dispersing their seeds. The seed stage is the only opportunity most plants have to send their offspring away from home, and seeds and seed pods have many ways to do this. These range from the forceful send-off of exploding seed pods, to seeds that hitch rides on passing animals, to those that are so small and light that they can float in water or almost fly (think of dandelions).

20. Gymnosperms include four major groups, the confers, cycads, gnetophytes, and the ginkgo. All of the approximately 800 species of gymnosperms are seed-bearing plants that produce ovules on the edge of a cone-like structure. If you were a dinosaur living in the middle of the Mesozoic period, 200 million years ago, the forests you walked through would consist entirely of gymnosperms�pine trees, redwoods, cycads, and their relatives. Flowering plants (angiosperms) would not appear for another 100 million years. Indeed, when it comes to population sizes, the range of habitats in which they can thrive, pine trees and their relatives are among the most evolutionary successful groups of plants on Earth, growing on every ice-free continent and extending from sea level to the tree-line on mountains (Figure 12-13 part 1 Overview of the gymnosperms: non-flowering plants with seeds. Shown (from left) are ginkgo, Douglas fir, welwitschia, and cycad).Gymnosperms include four major groups, the confers, cycads, gnetophytes, and the ginkgo. All of the approximately 800 species of gymnosperms are seed-bearing plants that produce ovules on the edge of a cone-like structure. If you were a dinosaur living in the middle of the Mesozoic period, 200 million years ago, the forests you walked through would consist entirely of gymnosperms�pine trees, redwoods, cycads, and their relatives. Flowering plants (angiosperms) would not appear for another 100 million years. Indeed, when it comes to population sizes, the range of habitats in which they can thrive, pine trees and their relatives are among the most evolutionary successful groups of plants on Earth, growing on every ice-free continent and extending from sea level to the tree-line on mountains (Figure 12-13 part 1 Overview of the gymnosperms: non-flowering plants with seeds. Shown (from left) are ginkgo, Douglas fir, welwitschia, and cycad).

21. Pines, spruces, firs, redwoods, and their relatives�collectively, the conifers�are the most familiar gymnosperms, at least to residents of the temperate regions, and they all have needle-like leaves, but that is not true of all gymnosperms. The ginkgo has distinctive fan-shaped leaves that are nearly identical in size and shape to fossils of ginkgo leaves. Cycads have palm-like fronds with many small leaflets, and these too are nearly identical to fossils from the Mesozoic. Figure 12-14 Major groups of gymnosperms: conifers, cycads, gnetophytes, and ginkgos. � Pines, spruces, firs, redwoods, and their relatives�collectively, the conifers�are the most familiar gymnosperms, at least to residents of the temperate regions, and they all have needle-like leaves, but that is not true of all gymnosperms. The ginkgo has distinctive fan-shaped leaves that are nearly identical in size and shape to fossils of ginkgo leaves. Cycads have palm-like fronds with many small leaflets, and these too are nearly identical to fossils from the Mesozoic. Figure 12-14 Major groups of gymnosperms: conifers, cycads, gnetophytes, and ginkgos. �

22. Gymnosperms The first seed plants � �Naked Seed� Replaced ferns as dominant plants Sperm transfer by pollen increased reproductive success Coniferous trees � Pines, Firs, Spruce Seeds � Multicellular �packages� of embryo, food & protection

23. The reproductive structures of gymnosperms�the cones�are male or female. The pine cones you are familiar with are the female cones, and these produce the seeds (Figure 12-15 Cones are the reproductive structures of gymnosperms). The male cones are smaller and release pollen that is blown by the wind to the ovules, which lie beneath the protruding scales of the female cones. The quantity of pollen released by conifers is beyond imagination�the air in a pine forest becomes hazy and every surface becomes coated with the yellow pollen. Wind dispersal of pollen is clearly an inefficient method of pollination�billions of pollen grains are wasted for each grain that lands on a female cone and produces sperm to fertilize an egg in an ovule. Nonetheless, this �brute force� method of ensuring fertilization works: pines have been using wind pollination successfully for more than 200 million years. �The reproductive structures of gymnosperms�the cones�are male or female. The pine cones you are familiar with are the female cones, and these produce the seeds (Figure 12-15 Cones are the reproductive structures of gymnosperms). The male cones are smaller and release pollen that is blown by the wind to the ovules, which lie beneath the protruding scales of the female cones. The quantity of pollen released by conifers is beyond imagination�the air in a pine forest becomes hazy and every surface becomes coated with the yellow pollen. Wind dispersal of pollen is clearly an inefficient method of pollination�billions of pollen grains are wasted for each grain that lands on a female cone and produces sperm to fertilize an egg in an ovule. Nonetheless, this �brute force� method of ensuring fertilization works: pines have been using wind pollination successfully for more than 200 million years. �

24. When the pollen (the haploid sperm) arrive at the female cones, a pollen tube forms transporting the sperm to the ovule where fertilization occurs and a diploid embryo begins to grow. The embryo develops slowly within the female cone over the course of many months until the scales of the cone open and release the seed, ready to sprout into a new plant (Figure 12-16 Assisted by the wind: the life cycle of the gymnosperms). � The evolution of seeds by gymnosperms almost completely eliminates the haploid life stage that we saw in mosses and ferns. Non-vascular plants spend most of their lives in the haploid stage of their cycle, and ferns produce spores that grow into free-living haploid plants. With the appearance of gymnosperms, plants developed a life history with no free-living haploid stage. �When the pollen (the haploid sperm) arrive at the female cones, a pollen tube forms transporting the sperm to the ovule where fertilization occurs and a diploid embryo begins to grow. The embryo develops slowly within the female cone over the course of many months until the scales of the cone open and release the seed, ready to sprout into a new plant (Figure 12-16 Assisted by the wind: the life cycle of the gymnosperms). � The evolution of seeds by gymnosperms almost completely eliminates the haploid life stage that we saw in mosses and ferns. Non-vascular plants spend most of their lives in the haploid stage of their cycle, and ferns produce spores that grow into free-living haploid plants. With the appearance of gymnosperms, plants developed a life history with no free-living haploid stage. �

25. The appearance of flowering plants (angiosperms) in the Cretaceous period (about 100 million years ago) set the stage for the botanical world we know today, with flowering trees, flowering bushes, and all the herbaceous (non-woody) plants and the grasses we see around us. The vast majority of plants on earth are flowering plants in the angiosperm group. Many of the early flowering plants would look familiar to us, and angiosperms dominate the plant world now, with some 250,000 species compared to the approximately 800 species of gymnosperms. Figure 12-18 Snapshot of the angiosperms. The angiosperms shown here (from left) are water lily, apple tree, Gewurztraminer grapes, and rhododendron in a forest.The appearance of flowering plants (angiosperms) in the Cretaceous period (about 100 million years ago) set the stage for the botanical world we know today, with flowering trees, flowering bushes, and all the herbaceous (non-woody) plants and the grasses we see around us. The vast majority of plants on earth are flowering plants in the angiosperm group. Many of the early flowering plants would look familiar to us, and angiosperms dominate the plant world now, with some 250,000 species compared to the approximately 800 species of gymnosperms. Figure 12-18 Snapshot of the angiosperms. The angiosperms shown here (from left) are water lily, apple tree, Gewurztraminer grapes, and rhododendron in a forest.

26. Angiosperms Flowering plants, food crops, all trees (except conifers), grasses, cacti Similar to sexual reproduction of gymnosperms Seeds are protected in outer layer of fruit Added attraction for seed dispersal Nutritious Endosperm tissue Flowers attract pollinators (Birds, insects) Now dominant plant group on Earth ~ 260,00 species to gymnosperms� 700 species

27. Flowers come in a bewildering variety of sizes, shapes, and colors but they all have the similar structures: a supporting stem with modified leaves�the flashy petals�and sepals, which are (usually) a green wrapping that encloses the flower while it is a bud. Most plants combine the male and female reproductive structures in the same flowers. The male structure is called the stamen and includes the anther, which produces the pollen, and its supporting stalk, the filament. The female reproductive structure within the flower is called the carpel and is made up of the pistil, which has an enclosed chamber called the ovary at its base containing one or more ovules in which eggs develop; a stalk (the style) extending from the ovary; and a sticky tip (the stigma). Figure 12-19 A flower houses a plant�s reproductive structures. Flowers come in a bewildering variety of sizes, shapes, and colors but they all have the similar structures: a supporting stem with modified leaves�the flashy petals�and sepals, which are (usually) a green wrapping that encloses the flower while it is a bud. Most plants combine the male and female reproductive structures in the same flowers. The male structure is called the stamen and includes the anther, which produces the pollen, and its supporting stalk, the filament. The female reproductive structure within the flower is called the carpel and is made up of the pistil, which has an enclosed chamber called the ovary at its base containing one or more ovules in which eggs develop; a stalk (the style) extending from the ovary; and a sticky tip (the stigma). Figure 12-19 A flower houses a plant�s reproductive structures.

28. A small number of angiosperm species achieve pollination by simply releasing their pollen to the wind, like the gymnosperms, or into water on the slim chance that through random luck, some of the pollen will land on the female reproductive organs of another plant. Given the astronomically low probability of any one pollen grain actually doing that, such wind and water pollinated plants respond in the only reasonable way: they produce tremendous amounts, in the tens of millions, of pollen grains per plant. Most angiosperms have a different way of moving pollen from the anthers of one flower to the stigma of another: they use animals to carry it�. Figure 12-20 Delivering precious cargo (inadvertently). The bee in this photo is completely covered in yellow pollen grains.A small number of angiosperm species achieve pollination by simply releasing their pollen to the wind, like the gymnosperms, or into water on the slim chance that through random luck, some of the pollen will land on the female reproductive organs of another plant. Given the astronomically low probability of any one pollen grain actually doing that, such wind and water pollinated plants respond in the only reasonable way: they produce tremendous amounts, in the tens of millions, of pollen grains per plant. Most angiosperms have a different way of moving pollen from the anthers of one flower to the stigma of another: they use animals to carry it�. Figure 12-20 Delivering precious cargo (inadvertently). The bee in this photo is completely covered in yellow pollen grains.

29. Why are flowers so flashy? Trickery and Bribery To assure that animals will be willing to visit a flower with their pollen cargo, two different and clever strategies for achieving pollination have evolved among the flowering plants: 1) Trickery: The plant deceives some animals into carrying their pollen from one plant to another. 2) Bribery: The plant bribes some animals to carry their pollen from one plant to another. To assure that animals will be willing to visit a flower with their pollen cargo, two different and clever strategies for achieving pollination have evolved among the flowering plants: 1) Trickery: The plant deceives some animals into carrying their pollen from one plant to another. 2) Bribery: The plant bribes some animals to carry their pollen from one plant to another.

30. 1) Trickery Plant deceit! Orchid species flowers that resemble female wasps Male wasps �riding a bucking bronco� 1) Trickery The plant deceives some animals into carrying their pollen from one plant to another. Among the tricksters are some orchid species that achieve pollination by producing flowers that resemble female wasps. The mimicry is so good that male wasps actually mount the flower and attempt to fly off and mate with it. Because the flower is attached to the plant, however, the male wasp resembles a cowboy riding a bucking bronco, twirling wildly on the flower and repeatedly whacking his head onto the strategically located anthers. In the process he doesn't end up having any reproductive success but he does succeed in getting pollen stuck all over his face and body. That is not enough for the plant to achieve pollination, but it�s a start. If that male wasp gets fooled again by a flower on another orchid, when he mounts that flower and tries to mate he will inadvertently deposit some of the pollen from his body onto the also-strategically-placed stigma of that flower. In the end, the wasp looks a bit foolish and does not gain from his actions, but the orchids have evolved an effective system of pollination. 1) Trickery The plant deceives some animals into carrying their pollen from one plant to another. Among the tricksters are some orchid species that achieve pollination by producing flowers that resemble female wasps. The mimicry is so good that male wasps actually mount the flower and attempt to fly off and mate with it. Because the flower is attached to the plant, however, the male wasp resembles a cowboy riding a bucking bronco, twirling wildly on the flower and repeatedly whacking his head onto the strategically located anthers. In the process he doesn't end up having any reproductive success but he does succeed in getting pollen stuck all over his face and body. That is not enough for the plant to achieve pollination, but it�s a start. If that male wasp gets fooled again by a flower on another orchid, when he mounts that flower and tries to mate he will inadvertently deposit some of the pollen from his body onto the also-strategically-placed stigma of that flower. In the end, the wasp looks a bit foolish and does not gain from his actions, but the orchids have evolved an effective system of pollination.

31. 2) Bribery Plants offer something of value for pollen transport. Requires: a sticky pollen a flower that catches the attention of the pollinator something of value to the pollinator. 2) Bribery The plant bribes some animals to carry their pollen from one plant to another. This more common plant strategy for achieving pollination involves the plant offering something of value to the animal. In order for this bribery method of pollination to work, the plant must produce: a) a sticky pollen, b) a flower that catches the attention of the pollinator and, most importantly, c) something of value to the pollinator. The payoff can be food, such as nutritious nectar rich in sugars and amino acids, or it may be a safe hospitable location for an insect to lay eggs. 2) Bribery The plant bribes some animals to carry their pollen from one plant to another. This more common plant strategy for achieving pollination involves the plant offering something of value to the animal. In order for this bribery method of pollination to work, the plant must produce: a) a sticky pollen, b) a flower that catches the attention of the pollinator and, most importantly, c) something of value to the pollinator. The payoff can be food, such as nutritious nectar rich in sugars and amino acids, or it may be a safe hospitable location for an insect to lay eggs.

32. The variety of flower structures is tremendous. They differ in shape, color, smell, time of day during which they are open, whether they produce nectar, and whether their pollen is edible. And just as the variety of flower types is wide, so too is the variety of pollinators great: birds (mostly hummingbirds), bees, flies, beetles, butterflies, moths, and even some mammals (mostly bats) (Figure 12-21 Evolving together: plants and pollinators). In each case there has been strong coevolution between the plants and their pollinators: the plants get more and more effective at attracting the pollinators and deterring other species from visiting the flower, whereas the pollinators get more and more effective at exploiting the resources offered by the plants. Because of this strong coevolution between the plant and animal species, we can now discern much about the pollinator of a particular species of plant simply by examining the flowers. In most cases, you can determine with certainty the type of animal that will pollinate a flower just by examining its features.The variety of flower structures is tremendous. They differ in shape, color, smell, time of day during which they are open, whether they produce nectar, and whether their pollen is edible. And just as the variety of flower types is wide, so too is the variety of pollinators great: birds (mostly hummingbirds), bees, flies, beetles, butterflies, moths, and even some mammals (mostly bats) (Figure 12-21 Evolving together: plants and pollinators). In each case there has been strong coevolution between the plants and their pollinators: the plants get more and more effective at attracting the pollinators and deterring other species from visiting the flower, whereas the pollinators get more and more effective at exploiting the resources offered by the plants. Because of this strong coevolution between the plant and animal species, we can now discern much about the pollinator of a particular species of plant simply by examining the flowers. In most cases, you can determine with certainty the type of animal that will pollinate a flower just by examining its features.

33. When we left off, a pollen grain�which will deliver the haploid male gamete�had just been delivered to the stigma, the female reproductive structure. The pollen grain forms a pollen tube that extends downward through the stigma to the ovary, and ultimately enters an ovule. The pollen grain forms two haploid sperm by mitosis that move down the pollen tube (Figure 12-22 Double fertilization fortifies the seeds of angiosperms). � When the pollen tube reaches the ovule, one of the two sperm fuses with the egg to form a zygote. The other sperm fuses with two cells in the middle of the ovule to form endosperm, which has three sets of chromosomes (called triploid). The process is called double fertilization because two sperm enter the ovule and combine with haploid female cells to form a zygote (with two sets of chromosomes) and an endosperm (with three sets of chromosomes). The final steps in producing a seed occur as the diploid zygote cell undergoes multiple mitotic divisions to form an embryo, while the triploid cells multiply mitotically to produce the endosperm, which will provide nutritional support for the seeding through its initial growth stages. � When we left off, a pollen grain�which will deliver the haploid male gamete�had just been delivered to the stigma, the female reproductive structure. The pollen grain forms a pollen tube that extends downward through the stigma to the ovary, and ultimately enters an ovule. The pollen grain forms two haploid sperm by mitosis that move down the pollen tube (Figure 12-22 Double fertilization fortifies the seeds of angiosperms). � When the pollen tube reaches the ovule, one of the two sperm fuses with the egg to form a zygote. The other sperm fuses with two cells in the middle of the ovule to form endosperm, which has three sets of chromosomes (called triploid). The process is called double fertilization because two sperm enter the ovule and combine with haploid female cells to form a zygote (with two sets of chromosomes) and an endosperm (with three sets of chromosomes). The final steps in producing a seed occur as the diploid zygote cell undergoes multiple mitotic divisions to form an embryo, while the triploid cells multiply mitotically to produce the endosperm, which will provide nutritional support for the seeding through its initial growth stages. �

34. Two Advantages of Double Fertilization Initiates formation of endosperm only when an egg is fertilized Smaller gametes can be produced ensures that seeds are produced quickly Double fertilization initiates formation of endosperm only when an egg is fertilized, whereas gymnosperms use hundreds of haploid female cells to make the endosperm before fertilization occurs. Waiting to be sure that an egg is fertilized is a good strategy because making endosperm is a large energy investment for a plant. Gymnosperms invest that energy up front, and the endosperm in ovules that are not fertilized is wasted because those seeds do not contain an embryo. In contrast, angiosperms do not waste energy forming endosperm in ovules that will not contain embryos. Angiosperms can produce smaller gametes than gymnosperms because the large energetic reserves will be produced only after fertilization occurs. The small size of the male and female gametes of angiosperms ensures that seeds are produced quickly. Double fertilization initiates formation of endosperm only when an egg is fertilized, whereas gymnosperms use hundreds of haploid female cells to make the endosperm before fertilization occurs. Waiting to be sure that an egg is fertilized is a good strategy because making endosperm is a large energy investment for a plant. Gymnosperms invest that energy up front, and the endosperm in ovules that are not fertilized is wasted because those seeds do not contain an embryo. In contrast, angiosperms do not waste energy forming endosperm in ovules that will not contain embryos. Angiosperms can produce smaller gametes than gymnosperms because the large energetic reserves will be produced only after fertilization occurs. The small size of the male and female gametes of angiosperms ensures that seeds are produced quickly.

35. Figure 12-23 (Overview of the haploid and diploid stages of plant life cycles) shows that as plants have evolved different reproductive strategies, their haploid gametes have become progressively smaller in size�. Rapid production of seeds allows angiosperms to grow as annual plants (i.e., plants that complete their life cycle from sprouting to seed production in one growing season), which is something gymnosperms cannot do. Figure 12-23 (Overview of the haploid and diploid stages of plant life cycles) shows that as plants have evolved different reproductive strategies, their haploid gametes have become progressively smaller in size�. Rapid production of seeds allows angiosperms to grow as annual plants (i.e., plants that complete their life cycle from sprouting to seed production in one growing season), which is something gymnosperms cannot do.

36. Because plants can�t run away from plant-eating animals, they have evolved a host of defensive devices that fall into two categories: 1) anatomical structures like thorns and 2) chemical compounds, including hallucinogens (Figure 12-25 Spines, sticky traps, and toxic compounds). � Spines, spikes, and thorns are a common way to discourage herbivores. The acacias, a group of plants that grow as large bushes or small trees, are notoriously thorny. Thorns on palm fronds carry pathogenic bacteria that infect the wounds the thorns create and provide a long-lasting reminder that it�s not a good idea to try to eat a palm frond. The surfaces of leaves and stems have microscopic spikes called trichomes. Most trichomes protect plants against insects by exuding a sticky fluid that traps the insect, but stinging plants like nettles use larger trichomes to inject a potent fluid into any animal that brushes against a leaf. Many chemical defenses are substances that make plants bitter or otherwise unpalatable, but some plants play hardball by producing chemicals that affect the nervous or reproductive systems of animals that eat them. Locoweeds, which occur all over western North America, contain substances called alkaloids that can cause permanent damage to the nervous system. When cattle and horses eat locoweed they become lethargic and stop feeding. Other defensive chemicals are hallucinogens. Tetrahydrocannabinol or THC is found in the leaves and buds of marijuana plants, and the disorientation it produces causes mammals to stop eating.Because plants can�t run away from plant-eating animals, they have evolved a host of defensive devices that fall into two categories: 1) anatomical structures like thorns and 2) chemical compounds, including hallucinogens (Figure 12-25 Spines, sticky traps, and toxic compounds). � Spines, spikes, and thorns are a common way to discourage herbivores. The acacias, a group of plants that grow as large bushes or small trees, are notoriously thorny. Thorns on palm fronds carry pathogenic bacteria that infect the wounds the thorns create and provide a long-lasting reminder that it�s not a good idea to try to eat a palm frond. The surfaces of leaves and stems have microscopic spikes called trichomes. Most trichomes protect plants against insects by exuding a sticky fluid that traps the insect, but stinging plants like nettles use larger trichomes to inject a potent fluid into any animal that brushes against a leaf. Many chemical defenses are substances that make plants bitter or otherwise unpalatable, but some plants play hardball by producing chemicals that affect the nervous or reproductive systems of animals that eat them. Locoweeds, which occur all over western North America, contain substances called alkaloids that can cause permanent damage to the nervous system. When cattle and horses eat locoweed they become lethargic and stop feeding. Other defensive chemicals are hallucinogens. Tetrahydrocannabinol or THC is found in the leaves and buds of marijuana plants, and the disorientation it produces causes mammals to stop eating.

37. Watch out for this �big gulp�! About 900 species of plants turn the tables and eat insects to supplement the nitrogen compounds they get from the soil. Insectivorous plants are most common in boggy areas because boggy soil often has low nitrogen concentrations, so the plants get nitrogen from consuming the proteins in insects (Figure 12-26 Carnivorous plants feed on insects). Pitcher plants are an example�their name comes from conspicuous funnel-shaped pitchers that capture insects. It�s easy for an insect to enter the open top of a pitcher, but hard to get out because the inner walls are lined with hair-like structures that point downward forcing the insect into a pool of liquid. Some pitcher plants merely absorb the nitrogen that is released when the trapped insects decay, but other species secrete digestive enzymes into the pool. These enzymes, which are basically the same as the enzymes in your stomach, digest the insects and make the nitrogen available more rapidly. �Watch out for this �big gulp�! About 900 species of plants turn the tables and eat insects to supplement the nitrogen compounds they get from the soil. Insectivorous plants are most common in boggy areas because boggy soil often has low nitrogen concentrations, so the plants get nitrogen from consuming the proteins in insects (Figure 12-26 Carnivorous plants feed on insects). Pitcher plants are an example�their name comes from conspicuous funnel-shaped pitchers that capture insects. It�s easy for an insect to enter the open top of a pitcher, but hard to get out because the inner walls are lined with hair-like structures that point downward forcing the insect into a pool of liquid. Some pitcher plants merely absorb the nitrogen that is released when the trapped insects decay, but other species secrete digestive enzymes into the pool. These enzymes, which are basically the same as the enzymes in your stomach, digest the insects and make the nitrogen available more rapidly. �