28 Green Algae and Land Plants Lecture Presentation by Cindy S. Malone, PhD, California State University Northridge 2017 Pearson Education, Inc. Chapter 28 Opening Roadmap. 2017 Pearson Education, Inc. Introduction
The Viridiplantae, or green plants, consist of the green algae and land plants Green algae are important photosynthetic organisms in freshwater habitats Land plants are the key photosynthesizers in terrestrial environments 2017 Pearson Education, Inc. Introduction Green algae have traditionally been considered protists, but we study them along with land plants for two reasons: 1. They are the closest living relatives to land plants 2. The transition from aquatic to terrestrial life occurred
when land plants evolved from green algae 2017 Pearson Education, Inc. Introduction Land plants were the first organisms that could thrive with their tissues completely exposed to the air Before land plants evolved, terrestrial life was limited to bacteria, archaea, and single-celled protists Plants transformed the nature of life on Earth 2017 Pearson Education, Inc. Why Do Biologists Study Green Plants?
Biologists study plants not only because they are fascinating organisms but also because we could not live without them People rely on plants for food, fuel, the fibers used to make clothing and other products, building materials, and pharmaceuticals Agriculture, forestry, and horticulture are among the most important industries based on plants 2017 Pearson Education, Inc. Why Do Biologists Study Green Plants? Biologists also study plants that cause problems for humans: Weeds that decrease crop productivity
Newly introduced species that invade and then degrade natural areas 2017 Pearson Education, Inc. Plants Provide Ecosystem Services An ecosystem consists of All of the organisms in a particular area Nonliving physical components of the environment, such as The atmosphere Sunlight Precipitation
Soil Surface water Nutrients 2017 Pearson Education, Inc. Plants Provide Ecosystem Services Ecosystem services provided by green algae and land plants include Producing oxygen via oxygenic photosynthesis Building soil by providing food for decomposers Holding soil and preventing nutrients from being lost
to wind or water erosion Holding water in the soil Moderating the local climate by providing shade and reducing the impact of wind on landscapes 2017 Pearson Education, Inc. Figure 28.1 2017 Pearson Education, Inc. Plants Are Primary Producers Land plants are the dominant primary producers in terrestrial ecosystems They convert energy in sunlight into chemical energy The sugars produced by land plants support virtually
all other organisms in terrestrial habitats 2017 Pearson Education, Inc. Plants Are Primary Producers Land plants are the key to the carbon cycle Take CO2 from the atmosphere and reduce it to make sugars Fix much more CO2 than they release The loss of plant-rich prairies has contributed to increased concentrations of CO2 in the atmosphere Partly responsible for rising temperatures associated with global climate change
2017 Pearson Education, Inc. Plants Provide Humans with Food, Fuel, Fiber, Building Materials, and Medicines Food Agricultural research began with the initial domestication of crop plants Artificial selection for plants with certain properties has led to dramatic changes in plant characteristics 2017 Pearson Education, Inc. Figure 28.2 (a) Plants were domesticated at an array of locations.
Wheat Sunflower Barley Rice Soybeans Maize Potato Millet (b) Artificial selection changes the traits of
domesticated species. Domestic maize Wild maize (teosinte) 2017 Pearson Education, Inc. Plants Provide Humans with Food, Fuel, Fiber, Building Materials, and Medicines Fuel Historically, humans relied on wood burning for energy In industrialized countries, fossil fuels including coal and petroleum or natural gas have replaced wood Fossil fuels are derived from plantsliving or
long-deceased 2017 Pearson Education, Inc. Plants Provide Humans with Food, Fuel, Fiber, Building Materials, and Medicines Fiber and Building Materials Plants provide us with important sources of raw material for clothing, rope, and household articles such as towels and linens Woody plants provide Lumber for houses and furniture Fibers used to make paper 2017 Pearson Education, Inc.
Plants Provide Humans with Food, Fuel, Fiber, Building Materials, and Medicines Medicines About 25% of the prescriptions written in the United States each year include at least one molecule derived from plants Most of these compounds are synthesized by plants to repel herbivores 2017 Pearson Education, Inc. Table 28.1
2017 Pearson Education, Inc. How Do Biologists Study Green Algae and Land Plants ? To understand diversification: 1. Compare morphological traits 2. Analyze the fossil record 3. Estimate phylogenetic trees 2017 Pearson Education, Inc. Analyzing Morphological Traits The green algae include species that Are unicellular, colonial, or multicellular Live in marine, freshwater, or moist terrestrial habitats
The vast majority of green algae are aquatic The vast majority of land plants are terrestrial 2017 Pearson Education, Inc. Similarities between Green Algae and Land Plants Biologists have long hypothesized that green algae are closely related to plants on the basis of several key traits: Their chloroplast structure is the same Their thylakoid arrangements are similar Their cell walls, sperm, and peroxisomes are similar in structure and composition
Their chloroplasts synthesize starch as a storage product 2017 Pearson Education, Inc. Similarities between Green Algae and Land Plants Three groups most similar to land plants: Zygnematophyceae (conjugating algae) Coleochaetophyceae (coleochaetes) Charophyceae (stoneworts) Largely multicellular and live in freshwater Hypothesis: Land plants evolved from green algae that lived in freshwater habitats
2017 Pearson Education, Inc. Figure 28.3 100 m Zygnematophyceae (conjugating algae) 2017 Pearson Education, Inc. 20 m Coleochaetophyceae (coleochaetes)
10 m Charophyceae (stoneworts) Major Morphological Differences among Land Plants 1. Nonvascular plants Lack vascular tissue Specialized groups of cells that conduct water or dissolved nutrients throughout the plant body Include mosses Use spores, not seeds, for reproduction and dispersal
2017 Pearson Education, Inc. Major Morphological Differences among Land Plants 2. Seedless vascular plants Have well-developed vascular tissue Do not make seeds; use spores for reproduction Includes ferns 2017 Pearson Education, Inc. Major Morphological Differences among Land
Plants 3. Seed plants Have vascular tissue Make seeds Seeds consist of an embryo and a store of nutritive tissue, surrounded by a tough protective layer Include angiosperms (encased-seeds), or flowering plants and gymnosperms (naked seeds) 2017 Pearson Education, Inc. Using the Fossil Record
Fossil record for green algae begins 700725 mya (million years ago) Fossil record for land plants begins about 475 mya Supports hypothesis that land plants are derived from green algae There have been five major events in the diversification of land plants 2017 Pearson Education, Inc. Figure 28.5 Most major morphological
First evidence innovations: Extensive of land plants: stomata, cuticle, spores, vascular tissue, coal-forming sporangia roots, leaves swamps 2017 Pearson Education, Inc. Both wet and dry environments blanketed with green plants for the first time Diversification of flowering
plants Origin of Land Plants Most of the earliest plant fossils are microscopic 1. Some are of thin sheets of waxy material like cuticle Watertight barrier that coats aboveground parts of todays land plants and helps them resist drying 2017 Pearson Education, Inc. Origin of Land Plants 2. Fossilized spores surrounded by material almost identical in structure to sporopollenin Waxy substance that encases the spores and pollen of
modern land plants and helps them resist drying 3. Fossilized spores found in association with sporeproducing structures (sporangia; singular: sporangium), that are similar to sporangia in some modern nonvascular plants 2017 Pearson Education, Inc. SilurianDevonian Explosion In rocks dated 416 to 359 mya, biologists find fossils from most of the major plant lineages Virtually all of the adaptations that allow plants to occupy dry, terrestrial habitats are present, including Water-conducting vascular tissue Roots
Plants colonized land in conjunction with symbiotic fungi 2017 Pearson Education, Inc. The Carboniferous Period Extensive deposits of coal were found in sediments dated from about 359 to 299 mya Carbon-rich rock packed with fossil spores, branches, leaves, and tree trunks Most of the fossils are derived from seedless vascular plants 2017 Pearson Education, Inc.
Diversification of Gymnosperms Gymnosperms are prominent in the fossil record from 299 mya to 145 mya Some major groups of gymnosperms living today: 1. Ginkgoes 2. Redwoods, junipers, and yews 3. Pines, spruces, and firs Grow readily in dry habitats Both wet and dry environments probably became blanketed with green plants for the first time during this interval 2017 Pearson Education, Inc.
Diversification of Angiosperms The fifth interval in the history of land plants is still underway Age of flowering plantsangiosperms Appear about 150 mya Plants that produced the first flowers are the ancestors of todays grasses, orchids, daisies, oaks, maples, and roses Produce pollen grains that are transported via wind or insects and that carry the cells that will later develop into sperm 2017 Pearson Education, Inc.
Evaluating Molecular Phylogenies The phylogenetic tree of green plants shows that The green plants are monophyletic A single common ancestor gave rise to all of the green algae and land plants Green algae are paraphyletic The green algae include some but not all of the descendants of a single common ancestor Zygnematophyceae is the closest living relative to land plants Land plants evolved from a multicellular green alga that lived in freshwater habitats 2017 Pearson Education, Inc.
Evaluating Molecular Phylogenies Land plants are monophyletic There was only one successful transition from freshwater environments to land The nonvascular plants are the earliest-branching groups among land plants The nonvascular plants are the most ancient living group of land plants The nonvascular plants are paraphyletic The nonvascular plants include some but not all descendants of a single common ancestor 2017 Pearson Education, Inc.
Evaluating Molecular Phylogenies The seedless vascular plants are paraphyletic, but the vascular plants as a whole are monophyletic Vascular tissue evolved only once The seed plantsthe gymnosperms plus angiospermsare monophyletic The seed evolved only once The gymnosperms and angiosperms are monophyletic groups, as are the angiosperms Among seed plants, there was a major divergence in seed development 2017 Pearson Education, Inc.
Figure 28.6 Glaucophyta (glaucophyte algae) PLANTAE Rhodophyta (red algae) GREEN PLANTS GREEN ALGAE Ulvophyceae (ulvophytes) Chloroplasts containing chlorophyll a + b and -carotene Charophyceae (stoneworts)
Coleochaetophyceae (coleochaetes) Common ancestor to all green plants Zygnematophyceae (conjugating algae) Freshwater habitat NONVASCULAR PLANTS Hepaticophyta (liverworts) Bryophyta (mosses) Anthocerophyta (hornworts)
Ability to live on land Bacteria Archaea LAND PLANTS VASCULAR PLANTS SEEDLESS PLANTS Lycophyta (club mosses) Psilotophyta (whisk ferns) Eukarya Pteridophyta (ferns)
PLANTAE Vascular tissue Equisetophyta (horsetails) SEED PLANTS GYMNOSPERMS Ginkgophyta (ginkgoes) Cycadophyta (cycads) Cupressophyta (redwoods et al.) Pinophyta (pines et al.) Seeds Gnetophyta (gnetophytes)
ANGIOSPERMS Anthophyta (angiosperms) 2017 Pearson Education, Inc. What Themes Occur in the Diversification of Land Plants? The evolution of land plants required adaptations that allowed photosynthetic organisms to move from aquatic to terrestrial environments Plants had to adapt to living and reproducing in a dry environment 2017 Pearson Education, Inc.
How Did Plants Adapt to Dry Conditions with Intense Sunlight?? Once green plants made the transition to survive out of water, resources such as light and carbon dioxide were more plentiful Natural selection favored early land plants with three main adaptations that solved the drying problem by 1. Preventing water loss, which kept cells from drying out and dying 2. Providing protection from harmful ultraviolet (UV) radiation 3. Moving water from tissues with direct access to water to tissues without direct access 2017 Pearson Education, Inc.
Preventing Water Loss: Cuticle and Stomata Cuticle is a watertight sealant that covers the aboveground parts of the plant and gives them the ability to survive in dry environments However, cuticle also keeps CO2 out of plant Most plants solve this problem with stoma (mouth; plural: stomata) that consists of an opening surrounded by specialized guard cells Pore opens and closes as guard cells change shape Gas exchange accomplished through pore 2017 Pearson Education, Inc. Figure 28.7
(a) Cuticle is a waxy layer that prevents water loss from stems and leaves. Cuticle Leaf cross section Moist photosynthetic cells (b) Stomata have pores that allow gas exchange in photosynthetic tissues. Pore 25 m
Guard cell Cuticle Stoma 2017 Pearson Education, Inc. Providing Protection from UV Irradiation Plants out of water exposed to harmful UV rays of the sun UV light damages DNA by causing thymine dimers Water absorbs UV light, so algae did not face this problem to the same extent 2017 Pearson Education, Inc.
Providing Protection from UV Irradiation Many species of algae probably colonized wet soil near home ponds, but only some were able to survive the harsh sunlight The plants that survived were those that by chance made compounds that absorb UV light Most plants today accumulate UV-absorbing compounds (flavonoids) that protect DNA from damage 2017 Pearson Education, Inc. The Importance of Upright Growth First land plants were small or had a low, sprawling growth habit
Had to grow in a way that kept many or most of their tissues in direct contact with moist soil Competition for space and light would have become intense soon after the first plants began growing on land In a terrestrial environment, individuals that can grow upright have much better access to sunlight than individuals that cannot 2017 Pearson Education, Inc. The Origin of Vascular Tissue Fossils from the Rhynie Chert formation in Scotland include early land plants that grew upright They contained elongated cells that were organized
into tissues along the length of the plant 2017 Pearson Education, Inc. The Origin of Vascular Tissue Biologists hypothesized that these cells were part of water-conducting tissue because some of the fossilized cells had Simple, cellulose-containing cell walls like waterconducting cells found in todays mosses Cell walls with thickened rings containing lignin Lignin is an extraordinarily strong polymer 2017 Pearson Education, Inc. Figure 28.8
(a) Simple waterconducting cells (b) First vascular tissue (c) Tracheids Some structural support. Elongated cells with Found in fossils little structural support. Found in fossils and present-day mosses (d) Vessel elements Increased structural
support. Found in all vascular plants Found in gnetophytes and angiosperms Ends and sides have pits, where secondary cell wall is absent Primary wall (with cellulose) 2017 Pearson Education, Inc.
Primary wall (with cellulose) Primary wall (with cellulose) Primary wall (with cellulose) Lignin (deposited as rings) Secondary wall (with lignin)
Secondary wall (with lignin) Ends have perforations, where both primary and secondary cell walls are absent Sides have pits Elaboration of Vascular Tissue: Tracheids and
Vessels Simple water-conducting tissues evolved by natural selection into more complex, efficient supportive and water-conducting tissues Long, thin, tapering, water-conducting cells called tracheids evolved about 380 mya 2017 Pearson Education, Inc. Elaboration of Vascular Tissue: Tracheids and Vessels Tracheids have A thickened, lignin-containing secondary cell wall in addition to a cellulose-based primary cell wall Pits in the sides and ends of the cell, which allow
water to flow efficiently between tracheids The secondary cell wall increased structural support, but water could still move easily through the cells because of the pits Today, all vascular plants contain tracheids 2017 Pearson Education, Inc. Elaboration of Vascular Tissue: Tracheids and Vessels Vessel elements, the most specialized type of waterconducting cell, appeared about 250 to 270 mya Vessel elements Are shorter and wider than tracheids Have gaps on both ends where both cell walls are missing
In stems and branches of some vascular plants, tracheids or a combination of tracheids and vessels form wood Strong support material 2017 Pearson Education, Inc. Mapping Evolutionary Changes on the Phylogenetic Tree Cuticle, stomata, and vascular tissue were key adaptations that allowed early plants to colonize land Fundamental adaptations to dry conditionssuch as cuticle, pores, stomata, vascular tissue, and tracheidsevolved just once
Convergent evolution also occurred, as vessels evolved independently in angiosperms, gnetophytes, and several species of seedless vascular plants 2017 Pearson Education, Inc. Figure 28.9 Red algae GREEN ALGAE Ulvophytes Stoneworts Spores or zygotes encased in tough coat of
sporopollenin Coleochaetes Zygnematophyceae NONVASCULAR PLANTS Liverworts Freshwater habitat Mosses Cuticle, pores Hornworts
Stomata SEEDLESS VASCULAR PLANTS Early vascular plants (fossils only) Club mosses Whisk ferns Vascular tissue Ferns Vessel elements Roots, tracheids
Horsetails GYMNOSPERMS Ginkgoes True leaves Cycads Redwoods et al. Pines et al. Vessel elements evolved more than once Wood
Vessel elements Vessel elements 2017 Pearson Education, Inc. Gnetophytes ANGIOSPERMS Angiosperms LAND PLANTS Most key innovations for living on land evolved
only once How Do Plants Reproduce in Dry Conditions? Life cycles of sexually reproducing eukaryotes serve several functions: Increasing genetic variability due to meiosis and fertilization Increasing the number of individuals Dispersing individuals to new habitats 2017 Pearson Education, Inc. How Do Plants Reproduce in Dry Conditions? Three innovations were instrumental for efficient plant reproduction in a dry environment:
1. Spores that resist drying because they are encased in a tough coat of sporopollenin 2. Gametes that were produced in complex, multicellular structures 3. Embryos that were retained on and nourished by the parent plant 2017 Pearson Education, Inc. Desiccation-Resistant Spores Spores resist drying because they are encased in a tough coat of sporopollenin Tough outer coating of spores helps them survive for fairly long periods of time Can be dispersed hundreds of miles by wind
currents Resistant, lightweight nature of spores helps increase their chances of being dispersed to a suitable environment for growth 2017 Pearson Education, Inc. Protective, Complex Reproductive Organs The fossilized structures of early plants contain specialized reproductive organs called gametangia (singular: gametangium) Charophyceae (stoneworts) also develop gametangia, but the gametangia found in land plants are larger and more complex
Protected gametes from drying and from physical damage Present in all land plants living today except angiosperms, where structures inside the flower perform the same functions 2017 Pearson Education, Inc. Protective, Complex Reproductive Organs Individuals produce distinctive male and female gametangia Antheridium (plural: antheridia)sperm-producing Archegonium (plural: archegonia)egg-producing Analogous to the testes and ovaries of animals
2017 Pearson Education, Inc. Figure 28.10 Male Antheridia (containing sperm) Moss gametophytes are either male or female Female Eggs
0.2 mm 2017 Pearson Education, Inc. Archegonia 0.2 mm Embryos Nourished by Parental Tissues Instead of shedding their eggs into the water or soil, as did their ancestors, land plants retain them Eggs form inside archegonia In contrast to most green algae, zygotes of land plants
Begin development on the parent plant Form multicellular embryos that remain attached to and can be nourished by the parent plant 2017 Pearson Education, Inc. Embryos Nourished by Parental Tissues The retention of the embryo was a key event in land plant evolution The groups formal name is Embryophyta, literally, the embryo-plants The retention of the fertilized egg in embryophytes is analogous to pregnancy in mammals 2017 Pearson Education, Inc.
Alternation of Generations All land plants undergo alternation of generations, in which individuals have A multicellular haploid phase called the gametophyte A multicellular diploid phase known as the sporophyte The two phases of the life cycle are connected by distinct types of reproductive cellsgametes and spores 2017 Pearson Education, Inc. Alternation of Generations
Alternation of generations does not occur in the algal groups most closely related to land plants In coleochaetes, stoneworts, and conjugating algae: The multicellular form is haploid Only the zygote is diploid Data suggest that alternation of generations in land plants Evolved independently of its evolution in other eukaryotes Originated early in their history 2017 Pearson Education, Inc. Figure 28.11
Haploid (n) Diploid (2n) Spores (n) Zygote (2n) (retained on parent) Multicellular adult (n) Sperm (n) Gametes are produced in
gametangia Egg (n) 2017 Pearson Education, Inc. Alternation of Generations Alternation of generations always involves the same sequence of events: 1. The sporophyte produces haploid spores by meiosis 2. Spores germinate and divide by mitosis and develop into multicellular, haploid gametophytes 3. Gametophytes produce unicellular haploid gametes by mitosis 4. Two gametes unite during fertilization to form a diploid zygote
5. The zygote divides by mitosis and develops into a multicellular, diploid sporophyte 2017 Pearson Education, Inc. Figure 28.12 Haploid (n) Diploid (2n) 1 (2n) Gametophyte (multicellular, haploid)
Sporophyte (multicellular, diploid) 5 MITOSIS 3 Gametes (n) Zygote (2n)
4 2017 Pearson Education, Inc. 2 Spores (n) 3 (n) Alternation of Generations Compare and contrast zygotes, spores, and gametes: Zygotes and spores are both single cells that divide by
mitosis to form a multicellular individual. Zygotes develop into sporophytes; spores develop into gametophytes Zygotes are diploid and spores and gametes are haploid Zygotes result from the fusion of two haploid cells, such as a sperm and an egg, but spores are not formed by the fusion of gametes Spores are produced by meiosis inside structures called sporangia; gametes are produced by mitosis inside gametangia 2017 Pearson Education, Inc. From Gametophyte-Dominant to SporophyteDominant In nonvascular plants, sporophyte is small and short lived and is largely dependent on gametophyte for nutrition
Gametophyte-dominant life cycle In ferns and other vascular plants, sporophyte is much larger and longer lived than gametophyte Sporophyte-dominant life cycle Gametophytes of gymnosperms and angiosperms are microscopic 2017 Pearson Education, Inc. Figure 28.13 Haploid (n) Diploid (2n) Mature
sporophyte (2n) Spores dispersed by wind (n) Developing gametophytes (n) Sperm swim to egg Developing sporophyte (2n)
Mature female gametophyte (n) Zygote (2n) Egg (n) Sperm 2 m develop in antheridia 2 m
FERTILIZATION Eggs develop in archegonia Archegonium 2017 Pearson Education, Inc. Mature female gametophyte (n) Mature male gametophyte (n) Figure 28.14
Haploid (n) Diploid (2n) Spores are produced in sporangia Spores dispersed by wind (n) Developing gametophyte (n) 1 mm
Sperm (n) develop in antheridia Sporophyte (2n) Zygote (2n) Egg (n) Mature sporophyte (2n) Gametophyte
(n; side view) 2017 Pearson Education, Inc. Sperm swim to egg Archegonium Eggs develop in archegonia Mature gametophyte (n)
From Gametophyte-Dominant to SporophyteDominant The transition from gametophyte-dominated life cycles to sporophyte-dominated life cycles is striking Sporophyte-dominated life cycles were advantageous Diploid cells can respond to varying environmental conditions more efficiently than haploid cells can This is especially true if the individual is heterozygous at many genes 2017 Pearson Education, Inc. Heterospory Heterosporyproduction of two distinct types of
spores by different structures All of the nonvascular plants and most of the seedless vascular plants are homosporous Produce a single type of spore Spores develop into bisexual gametophyte that produces both eggs and sperm These gametophytes can self-fertilize and produce offspring 2017 Pearson Education, Inc. Figure 28.16a (a) Nonvascular plants and most seedless vascular plants are homosporous.
2017 Pearson Education, Inc. Heterospory The two types of spore-producing structures in heterosporous species are microsporangia and megasporangia Microsporangia produce microspores that develop into male gametophytes, which produce small gametes called sperm Megasporangia produce megaspores that develop into female gametophytes, which produce large gametes called eggs The gametophytes of seed plants are either male or
female, but never both 2017 Pearson Education, Inc. Figure 28.16b (b) Seed plants are heterosporous. 2017 Pearson Education, Inc. Pollen Sperm of the nonvascular and seedless vascular plants have to swim to the egg to fertilize it Water must be available for fertilization to occur Pollen grain in land plants allowed plants living in
dry habitats to reproduce efficiently Tiny male gametophytes surrounded by a tough coat of sporopollenin Can be exposed to air for long periods of time without drying out Carried to female gametophyte by wind or animals 2017 Pearson Education, Inc. Seeds The evolution of embryo retention had a downside: In ferns and horsetails, sporophytes have to live in the same place as their parent gametophyte Seed plants overcome this limitation Embryos of seed plants are portable and can
disperse to new locations 2017 Pearson Education, Inc. Seeds A seed is a structure that includes an embryo and a store of nutrients provided by the mother and surrounded by a tough, protective coat Spores are an effective dispersal stage for nonvascular plants and seedless vascular plants, but they lack the stored nutrients found in seeds 2017 Pearson Education, Inc. Figure 28.17
Embryo Nutritive tissue Protective coat 2017 Pearson Education, Inc. 1 mm Seeds Life cycle of a pine treetypical heterospory in gymnosperms: 1. Starting with the sporophyte on the left, note separate
structures, called cones, where microsporangia and megasporangia develop 2. Microsporangia contain microspore mother cells that divide by meiosis to form microspores, which then divide by mitosis to form pollen grains 3. Megasporangia are found inside protective structures called ovules. Each megasporangium contains a megaspore mother cell that divides by meiosis to form a megaspore 2017 Pearson Education, Inc. Seeds Life cycle of a pine treetypical heterospory in gymnosperms: 4. Megaspore undergoes mitosis to form the female
gametophyte, which then produces egg cells through further rounds of mitosis 5. The female gametophyte stays attached to the sporophyte as pollen grains arrive and produce sperm that fertilize the eggs 6. Seeds mature as the embryo develops. Inside the seed, cells derived from the female gametophyte become packed with nutrients provided by the sporophyte 2017 Pearson Education, Inc. Figure 28.18 Pollen grains disperse via wind
Haploid (n) Diploid (2n) Cones with microsporangia Microspore (n) forms pollen grain Pollen grain (male gametophyte) Megasporangium Mother cell (2n) Ovulate cone Mature
sporophyte (2n) 2017 Pearson Education, Inc. Developing sporophyte Seeds (disperse via wind or animals) Three meiotic products die Pollen grain Ovules (contain
megasporangia) Embryo (2n) Four meiotic products; one is large and forms the megaspore (n) Female gametophyte (n) Egg (n) Pollen tube
Megaspore divides to form female gametophyte (n), which forms eggs by mitosis. (Only one egg is fertilized and develops.) Pollen tube delivers sperm to egg Flowers Flowering plants, or angiosperms, are the most diverse land plants living today About 350,000 species have been described, and more are discovered each year
Their success revolves around a reproductive organ the flower The stamen contains anther, where microsporangia develop The carpel contains ovary where ovules are found Ovules contain the megasporangia 2017 Pearson Education, Inc. Flowers Double fertilizationangiosperm fertilization involves two sperm cells One fuses with egg to form diploid (2n) zygote One fuses with two nuclei in the female gametophyte to form a triploid (3n) nutritive tissue (endosperm)
2017 Pearson Education, Inc. Figure 28.19 Pollen grains disperse via wind or animals Haploid (n) Diploid (2n) Microspore (n) forms pollen grain Anther
Top of stamen Pollen grain (male gametophyte) Pollen lands near female gametophyte; produces pollen tube and sperm Sperm travel down growing
pollen tube to reach egg Ovule Ovary Bottom of carpel Megasporangium Megaspore (n: retained in ovary) Embryo
(2n) Developing sporophyte (2n) 2017 Pearson Education, Inc. Endosperm (3n) forms nutritive tissue in seed Nutritive tissue (3n)
Mature sporophyte (2n) Seed (disperses via wind or animals) Egg (n) Female gametophyte (n: retained in ovary) Zygote (2n)
Fruit (develops from ovary wall) containing seed Pollination by Insects and Other Animals After they evolved, stamens and carpels later became enclosed by modified leaves called sepals and petals The four structures then diversified to produce a fantastic array of sizes, shapes, and colors Specialized cells inside flowers also began producing a wide range of scents 2017 Pearson Education, Inc.
Figure 28.20 (a) Carrion flowers: Smell like(b) Hummingbird-pollinated (c) Bee-pollinated flowers: rotting flesh and attract carrion flowers: Red, long tubes with Often bright purple flies nectar at the base 2017 Pearson Education, Inc. Pollination by Insects and Other Animals Flowers may be adaptations to increase the probability that an animal will perform pollination The transfer of pollen from one individuals stamen to another individuals carpel
Biologists proposed the directed-pollination hypothesis: Natural selection favored structures that reward an animal for carrying pollen directly from one flower to another Flowers vary in size, structure, scent, and color in order to attract specific pollinators 2017 Pearson Education, Inc. Pollination by Insects and Other Animals Flowers attract pollinators by providing them with foodeither protein-rich pollen or nectar, a sugarrich fluid The relationship between flowering plants and their pollinators is mutually beneficial
The pollinator gets food, and the plant gets fertilized Directed-pollination hypothesis has strong experimental support 2017 Pearson Education, Inc. Figure 28.21-2 preference? Does flower color influence pollinator Hawk moths prefer white petunias while bumblebees prefer purple, even when the flowers are otherwise identical.
Neither insect has a clear preference for whiteor purple-flowered petunias. 1. Isolate AN2 gene for purple flower color from a related species (P. integrifolia) and insert it into P. axillaris. Wild-type Genetically altered P. axillaris P. axillaris 2. Grow wild-type (white) and genetically altered (purple) P. axillaris in controlled greenhouse conditions. 3. Count number of visits by
hawk moths and bumblebees to white and purple flowers. 2017 Pearson Education, Inc. Figure 28.21-4 Hawk moths will visit white-flowered P. axillaris more frequently, while bumblebees will visit purple-flowered P. axillaris more frequently. Both insects will visit white and purple flowers equally. Wild type
Genetically altered Bumblebees visited purple flowers 7 times more frequently than white flowers Number of visits per flower per period (2 hrs) Number of visits per flower per period (5 min) Hawk moths visited white flowers 4 times more
frequently than purple flowers Wild type Genetically altered Petunia flower preference among bumblebees and hawk moths is significantly influenced by flower color. 2017 Pearson Education, Inc. Pollination by Insects and Other Animals The spectacular diversity of angiosperms resulted from coevolution with animal pollinators Evolutionary changes in angiosperms and corresponding changes in their pollinators were highly dependent on each other
Many animals and the flowering plants they pollinate depend on each other for their survival 2017 Pearson Education, Inc. Fruits A fruit is a structure that is derived from the ovary and encloses one or more seeds Tissues derived from the ovary are often nutritious and brightly colored While the evolution of flowers made efficient pollination possible, the evolution of fruit made efficient seed dispersal possible 2017 Pearson Education, Inc.
Figure 28.22 (a) Fruits are derived from ovaries and contain seeds. Wall of ovary Seed (b) Many fruits are dispersed by animals. 2017 Pearson Education, Inc. Figure 28.23 Red algae
GREEN ALGAE Ulvophytes Stoneworts Coleochaetes Simple gametangia, egg retention on parent Zygnematophyceae NONVASCULAR PLANTS Liverworts Mosses
Thick-walled spores, complex gametangia, embryo retention, alternation of generations Hornworts SEEDLESS VASCULAR PLANTS Club mosses Heterospory Whisk ferns GYMNOSPERMS Ginkgoes Redwoods
et al. Pines et al. Heterospory, pollen, seeds Gnetophytes ANGIOSPERMS Angiosperms Flowers and fruit 2017 Pearson Education, Inc. SEED PLANTS Cycads
VASCULAR PLANTS Horsetails LAND PLANTS Ferns Sporophyte-dominated life cycle The Angiosperm Radiation An adaptive radiation occurs when a single lineage produces a large number of descendant species that are adapted to a wide variety of habitats Angiosperms represent one of the great adaptive radiations in the history of life
2017 Pearson Education, Inc. The Angiosperm Radiation The diversification of angiosperms is associated with three key adaptations: 1. Water-conducting vessels 2. Flowers 3. Fruits These adaptations allow angiosperms to transport water, pollen, and seeds efficiently 2017 Pearson Education, Inc.
The Angiosperm Radiation On the basis of morphological traits, angiosperms have traditionally been divided into two major groups: 1. Monocotyledons (monocots) 2. Dicotyledons (dicots) The groups are divided based on differences in their cotyledons, or first leaves Cotyledons store nutrients and provide them to the embryo Monocots have one cotyledon Dicots have two cotyledons 2017 Pearson Education, Inc. Figure 28.24
MONOCOTS Cotyledons Vascular tissue Veins Flowers Vascular tissue scattered throughout stem Parallel veins in leaves (bundles of vascular tissue)
Petals in multiples of 3 Vascular tissue in circular arrangement in stem Branching veins in leaves Petals in multiples of 4 or 5 Cotyledon DICOTS One cotyledon
(corn embryo) Cotyledons Two cotyledons (mustard embryo) 2017 Pearson Education, Inc. The Angiosperm Radiation Monocots as a group are monophyletic Dicots are paraphyletic Biologists have adjusted the names assigned to angiosperm lineages to reflect this new knowledge of phylogeny
The most important of these changes was identifying the eudicots (true dicots) as a monophyletic lineage that includes most of the plants once considered dicots 2017 Pearson Education, Inc. Figure 28.25 Non-angiosperms ANGIOSPERMS Oldest living angiosperm lineages Monocots
Several lineages related to magnolias Lineages in red were traditionally called dicots, but this tree shows that dicots are not a natural grouping 2017 Pearson Education, Inc. Eudicots Key Lineages of Green Algae and Land Plants The green algae are a paraphyletic group that totals
about 8000 species Green algae are important primary producers in All types of freshwater habitats Unusual environments such as snowfields and ice floes 2017 Pearson Education, Inc. Green Algae Green algae live in close association with an array of other organisms: Unicellular green algae are common endosymbionts in planktonic protists that live in lakes and ponds Lichens are stable associations between green algae or cyanobacteria and fungi
Often found in terrestrial environments that lack soil Approximately 85% of the 17,000 species of lichens involve green algae 2017 Pearson Education, Inc. Figure 28.26 (a) Green algae are responsible for green snow. (b) Many unicellular protists harbor green algae. (c) Most lichens are an
association between fungi and microscopic green algae. Algal cells 10 m 2017 Pearson Education, Inc. 1 cm Table 28.2-1 2017 Pearson Education, Inc.
Table 28.2-1 2017 Pearson Education, Inc. Table 28.2-2 2017 Pearson Education, Inc. Table 28.2-2 2017 Pearson Education, Inc. Nonvascular Plants Nonvascular plants
First lineages to branch off phylogeny of land plants Gametophyte is dominant and longer-lived phase of life cycle Individuals anchored to soil, rocks, or tree bark by rhizoids Lack vascular tissue with lignin-reinforced cell walls Flagellated sperm that swim to eggs Spores dispersed by wind 2017 Pearson Education, Inc. Table 28.3 2017 Pearson Education, Inc.
Table 28.3 2017 Pearson Education, Inc. Table 28.3 2017 Pearson Education, Inc. Seedless Vascular Plants Paraphyletic group Vascular tissue comprised of lignin-reinforced cells Sporophyte dominant, longer-lived phase of life cycle But, gametophyte physically independent of sporophyte
Eggs retained on gametophyte, and sperm swim to egg with flagella Sporophytes develop on gametophyte and are nourished by gametophyte when small 2017 Pearson Education, Inc. Table 28.4-1 2017 Pearson Education, Inc. Table 28.4-1 2017 Pearson Education, Inc.
Table 28.4-2 2017 Pearson Education, Inc. Table 28.4-2 2017 Pearson Education, Inc. Seed Plants: Gymnosperms and Angiosperms Seed plants Are a monophyletic group Include gymnosperms and the angiosperms Defined by two key synapomorphies: Production of seeds
Production of pollen grains Angiosperms produce seeds in ovaries, gymnosperms do not 2017 Pearson Education, Inc. Table 28.5-1 2017 Pearson Education, Inc. Table 28.5-1 2017 Pearson Education, Inc. Table 28.5-2
2017 Pearson Education, Inc. Table 28.5-2 2017 Pearson Education, Inc. Table 28.5-2 2017 Pearson Education, Inc. Table 28.6-1 2017 Pearson Education, Inc.
Table 28.6-1 2017 Pearson Education, Inc. Table 28.6-2 2017 Pearson Education, Inc. Table 28.6-2 2017 Pearson Education, Inc.