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

Evolution of Plants Flowering plants Cone-bearing plants Ferns and their relatives Mosses and their relatives Green algae ancestor Flowers; Seeds Enclosed in Fruit Seeds Water-Conducting (Vascular) Tissue Vascular w/ Seeds Angiosperms Vascular w/ Seeds Gymnosperms Vascular Seedless Pterophyta Non-Vascular Bryophytes

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Overview: Feeding the World Seeds changed the course of plant evolution – Enabling their bearers to become the dominant producers in most terrestrial ecosystems Figure 30.1

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Overview of Seed Plant Evolution 1.Reduction of gametophyte continued with the evolution of seed plants. 2.Seeds became an important means of dispersing offspring. 3.Pollen eliminated the liquid-water requirement for fertilization. 4.The two clades of seed plants are gymnosperms and angiosperms.

Figure 30.1 Three variations on gametophyte/sporophyte relationships

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Two Groups of Seed Plants 1.Gymnosperms – “naked seed” plants – most ancient of seed plants; produce cones with seeds Conifers Cycads Ginkos Gnetophytes 2.Angiosperms – covered seed plants - these produce flowers….then fruits that have the seeds inside – fruits provide seed protection and better guarantees seed dispersal when eaten by animals Grasses Flowering trees and shrubs All flowers

Seed coat Embryo Stored food supply Seed Wing A B Section 22-4 The Structure of a Seed Go to Section: Seed: embryo of plant that is wrapped in a protective covering and surrounded by a food supply. Presence of a seed allows for reproduction free of water.

Figure 30.2 From ovule to seed a) A fleshy megasporangium is surrounded by protective layers of tissue called integument. b) A megaspore develops into a multicellular female gametophyte. The micropyle, the only opening through the integument, allows entry of the pollen grain. The pollen grain contains a male gametophyte, which develops a pollen tube that discharges sperm. c) Fertilization initiates the transformation of the ovule into a seed, which consists of a sporophyte embryo, a food supply, and a protective seed coat derived from the integument.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Ovules and Production of Eggs An ovule consists of – A megasporangium, megaspore, and protective integuments Figure 30.3a (a) Unfertilized ovule. In this sectional view through the ovule of a pine (a gymnosperm), a fleshy megasporangium is surrounded by a protective layer of tissue called an integument. (Angiosperms have two integuments.) Integument Spore wall Megasporangium (2n) Megaspore (n)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Pollen and Production of Sperm Microspores develop into pollen grains – Which contain the male gametophytes of plants Pollination – Is the transfer of pollen to the part of a seed plant containing the ovules

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Pollen and the Production of Sperm If a pollen grain germinates – It gives rise to a pollen tube that discharges two sperm into the female gametophyte within the ovule Figure 30.3b (b) Fertilized ovule. A megaspore develops into a multicellular female gametophyte. The micropyle, the only opening through the integument, allows entry of a pollen grain. The pollen grain contains a male gametophyte, which develops a pollen tube that discharges sperm. Spore wall Male gametophyte (within germinating pollen grain) (n) Female gametophyte (n) Egg nucleus (n) Discharged sperm nucleus (n) Pollen grain (n) Micropyle

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Seed Plant Characteristics In addition to seeds, the following are common to all seed plants – Reduced gametophytes Egg and sperm are protected in ovules and pollen grains. – Heterospory Plants in which the sporophyte produces two kinds of spores that develop into either male or female gametophytes. – Ovules Structure that develops in the plant ovary and contains the female gametophyte. – Pollen Structure that contains immature male gametophyte.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Evolutionary Advantage of Seeds A seed – Is a sporophyte embryo, along with its food supply, packaged in a protective coat – Develops from the whole ovule Figure 30.3c Gymnosperm seed. Fertilization initiates the transformation of the ovule into a seed, which consists of a sporophyte embryo, a food supply, and a protective seed coat derived from the integument. (c) Seed coat (derived from Integument) Food supply (female gametophyte tissue) (n) Embryo (2n) (new sporophyte)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Advantages of Reduced Gametophytes The gametophytes of seed plants – Develop within the walls of spores retained within tissues of the parent sporophyte – Because of this, the delicate female gametophytes do not have to cope with many environmental stresses The gametophyte and the embryo produced after fertilization are sheltered from drought and UV radiation by their enclosure in the moist reproductive tissues of the parental sporophyte generation. This arrangement also makes it possible for the gametophytes to obtain nutrients from their parents.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Gametophyte/Sporophyte Relationships Figure 30.2a–c Sporophyte dependent on gametophyte (mosses and other bryophytes). (a) Large sporophyte and small, independent gametophyte (ferns and other seedless vascular plants). (b) Microscopic female gametophytes (n) in ovulate cones (dependent) Sporophyte (2n), the flowering plant (independent) Microscopic male gametophytes (n) inside these parts of flowers (dependent) Microscopic male gametophytes (n) in pollen cones (dependent) Sporophyte (2n) (independent) Microscopic female gametophytes (n) inside these parts of flowers (dependent) Reduced gametophyte dependent on sporophyte (seed plants: gymnosperms and angiosperms). (c) Gametophyte (n) Gametophyte (n) Sporophyte (2n) Sporophyte (2n)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Heterospory: The Rule Among Seed Plants Seed plants evolved from plants that had megasporangia – Which produce megaspores that give rise to female gametophytes Seed plants evolved from plants that had microsporangia – Which produce microspores that give rise to male gametophytes

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Evolutionary Advantage of Pollen Pollen, which can be dispersed by air or animals – Eliminated the water requirement for fertilization – Is light weight, so it can be carried away by wind or animals after their release from the microsporangium In seed plants, the use of resistant, far-traveling, airborne pollen to bring gametes together is a terrestrial adaptation that led to even greater success and diversity of plants on land. – As opposed to bryophytes and pterophytes which have flagellated sperm that must swim through a film of water to reach egg cells in archegonia.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Gymnosperms – Cone Bearers Gymnosperms bear “naked” seeds, typically on cones Among the gymnosperms are many well-known conifers – Or cone-bearing trees, including pine, fir, and redwood The gymnosperms include four plant phyla – Cycadophyta – Gingkophyta – Gnetophyta – Coniferophyta

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 30.4 Gnetum Ephedra Ovulate cones Welwitschia PHYLUM GNETOPHYTA PHYLUM CYCADOPHYTA PHYLUM GINKGOPHYTA Cycas revoluta Exploring Gymnosperm Diversity

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Exploring Gymnosperm Diversity Figure 30.4 Douglas fir Pacific yew Common juniper Wollemia pine Bristlecone pine Sequoia PHYLUM CYCADOPHYTA

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A Closer Look at the Life Cycle of a Pine Key features of the gymnosperm life cycle include – Dominance of the sporophyte generation, the pine tree – The development of seeds from fertilized ovules – The role of pollen in transferring sperm to ovules – Seeds typically require wind for dispersal

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 30.6 Ovule Megasporocyte (2n) Integument Longitudinal section of ovulate cone Ovulate cone Pollen cone Mature sporophyte (2n) Longitudinal section of pollen cone Microsporocytes (2n) Pollen grains (n) (containing male gametophytes) MEIOSIS Micropyle Germinating pollen grain Megasporangium MEIOSIS Sporophyll Microsporangium Surviving megaspore (n) Germinating pollen grain Archegonium IntegumentEgg (n) Female gametophyte Germinating pollen grain (n) Discharged sperm nucleus (n) Pollen tube Egg nucleus (n) FERTILIZATION Seed coat (derived from parent sporophyte) (2n) Food reserves (gametophyte tissue) (n) Embryo (new sporophyte) (2n) Seeds on surface of ovulate scale Seedling Key Diploid (2n) Haploid (n) The Life Cycle of a Pine A pollen cone contains many microsporangia held in sporophylls. Each microsporangium contains microsporocytes (microspore mother cells). These undergo meiosis, giving rise to haploid microspores that develop into pollen grains. 3 In most conifer species, each tree has both ovulate and pollen cones. 1 A pollen grain enters through the micropyle and germinates, forming a pollen tube that slowly digests through the megasporangium. 4 While the pollen tube develops, the megasporocyte (megaspore mother cell) undergoes meiosis, producing four haploid cells. One survives as a megaspore. 5 The female gametophyte develops within the megaspore and contains two or three archegonia, each with an egg. 6 By the time the eggs are mature, two sperm cells have developed in the pollen tube, which extends to the female gametophyte. Fertilization occurs when sperm and egg nuclei unite. 7 Fertilization usually occurs more than a year after pollination. All eggs may be fertilized, but usually only one zygote develops into an embryo. The ovule becomes a seed, consisting of an embryo, food supply, and seed coat. 8 An ovulate cone scale has two ovules, each containing a mega- sporangium. Only one ovule is shown. 2

Figure 30.3 Winged seed of a White Pine (Pinus strobus)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Female vs. Male Pine Cones Female pine cones are the large, ‘normal’ cones – ovulate cone Male pine cones are the clusters of small, worm-like structures at the tips of the branches – pollen cone

Evolution of Plants Flowering plants Cone-bearing plants Ferns and their relatives Mosses and their relatives Green algae ancestor Flowers; Seeds Enclosed in Fruit Seeds Water-Conducting (Vascular) Tissue Vascular w/ Seeds Angiosperms Vascular w/ Seeds Gymnosperms Vascular Seedless Pterophyta Non-Vascular Bryophytes

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Angiosperms – Flower and Fruit Producers The reproductive adaptations of angiosperms include flowers and fruits Angiosperms – Are commonly known as flowering plants – Are seed plants that produce the reproductive structures called flowers and fruits – Are the most widespread and diverse of all plants

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Characteristics of Angiosperms The key adaptations in the evolution of angiosperms – Are flowers and fruits The flower – Is an angiosperm structure specialized for sexual reproduction Fruits – Typically consist of a mature ovary

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Angiosperms – Flowering Plants Angiosperm means “enclosed seed” Angiosperms have unique reproductive organs known as flowers – Flowers attract pollinators, which makes spreading seeds more efficient than the wind pollination of most gymnosperms Flowers contain ovaries, which surround and protect the seeds – After pollination, the ovary develops into a fruit, which protects the seed and aids dispersal – Fruit is a thick wall of tissue and another reason why angiosperms are successful – the fruit attracts herbivores – which eat the fruit and then spread the seeds

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Flowers A flower is a specialized shoot with modified leaves – Sepals, which enclose the flower – Petals, which are brightly colored and attract pollinators – Stamens, which produce pollen – Carpels, which produce ovules Figure 30.7 Anther Filament Stigma Style Ovary Carpel Petal Receptacle Ovule Sepal Stamen

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Fruits Figure 30.8a–e (b) Ruby grapefruit, a fleshy fruit with a hard outer layer and soft inner layer of pericarp (a) Tomato, a fleshy fruit with soft outer and inner layers of pericarp (c) Nectarine, a fleshy fruit with a soft outer layer and hard inner layer (pit) of pericarp (e) Walnut, a dry fruit that remains closed at maturity (d) Milkweed, a dry fruit that splits open at maturity

Figure Relationship between a pea flower and a fruit (pea pod)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Fruit Adaptations Enhance Seed Dispersal Can be carried by wind, water, or animals to new locations, enhancing seed dispersal Figure 30.9a–c Wings enable maple fruits to be easily carried by the wind. (a) Seeds within berries and other edible fruits are often dispersed in animal feces. (b) The barbs of cockleburs facilitate seed dispersal by allowing the fruits to “hitchhike” on animals. (c)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Fruit types Depends on their developmental origin: – Simple fruit – comes from a single ovary ex. Cherry, soybean pod – Aggregate fruit – single flower with several carpels ex. Blackberry – Multiple fruit – develops from an inflorescence (group of flowers tightly clustered together) ex. pineapple

Table 30.1 Classification of Fleshy Fruits

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Angiosperm Life Cycle In the angiosperm life cycle – Double fertilization occurs when a pollen tube discharges two sperm into the female gametophyte within an ovule – One sperm fertilizes the egg, while the other combines with two nuclei in the center cell of the female gametophyte and initiates development of food-storing endosperm The endosperm nourishes the developing embryo

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure Key Mature flower on sporophyte plant (2n) Ovule with megasporangium (2n) Female gametophyte (embryo sac) Nucleus of developing endosperm (3n) Discharged sperm nuclei (n) Pollen tube Male gametophyte (in pollen grain) Pollen tube Sperm Surviving megaspore (n) Microspore (n) Generative cell Tube cell Stigma Ovary MEIOSIS Megasporangium (n) Pollen grains Egg Nucleus (n) Zygote (2n) Antipodal cells Polar nuclei Synergids Egg (n) Embryo (2n) Endosperm (food Supply) (3n) Seed coat (2n) Seed FERTILIZATION Haploid (n) Diploid (2n) Anther Sperm (n) Pollen tube Style Microsporangium Microsporocytes (2n) Germinating Seed Anthers contain microsporangia. Each microsporangium contains micro- sporocytes (microspore mother cells) that divide by meiosis, producing microspores. 1 Microspores form pollen grains (containing male gametophytes). The generative cell will divide to form two sperm. The tube cell will produce the pollen tube. 2 In the megasporangium of each ovule, the megasporocyte divides by meiosis and produces four megaspores. The surviving megaspore in each ovule forms a female gametophyte (embryo sac). 3 After pollina- tion, eventually two sperm nuclei are discharged in each ovule. 4 Double fertilization occurs. One sperm fertilizes the egg, forming a zygote. The other sperm combines with the two polar nuclei to form the nucleus of the endosperm, which is triploid in this example. 5 The zygote develops into an embryo that is packaged along with food into a seed. (The fruit tissues surround- ing the seed are not shown). 6 When a seed germinates, the embryo develops into a mature sporophyte. 7 The Angiosperm Life Cycle

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Angiosperm Diversity The two main groups of angiosperms – Are monocots and dicots Basal angiosperms – Are less derived and include the flowering plants belonging to the oldest lineages Magnoliids – Share some traits with basal angiosperms but are more closely related to monocots and eudicots

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Section 22-5 Go to Section: Comparison of Monocots and Dicots

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Exploring Angiosperm Diversity Figure Amborella trichopoda Water lily (Nymphaea “Rene Gerard”) Star anise (Illicium floridanum) BASAL ANGIOSPERMS HYPOTHETICAL TREE OF FLOWERING PLANTS MAGNOLIIDS Amborella Water lilies Star anise and relatives Magnoliids Monocots Eudicots Southern magnolia (Magnolia grandiflora)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Exploring Angiosperm Diversity Figure Orchid (Lemboglossum fossii) Monocot Characteristics Embryos Leaf venation Stems Roots Pollen Flowers Pollen grain with one opening Root system Usually fibrous (no main root) Vascular tissue scattered Veins usually parallel One cotyledonTwo cotyledons Veins usually netlike Vascular tissue usually arranged in ring Taproot (main root) usually present Pollen grain with three openings Zucchini (Cucurbita Pepo), female (left) and male flowers Pea (Lathyrus nervosus, Lord Anson’s blue pea), a legume Dog rose (Rosa canina), a wild rose Pygmy date palm (Phoenix roebelenii) Lily (Lilium “Enchant- ment”) Barley (Hordeum vulgare), a grass Anther Stigma California poppy (Eschscholzia californica) Pyrenean oak (Quercus pyrenaica) Floral organs usually in multiples of three Floral organs usually in multiples of four or five Filament Ovary Eudicot Characteristics MONOCOTS EUDICOTS

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Evolutionary Links Between Angiosperms and Animals Pollination of flowers by animals and transport of seeds by animals are two important relationships in terrestrial ecosystems Figure 30.13a–c (a) A flower pollinated by honeybees. This honeybee is harvesting pollen and nectar (a sugary solution secreted by flower glands) from a Scottish broom flower. The flower has a tripping mechanism that arches the stamens over the bee and dusts it with pollen, some of which will rub off onto the stigma of the next flower the bee visits. (c) A flower pollinated by nocturnal animals. Some angiosperms, such as this cactus, depend mainly on nocturnal pollinators, including bats. Common adaptations of such plants include large, light-colored, highly fragrant flowers that nighttime pollinators can locate. (b) A flower pollinated by hummingbirds. The long, thin beak and tongue of this rufous hummingbird enable the animal to probe flowers that secrete nectar deep within floral tubes. Before the hummer leaves, anthers will dust its beak and head feathers with pollen. Many flowers that are pollinated by birds are red or pink, colors to which bird eyes are especially sensitive.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings are categorized as that complete their life cycle in Section 22-5 Plants Annuals Biennials Perennials 1 growing season 2 years More than 2 years Go to Section:

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Human Connection to Seed Plants Human welfare depends greatly on seed plants No group is more important to human survival than seed plants Humans depend on seed plants for – Food – Wood – Many medicines

Table 30.2 A Sampling of Medicines Derived from Plants