Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings PowerPoint ® Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Chapter 30 Plant Diversity II: The Evolution of Seed Plants

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Overview: Transforming the World (Common to all seed plants) Seed - embryo and nutrients surrounded by a protective coat Reduced gametophytes - develop within the walls of spores & retained within tissues of the parent sporophyte Heterospory (male and female parts) Ovules - consists of a megasporangium, megaspore, and one or more protective integuments (Gymnosperm have 1; Angiosperm have 2) Pollen - Pollen grains contain the male gametophytes. If a pollen grain germinates, it gives rise to a pollen tube that discharges two sperm into the female gametophyte within the ovule Pollination - transfer of pollen to the part of a seed plant containing the ovules

Fig. 30-UN3 Reduced gametophytes Microscopic male and female gametophytes (n) are nourished and protected by the sporophyte (2n) Five Derived Traits of Seed Plants Male gametophyte Female gametophyte HeterosporyMicrospore (gives rise to a male gametophyte) Megaspore (gives rise to a female gametophyte) Ovules Ovule (gymnosperm) Pollen Pollen grains make water unnecessary for fertilization Integument (2n) Megaspore (2n) Megasporangium (2n) Seeds Seeds: survive better than unprotected spores, can be transported long distances Integument Food supply Embryo

Fig Reduced (usually microscopic), dependent on surrounding sporophyte tissue for nutrition Reduced, independent (photosynthetic and free-living) Gametophyte Sporophyte (2n) Gametophyte (n) Sporophyte Example Gametophyte (n) Dominant Reduced, dependent on gametophyte for nutrition Mosses and other nonvascular plants Ferns and other seedless vascular plants Seed plants (gymnosperms and angiosperms) PLANT GROUP GymnospermAngiosperm Microscopic female gametophytes (n) inside ovulate cone Microscopic male gametophytes (n) inside pollen cone Sporophyte (2n) Microscopic female gametophytes (n) inside these parts of flowers Microscopic male gametophytes (n) inside these parts of flowers

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Evolutionary Advantage of Seeds develops from the whole ovule is a sporophyte embryo, along with its food supply, packaged in a protective coat Seeds provide some evolutionary advantages over spores: – They may remain dormant for days to years, until conditions are favorable for germination – They may be transported long distances by wind or animals

Fig From ovule to seed in a gymnosperm Seed coat (derived from integument) (c) Gymnosperm seed Embryo (2n) (new sporophyte) Food supply (female gametophyte tissue) (n) (b) Fertilized ovule(a) Unfertilized ovule Integument Immature female cone Spore wall Megasporangium (2n) Male gametophyte (within a germinated pollen grain) (n) Megaspore (n) MicropylePollen grain (n) Egg nucleus (n) Discharged sperm nucleus (n) Female gametophyte (n)

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Concept 30.2: Gymnosperms bear “naked” seeds, typically on cones The gymnosperms have “naked” seeds not enclosed by ovaries and consist of four phyla: – Cycadophyta (cycads) – Gingkophyta (one living species: Ginkgo biloba) – Gnetophyta (three genera: Gnetum, Ephedra, Welwitschia) – Coniferophyta (conifers, such as pine, fir, and redwood)

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Phylum Cycadophyta Large cones and palmlike leaves. These thrived during the Mesozoic, but relatively few species exist today. Phylum Ginkgophyta This phylum consists of a single living species, Ginkgo biloba It has a high tolerance to air pollution and is a popular ornamental tree

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Phylum Gnetophyta ( 3 genera ) Species vary in appearance, and some are tropical whereas others live in deserts Largest of the gymnosperm phyla Most conifers are evergreens and can carry out photosynthesis year round Phylum Coniferophyta

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Life Cycle of a Pine: A Closer Look Three key features of the gymnosperm life cycle are: – Dominance of the sporophyte generation – Development of seeds from fertilized ovules – The transfer of sperm to ovules by pollen The pine tree is the sporophyte and produces sporangia in male and female cones Small cones produce microspores called pollen grains, each of which contains a male gametophyte The familiar larger cones contain ovules, which produce megaspores that develop into female gametophytes It takes nearly three years from cone production to mature seed

Fig Microsporangium (2n) Microsporocytes (2n) Pollen grains (n) Pollen cone Microsporangia MEIOSIS Mature sporophyte (2n) Haploid (n) Diploid (2n) Key MEIOSIS Surviving megaspore (n) Pollen grain Megasporocyte (2n) Ovule Integument Ovulate cone FERTILIZATION Pollen tube Female gametophyte Sperm nucleus (n) Egg nucleus (n) Archegonium Seedling Seeds Seed coat (2n) Food reserves (n) Embryo (2n) Megasporangium (2n)

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Characteristics of Angiosperms All angiosperms are classified in a single phylum, Anthophyta (Greek anthos, flower) Flower - angiosperm structure specialized for sexual reproduction A flower is a specialized shoot with up to four types of modified leaves: – Sepals - enclose the flower – Petals - brightly colored & attract pollinators – Stamens - produce pollen on terminal anthers – Carpels - produce ovules (ovary at the base and a style leading up to a stigma, where pollen is received)

Fig Carpel Ovule Sepal Petal Stigma Style Ovary Stamen Anther Filament

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fruits Fruit - typically consists of a mature ovary but can also include other flower parts – protect seeds & aid in dispersal – can be either fleshy or dry – adaptations help disperse seeds(wind, water, or animals)

Fig Some variations in fruit structure Hazelnut Ruby grapefruit Tomato Nectarine Milkweed

Fig Fruit adaptations that enhance seed dispersal Barbs Seeds within berries Wings

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Angiosperm Life Cycle The flower of the sporophyte is composed of both male and female structures Male gametophytes are contained within pollen grains produced by the microsporangia of anthers The female gametophyte, or embryo sac, develops within an ovule contained within an ovary at the base of a stigma Most flowers have mechanisms to ensure cross- pollination btwn flowers from different plants of the same species

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings A pollen grain that has landed on a stigma germinates and the pollen tube of the male gametophyte grows down to the ovary Micropyle – pore in the ovule Double fertilization - pollen tube discharges two sperm into the female gametophyte within an ovule One sperm fertilizes the egg the other combines with two nuclei in the central cell of the female gametophyte and initiates development of food- storing endosperm Within a seed, the embryo consists of a root and two seed leaves called cotyledons

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

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Angiosperm Diversity The two main groups of angiosperms are monocots (one cotyledon) and eudicots (“true” dicots) Basal angiosperms - less derived and include the flowering plants belonging to the oldest lineages (Eg. Amborella trichopoda, water lilies, and star anise) Magnoliids - share some traits with basal angiosperms but are more closely related to monocots and eudicots (Eg. magnolias, laurels, and black pepper plants)

Fig n Angiosperm diversity Monocot Characteristics Eudicot Characteristics Vascular tissue usually arranged in ring Veins usually parallel Vascular tissue scattered Leaf venation One cotyledon Embryos Two cotyledons Stems Veins usually netlike

Fig o Angiosperm diversity Roots Pollen Root system usually fibrous (no main root) Pollen grain with three openings Pollen grain with one opening Floral organs usually in multiples of three Flowers Floral organs usually in multiples of four or five Monocot Characteristics Eudicot Characteristics Taproot (main root) usually present

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Evolutionary Links Between Angiosperms and Animals Pollination of flowers and transport of seeds by animals are two important relationships in terrestrial ecosystems Clades with bilaterally symmetrical flowers have more species than those with radially symmetrical flowers This is likely because bilateral symmetry affects the movement of pollinators and reduces gene flow in diverging populations