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What Human Reproductive Organ Is Functionally Similar to This Seed?

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Fig. 30-1 What human reproductive organ is functionally similar to this seed? Overview: Transforming the World • Seeds changed the course of plant evolution, enabling their bearers to become the dominant producers in most terrestrial ecosystems • A seed consists of an embryo and nutrients surrounded by a protective coat Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 30-1 What human reproductive organ is functionally similar to this seed? Seeds and pollen grains are key adaptations for life on land • In addition to seeds, the following are common to all seed plants – Reduced gametophytes – Heterospory – Ovules – Pollen Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Advantages of Reduced Gametophytes • The gametophytes of seed plants develop within the walls of spores that are retained within tissues of the parent sporophyte • Protect female gametophyte from UV and desiccation (good for the land life!) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 30-2 PLANT GROUP Mosses and other Ferns and other seedless Seed plants (gymnosperms and angiosperms) nonvascular plants vascular plants Reduced, independent Reduced (usually microscopic), dependent on surrounding (photosynthetic and Gametophyte Dominant sporophyte tissue for nutrition free-living) Sporophyte Reduced, dependent on Dominant Dominant gametophyte for nutrition Gymnosperm Angiosperm Sporophyte Microscopic female (2n) gametophytes (n) inside ovulate cone Microscopic Sporophyte female (2n) gametophytes (n) inside Gametophyte these parts (n) of flowers Example Microscopic male gametophytes Microscopic male (n) inside gametophytes (n) these parts inside pollen cone of flowers Sporophyte (2n) Sporophyte (2n) Gametophyte (n) Fig. 30-2c Seed plants (gymnosperms and angiosperms) Reduced (usually microscopic), dependent on surrounding Gametophyte sporophyte tissue for nutrition Sporophyte Dominant Gymnosperm Angiosperm Microscopic female gametophytes (n) inside ovulate cone Microscopic female gametophytes Microscopic (n) inside male these parts gametophytes of flowers Example (n) inside these parts of flowers Microscopic male gametophytes (n) inside pollen cone Sporophyte (2n) Sporophyte (2n) Heterospory: The Rule Among Seed Plants • The ancestors of seed plants were likely homosporous (one type of spore [like ferns]), while seed plants are heterosporous • Megasporangia produce megaspores that give rise to female gametophytes • Microsporangia produce microspores that give rise to male gametophytes Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Ovules and Production of Eggs • An ovule consists of a megasporangium, megaspore, and one or more protective integuments • Gymnosperm megaspores have one integument • Angiosperm megaspores usually have two integuments Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 30-3-1 Integument Spore wall Immature female cone Megasporangium (2n) Megaspore (n) (a) Unfertilized ovule Pollen and Production of Sperm • Microspores develop into pollen grains, which contain the male gametophytes Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Pollen and Production of Sperm • Microspores develop into pollen grains, which contain the male gametophytes • Pollination is the transfer of pollen to the part of a seed plant containing the ovules Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Pollen and Production of Sperm • Microspores develop into pollen grains, which contain the male gametophytes • Pollination is the transfer of pollen to the part of a seed plant containing the ovules • Pollen eliminates the need for a film of water and can be dispersed great distances by air or animals Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Pollen and Production of Sperm • Microspores develop into pollen grains, which contain the male gametophytes • Pollination is the transfer of pollen to the part of a seed plant containing the ovules • Pollen eliminates the need for a film of water and can be dispersed great distances by air or animals • If a pollen grain germinates, it gives rise to a pollen tube that discharges two sperm into the female gametophyte within the ovule Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 30-3-2 Female gametophyte (n) Spore wall Egg nucleus (n) Male gametophyte (within a germinated Discharged pollen grain) (n) sperm nucleus (n) Micropyle Pollen grain (n) (b) Fertilized ovule The Evolutionary Advantage of Seeds • A seed develops from the whole ovule Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Evolutionary Advantage of Seeds • A seed develops from the whole ovule • A seed is a sporophyte embryo, along with its food supply, packaged in a protective coat Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Evolutionary Advantage of Seeds • A seed develops from the whole ovule • A seed 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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Evolutionary Advantage of Seeds • A seed develops from the whole ovule • A seed 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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 30-3-3 (c) Gymnosperm seed Fig. 30-3-3 Seed coat (derived from integument) Food supply (female gametophyte tissue) (n) Embryo (2n) (new sporophyte) (c) Gymnosperm seed Fig. 30-3-4 Seed coat Integument Female (derived from gametophyte (n) integument) Spore wall Egg nucleus (n) Immature Food supply female cone (female gametophyte Male gametophyte tissue) (n) Megasporangium (within a germinated Discharged pollen grain) (n) (2n) sperm nucleus (n) Embryo (2n) Megaspore (n) Micropyle Pollen grain (n) (new sporophyte) (a) Unfertilized ovule (b) Fertilized ovule (c) Gymnosperm seed 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 Fig. 30-UN1 Nonvascular plants (bryophytes) Seedless vascular plants Gymnosperms Angiosperms Gymnosperm Evolution (fun fact) • Fossil evidence reveals that by the late Devonian period some plants, called progymnosperms, had begun to acquire some adaptations that characterize seed plants Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 30-4 Archaeopteris, a progymnosperm • Living seed plants can be divided into two clades: gymnosperms and angiosperms Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • Living seed plants can be divided into two clades: gymnosperms and angiosperms • Gymnosperms appear early in the fossil record and dominated the Mesozoic terrestrial ecosystems Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • Living seed plants can be divided into two clades: gymnosperms and angiosperms • Gymnosperms appear early in the fossil record and dominated the Mesozoic terrestrial ecosystems • Gymnosperms were better suited than nonvascular plants to drier conditions Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • Living seed plants can be divided into two clades: gymnosperms and angiosperms • Gymnosperms appear early in the fossil record and dominated the Mesozoic terrestrial ecosystems • Gymnosperms were better suited than nonvascular plants to drier conditions • Today, cone-bearing gymnosperms called conifers dominate in the northern latitudes Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Phylum Cycadophyta • Individuals have large cones and palmlike leaves • These thrived during the Mesozoic, but relatively few species exist today Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 30-5a Cycas revoluta Very successful during Mesozoic (age of cycads) 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 Fig. 30-5b Ginkgo biloba pollen-producing (male) tree Fig. 30-5c Ginkgo biloba leaves and fleshy seeds Phylum Gnetophyta • This phylum comprises three genera • Species vary in appearance, and some are tropical whereas others live in deserts Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 30-5d Gnetum Fig. 30-5e Ephedra “Morman Tea” caffeine + ephedrine! Fig. 30-5f Welwitschia SW Africa some of the biggest leaves Fig. 30-5g Ovulate cones Welwitschia Phylum Coniferophyta • This phylum
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