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Chapter 30 Plant Diversity II: The Evolution of Seed Plants PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 30.1: The reduced gametophytes of seed plants are protected in ovules and pollen grains • In addition to seeds, the following are common to all seed plants: – Reduced gametophytes – Heterospory – Ovules – Pollen 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 30-2 Sporophyte (2n) Sporophyte (2n) Gametophyte (n) Sporophyte dependent on gametophyte (mosses and other bryophytes) Microscopic female gametophytes (n) in ovulate cones (dependent) Gametophyte (n) Large sporophyte and small, independent gametophyte (ferns and other seedless vascular plants) Sporophyte (2n), the flowering plant (independent) Microscopic male gametophytes (n) in inside these parts of flowers (dependent) Microscopic male gametophytes (n) in pollen cones (dependent) Sporophyte (2n), (independent) Microscopic female gametophytes (n) in inside these parts of flowers (dependent) Reduced gametophyte dependent on sporophyte (seed plants: gymnosperms and angiosperms) Heterospory: The Rule Among Seed Plants • Seed plants evolved from plants with megasporangia, which produce megaspores that give rise to female gametophytes • Seed plants evolved from plants with microsporangia, which produce microspores that give rise to male gametophytes Copyright © 2005 Pearson Education, Inc. publishing as 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 © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 30-3 Integument Female gametophyte (n) Seed coat (derived from integument) Spore wall Egg nucleus (n) Megasporangium (2n) Megaspore (n) Unfertilized ovule Male gametophyte (within germinating pollen grain) (n) Micropyle Fertilized ovule Discharged sperm nucleus (n) Pollen grain (n) Food supply (female gametophyte tissue) (n) Embryo (2n) (new sporophyte) Gymnosperm seed 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 can be dispersed by air or animals, eliminating the water requirement for fertilization • If a pollen grain germinates, it gives rise to a pollen tube that discharges two sperm into the female gametophyte within the ovule Copyright © 2005 Pearson Education, Inc. publishing as 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 © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 30.2: Gymnosperms bear “naked” seeds, typically on cones • The gymnosperms include 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 © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 30-4aa Cycas revoluta LE 30-4ab LE 30-4ac LE 30-4ad Gnetum. This genus includes about 35 species of tropical trees, shrubs, and vines, mainly native to Africa and Asia. Their leaves look similar to those of flowering plants, and their seeds look somewhat like fruits. LE 30-4ae Ephedra. This genus includes about 40 species that inhabit arid regions throughout the world. Known in North America as “Mormon tea,” these desert shrubs produce the compound ephedrine, commonly used as a decongestant. LE 30-4af Welwitschia. This genus consists of one species Welwitschia mirabilis, a plant that lives only in the deserts of southwestern Africa. Its strap like leaves are among the largest known. LE 30-4ag Ovulate cones LE 30-4ba Douglas fir. “Doug fir” (Pseudotsuga menziesii) provides more timber than any other North American tree species. Some uses include house framing, plywood, pulpwood for paper, railroad ties, and boxes and crates.