Chapter 16Plants, Fungi, and the Move onto LandBiology and Society: Will the Blight End the Chestnut?• American chestnut trees– Once dominated forests of the eastern United States – Were prized for their– Rapid growth – Huge size– Rot-resistant wood•• Around 1900, an Asian fungus was accidentally introduced from China into North America, and in just 25 years, blight caused by the fungus killed virtually alladult American chestnut trees.• Fortunately, this type of harmful interaction between plant and fungus is unusual.• Many plants and fungi benefit from each other’sexistence.COLONIZING LAND• Plants are terrestrial organisms that include forms that have returned to water, such as water lilies.Terrestrial Adaptations of Plants Structural Adaptations• A plant is– A multicellular eukaryote – A photoautotroph, making organic molecules byphotosynthesis• In terrestrial habitats, the resources that a photosynthetic organism needs are found in two very different places: – Light and carbon dioxide are mainly available inthe air – Water and mineral nutrients are found mainly in the soil •• The complex bodies of plants are specialized to take advantage of these two environments by having– Aerial leaf-bearing organs called shoots – Subterranean organs called roots• Most plants have mycorrhizae, symbiotic fungiassociated with their roots, in which the fungi– Absorb water and essential minerals from the soil– Provide these materials to the plant– Are nourished by sugars produced by the plant • Leaves are the main photosynthetic organs of most plants, with– Stomata for the exchange of carbon dioxide andoxygen with the atmosphere– Vascular tissue for transporting vital materials– A waxy cuticle surface that helps the plant retain water• Vascular tissue in plants is also found in the– Roots – Shoots• Two types of vascular tissue exist in plants:– Xylem transports water and minerals from rootsto leaves – Phloem distributes sugars from leaves to the roots and other nonphotosynthetic parts of the plantReproductive Adaptations• Plants produce their gametes in protective structures called gametangia, which have a jacket of protective cells surrounding a moist chamber where gametes can develop without dehydrating.• The zygote develops into an embryo while still contained within the female parent in plants but not in algae.The Origin of Plants from Green Algae• The algal ancestors of plants– Carpeted moist fringes of lakes or coastal salt marshes – First evolved over 500 million years ago• Charophytes– Are a modern-day lineage of green algae – May resemble one of these early plant ancestorsPLANT DIVERSITY• The history of the plant kingdom is a story of adaptation to diverse terrestrial habitats.Highlights of Plant Evolution• The fossil record chronicles four major periods of plant evolution.• (1) About 475 million years ago plants originated from an algal ancestor giving rise to bryophytes, nonvascular plants, including mosses, liverworts, and hornworts that are nonvascular plants without– Lignified walls– True roots– True leaves• (2) About 425 million years ago ferns evolved– With vascular tissue hardened with lignin– But without seeds• (3) About 360 million years ago gymnosperms evolved with seeds that consisted of an embryo packaged along with a store of food within a protective covering but not enclosed in any specialized chambers.• Today, conifers, consisting mainly of cone-bearing trees such as pines, are the most diverse and widespread gymnosperms.• (4) About 140 million years ago angiosperms evolved with complex reproductive structures called flowers that bear seeds within protective chambers called ovaries.• The great majority of living plants– Are angiosperms– Include fruit and vegetable crops, grains, grasses, and most trees– Are represented by more than 250,000 speciesBryophytes• Bryophytes, most commonly mosses– Sprawl as low mats over acres of land– Need water to reproduce because their sperm swim to reach eggs within the female gametangium– Have two key terrestrial adaptations:– A waxy cuticle that helps prevent dehydration – The retention of developing embryos within the mother plant’s gametangium • Mosses have two distinct forms:– The gametophyte, which produces gametes – The sporophyte, which produces spores• The life cycle of a moss exhibits an alternation of generations shifting between the gametophyte and sporophyte forms.• Mosses and other bryophytes are unique in having the gametophyte as the larger, more obvious plant. Ferns• Ferns are– Seedless vascular plants – By far the most diverse with more than 12,000 known species• The sperm of ferns, like those of mosses– Have flagella – Must swim through a film of water to fertilize eggs• During the Carboniferous period, from about 360 to 300 million years ago, ferns– Were part of a great diversity of seedless plants – Formed swampy forests over much of what is now Eurasia and North America• As they died, these forests formed coal.• Fossil fuels– Include coal, oil, and natural gas– Formed from the remains of long-dead organismsGymnosperms• At the end of the Carboniferous period, the climate turned drier and colder, favoring the evolution of gymnosperms, which can – Complete their life cycles on dry land – Withstand long, harsh winters• The descendants of early gymnosperms include the conifers, or cone-bearing plants.Conifers• Conifers– Cover much of northern Eurasia and North America– Are usually evergreens, which retain their leavesthroughout the year– Include the tallest, largest, and oldest organisms on EarthTerrestrial Adaptations of Seed Plants• Conifers and most other gymnosperms have three additional terrestrial adaptations:– Further reduction of the gametophyte– Pollen– Seeds• Seed plants have a greater development of the diploid sporophyte compared to the haploid gametophyte generation.• A pine tree or other conifer is actually a sporophyte with tiny gametophytes living in cones.• A second adaptation of seed plants to dry land was the evolution of pollen.• A pollen grain– Is actually the much-reduced male gametophyte – Houses cells that will develop into sperm• The third terrestrial adaptation was the development of the seed, consisting of– A plant embryo – A food supply packaged together within a