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Adaptations of Land Plant • Offspring develop from multicellular embryos that remain attached to the “mother” plant for protection and nourishment. • Vascular tissue is present in all but the bryophytes ( some of these have some type of transport vessels but lack TRUE roots, stems and leaves. There are four main groups of land plants • Bryotphytes – mosses • Pteriodophytes – ferns • Gymnosperm – conifers • Angiosperms – flowering plants Charophyceans are the green algae most closely related to land plants • Charophyceans are the green algae most closely related to land plants Features that distinguish land plants. • Plasma membranes containing rosette cellulose – synthesizing proteins • Peroxisomes – help maximize the loss of organic products due to photorespiration. • Flagellated sperm are similar • Cell division – formation of phragmoplast Five Characteristics Unique to Land Plants • Apical meristem – localized regions of active cell division in roots and shoots • Embryophtes – multicellular dependent embryos • Alternation of Generations • Walled spores produced in sporangia • Multicellular reproductive structures – antheridia and archegonia What Is a Plant? • Multicellular eukaryotes that are photosynthetic autotrophs • Cell walls made of cellulose • Store surplus carbohydrates as starch • Mostly terrestrial Terrestrial Adaptations Are Complimented by Chemical Adaptations • Secondary products – Synthesized by side branches of main metabolic pathway – Many protect the plant against excessive damage by herbivores – Examples • Cuticle • Lignin • Sporopollenin Reproduction • Plants produce their gametes within GAMETANGIA • Zygote develops into an embryo within a jacket of protective cells • Embryophytes – a key adaptation to the success of plants on land ALTERNATION OF GENERATIONS • Occurs in life cycle of all plants • One generation is a multicellular haploid condition and the next is a multicellular diploid condition Obstacles Plants Overcome • Absorb Minerals • Conserve Water – Cuticle – Stomata – Guard Cells • Reproduce on Land A Vascular System Enables Plants to Thrive on Land • Most plants need a “plumbing” system to transport water, minerals and nutrients. This system is known as the VASCULAR SYSTEM. •Plants are monophylogenetic Key to Modern Plant Diversity • There are four main periods of plant evolution. Each period was an adaptative radiation that follow the evolution of structures that open the new opportunities on land. • The first terrestrial adaptations included spores toughened by sporopollenin and jacketed in gametangia that protect the gametes. • The second major period was plant diversification in the Devonian period – earliest vascular plants lacking seeds • The third major period of evolution was the origin of the seed. • The fourth was the emergence of flowering plants. Bryophytes – the Liverworts • Simplest of plants (gametophytes are dominate • Flat leafy body lacking cuticle, stomata, roots, stems or leaves – the Hornworts • Dominate gametophyte and have stomata – the Mosses • Small, most have simple vascular tissue • Sporophyte with slender stalk and spore capsule • “leafy” green gametophyte that lacks roots, stems and leaves Bryophyta liverwort Sphagnum moss moss hornwort Nonvascular, no true leaves roots and stems, root-like structures call rhizoids anchor plant to the soil, pioneer plants, gametophyte is the dominate generation Moss genertations Phylum Pterophyta • Ferns are very divserse • Largest ferns are 82 feet tall with fronds 16 feet long • Leaves are called fronds • A fiddlehead is a tightly coiled new leaf • Underground stem called a rhizome • In vascular plants the branched sporophyte is dominant and is independent of the parent gametophyte. • The first vascular plants, pteridophytes, were seedless. • Vascular plants built on the tissue-producing meristems, gametangia, embryos and sporophytes, stomata, cuticles, and sproropollenin-walled spores that they inherited from mosslike ancestors. Pteridophytes provide clues to the evolution of roots and leaves • Most pteridophytes have true roots with lignified vascular tissue. • These roots appear to have evolved from the lowermost, subterranean portions of stems of ancient vascular plants. – It is still uncertain if the roots of seed plants arose independently or are homologous to pteridophyte roots. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • The seedless vascular plants, the pteridophytes consists of two modern phyla: – phylum Lycophyta - lycophytes – phylum Pterophyta - ferns, whisk ferns, and horsetails • These phyla probably evolved from different ancestors among the early vascular plants. Fig. 29.21 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • Ferns also demonstrate a key variation among vascular plants: the distinction between homosporous and heterosporous plants. • A homosporous sporophyte produces a single type of spore. – This spore develops into a bisexual gametophyte with both archegonia (female sex organs) and antheridia (male sex organs). Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings A sporophyte-dominant life cycle evolved in seedless vascular plants • From the early vascular plants to the modern vascular plants, the sporophyte generation is the larger and more complex plant. – For example, the leafy fern plants that you are familiar with are sporophytes. – The gametophytes are tiny plants that grow on or just below the soil surface. – This reduction in the size of the gametophytes is even more extreme in seed plants. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 29.23 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • Ferns first appeared in the Devonian and have radiated extensively until there are over 12,000 species today. – Ferns are most diverse in the tropics but are also found in temperate forests and even arid habitats. • Ferns often have horizontal rhizomes from which grow large megaphyllous leaves with an extensively branched vascular system. – Fern leaves or fronds may be divided into many leaflets. Fig. 29.21d Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • A heterosporous sporophyte produces two kinds of spores. – Megaspores develop into females gametophytes. – Microspores develop into male gametophytes. • Regardless of origin, the flagellated sperm cells of ferns, other seedless vascular plants, and even some seed plants must swim in a film of water to reach eggs. • Because of this, seedless vascular plants are most common in relatively damp habitats. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • Coal powered the Industrial Revolution but has been partially replaced by oil and gas in more recent times. – Today, as nonrenewable oil and gas supplies are depleted, some politicians have advocated are resurgence in coal use. – However, burning more coal will contribute to the buildup of carbon dioxide and other “greenhouse gases” that contribute to global warming. – Energy conservation and the development of alternative energy sources seem more prudent. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • Ferns produce clusters of sporangia, called sori, on the back of green leaves (sporophylls) or on special, non-green leaves. – Sori can be arranged in various patterns that are useful in fern identification. – Most fern sporangia have springlike devices that catapult spores several meters from the parent plant. – Spores can be carried great distances by the wind. Fig. 29.24a, b Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings