Plant Diversity I

Terrestrial environments - deserts, grasslands, forests. 4 groups of land plants: bryophytes, pteridophytes, gymnosperms, and angiosperms. Most common bryophytes - mosses. Pteridophytes - ferns. Gymnosperms – pines, conifers. Angiosperms - flowering plants.

Copyright © 2002 Pearson Education, Inc Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Bryophytes - offspring remain attached to parent plant. Non-vascular plants. Vascular plants - vascular tissues, cells join into tubes that transport water, nutrients throughout plant body.

http://www.science.siu.edu/landplants/Bryophyta/images/Physcomitrium.JPEG

Ferns - seedless plants. Seed - plant embryo packaged along with food supply within protective coat. Early seed plants gave rise to diversity of present-day gymnosperms, including conifers. Modern plants angiosperms.

http://www. rockhillridge http://www.rockhillridge.com/images/hayes/Ferns,%20Hayes%20Tract%206%2003-web.jpg Fern

Plant evolution: 1Origin of bryophytes from algal ancestors. 2Origin, diversification of vascular plants. 3Origin of seeds. 4Evolution of flowers.

Plants – multicellular, derive energy and nutrition through photosynthesis. Plant cell walls - cellulose. Different from algae - apical meristems, alternation of generations, sporangia that produce walled spores.

http://www. botany. hawaii http://www.botany.hawaii.edu/faculty/webb/BOT311/bot311-00/PlantCellWalls00/CellWallHemiLab.jpg

Plants need to grow to maximize absorption. Done through apical meristems - undifferentiated cells that divide when needed. Located at tips of roots, shoots.

Multicellular plant embryos develop from zygotes - stay in tissues of female parent. Land plants - embryophytes. Parent provides nutrients to embryo.

Alternation of generations - gametophyte produces haploid gametes that get fertilized; form a diploid zygote that will grow into mature sporophyte.

http://fig.cox.miami.edu/~cmallery/150/mitosis/sf9x7c.jpg

Sporophyte produces haploid single-celled spores - grow into gametophyte. Spore - reproductive cell that can develop into new organism. Size of sporophyte and gametophyte differ in plant species.

Bryophytes - gametophyte dominant generation. Pteridophytes, gymnosperms, and angiosperms - sporophyte dominant generation.

http://www. sbs. auckland. ac http://www.sbs.auckland.ac.nz/info/schools/nzplants/images/moss/moss_major_parts1.jpg

Spores - haploid reproductive cells -grow into gametophyte by mitosis. Covered by sporopollenin – resistant to outside stress. Sporangia found on sporophyte - produce spores.

Female gametangium (gamete producing organ) – archegonium - produces single egg cell in vase-shaped organ. Male gametangia – antheridia - produce many sperm cells released to environment. Sperm fuses with egg in archegonium.

Female

Fusion of sperm and egg

Land plants have cuticle – protects from drying out, microbes. Stomata, in epidermis of leaves allow exchange of carbon dioxide and oxygen between outside air and leaf interior.

Land plants - true roots, stems, leaves. Xylem carry water, minerals up from roots. Dead at maturity. Phloem - living tissue - nutrient-conducting cells arranged into tubes distribute sugars, amino acids, other organic products.

http://www.bbc.co.uk/schools/gcsebitesize/img/bixylemphloem.gif

Plants also produce secondary compounds. Include alkaloids, terpenes, tannins, and phenolics such as flavonoids - bitter tastes, strong odors, or toxic effects. Some used for medicinal purposes.

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Origin of land plants Chloroplasts of land plants most similar to plastids of green algae. In both - cellulose comprises 20-26% of cell wall.

http://www. rsbs. anu. edu http://www.rsbs.anu.edu.au/profiles/Brian_Gunning/Web%20PCB/Ch%2010%20Plastids/Topic%2005%20Chloroplasts-Charophyceae/10%2005%2010.jpg

Bryophytes 3 phyla - phylum Hepatophyta – liverworts, phylum Anthocerophyta – hornworts, phylum Bryophyta – mosses. Gametophytes dominant phase of life cycle.

Bryophytes anchored by tubular cells or filaments of cells - rhizoids. Lack conducting tissues to distribute water and organic compounds within gametophyte – very small.

http://userwww.sfsu.edu/~biol240/labs/lab_10plantoverview/media/rhizoids.jpg

“Leaves” of most mosses lack a cuticle and are only 1 cell thick – allow quick absorption from surroundings. Mature gametophores of bryophytes produce gametes in gametangia.

http://io.uwinnipeg.ca/~simmons/Chap29a98/img016.jpg

Archegonium - single egg. Antheridia - many flagellated sperm. Sperm swim toward archegonia, drawn by chemical attractants. Zygotes and young sporophytes retained and nourished by parent gametophyte.

Moss sporophytes consist of foot, elongated stalk (seta), and sporangium (capsule). Foot gathers nutrients and water from parent gametophyte via transfer cells. Stalk conducts materials to capsule. Capsule – disperse spores.

Common in wetlands, wind dispersal allows for inhabiting many different areas. Sphagnum, wetland moss, abundant and widespread – forms deposits of undecayed organic material – peat. Forms peat bogs.

Vascular plants have food transport tissues (phloem) and water conducting tissues (xylem) with lignified cells. 1st vascular plants, pteridophytes, were seedless.

http://www. florelaurentienne http://www.florelaurentienne.com/flore/Groupes/Pteridophytes/images/Adiantum_pedatum_940528_21_800.jpg

Seedless Vascular Plants Cooksonia, extinct plant over 400 million years old, earliest known vascular plant. Seedless vascular plants, pteridophytes consists of 2 modern phyla: Phylum Lycophyta – lycophytes. Phylum Pterophyta -- ferns, whisk ferns, and horsetails.

Cooksonia

Lycophytes have small leaves (microphylls) with single unbranched vein. Leaves of other vascular plants, megaphylls much larger and highly-branched.

Homosporous sporophyte produces a single type of spore. Heterosporous sporophyte produces 2 kinds of spores. Megaspores - females gametophytes. Microspores - male gametophytes.

Fig. 29.23 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Modern lycophytes include tropical species that grow on trees as epiphytes, using the trees as substrates, not as hosts. Specialized leaves (sporophylls) bear sporangia clustered to form club-shaped cones.

http://www.tcr.gov.nl.ca/nfmuseum/images/osmundaclaytoniana3barrdharbourhilljuly122002.jpg

Phylum Pterophyta – ferns and relatives. 1Psilophytes - whisk ferns. 2Sphenophytes – horsetails - often found in marshy habitats and along streams and sandy roadways. Roots develop from horizontal rhizomes that extend along ground.

3Ferns - horizontal rhizomes. Fern leaves (fronds) may be divided into many leaflets. Produce clusters of sporangia (sori) on back of green leaves (sporophylls) or on special, non-green leaves. Dispersed by wind.