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Chapter 25

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Chapter 25

  1. 1. Seedless Plants Chapter 25
  2. 2. Origin of Land Plants • All green algae and the land plants shared a common ancestor a little over 1 BYA – Kingdom Viridiplantae – Not all photoautotrophs are plants • Red and brown algae are photoautotrophs but not classified as plants • A single species of freshwater green algae gave rise to the entire terrestrial plant lineage 2
  3. 3. 3 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ancestral alga Chlorophytes Charophytes Liverworts HornwortsMosses Lycophytes Gymnosperms Angiosperms Seed plants Euphyllophytes Bryophytes Land plants Streptophyta Green plants Green algaeGreen algae Red Algae Tracheophytes Ferns + Allies
  4. 4. Focus on Land Plants •Adaptations to terrestrial life – Protection from desiccation (“drying out”) • all land plants have at least some adaptations for this! – Alternation of generations • all land plants have this lifecycle! – Vascular tissue allows plants to grow taller • Xylem and phloem to conduct water and food • Only “vascular” plants have this! 4
  5. 5. 5 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Spore Spore n n nn Spore mother cell 2n Sporangia Sporophyte (2n) 2n 2n Zygote Embryo Egg Sperm MEIOSIS MITOSIS FERTILIZATION n 2n Gametophyte (n)
  6. 6. Alternation of generations (also called the haplodiplontic cycle) • Multicellular diploid stage – The whole plant in this stage is called the sporophyte – All the cells in the sporophyte plant are diploid at first. – A few cells called sporocytes are located in the organ called the sporangium – Only the sporocytes go through meiosis to produce haploid cells called spores – The sporocytes are found in the sporangium. When meiosis is complete, the spores (daughter cells of meiosis) are still in the sporangium. – Then the sporangium cracks open and releases the spores 6
  7. 7. 7 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. © Edward S. Ross Sporophyte Gametophyte Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. n 2n 2n 2n 1n 1n Sperm Sporangium Antheridia Egg Archegonia Gametophytes Spores Rhizoids Female Male Zygote MITOSIS FERTILIZATION Mature sporophyte Developing sporophyte in archegonium Parent gametophyte MITOSIS M IEIO SIS Germinating spores Notice that the words “leaf,” stem,” and “root” are not used with bryophytes
  8. 8. • Multicellular haploid stage – The plant in this stage is called the gametophyte – When a haploid spore is released from the sporangium, it lands on moist soil and germinates (ie it divides by mitosis) until the whole gametophyte is grown – A few cells in the organ called the gametangium go through a “special” mitosis to form gametes. – Sperm will leave their gametangium and swim to the eggs in the female gametangium – Gametes fuse to form diploid zygote – Zygotes grows by mitosis into the next sporophyte plant 8 Alternation of generations (also called the haplodiplontic cycle)
  9. 9. 9 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. © Edward S. Ross Sporophyte Gametophyte Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. n 2n 2n 2n 1n 1n Sperm Sporangium Antheridia Egg Archegonia Gametophytes Spores Rhizoids Female Male Zygote MITOSIS FERTILIZATION Mature sporophyte Developing sporophyte in archegonium Parent gametophyte MITOSIS M IEIO SIS Germinating spores Notice that the words “leaf,” stem,” and “root” are not used with bryophytes
  10. 10. Bryophytes – seedless nontracheophytes • Closest living descendants of the first land plants • Called “nontracheophytes” because they lack tracheids – (often called “nonvascular,” but that’s not exactly accurate) • Symbiotic relationships between fungi and plants are important for absorption 10 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Charophytes Liverworts Mosses Hornworts Tracheophytes
  11. 11. • Simple, but highly adapted to diverse terrestrial environments • 24,700 species in 3 clades – Liverworts – Mosses – Hornworts • Gametophyte – the most noticeable part, and the photosynthetic part – Sporophytes are small and dependent • Require water for sexual reproduction 11
  12. 12. Tracheophyte Plants • Cooksonia, the first vascular land plant – Appeared about 420 MYA • Only a few centimeters tall – No roots or leaves – Homosporous – only 1 type of spore 12 Sporangia Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
  13. 13. Vascular tissues • Xylem – Consists of dead cells called tracheids that form a tube – Conducts water and dissolved minerals upward from the roots • Phloem – Consists of living cells – Conducts sucrose and hormones throughout the plant • Vascular tissues develop in sporophyte but not gametophyte, so gametophyte is smaller 13
  14. 14. Tracheophytes • Vascular plants include seven extant phyla grouped in three clades 1. Lycophytes (club mosses) 2. Pterophytes (ferns, whisk ferns, and horsetails) 3. Seed plants • Gametophyte has been reduced in size relative to the sporophyte during the evolution of tracheophytes 14
  15. 15. 15
  16. 16. • 40 million years between appearance of vascular tissue and true leaves – Stems, then roots • Provide transport and support – Then leaves • Increase surface area for photosynthesis • Seeds - didn’t evolve until Mesozoic Era – Highly resistant to desiccation – Contain an embryo plus a food supply – Lycophytes and pterophytes do not have seeds 16
  17. 17. 17 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ancestral alga Chlorophytes Charophytes Liverworts HornwortsMosses Lycophytes Gymnosperms Angiosperms Chlorophyll a and b Plasmodesmata Cuticle Antheridia and archegonia Multicellular embryo Stomata Euphylls Seeds Flowers Fruits Dominant sporophyte Stems, roots, leaves Ferns + Allies Vascular tissue Bryophytes are seedless nontracheophytes Club mosses and ferns are seedless tracheophytes Antheridia are the male gametangia; archegonia are the female gametangia
  18. 18. Lycophytes – misnamed “club moss” 18 Pterophytes •Whisk ferns •Horsetails •Ferns (see next slide) Seedless Tracheophytes
  19. 19. Ferns • Most abundant group of seedless vascular plants – About 11,000 species • Coal formed from forests 300 mya • The larger sporophyte and much smaller gametophyte are both photosynthetic 19
  20. 20. 20 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. MEIOSIS n 2n Archegonium Archegonium Antheridium Antheridium Egg Sperm Embryo 1n Gametophyte Rhizome Sporangium Spores Rhizoids Gametophyte MITOSIS Underside of leaf frond Mature sporangium Sorus (cluster of sporangia) Adult sporophyte Mature frond Leaf of young sporophyte MITOSIS Zygote 2n FERTILIZATION
  21. 21. Fern reproduction • Produce distinctive sporangia in clusters called “sori” on the back of the fronds • Diploid spore mother cells (also called sporocytes) in sporangia produce haploid spores by meiosis • Every spore germinates into bisexual gametophyte (contains archegonia and antheridia on same gametophyte plant) • Flagellated sperm 21

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