Download to read offline
Charleen Baker - Botany Lecture - Lecture
- 1. This is apresentation used during Botany lecture on nonvascular plants. To complete the entire lecture would be about 2 lectures. When questions are stated in the presentation, usually students get into groups to discuss, then we will have a general class discussion on the question and at the end of the lecture an activity sheet was given as review Charleen Baker
- 2. Chapter 20 Nonvascular Plants:Mosses, Liverworts, and Hornworts
- 3. Review of Terms •Meiosis occurs at some point for organisms that reproduce sexually • When gametes unite forming a zygote which has 2 complete sets of chromosomes • A cell with one set of chromosomes – haploid • A cell with two sets of chromosomes – diploid • End of meiosis – 4 haploid cells produced from 1 diploid cell
- 4. • Many plantscontain more than 2 sets of chromosomes & called polyploidy • 3 sets of chromosomes – Triploid – ex) navel oranges & seedless watermelons – gametes are not inviable & no seeds produced • Bread wheat – hexaploid (6 sets) • Strawberry – octaploid (8 sets)
- 5. Alternation of Generations •In animals – only haploid cells have single set of chromosomes - called gametes (egg & sperm), Generally this is not true in plants • Complete life cycle of a diploid species that undergoes sexual reproduction there is an alternation between sporophyte (2n, diploid) and haploid gametophyte (n) phase • This is a called Alternation of Generations • 2n – refers to sporophyte generation or the stages in the life cycle produced by fertilization • 1n – refers to the gametophyte generation or stages in the life cycle produced by meiosis
- 6. • Diploid body– sporophyte • Develops from a zygote • Eventually produces sporocytes which each undergoes meiosis & produces a spore • Haploid body – gametophyte • Develops from a mitotic divisions of spores produced by the sporophyte • Specialized cells within gametophytes function as gametes
- 7. Six rules forAlternation of Generation 1. First cell of the gametophyte generation is a spore & the last cell is a gamete 2. Any cell of the gametophyte generation (n) contains half as many chromosomes as the sporophyte generation
- 8. 3. First cellof the sporophyte generation is a zygote and the last cell is a spore 4. Any cell of sporophyte generation (2n) contains twice as many chromosomes as the gametophyte generation 5. Change from sporophyte to gametophyte generation occurs as a result of meiosis 6. Change from gametophyte to sporophyte generation occurs as a result of fusion of gametes at fertilization
- 9. Advantages and Disadvantagesof Alternation of Generation Think, Discuss and Share
- 10. 3 Groups of Plants •Have neither vascular tissues nor seeds, the non-vascular plants (often called “bryophytes”) • Have vascular tissue but not seeds, the vascular cryptogams • Have both vascular tissue and seeds, spermatophytes
- 11. Objectives for NonVascularPlants • Describe structural adaptations for moving to land • Explain their alternation of generation • Compare mosses, liverwort & hornwort • Ecological & Economic Importance
- 12. List some ofthe problems associated with a terrestrial environment How can these problems be solved by plants?
- 13. Characteristics of NonvascularPlants • World War I – nurses used green material found by a lake as a bandage – which was much better than cotton bandages • It was Sphagnum moss – which has antiseptic properties, has specialized water absorbing leaves & used as packing material • One of about 23,000 species of bryophytes • Ex) moss, liverworts & hornworts
- 14. • Some canwithstand long periods of desiccation – found on bare rocks • Others occur on frozen alpine slopes • Habitats range from sea level up to 5,500 or more meters in mountains • Some highly restricted and other not in their habitat
- 15. • Often havemycorrhizal fungi associated with their rhizoids • Widespread peat moss are ecologically very important in bogs & transformation of bogs to dry land • Peat moss can form a mat over water & keep conditions acidic inhibit other growth so many organisms can be preserved in bogs
- 16. • None havetrue xylem or phloem • To be able to sexually reproduce must have external water usually in the form of dew or rain • Many have special water & mineral conducting cells called hydroids in the center of the stems • Few have food conducting cells called leptoids surrounding the hydroids • Neither conduct efficiently, most absorb directly though the surface
- 17. • Bryophytes aresoft & pliable • Birds use them for their nests • Leafy plant is the major part – gametophyte generation produces gametes • Sporophyte generation – which grows from leafy gametophyte produces spores • Being embryophytes, they have multicellular sporangia and gametangia alternation of heteromorphic generations
- 18. • Nonvascular plantsare almost exclusively terrestrial and have a cuticle over much of their bodies, and many have stomata • Nonvascular plants can never grow to be really large, but being small & simple provides great selective advantage in certain habitats • All bryophytes have similar life cycles & growth habits however based on their structure & reproduction they are separated into 3 groups
- 19.
- 20. General Characteristics ofMosses • Gametophyte – plant you see the most • “Leaves” – have no mesophyll tissue, stomata or veins • Blades usually 1 cell thick, except midrib • No petiole • Contains numerous lens shaped chloroplasts
- 21. • Axis issomewhat stem like but no xylem or phloem • Base – root like rhizoids consisting of several rows of colorless cells that anchor the plant • All moss stems have leaves, but because they are parts of a gametophyte, not a sporophyte, they are not homologous with those of vascular plants
- 22. • Moss gametophytesare both large and photosynthetic, and they support the sporophyte throughout its entire life • All moss sporophytes form from the zygote and have 3 basic components at maturity: foot, capsule (where spores are produced), and seta • None is ever branched or has leaves, bracts, or buds of any kind
- 23. • Certain mossescan grow on hard, impervious surfaces because they have no roots that must penetrate the substrate • The majority of mosses lack hydroids and leptoids; water is conducted along the exterior of their stems by capillary action • Some water absorbed by rhizoids rises up the central strand • Closely packed habit & they rarely extend more than a few centimeters into the air, favors such water movement • Water absorbed directly through the plant surfaces
- 24. Always a welcomesight, the White Water-lily attracts us (and a wide variety of insects) with its perfumed scent, as well.This very common herbaceous plant can be found throughout the Pinelands, and is one of the most noticeable of all the aquatic plants, even when not flowering. The flat “lily pads” floating on the surface appear fresh and delicate when they first emerge. They provide food for a variety of creatures and finally disappear as winter comes along. But the plants are perennial, so those that live through the winter send new shoots to the surface each spring, and the seeds that germinate create new plants. Duration: Perennial Flower: early June to late September. Habitat: ponds, cranberry reservoirs, streams. White Water-lily Nymphaea odorata subsp. odorata
- 25. List some ofthe problems associated with a terrestrial environment How can these problems be solved by plants?
- 26.
- 27. • Gametophyte generation formswhen haploid spore germinates & produces a protonema filament • From protonema, shoots (gametophytes) arise
- 28. • Gametophytes producemale & female gametangia – often on the same plant but can be on separate plants • Archegonia – Female gametangia) – cylindrical & project upward from the base of extended gametophyte tip • Single egg produced in cavity
- 29. • Antheridia (malegametangia) – walls 1 cell thick • Borne on short stalks • Sperm forced out of the top of the Antheridium when it absorbs water & swells • Each sperm has flagella
- 30. • Secretion ofsucrose from the archegonia guides sperm as they swim toward the archegonia and then to the egg, where one sperm cell effects fertilization & a zygote is formed • Embryo breaks down archegonium & becomes attached to the stem by a swollen knob called the foot • It grows & when it breaks through the top of the venter it is a sporophyte • Sporophyte is first photosynthetic but is still dependent on the gametophyte • When mature, capsule opens and releases haploid spores
- 31. Asexual Reproduction • Mayoccur by fragmentation or gemmae • Pieces of gametophyte can break off & form new plants • Gemmae are tiny, cup shaped structures on the gametophyte • Raindrops separate gemmae from the parent so it spreads them out
- 32. Metabolism and Ecology •The small size and lack of conducting tissues are two critical factors in the metabolism and ecology of mosses • Without vascular tissue, stems and leaves can become desiccated, even while the rhizoids are in contact with moist soil or tree bark • Several mechanisms compensate for the inability of mosses to retain water, such as life in moist habitats
- 33.
- 34. General Characteristics ofLiverworts • Small plants that have an alternation of heteromorphic generations • The sporophyte is even less conspicuous than in mosses and is also completely dependent on the gametophyte • About 8000 species • Types – Leaflike or Thalloid
- 35. • Liverwort gametophoresmay be either bisexual, producing both antheridia and archegonia, or unisexual, depending on the species
- 38.
- 39. General Characteristics ofHornworts • Leafy like liverworts • Archegonia & antheridia form inside the plant • After fertilization, zygotes develop into long, horn shaped sporophytes • Sporophytes capable of photosynthesis
- 40. • Hornworts area group of small, inconspicuous thalloid plants that grow on moist soil, hidden by grasses and other herbs • Hornworts superficially resemble thalloid liverworts, but never contain oil bodies • One of the most striking features is the presence of a single large chloroplast in each cell as opposed to the numerous small plastids present in all other nonalgal plants
- 41. Ecological Importance • Pioneersof bare rock • Can retain water (especially mosses) • Reduce flooding & erosion • Peat moss – packing, acidity, soil conditioner & as a fuel
- 42. Summary • They evolvedto survive the occasional drying of their streams, small lakes and ocean-mud flats. • One strategy for surviving temporary dry spells was the evolution of drought-resistant spores. • Large, compact, multicellular body retains water better than small unicellular or filamentous bodies. • Water-proofing cuticle would be advantageous • Coordination of gamete production with moisture for swimming sperm
- 43. • Due todry land conditions, gamete and spore mother cells needed protection from dryness • Such reproductive modifications resulted in the grouping and protection of spore and gamete mother cells into the sporangia and gametangia characteristic of all embryophytes —more massive than those of algae and protected by a layer of sterile cells.
- 44. Most mosses donot retain water well. What adaptations have evolved to permit them to inhabit terrestrial areas?
- 45. Next Steps! • Asa truly terrestrial existence became more successful, the environment became selective for mutations that produced an upright body that could grow into brighter light. • Production of pollen and seeds eliminates the need for environmental water for reproduction • Vascular tissue, especially phloem, also made feasible the evolution of truly heterotrophic tissues—roots, meristems, and organ primordia