Plants and Conquest of Land PDF

Plants and Conquest of Land Tuesday, February 11, 2025 12:24 AM How can we Define the Term Plants? Multicellular eukaryotic organisms composed of cells having plastids Several hundred thousands of modern Plant species that make up the Kingdom Plantae Primarily live on land Evolved fro...

Plants and Conquest of Land Tuesday, February 11, 2025 12:24 AM How can we Define the Term Plants? Multicellular eukaryotic organisms composed of cells having plastids Several hundred thousands of modern Plant species that make up the Kingdom Plantae Primarily live on land Evolved from green algal ancestors that lived in aquatic habitats Distinguished from modern algal relatives by adaptation to terrestrial life What is the Significance of the Plant Embryo? Charophyceans(type of algae) lack embryos One of the first critical innovations of land plants Plant embryos are young sporophytes that develop from zygotes What are the THREE FEATURES? Multicellular and diploid Zygote and embryos retained in maternal tissue Depends on organic and mineral materials supplied by mother plant; placental transfer issues Placental Transfer Tissue: New Section 2 Page 1  Often in gametophyte tissues closest to embryos and in the embryos themselves Cells are specialized to promote the movement of solutes from gametophyte to embryo Finger-like ingrowths of cell wall increase surface area of plasma membrane for transport proteins What do we know about the Ancestry of Plants? Plantae originated from a photosynthesis protist ancestor that, if presents today, would be classified among the streptophyte algae Modern plants and their closest green algal relatives are together known as streptophytes Complex streptophyte algae share several derived traits with land plants Distinctive type of cytokinesis, intracellular connections Plasmodesmata Sexual reproduction using egg and smaller sperm How have Land Plants Changed the Earth? A billion years ago, the land surface of the earth was bare Except for some cyanobacteria crusts Origin of land plants was key to….. Development of substantial soils New Section 2 Page 2  Rise of modern levels of atmospheric oxygen Evolution of modern plant communities Colonization of land by animals How did Plants Transform Earth's Atmosphere? Photosynthesis Uses CO2 from the atmosphere to produce carbon-containing organic molecules A by-product of photosynthesis is oxygen (O2) Influenced Earth's climate By reducing the concentration of atmospheric CO2 and increasing the concentration of O2 Several types of decay-resistant materials are produced by plants Includes sporopollenin, cutin, and lignin When ancient plants died… Some organic molecules were not completely degraded, but buried in sediments that eventually transformed into rock What Happened During the Coal Age? Dead plants fell into the water Low levels of oxygen present in swamp sediments inhibited decomposition New Section 2 Page 3  Low levels of oxygen present in swamp sediments inhibited decomposition Organic carbon accumulated in sediments that later formed coal Much of today's coal From the abundant remains of Coal Age plants The storage of plant organic matter in sediments caused atmospheric CO2 levels to fall and oxygen levels to increase Explains the Coal Age existence of insects such as giant dragonflies whose large size increased their need for oxygen What are some Distinctive Features of Land Plants Land plants can be distinguished from their close algae relatives by several features that represent early adaptations to land habitat Bodies composed of three-dimensional tissue Increased ability to avoid water loss Tissues arise from apical meristems (fast dividing cells) at growing tips Able to produce thick, robust bodies Tissues and organs with specialized functions Reproductive Features? Aid in survival in terrestrial habitats Alternation of generations: two types of multicellular bodies alternate in time The diploid (2n) sporophyte produces spores by meiosis; the haploid (1n) gametophyte produces gametes by mitosis The sporophyte embryo is nourished and protected by maternal tissues Allows land plants to produce many more spores per zygote than do streptophyte algae Land plant sporophytes produces tough-walled nonflagellate spores that survive dispersal through dry air New Section 2 Page 4  through dry air Allows plants to spread widely across land surfaces Other Reproductive Advantages? Matrotrophy: zygotes remain sheltered and fed within gametophyte tissue All groups of land plants possess matrotrophic embryos, so they are known as Embryophytes When mature, spores are produced in protective enclosures known as sporangia Sporopollenin: tough material in plant spore cell walls that helps prevent cellular damage During evolution, plant sporophytes became larger and more complex Evolution of Reproductive Features in Land Plants: Multicellular diploid sporophyte generations is advantageous because it allows a single plant to disperse widely Uses meiosis to produce numerous, genetically variable haploid spores Each spore has the potential to grow into a gametophyte What are Gametophytes? Role: to produce haploid gametes Produced by mitosis Gametangia protects developing gametes from drying out and microbial attack Antheridia: spherical or elongate gametangia producing sperm Archegonia: flask-shaped gametangia enclosing an egg Sperm swim to egg and fuse to form diploid zygote Zygote grow into sporophytes New Section 2 Page 5 Zygote grow into sporophytes 1. Gametophyte Stage (Haploid, n) This is the dominant stage in mosses. Mosses have male (antheridia) and female (archegonia) reproductive structures. The male antheridia produce sperm, while the female archegonia contain egg cells. 2. Fertilization (Formation of Zygote) Water is essential because sperm must swim to the egg. When sperm reaches the egg in the archegonium, fertilization occurs, forming a diploid (2n) zygote. 3. Sporophyte Stage (Diploid, 2n) The zygote grows by mitosis into a sporophyte, which remains attached to the gametophyte. The sporophyte consists of: Foot (anchors to gametophyte) Seta (stalk) Capsule (sporangium) where spores form. 4. Meiosis (Spore Formation) Inside the capsule, meiosis occurs, producing haploid spores (n). These spores are genetically diverse due to recombination. 5. Spore Dispersal & Germination Spores are released and dispersed by wind or water. If they land in a suitable environment, they germinate into a protonema (a thread-like structure). This protonema develops into a new gametophyte, restarting the cycle. 6. Spore Dispersal & Germination After meiosis occurs inside the capsule of the sporophyte, thousands of haploid spores (n) are produced. These spores must now be dispersed to start a new generation. What are the Nine Plant Phyla? Liverworts: Hepatophyta New Section 2 Page 6  Liverworts: Hepatophyta Hornworts: Anthocerophyta Cycads: Cycadophyta Ginkgos: Ginkophyta Conifers: Coniferophyta Angiosperms (flowering plants): Anthophyta Lycophytes: Lychophyta Pteridophytes: Pteridophytes Mosses: Bryophyta (Bryophytes) Include liverworts, hornworts, and mosses that share common structural, reproductive, and ecological features Each forms a monophyletic phylum (descended from common ancestor) Relatively small in stature Most common and diverse in moist habitats since they lack traits allowing them to grow tall or reproduce in dry places Have reproductive features that evolved early in the history of land plants Alternation of generations, multicelluar embryos, and tough-walled spores Bryophyte Generations: GAMETOPHYTES are the dominant generation of bryophytes Sporophytes are DEPENDENT ON GAMETOPHYTE Sporophytes are small and short-lived Lycophytes: Lycophyta Pteridophytes: Pteridophytes BOTH SEEDLESS VASCULAR PLANTS Possesses vascular tissue Internal water and nutrient conducting tissues that also provide structural support BOTH DO NOT POSSESS SEEDS New Section 2 Page 7  Known as tracheophytes: name taken from tracheids, a type of specialized cell that conducts water and dissolved minerals and provides structural support Lycophytes are more numerous and larger in the past but now about 1000 relatively small species Lycophytes roots and leaves differ from those of other tracheophytes Pteridophytes are diversified more recently than lycophytes More than 12,000 modern species of Pteridophytes Pteridophytes include horsetails, whisk ferns, and other ferns Lycophyte & Pteridophyte Generations: Lycophyte and pteridophyte reproduction is limited by dry conditions, like bryophytes HOWEVER…. If fertilization occurs, lychophytes and pteridophytes can produce many more spores due to their larger sporophyte generation Vascular plant sporophytes are dependent upon maternal gametophytes for only a short time during early embryo development Stems of vascular plant sporophytes are able to produce branches, forming relatively large adult plants with many leaves New Section 2 Page 8 Overview of the Fern Life Cycle: 1. Diploid Sporophyte (2n) as the Dominant Generation: The fern’s dominant stage is the diploid sporophyte, which is the leafy plant structure we typically recognize as a fern. This is the primary phase of its life cycle. 2. Formation of Sporangia on the Underside of Sporophyte Leaves: The mature fern sporophyte develops sporangia, which are small structures located in clusters called sori (singular: sorus) on the underside of its leaves. 3. Meiosis Produces Haploid Spores (n): New Section 2 Page 9 3. Meiosis Produces Haploid Spores (n): Inside the sporangia, specialized cells undergo meiosis, producing haploid spores (n). These spores are then dispersed by the wind. 4. Spore Germination and Formation of Gametophyte (n): When spores land in favorable conditions, they germinate and grow through mitosis into a gametophyte (n). This is a small, heart-shaped structure anchored by root-like rhizoids. 5. Development of Gametangia: Male (Antheridia) and Female (Archegonia): The mature gametophyte develops specialized reproductive structures. Male gametangia (antheridia) produce sperm, while female gametangia (archegonia) produce eggs. 6. Fertilization Occurs in the Presence of Water: When water is available, the sperm swim from the antheridia to the archegonia, where fertilization takes place. The sperm fuses with the egg, forming a diploid zygote (2n). 7. Zygote Develops into a Multicellular Embryo (2n) on the Gametophyte: The zygote undergoes mitosis and begins growing into an embryo while still attached to the gametophyte. The gametophyte provides essential nutrients for New Section 2 Page 10  attached to the gametophyte. The gametophyte provides essential nutrients for early development. 8. Maturation into a Sporophyte (2n): The embryo continues to grow, eventually developing into a mature sporophyte with leaves and roots. Over time, it becomes independent, and the gametophyte withers away. The cycle then repeats. Roots, Stems, and Leaves of Vascular Plants: Stems: Produce leaves and sporangia Contain phloem: a specialized conducting tissue in the stem, and xylem: contains tracheids and ligin Roots: Specialized for uptake of water and minerals from the soil Leaves: Photosynthetic function What is the Origin and Evolutionary Importance of Leaves and Seeds? New Section 2 Page 11 Provides a high surface area that helps leaves to effectively capture sunlight for use in photosynthesis Lycophytes produce simplest, most ancient leaves called lycophylls (small leaf) or microphylls Other vascular plants have leaves with extensively branched veins, euphylls (large leaf) or megaphylls Larger size provide considerable advantage Evolved in a series of steps What is an Ovule? Sporangium with single spore and a very small egg-producing gametophyte inside Enclosed by integuments Seed plants produce two distinct types of spores in two different types of sporangia Microsporangia produce small microspores that give rise to male gametotypes (pollen grains) Megasporangia produced larger megaspores that give rise to female gametophytes that produce eggs New Section 2 Page 12  female gametophytes that produce eggs In order for Embryos and Seeds to Develop…… POLLINATION MUST FIRST OCCUR: Definition: the process by which pollen comes into contact with ovules Typically occurs by means of wind or animal transport Following pollination, the pollen will germinate, producing sperm Fertilization cannot occur until after pollination What is Seed Development? Double fertilization One sperm fertilizes egg to become an embryo Other sperm fuses with different gametophyte tissue to form endosperm New Section 2 Page 13  Ovule's integument develops into a protective, hard and tough seed coat Seeds allow embryos access to food supplied by the older sporophyte generation Seeds Confer Significant Reproductive Advantages, what are they? Seeds are a key adaptation to reproduction in a land habitat Able to remain dormant in the soil; can wait for favorable conditions Adaptations to improve dispersal Can store considerable amounts of food Sperm can reach egg without having to swim through water Descent with Modification: New Section 2 Page 14  Seed plants have not "replaced" spores with seeds Ovules and seeds added to life history including spores Most lycophytes and pteridophytes release one type of spore and one type of gametophyte (homospory) Others produce microspores and megaspores (heterospory) These protected gametophytes grow inside microspore and megaspore walls; endosporic gametophytes Heterospory advantage: increase cross-fertilization What are some Adaptations that Foster Stable Water Content? 1. Waxy cuticle present on most surfaces of vascular plant sporophytes; prevents dessication Cutin: found in cuticle that contains wax, which prevents loss of water; New Section 2 Page 15  Cutin: found in cuticle that contains wax, which prevents loss of water; helps block pathogens 2. Stomata: specialized cells that associate with pores that open and close to allow gas exchange while minimizing water loss Pores aid in the drying process; allow intake of CO2 What Happened During The Age of the Gymnosperms? The removal of large amounts of CO2 from the atmosphere by Coal Age plants Had a cooling effect on the climate, which also became drier due to cold air holds less moisture than warm air This Global climate change led to the extinction of many of the tall lychophytes and pteridophytes Cooler, drier condition favored diversification of the first seed plants, gymnosperms Diverse phyla of gymnosperms dominated Earth's vegetation through the Mesozoic era (248-65mya) What are Gymnosperms? Ancient seed plant New Section 2 Page 16  Classified within Cycads, ginkgos, and confiers Reproduce using spores and seeds (like angiosperms) Seed plants Seeds protect and provide energy for young sporophyte "Naked seeds": seeds are not enclosed by fruit What Occurred on the Rise of Angiosperms? Gymnosperms and early angiosperms were probably major sources of food for early mammals as well as herbivorous dinosaurs One day, about 65 million years ago, at least one large meteorite or comet crashed near Yucatan Peninsula in Mexico Background Information on the Impact Event: The meteor impact, together with substantial volcanic activity Produced huge amounts of ash, smoke and haze that dimmed sunlight long enough to kill many of the world's plants With a severely reduced food supply, most dinosaurs were also doomed (with the exception of their descendants--birds) New Section 2 Page 17  (with the exception of their descendants--birds) In the aftermath, surviving flowering plants diversified Extinction of the dinosaurs left room for birds and mammals to adapt What are Angiosperms? Distinguished by the presence of flowers and endosperm Flowers: Specialized to enhance seed production Fruits develop from flowers and enclose the seed and foster seed dispersal Endosperm: A nutritive seed tissue with increased storage efficiency Summary of Plant Features: The evolutionary lineage of seed plants required the adaptation to land These seed plants have also played a role in shaping Earth's ecosystems New Section 2 Page 18 New Section 2 Page 19