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Plant lecture 7

  1. Evolutionary History of Plants
  2. Evolutionary History of Plants Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. flowers, double fertilization, endosperm, fruit common ancestor Flowering plants Seed seeds megaphylls Vascular Gymnosperms vascular tissue Seedless Ferns and allies apical growth microphylls embryo protection Bryophytes Mosses Hornworts common green algal ancestor Liverworts Nonvascular Lycophytes Charophytes 550 500 450 400 350 Million Years Ago (MYA) 300 250 PRESENT 5
  3. Gametophyte Mitosis Mitosis n n n Spore n Gamete MEIOSIS Apical meristem of shoot Developing leaves FERTILIZATION 2n Zygote Haploid Diploid Mitosis Sporophyte 1 Alternation of generations Archegonium with egg 2 Apical meristems Antheridium with sperm Sporangium Spores 1 µm 3 Multicellular gametangia 4 Walled spores in sporangia
  4. Alternation of Generations Life cycle involves alternation of generations Sporophyte (2n): Multicellular individual that produces spores by meiosis Spores is haploid cell that will become gametophyte Gametophyte (1n): Multicellular individual that produces the gametes Gametes fuse in fertilization to form zygote Zygote is a diploid cell that becomes a s sporophyte 7
  5. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. spores G a m e t o p h y t e seed seed spores S roots p o roots r o rhizoids roots p h rhizoids (n) y t Moss Fern Gymnosperm Angiosperm e (2n) 8
  6. Other Terrestrial Adaptations Vascular tissue transports water and nutrients to the body of the plant Cuticle provides an effective barrier to water loss Stomata bordered by guard cells that regulate opening, and thus water loss 9
  7. Nonvascular Plants: Bryophytes Nonvascular plants (bryophytes) Lack specialized means of transporting water and organic nutrients Do not have true roots, stems, and leaves  Dependent sporophyte consists of a foot, stalk and sporangium Gametophyte is dominant generation  Produce eggs in archegonia  Produce sperm in antheridia  Sperm swim to egg in film of water to make zygote 10
  8. Nonvascular Plants Hornworts (phlym Anthocerophyta) have small sporophytes that carry on photosynthesis Liverworts (phylum Hepatophyta) have either flattened thallus or leafy appearance Mosses (phylum Bryophyta) usually have a leafy shoot, although some are secondarily flattened  Can reproduce asexually by fragmentation 11
  9. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 4. The sporophyte: The mature sporophyte has a foot buried in female gametophyte tissue, a stalk, and an upper capsule (the sporangium), where meiosis occurs and spores are developing sporophyte 3. The zygote: The zygote and developing sporophyte are retained within the archegonium. capsule 5. The spores: When the calyptra and lid (operculum) of a capsule fall off, the spores are mature. One or two rings of teeth project inward from the margin of teeth the capsule. The operculum teeth close the opening, except when the weather is dry. Sporangium calyptra Mitosis stalk Sporophyte zygote diploid (2n) FERTILIZATION 2. Fertilization: Flagellated sperm produced in antheridia swim in external water to archegonia, each bearing a single egg. sperm MEIOSIS haploid (n) Spores foot (n) egg Mitosis Archegonia buds Protonema Antheridia 1. The mature gametophytes: In mosses, the leafy gametophyte shoots bear either antheridia or archegonia, where gametes are 7. The immature gametophyte: A spore germinates into a male or female protonema, the first stage of the male and the female gametophytes. Gametophytes rhizoids (Top): © Heather Angel/Natural Visions; (Bottom): © Bruce Iverson 12 6. Spore dispersal: Spores are released when they are most likely to be dispersed by air currents.
  10. Seedless Vascular Plants: Lycophyta Club Mosses (phylum Lycophyta) Typically, branching rhizome sends up short aerial stems Leaves are microphylls (have only one strands of vascular tissue) Most likely evolved as a simple side extensions of the stem Sporangia occur on surfaces of sporophylls  13 Grouped into club-shaped strobili
  11. Seedless Vascular Plants Roots evolved as lower extensions of the stem  today’s lychophytes, also called club mosses, include three groups of 1,150 species: o Ground pines (Lycopodium) o Spike mosses (Selaginella) o Quillwort (Iseotes) 14
  12. Seedless Vascular Plants: Pteridophytes Includes Ferns and their Allies (horsetails and whisk ferns) Have megaphylls (broad leaves)   allow plants to effectively collect solar energy Produce more food and the possibility of producing more offspring than plants without megaphylls Horsetails  rhizome produces tall aerial stems  Contains whorls of slender, green branches  Small, scale like leaves also form whorl at the joint 15
  13. Microphylls and Megaphylls single strand of vascular tissue a. Microphyll branched vascular tissue Megaphyll One branch began to dominate the stem system. branched stem system b. Megaphyll evolution process 16 The side branches flattened into a single plane. Tissue filled in the spaces between the side branches. megaphyll leaf
  14. Ferns Whisk Ferns (phylum Psilotophyta) Branched rhizome has rhizoids (extensions) Mutualistic mycorrhizal fungus helps gather nutrients Ferns (phylum Pterophyta) Large conspicuous fronds  divide into leaflets Dominant sporophyte produces windblown spores 17
  15. Figure 29.13-3 Key Haploid (n) Diploid (2n) MEIOSIS Spore dispersal Spore (n) Rhizoid Underside of mature gametophyte (n) Sporangium Sporangium Antheridium Young gametophyte Mature sporophyte (2n) Sorus New sporophyte Sperm Archegonium Egg Zygote (2n) FERTILIZATION Gametophyte Fiddlehead (young leaf) 1 µm In contrast with bryophytes, sporophytes of seedless vascular plants are the larger generation, as in familiar ferns
  16. Seed Plants Seed plants are the most plentiful plants in the biosphere Seed coat and stored food allow an embryo to survive harsh conditions during long period of dormancy Heterosporous Drought-resistant pollen grains Ovule develops into seed 19
  17. Gymnosperms  Gymnosperms have ovules and seeds exposed on the surface of sporophylls  Conifers  Conifers, as well as other gymnosperm phyla, bear cones  Tough, needlelike leaves of pines conserve water with a thick cuticle and recessed stomata  Considered a “soft” wood because it consist primarily of xylem tissue (water flow)  Cycads  Large, finely divided leaves that grow in clusters at the top of the stem  Pollen and seed coats on separate plants  Ginkgoes  Dioecious: Some trees producing seeds and others producing pollen  Gnetophytes  20 None have archegonia
  18. Figure 30.3-3 If a pollen grain germinates, Immature it gives rise to a pollen tube ovulate cone that discharges sperm into the female gametophyte within the ovule Female gametophyte (n) Integument (2n) Spore wall Micropyle Pollen grain (n) (a) Unfertilized ovule Spore wall Egg nucleus (n) Megaspore (n) Megasporangium (2n) Seed coat Discharged sperm nucleus (n) Pollen tube Male gametophyte (n) (b) Fertilized ovule Food supply (n) Embryo (2n) (c) Gymnosperm seed A seed is a sporophyte embryo, along with its food supply, packaged in a protective coat
  19. Angiosperms Ovules are always enclosed within diploid tissues Two classes of flowering plants   22 Monocotyledones (Monocots) – 1 cotyledon Eudicotyledones (Dicots) – 2 cotyledons
  20. Monocots vs Eudicots  Number of cotyledons -- The cotyledons are the "seed leaves" produced by the embryo. They serve to      absorb nutrients packaged in the seed, until the seedling is able to produce its first true leaves and begin photosynthesis.  The number of cotyledons found in the embryo is the actual basis for distinguishing the two classes of angiosperms, and is the source of the names Monocots ("one cotyledon") and Eudicots ("two cotyledons"). Number of flower parts -- Monocot flowers = divisible by three, usually three or six. Dicot flowers = multiples of four or five  This character is not always reliable, however, and is not easy to use in some flowers with reduced or numerous parts. Leaf veins – Monocots = veins which run parallel the length of the leaf. Eudicots, = numerous veins which reticulate between the major ones. Stem vascular arrangement -- Vascular tissue occurs in long strands called vascular bundles. These bundles are arranged within the stem of eudicots to form a cylinder, appearing as a ring of spots when you cut across the stem. In monocots, these bundles appear scattered through the stem, with more of the bundles located toward the stem periphery than in the center. Root development -- In most eudicots (and gymnosperms) the root develops from the lower end of the embryo, from a region known as the radicle. The radicle gives rise to an apical meristem which continues to produce root tissue for much of the plant's life. By contrast, the radicle dies in monocots, and new roots arise from nodes in the stem.  These roots may be called prop roots when they are clustered near the bottom of the stem. Secondary growth – Gymnosperm and eudicots increase their diameter through secondary growth, producing wood and bark. Monocots (and some dicots) do not produce wood.
  21. Figure 30.13ea Monocot Characteristics Eudicot Characteristics Embryos Two cotyledons One cotyledon Leaf venation Veins usually netlike Veins usually parallel Stems Vascular tissue scattered Vascular tissue usually arranged in ring
  22. Figure 30.13eb Monocot Characteristics Eudicot Characteristics Roots Taproot (main root) usually present Root system usually fibrous (no main root) Pollen Pollen grain with one opening Pollen grain with three openings Flowers Floral organs usually in multiples of three Floral organs usually in multiples of four or five
  23. The Flower Peduncle (flower stalk) expands at tip into a receptacle  Bears sepals, petals, stamens, and carpels, all attached to receptacle in whorls  Each stamen consists of an anther and a filament (stalk)  Carpel has three major regions  Ovary – swollen base  Style – elevates stigma  Stigma – sticky receptor of pollen grains  fruit  Calyx (collection of sepals) protects flower bud before it opens  Corolla (collection of petals) 26
  24. Figure 38.2b Anther Germinated pollen grain (n) (male gametophyte) Ovary Ovule Embryo sac (n) (female gametophyte) Pollen tube Egg (n) FERTILIZATION Sperm (n) Key Zygote (2n) Mature sporophyte plant (2n) Haploid (n) Diploid (2n) (b) Simplified angiosperm life cycle Germinating seed Seed Seed Simple fruit Embryo (2n) (sporophyte)
  25. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Stamen Carpel stigma anther style filament ovary ovule 7. The sporophyte: The embryo within a seed is the immature sporophyte. When a seed germinates, growth and differentiation produce the mature sporophyte of a flowering plant. The ovules: In an ovule (megasporangium) within an ovary, meiosis produces four megaspores. Mitosis stigma fruit (mature ovary) Sporophyte 1. The stamen: An anther at the top of a stamen has four pollen sacs. Pollen grains are produced in pollen seed (mature ovule) 6. The seed: The ovule now develops into the seed, which contains an embryo and food enclosed by a protective seed coat. The wall of the ovary and sometimes adjacent parts develop into a fruit that 2. The pollen sacs: In pollen sacs (microsporangia) of the anthe ,r meiosis produces microspores. Pollen sac (microsporangium) Ovule (megasporangium) The carpel: The ovary at the base of a carpel contains one or more ovules. The contents of an ovule change during the flowering plant life cycle. seed coat embryo endosperm (3n) style ovary Anther Seed diploid (2n) FERTILIZATION MEIOSIS haploid (n) (Mature male gametophyte) tube cell ovule wall polar nuclei sperm pollen tube sperm egg tube cell nucleus Microspores Megaspores ovule wall antipodals polar nuclei egg to mi pollen tube generative cell sis Pollination to mi degenerating megaspores sis 5. Double fertilization: On reaching the ovule, the pollen tube discharges the sperm. One of the two sperm migrates to and fertilizes the egg, forming a zygote; the other unites with the two polar nuclei, producing a 3n (triploid) endosperm nucleus. The endosperm nucleus divides to form MEIOSIS Pollen grain synergids Embryo sac (mature female gametophyte) 4. The mature male gametophyte: A pollen grain that lands on the carpel of the same type of plant germinates and produces a pollen tube, which grows within the style until it reaches an ovule in the ovary. Inside the pollen tube, the generative cell nucleus divides and produces two nonflagellated sperm. A fully germinated pollen grain is the mature 28 The mature female gametophyte: The ovule now contains the mature female gametophyte (embryo sac), which typically consists of eight haploid nuclei embedded in a mass of cytoplasm. The cytoplasm differentiates into cells, one of which is an egg and another of which contains two polar nuclei. 3. The microspores: Each microspore in a pollen sac undergoes mitosis to become an immature pollen grain with two cells: the tube cell and the generative cell. The pollen sacs open, and the pollen grains are windblown or carried by an animal carrier, usually to other flowers. This is pollination. The megaspores: Inside the ovule of an ovar y , three megaspores disintegrate, and only the remaining one undergoes mitosis to become a female gametophyte.
  26. Figure 30.2 PLANT GROUP Mosses and other nonvascular plants Gametophyte Dominant Sporophyte Ferns and other seedless vascular plants Seed plants (gymnosperms and angiosperms) Reduced, independent (photosynthetic and free-living) Reduced (usually microscopic), dependent on surrounding sporophyte tissue for nutrition Reduced, dependent on Dominant gametophyte for nutrition Dominant Gymnosperm Sporophyte (2n) Sporophyte (2n) Microscopic female gametophytes (n) inside ovulate cone Gametophyte (n) Angiosperm Microscopic female gametophytes (n) inside these parts of flowers Example Gametophyte (n) Microscopic male gametophytes (n) inside pollen cone Sporophyte (2n) Microscopic male gametophytes (n) inside these parts of flowers Sporophyte (2n)
  27. Bryophytes Gametophyte dominant; sporophyte dependent; gametophyte independent Seedless vascular plants Sporophyte dominant; sporophyte initially dependent; gametophyte independent Seed plants Sporophyte dominant; sporophyte independent; gametophyte dependent & microscopic Gymnosperms Gametophytes develop inside cones Angiosperms Gametophytes develop inside flowers
  29. Pearson – The Biology Place -
  30. Ground Tissue Parenchyma cells – – – – – Have thin and flexible primary walls Lack secondary walls Are the least specialized Perform the most metabolic functions Retain the ability to divided and diffrentiate Collenchyma cells help support young parts of the plant shoot  They have thicker and uneven cell walls  The cells provide flexible support without restraining growth Sclerenchyma cells are rigid because of thick secondary walls strengthened with lignin  They are dead at functional maturity  There are two types: 1. Sclereids are short and irregular in shape and have thick lignified secondary walls 2. Fibers are long and slender and arranged in threads
  31. Roots A root is an organ with important functions: 1. anchoring the plant 2. Absorbing minerals and water 3. Storing carbohydrates In most plants, absorption of water and minerals occurs near the root hairs, where vast numbers of tiny root hairs increase the surface area
  32. Figure 35.14 Epidermis Cortex Endodermis Vascular cylinder 100 µm (a) Root with xylem and phloem in the center (typical of eudicots) 50 µm Pericycle Core of parenchyma cells Xylem Phloem Endodermis Pericycle Xylem Phloem 100 µm (b) Root with parenchyma in the center (typical of monocots) Key to labels Dermal Ground Vascular
  33. Figure 35.13 Cortex Vascular cylinder Epidermis Root hair Zone of differentiation Key to labels Dermal Ground Vascular Zone of elongation Zone of cell division (including apical meristem) Root cap Mitotic cells 100 µm
  34. Most eudicots and gymnosperms have a taproot system, which consists of: A taproot, the main vertical root Lateral roots, or branch roots, that arise from the taproot Most monocots have a fibrous root system, which consists of: Adventitious roots that arise from the stems or leaves Lateral roots that arise from adventitious roots
  35. Stems  A stem is an organ consisting of  An alternating system of nodes, the point at which leaves are attached  Internodes, the stem segments between nodes  An axillary bud is a structure that has the potential to form a lateral shoot, or branch  An apical bud, or terminal bud, is located near the shoot tip and causes elongation of a young shoot  Apical dominance helps to maintain dormancy in most axillary buds  Many plants have modified stems (eg. Rhizoids, bulbs, stolons, tuber)
  36. The vascular tissue of a stem or root is collectively called the stele In angiosperms the stele of the root is a solid central vascular cylinder The stele of stems and leaves is divided into vascular bundles, strands of xylem and phloem
  37. Figure 35.17 Phloem Xylem Sclerenchyma (fiber cells) Pith Epidermis Cortex Vascular bundle Ground tissue Ground tissue connecting pith to cortex 1 mm (a) Cross section of stem with vascular bundles forming a ring (typical of eudicots) Epidermis Key to labels Dermal Ground Vascular Vascular bundles 1 mm (b) Cross section of stem with scattered vascular bundles (typical of monocots)
  38. Seeds Seed coat, or testa can be impenertrable, especially in long dormancy need Cotyledons are leaf-like structures in the seed that provide nourishment while the seed germinates Radicle = embryonic root Plumule = seed shoot Epicotyl = portion of stem above the point where the stem is attached to the cotyledon Hypocotyl = portion of stem below the cotyledon Endosperm = source of nutrients Hillum = point of attachment of seed to the ovary wall Micropyle = small opening near hillum
  39. Secondary growth increases the diameter of stems and roots in woody plants  Secondary growth occurs in stems and roots of woody plants but rarely in leaves  The secondary plant body consists of the tissues produced by the vascular cambium and cork cambium  Secondary growth is characteristic of gymnosperms and many eudicots, but not monocots
  40. Lateral meristems add thickness to woody plants, a process called secondary growth There are two lateral meristems: the vascular cambium and the cork cambium The vascular cambium adds layers of vascular tissue called secondary xylem (wood) and secondary phloem The cork cambium replaces the epidermis with periderm, which is thicker and tougher
  41. Figure 35.11 Primary growth in stems Epidermis Cortex Primary phloem Shoot tip (shoot apical meristem and young leaves) Axillary bud meristem Primary xylem Pith Vascular cambium Secondary growth in stems Lateral Cork meristems cambium Cork cambium Periderm Cortex Primary phloem Root apical meristems Secondary phloem Pith Primary xylem Secondary xylem Vascular cambium

Notas do Editor

  1. Figure 29.UN05 Summary figure, Concept 29.1
  2. Figure 29.13 The life cycle of a fern.
  3. Figure 30.3 From ovule to seed in a gymnosperm.
  4. Figure 30.13 Exploring: Angiosperm Diversity
  5. Figure 30.13 Exploring: Angiosperm Diversity
  6. Figure 38.2 An overview of angiosperm reproduction.
  7. Figure 30.2 Gametophyte-sporophyte relationships in different plant groups.
  8. Figure 35.14 Organization of primary tissues in young roots.
  9. Figure 35.13 Primary growth of a root.
  10. Figure 35.17 Organization of primary tissues in young stems.
  11. Figure 35.11 An overview of primary and secondary growth.