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Chapter 24 lecture- Seeds


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Chapter 24 lecture for Lab Bio on seeds

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Chapter 24 lecture- Seeds

  1. 1. 24–1 Reproduction With Cones and Flowers
  2. 2. Alternation of Generations <ul><li>All plants have a life cycle in which a diploid sporophyte generation alternates with a haploid gametophyte generation. </li></ul><ul><ul><ul><li>Male and female gametes of a gametophyte plant join and form a zygote that begins the next sporophyte generation. </li></ul></ul></ul><ul><ul><ul><li>In mosses & ferns, the two stages of the life cycle are distinct, independent plants. </li></ul></ul></ul>
  3. 3. <ul><li>In seed plants, gametophytes are found within tissues of the sporophyte plant. </li></ul><ul><li>In gymnosperms, they are found inside cones. </li></ul><ul><li>In angiosperms, they are found inside flowers. </li></ul><ul><li>Cones and flowers represent two different methods of reproduction. </li></ul>Alternation of Generations
  4. 4. <ul><ul><li>Reproduction in gymnosperms takes place in cones, which are produced by a mature sporophyte plant. </li></ul></ul><ul><ul><li>Gymnosperms produce two types of cones: pollen cones and seed cones. </li></ul></ul>Life Cycle of Gymnosperms
  5. 5. <ul><ul><li>Pollen Cones and Seed Cones  </li></ul></ul><ul><ul><ul><li>Pollen cones produce the male gametophytes, also called pollen grains. </li></ul></ul></ul>Life Cycle of Gymnosperms Pollen grain (N) (male gametophytes)
  6. 6. <ul><li>Seed cones produce female gametophytes and are generally larger than pollen cones. </li></ul><ul><li>Female gametophytes develop in two ovules located near the base of each scale. </li></ul>Life Cycle of Gymnosperms
  7. 7. <ul><li>Within the ovules, meiosis produces haploid cells that grow and divide to produce female gametophytes. </li></ul><ul><li>Each gametophyte contains egg cells. </li></ul>Life Cycle of Gymnosperms
  8. 8. <ul><ul><li>Pollination </li></ul></ul><ul><ul><ul><li>The gymnosperm life cycle typically takes two years to complete. </li></ul></ul></ul><ul><ul><ul><li>The cycle begins as male cones release pollen grains. </li></ul></ul></ul><ul><ul><ul><li>Pollen grains are carried by the wind and reach female cones. </li></ul></ul></ul>Life Cycle of Gymnosperms
  9. 9. Life Cycle of Gymnosperms Meiosis Fertilization
  10. 10. <ul><li>Male Cones </li></ul>Life Cycle of Gymnosperms Mature sporophyte Pollen cone Pollen grain (N) (male gametophytes)
  11. 11. <ul><li>Female Cones </li></ul>Life Cycle of Gymnosperms Mature sporophyte Seed cone Cone scale Ovules Diploid cell (2N) Ovule Four haploid cells (N) Female gametophyte (N)
  12. 12. <ul><li>If pollen grains land on and enter an ovule, pollination occurs. </li></ul><ul><li>A pollen tube grows out of each pollen grain and releases sperm near an egg. </li></ul>Life Cycle of Gymnosperms Egg cells Discharged sperm nucleus Pollen tube
  13. 13. <ul><li>Fertilization produces a diploid zygote which develops into a new sporophyte plant. </li></ul>Life Cycle of Gymnosperms Zygote (2N) (new sporophyte)
  14. 14. <ul><li>The zygote grows into an embryo and is encased within what will develop into a seed. </li></ul>Life Cycle of Gymnosperms Gametophyte tissue Embryo (2N) Seed coat (old sporophyte) Seed
  15. 15. <ul><li>The seed is then dispersed by wind. </li></ul><ul><li>When conditions are favorable, the seed germinates and its embryo grows into a seedling. </li></ul>Life Cycle of Gymnosperms
  16. 16. Structure of Flowers <ul><ul><li>Flowers are reproductive organs that have four kinds of specialized leaves : sepals, petals, stamens, and carpels. </li></ul></ul>
  17. 17. <ul><ul><li>  </li></ul></ul><ul><ul><ul><li>Sepals enclose the bud before it opens and protect the flower while it is developing. </li></ul></ul></ul>Structure of Flowers Sepal
  18. 18. <ul><ul><ul><li>Petals are often brightly colored and are found just inside the sepals. </li></ul></ul></ul><ul><ul><ul><li>Petals attract insects and other pollinators to the flower. </li></ul></ul></ul>Structure of Flowers Petal
  19. 19. <ul><ul><li>  </li></ul></ul><ul><ul><ul><li>The male parts of a flower consist of an anther and a filament, which together make up the stamen. </li></ul></ul></ul>Structure of Flowers Filament Anther Stamen
  20. 20. <ul><li>An anther is an oval sac where meiosis takes place, producing pollen grains. </li></ul>Structure of Flowers Anther
  21. 21. <ul><li>The filament is a long, thin stalk that supports an anther. </li></ul>Structure of Flowers Filament
  22. 22. <ul><li>The innermost parts are carpels(pistils). </li></ul>Structure of Flowers Carpel Style Stigma Ovary
  23. 23. <ul><li>Each carpel has a broad base forming an ovary where female gametophytes are produced. </li></ul>Structure of Flowers Ovary Ovule
  24. 24. <ul><li>The narrow stalk of the carpel is the style. </li></ul>Structure of Flowers Style
  25. 25. <ul><li>At the top of the style is the stigma — a sticky portion where pollen grains frequently land. </li></ul>Structure of Flowers Stigma
  26. 26. <ul><ul><ul><li>Parts of a Typical Flower </li></ul></ul></ul>Structure of Flowers Ovary Ovule Carpel Style Stigma Ovary Filament Anther Stamen Sepal Petal
  27. 27. <ul><li>A typical flower produces both male and female gametophytes. </li></ul><ul><li>In some plants, male and female gametophytes are produced in separate flowers on the same individual. </li></ul>Structure of Flowers
  28. 28. Life Cycle of Angiosperms <ul><ul><li>Reproduction in angiosperms takes place within the flower. Following pollination and fertilization, the seeds develop inside protective structures. </li></ul></ul>
  29. 29. Life Cycle of Angiosperms
  30. 30. <ul><li>Each flower contains anthers and an ovary. </li></ul><ul><li>In anthers, cells undergo meiosis to make a haploid spore cell. </li></ul><ul><li>Spore nuclei undergo mitosis to make two haploid nuclei = pollen </li></ul>Life Cycle of Angiosperms
  31. 31. <ul><li>The pollen grain usually stops growing until it is released from the anther and deposited on a stigma. </li></ul>Life Cycle of Angiosperms Pollen grains (N) (male gametophyte) Stigma
  32. 32. <ul><li>In the ovule, a single diploid cell undergoes meiosis to produce four haploid cells that become the female gametophyte. </li></ul>Life Cycle of Angiosperms Haploid cell (N) Ovule Ovary (2N)
  33. 33. <ul><li>Only one of the four cells undergoes mitosis to produce eight nuclei, called the embryo sac. </li></ul>Life Cycle of Angiosperms Pollen tube Egg cell Sperm Polar nuclei Embryo sac (N) (female gametophyte)
  34. 34. <ul><li>The embryo sac is the female gametophyte. </li></ul><ul><li>One of the eight nuclei is the egg nucleus—the female gamete. </li></ul>Life Cycle of Angiosperms Pollen tube Embryo sac (N) (female gametophyte) Egg cell Sperm Polar nuclei
  35. 35. <ul><li>When fertilization takes place, this cell becomes the zygote that grows into a new sporophyte plant. </li></ul>Life Cycle of Angiosperms Endosperm (3N) Zygote (2N)
  36. 36. Fertilization in Angiosperms <ul><li>Fertilization in Angiosperms </li></ul><ul><ul><ul><li>If a pollen grain lands on the stigma of a flower of the same species, it grows a pollen tube. </li></ul></ul></ul>Pollen grains (N) (male gametophyte) Pollen tubes Ovule
  37. 37. <ul><ul><ul><li>The pollen tube grows into the style, reaches the ovary, and enters the ovule. </li></ul></ul></ul>Fertilization in Angiosperms Pollen grains (N) (male gametophyte) Pollen tubes Ovule
  38. 38. <ul><ul><ul><li>One of the sperm nuclei fuses with the egg nucleus to produce a diploid zygote. </li></ul></ul></ul><ul><ul><ul><li>The zygote will grow into the new plant embryo. </li></ul></ul></ul>Zygote (2N)
  39. 39. <ul><li>The other sperm nucleus fuses with two polar nuclei in the embryo sac to form a triploid (3N) cell = endosperm. </li></ul><ul><li>This cell will grow into a food-rich tissue known as endosperm, which nourishes the seedling as it grows. </li></ul>Fertilization in Angiosperms Endosperm (3N) Zygote (2N)
  40. 40. <ul><li>Because two fertilization events take place between the male and female gametophytes, this process is known as double fertilization . </li></ul><ul><li>1 makes zygote </li></ul><ul><li>1 makes endosperm </li></ul>Fertilization in Angiosperms
  41. 41. Pollination <ul><ul><li>Most gymnosperms and some angiosperms are wind pollinated, whereas most angiosperms are pollinated by animals. </li></ul></ul>
  42. 42. Pollination <ul><li>Wind pollination </li></ul><ul><ul><ul><li>is less efficient than animal pollination </li></ul></ul></ul><ul><ul><ul><li>relies on weather </li></ul></ul></ul><ul><ul><li>Animal pollination </li></ul></ul><ul><ul><ul><li>plants have bright colors and sweet nectar to attract animals </li></ul></ul></ul><ul><ul><ul><li>benefits both the plants and the animals that pollinate them </li></ul></ul></ul>
  43. 43. 24-2 Seed Development and Germination
  44. 44. <ul><ul><li>As angiosperm seeds mature, the ovary walls thicken to form a fruit that encloses the developing seeds. </li></ul></ul>Seed and Fruit Development
  45. 45. <ul><li>A fruit is a ripened ovary that contains angiosperm seeds. </li></ul><ul><li>As seeds mature, the ovary walls thicken to form a fruit that encloses the developing seeds. </li></ul>Seed and Fruit Development
  46. 46. Seed Dispersal <ul><li>Seeds are dispersed by </li></ul><ul><ul><ul><li>Animals- typically in fleshy, nutritious fruits. </li></ul></ul></ul><ul><ul><ul><li>Wind- flying seeds </li></ul></ul></ul><ul><ul><ul><li>Water- floating seeds </li></ul></ul></ul>
  47. 47. Seed Dispersal <ul><li>Seeds of many plants are eaten by animals. </li></ul><ul><li>These seeds are covered with tough coatings that protect them from digestive chemicals, allowing them to pass through an animal’s digestive system unharmed. </li></ul><ul><li>The seeds then sprout in the feces eliminated from the animal. </li></ul>
  48. 48. <ul><ul><li>Seeds dispersed by wind or water are typically lightweight, allowing them to be carried in the air or to float on the surface of the water. </li></ul></ul>
  49. 49. Seed Dispersal <ul><li>Some seeds are encased in winglike structures that spin and twirl, helping them glide from their parent plants. </li></ul>
  50. 50. Seed Dispersal <ul><li>A coconut is buoyant enough to float in seawater within its protective coating for many weeks. </li></ul>
  51. 51. Seed Dispersal <ul><li>Tumbleweed plants break off at their roots and scatter their seeds as they are blown by the wind. </li></ul>
  52. 52. Seed Dormancy <ul><ul><ul><li>Many seeds will not grow when they first mature. </li></ul></ul></ul><ul><ul><ul><li>Many seeds enter a period of dormancy , during which the embryo is alive but not growing. </li></ul></ul></ul><ul><ul><ul><li>The length of dormancy varies in different plant species. </li></ul></ul></ul>
  53. 53. Seed Dormancy <ul><ul><li>Environmental factors such as temperature and moisture can cause a seed to end dormancy and germinate. </li></ul></ul><ul><ul><li>Seed dormancy can be adaptive in several ways: </li></ul></ul><ul><ul><ul><li>allows for long-distance dispersal </li></ul></ul></ul><ul><ul><ul><li>allows seeds to germinate under ideal growth conditions </li></ul></ul></ul>
  54. 54. Seed Germination <ul><ul><ul><li>Seed germination is the early growth stage of the plant embryo. </li></ul></ul></ul><ul><ul><ul><li>Seeds absorb water which causes food-storing tissues to swell and crack open the seed coat. </li></ul></ul></ul><ul><ul><ul><li>The young root grows through the cracked seed coat. </li></ul></ul></ul>
  55. 55. Seed Germination <ul><li>In most monocots, the single cotyledon remains underground. </li></ul><ul><li>The growing shoot emerges while protected by a sheath. </li></ul>
  56. 56. Seed Germination Corn (monocot) Young shoot Germinating seed Primary root Foliage leaves
  57. 57. Seed Germination <ul><li>In dicots, germination takes place in one of two ways. </li></ul><ul><ul><ul><li>In some species, the cotyledons emerge above ground, protecting the stem and first foliage leaves. </li></ul></ul></ul><ul><ul><ul><li>In other species, the cotyledons stay underground and provide a food source for the growing seedling. </li></ul></ul></ul>
  58. 58. Seed Germination Cotyledons Bean (dicot) Germinating seed Primary root Young shoot Cotyledons Seed coat Foliage leaves
  59. 59. 24-3 Plant Propagation and Agriculture
  60. 60. Vegetative Reproduction <ul><li>Vegetative reproduction is a method of asexual reproduction used by flowering plants that enables a single plant to produce many offspring genetically identical to itself. </li></ul>
  61. 61. <ul><ul><li>Vegetative reproduction includes the production of new plants from horizontal stems, from plantlets, and from underground roots. </li></ul></ul>Vegetative Reproduction
  62. 62. <ul><li>Some angiosperms produce tiny plants, or plantlets, at the tips of elongated stems. </li></ul>Vegetative Reproduction
  63. 63. <ul><li>Some plants grow horizontal stems, called stolons , that produce roots when they touch the ground. </li></ul>Vegetative Reproduction
  64. 64. <ul><li>Once the roots are well established, each stolon may be broken, forming a new independent plant. </li></ul>Vegetative Reproduction
  65. 65. Plant Propagation <ul><ul><li>In plant propagation , horticulturists make many identical copies of a plant or produce offspring from seedless plants. </li></ul></ul>
  66. 66. Plant Propagation <ul><ul><li>Cuttings </li></ul></ul><ul><ul><ul><li>One of the simplest ways to reproduce plants vegetatively is by cuttings. </li></ul></ul></ul><ul><ul><ul><li>A grower “cuts” a plant stem that includes buds containing meristematic tissue. </li></ul></ul></ul><ul><ul><ul><li>That stem is then partially buried in soil or in a special rooting mixture. </li></ul></ul></ul><ul><ul><ul><li>Some plants are treated with rooting powders to help them grow. </li></ul></ul></ul>
  67. 67. Plant Propagation <ul><ul><li>Grafting and Budding  </li></ul></ul><ul><ul><ul><li>Grafting and budding are used to reproduce seedless plants and varieties of woody plants that do not produce strong root systems. </li></ul></ul></ul><ul><ul><ul><li>A piece of stem or a lateral bud is cut from the parent plant and attached to another plant. </li></ul></ul></ul>
  68. 68. Plant Propagation <ul><li>The cut piece is called the scion, and the plant to which it is attached is called the stock. </li></ul><ul><li>When stems are used as scions, the process is called grafting. </li></ul><ul><li>When buds are used as scions, the process is called budding. </li></ul>
  69. 69. Agriculture <ul><ul><ul><li>Agriculture is the systematic cultivation of plants. </li></ul></ul></ul>
  70. 70. Agriculture <ul><ul><li>Worldwide Patterns of Agriculture </li></ul></ul><ul><ul><ul><li>Most of the people of the world depend on a few crop plants, such as wheat, rice, and corn, for the bulk of their food supply. </li></ul></ul></ul><ul><ul><ul><li>Roughly 80 percent of all U.S. cropland is used to grow wheat, corn, soybeans, and hay. </li></ul></ul></ul>
  71. 71. Agriculture <ul><ul><li>Changes in Agriculture </li></ul></ul><ul><ul><ul><li>The efficiency of agriculture has been improved through: </li></ul></ul></ul><ul><ul><ul><ul><li>improvements in farming techniques </li></ul></ul></ul></ul><ul><ul><ul><ul><li>the selective breeding of crop plants </li></ul></ul></ul></ul><ul><ul><ul><li>Selective breeding allows only organisms with certain traits to produce the next generation. </li></ul></ul></ul>
  72. 72. Agriculture <ul><li>Improvements in farming techniques have contributed to dramatic improvements in crop yields. </li></ul><ul><li>Some of the most important techniques have been the use of pesticides and fertilizers. </li></ul>