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Chapter 24- Seeds & Flowers


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Chapter 24- Seeds & Flowers

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Chapter 24- Seeds & Flowers

  1. 1. 24–1 Reproduction With Cones and Flowers Freedom from water
  2. 2. 2
  3. 3. Alternation of Generations All plants have a life cycle in which a diploid sporophyte generation alternates with a haploid gametophyte generation. Male and female gametes join to form a zygote that begins the next sporophyte generation. In mosses & ferns, the two stages of the life cycle are distinct, independent plants.
  4. 4. In seed plants, gametophytes are found within tissues of the sporophyte plant. In gymnosperms, they are found inside cones. In angiosperms, they are found inside flowers. Cones and flowers represent two different methods of reproduction. Alternation of Generations
  5. 5. Reproduction in gymnosperms takes place in cones, which are produced by a mature sporophyte plant. Gymnosperms produce two types of cones: pollen cones and seed cones. Life Cycle of Gymnosperms
  6. 6. Pollen Cones and Seed Cones Pollen cones produce the male gametophytes, also called pollen grains. Pollen grain (N) (male gametophytes) Life Cycle of Gymnosperms

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