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Chapter 35

Chapter 35. Reproduction in Flowering Plants. A flower may contain Sepals Petals Stamens Carpels (pistils). An Arabidopsis thaliana flower. Sepals Cover and protect the flower parts when the flower is a bud Petals Play an important role in attracting animal pollinators. Stamens

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Chapter 35

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  1. Chapter 35 Reproduction in Flowering Plants

  2. A flower may contain • Sepals • Petals • Stamens • Carpels (pistils)

  3. An Arabidopsis thaliana flower

  4. Sepals • Cover and protect the flower parts when the flower is a bud • Petals • Play an important role in attracting animal pollinators

  5. Stamens • Produce pollen grains • Each stamen consists of • A filament attached to an anther • An anther (a saclike structure) • Carpel • Female reproductive unit

  6. Pistil • May consist of either • A single carpel or • A group of fused carpels • Each pistil has three sections • Stigma for pollen grains to land on • Style for pollen tube to grow through • Ovary containing one or more ovules

  7. Cutaway view of an Arabidopsis flower

  8. Pollen • Forms within pollen sacs in the anther • Each pollen grain contains two cells • One generates two sperm cells • The other produces a pollen tube so sperm cells can reach the ovule

  9. In the ovule the following are formed • An egg • Two polar nuclei • Several other nuclei • Both egg and polar nuclei participate directly in fertilization

  10. Development of female and male gametophytes

  11. Insect-pollinated flowers • Often yellow or blue • Have a scent • Bird-pollinated flowers • Often yellow, orange, or red • Do not have a strong scent

  12. Ultraviolet markings on insect-pollinated flowers

  13. Bat-pollinated flowers • Often have dusky white petals • Are scented • Wind-pollinated flowers • Often have smaller petals or none at all • Have neither scent nor nectar • Make large amounts of pollen

  14. Animal pollinators: Archilochus colubris obtains nectar

  15. Animal pollinators:Leptonycteris curasoae obtains nectar

  16. Wind pollination

  17. Coevolution • Reciprocal adaptation • Caused by two species • Forming interdependent relationship • Affecting the course of each other’s evolution • E.g., certain showy flowers + bees

  18. Pollination • Transfer of pollen grains from anther to stigma • Fertilization • Fusion of gametes • Occurs after pollination

  19. Pollination, pollen tube growth, and fertilization

  20. Double fertilization • In the ovule, egg fuses with first sperm cell • Zygote is formed • Zygote develops into a multicellular embryo in the seed

  21. A longitudinal section through a heart-shaped fruit of Capsella bursa-pastoris reveals numerous tiny seeds, each containing a mature embryo. Each seed developed from an ovule.

  22. Double fertilization, cont. • Two polar nuclei fuse with second sperm cell • Triploid nutritive tissue (endosperm) is formed

  23. Stages of embryo development • Dicot embryo develops in the seed • From proembryo • To globular embryo • To heart stage • To the torpedo stage

  24. As cell division continues, the embryo becomes a ball of cells, called the globular stage The proembryo in Capsella bursa-pastoris (the ovule is shown apart from the ovary)

  25. As the two cotyledons begin to emerge, the embryo is shaped like a heart The cotyledons continue to elongate, forming the torpedo stage

  26. Mature flowering plant embryo consists of • A radicle • A hypocotyl • A plumule • Cotyledons (one in monocots, two in dicots)

  27. For use during germination, a mature seed contains both • A young embryo • Nutritive tissue (stored in endosperm or cotyledons)

  28. A maturing embryo within the seed. The food originally stored in the endosperm has been almost completely depleted during embryonic growth and development; most of the food for the embryonic plant is stored in its cotyledons

  29. Ovules • Structures with the potential to develop into seeds • Ovaries • Structures with the potential to develop into fruits

  30. Seeds • Enclosed within fruits • Fruits • Mature, ripened ovaries

  31. Simple fruits • Develop from a single pistil consisting of • Either a single carpel • Several fused carpels • Some are fleshy at maturity • Others are dry

  32. Aggregate fruits • Develop from a single flower with many separate ovaries • Multiple fruits • Develop from the ovaries of many flowers growing close together on a common axis

  33. A developing blackberry fruit is an aggregate of tiny drupes. The little “hairs” on the blackberry are remnants of stigmas and styles Cutaway view of a Rubus flower, showing the many separate carpels in the center of the flower

  34. Accessory fruits • The major part of the fruit consists of tissue other than ovary tissue • Dispersal methods of seeds and fruits include • Animals • Wind • Water • Explosive dehiscence

  35. An accessory fruit

  36. Stems specialized for asexual reproduction • Rhizomes • Tubers • Bulbs • Corms • Stolons

  37. Rhizome • Horizontal underground stem • Tuber • Fleshy underground stem enlarged for food storage

  38. Irises have horizontal underground stems called rhizomes. New aerial shoots arise from buds that develop on the rhizome

  39. Potato plants form rhizomes, which enlarge into tubers (the potatoes) at the ends

  40. Bulb • Modified underground bud with • Fleshy storage leaves attached to • Short stem • Corm • Short erect underground stem covered by papery scales

  41. A bulb is a short underground stem to which overlapping, fleshy leaves are attached; most of the bulb consists of leaves

  42. A corm is an underground stem that is almost entirely tissue surrounded by a few papery scales

  43. Stolon • Horizontal aboveground stem with long internodes • Plantlets (detachable) • Arise from meristematic tissue along margins of some leaves

  44. Strawberries reproduce asexually by forming stolons, or runners; new plants (shoots and roots) are produced at every other node

  45. Plantlets

  46. Suckers • Develop from adventitious buds developed from roots • Produce additional roots • May give rise to new plants

  47. Apomixis • Production of seeds and fruit without sexual reproduction • Sexual reproduction • Involves union of two gametes • Offspring produced are genetically variable

  48. Sexual reproduction, cont. • Parental genotypes are not preserved in offspring • Genetic diversity among offspring • May be selectively advantageous • May let individuals exploit new environments

  49. Sexual reproduction, cont. • Costly because both male and female gametes • Must be produced • Must meet

  50. Asexual reproduction • Involves formation of offspring without fusion of gametes • Offspring are virtually genetically identical to single parent • Genetic similarity may be selectively advantageous

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