Sexual reproduction in plants

• What is the calyx?
• Describe the adaptations of wind-pollinated plants
• What is an insect-pollinated flower?
• Corolla

  All of the petals of a flower
• What is the stamen?
• Adaptations of insect-pollinated plants

  • Internal anthers and small stigma directly touch insects
  • Large, bright petals and nectar from glands attract insects
  • May produce chemicals to mimic the scent of female insects or to intoxicate insects
  • Grow individually
  • Large pollen grains, sometimes with projections that attach to insects
• Insect-pollinated flower

  A type of flower that relies on insects to transfer pollen grains between flowers
• What is a wind-pollinated plant?
• What is a dicotyledon?
• What is the carpel?
• Calyx


  The first part of the flower that is formed, consists of leafy structures that protect the flower during development
• Stamen


  The male part of the plant consisting of an anther and a filament that is involved in the production of male gametes in the form of pollen grains
• What is the corolla?
• Label the diagram of the insect-pollinated flower below
• Dicotyledon


  A plant that produces seeds that contain two cotyledons; they have two primary leaves
• Describe the adaptations of insect-pollinated plants
• Carpel


  The female part of the plant consisting of a stigma, a style, and an ovary
• Wind-pollinated plant


  A type of flower that relies on wind to transfer pollen grains between flowers
• Describe the role of the tapetum in pollen grain development

  1. Specialised layer of cells in the anther

  2. Provides nutrients to developing pollen grains
• How does the ovule form in the ovary?
• How does a pollen grain form in the anther?
• Define dehiscence
• Describe the structure of the embryo sac
• Describe the structure of mature pollen grains
• How does a pollen grain form in the anther?

  1. Large numbers of pollen mother cells produced by mitosis

  2. Meiosis of diploid mother cells in the anther forms four haploid microspores

  3. Haploid microspores mature into pollen grains via mitosis
• Describe the structure of the embryo sac

  1. Two polar nuclei form endosperm

  2. Ovum forms zygote

  3. Two synergids help generative nucleus of pollen grain to reach ovum

  4. Three antipodal cells

  5. Outer protective coating
• Describe the role of the tapetum in pollen grain development
• Adaptations of wind-pollinated plants

  • External anthers optimise pollen dispersal
  • Excess pollen compensates for wind wastage
  • Feathery stigma catches pollen from the air
  • Small, dull petals (no need to attract insects)
  • Grow densely over large areas
  • Light pollen grains
• Describe the structure of mature pollen grains

  1. Generative cell (haploid nucleus) produces two male gametes via mitosis

  2. Pollen tube cell (also has its own nucleus) elongates to penetrate ovule

  3. Outer protective coating
• Define pollination
• How does the ovule form in the ovary?

  1. Meiosis of megaspore cell produces four haploid megaspores

  2. Growth and development (involving three mitotic divisions) of one of the megaspores

  3. Embryo sac forms containing eight haploid nuclei
• Adaptations of flowers promoting cross-pollination

  1. Maturation of pollen and ovary at different times

  2. Physical features prevent self-pollination, e.g. heterostyly, male and female flowers on different parts of the plant
• Pollen tube entering the embryo sac

  1. Pollen tube grows from the grain down to the ovule via the digestion of the style

  2. Pollen tube delivers two male gametes
• Male nuclei reaching the embryo sac

  1. Pollen grain from one plant lands on the stigma of another

  2. Mitosis of pollen grain to form a pollen tube nucleus and two male gametes

  3. Pollen tube grows from the grain down to the ovule via the digestion of the style

  4. Pollen tube delivers two male gametes
• Types of pollination

  • Cross-pollination
  • Self-pollination
• Double fertilisation occurs in the embryo sac of the ovule
• Embryo sac formation

  1. Two polar nuclei form endosperm

  2. Ovum forms zygote

  3. Two synergids help generative nucleus of pollen grain to reach ovum

  4. Three antipodal cells

  5. Outer protective coating
• What structure forms the testa?
• How is the endosperm formed?
• What happens during double fertilisation?