Reproduction of flowering plants

• Asexual Reproduction


  • Involves only one parent
  • No meiosis, no gametes
  • The offspring are genetically identical to the parent (clones)
• Sexual Reproduction


  • Involves the union of two sex cells or gametes
  • Gametes are haploid cells capable of fusion
  • Two gametes fuse to form a diploid cell called a zygote
• Structure of the flower


  • Receptacle
  • Sepals
  • Petals
• Functions of the floral parts - Receptacle


  This is the part of the flower from which the floral parts arise. It supports these parts.
• Functions of the floral parts - Sepals


  Green, leaf-like structures. Their function is to protect the flower when it is in bud.
• Functions of the floral parts - Petals


  In animal-pollinated plants, petals are large and brightly coloured to attract insects. In wind-pollinated plants, petals are small (or absent) and green.
• Function of floral parts - Stamen (Male Parts)


  • Anther: Produces pollen
  • Filament: Holds the anther in place
  • Stamen: The function of the stamen is to produce the pollen grains in the anthers. (Each pollen grain produces two male gametes, one of which can fertilise an egg cell)
• Function of floral parts - Carpel (Female parts)


  • Stigma: Where pollen lands after pollination
  • Style: Pollen travels down this
  • Ovary: Contains ovules
  • Carpel: To produce the ovules (Each ovule contains an egg cell inside an embryo sac)
• Pollen grain development


  1. An anther consists of four chambers called pollen sacs

  2. Each pollen sac is protected by a epidermis & fibrous layer

  3. Inside the fibrous layer is the tapetum - a food store that supplies energy for cell divisions in the pollen sac

  4. Inside each pollen sac are diploid microspore mother cells (Pollen Mother cells)

  5. They divide by meiosis to produce 4 haploid pollen grains-microspores
• Pollen Grain development


  1. While still in the pollen sac, the pollen grains divide by mitosis producing two haploid nuclei:

  2. Tube nucleus - forms the pollen tube and then degenerates

  3. Generative nucleus - form the male gametes
• When pollen grains have matured the walls of the anther dry and split. Pollen grains are then exposed and are ready for pollination.
• After pollination


  1. The generative nucleus (n) divides by mitosis to form two sperm nuclei (n)

  2. These will each play a role in double fertilisation
• Pollen Grain


  • Exine = Outer Protective Layer
  • Intine = Inner Protective Layer
• Ovule


  • Each ovary contains one or more ovules
  • An ovary has two walls called integuments
  • Between the integuments is a small opening (micropyle) through which a pollen tube can enter
  • The nucellus provides nutrients for growth in the ovule
• Embryo sac development


  1. One cell in the ovule, is called the megaspore mother cell (2n). It divides by meiosis to form four haploid cells

  2. Three of these cells disintegrate

  3. The remaining cell is called the embryo sac (n)
• Embryo sac development


  1. The embryo sac (n) then divides by mitosis three times forming eight haploid nuclei

  2. Five of these nuclei will later die

  3. The remaining three are the gametes - two polar nuclei (n) and one egg cell (n)
• Pollination


  Transfer of pollen from the anther to the stigma of a flower of the same species
• Methods of pollination


  • Animal Pollination
  • Wind Pollination
• Adaptations for animal (insect) pollination

  • Petals brightly coloured, scented with nectaries
  • Small amounts of sticky pollen
  • Anthers inside petals
  • Stigmas sticky, inside petals
• Adaptations for wind pollination

  • Petals small, not coloured brightly
  • Anthers outside petals
  • Stigmas large, feathery and outside petals
  • Pollen is made in large numbers and is light, dry and small
• Fertilisation


  • Fertilisation is the fusion of the male (n) and female (n) gametes to produce a zygote (2n)
  • One sperm nucleus (n) fuses with the egg nucleus (n) to form a diploid zygote. This will develop into an embryo
  • The second sperm nucleus (n) joins with the two polar nuclei (2n) forming a triploid (3n) endosperm nucleus
• Events leading to fertilisation

  1. Once pollination has occurred the pollen tube nucleus forms the pollen tube which moves down the style to the ovule in the ovary

  2. The tube nucleus moves towards chemicals released from the ovule (chemotropism)

  3. The tube nucleus degenerates when the pollen tube reaches the opening of the ovule (micropyle)

  4. The generative nucleus (n) divides by mitosis as it moves down the pollen tube

  5. Two haploid sperm nuclei result

  6. These are the male gametes

  7. On reaching the embryo sac a double fertilisation will take place
• Seed formation


  • Endospermic
  • Non-Endospermic
• Seed Formation


  • The fertilised ovule becomes the seed
  • The walls of the ovule (integuments) dry up to become the wall of the seed/seed coat (testa)
  • The zygote divides repeatedly by mitosis to form an embryo
  • The embryo consists of a plumule (future shoot), a radical (future root) and cotyledons (food stores needed for germination)
• Seed Formation - Endospermic


  The endosperm nucleus (3N) divides repeatedly by mitosis to form the endosperm in endospermic seeds. This endosperm acts as a food store for the developing seed
• Seed Formation - Non-Endospermic


  In non-endospermic seeds the endosperm is used up in the early stages of seed development so the food is stored in the cotyledons
• The white material in popcorn is the endosperm
• Endosperm


  Food store for developing embryo
• Embryo


  Plumule, radicle, cotyledons
• Seed Formation


  • If all of the endosperm isn't absorbed by the developing embryo the seed is an endospermic seed e.g. Maize, corn
  • If all of the endosperm is absorbed by the developing embryo the seed is a non endospermic seed e.g. broad bean, peanut
• Seed types and structure

  • Plumule (immature shoot)
  • Radicle (immature root)
  • Cotyledon (food supply or seed leaf)
  • Endosperm (Food store)
  • All seeds
  • In some seeds
• Classification of seeds


  • Number of cotyledons (Seed leaves):
  • Monocotyledon - one cotyledon
  • Dicotyledon - Two cotyledons
  • Presence of endosperm:
  • Present - Endospermic e.g. maize
  • Absent - Non-endospermic e.g. broad bean
• Broad Bean - Non-Endospermic Dicot


  • Testa
  • 2 Cotyledons
• Fruit Formation


  • The ovule becomes the seed
  • The ovary becomes the fruit
  • The process of fruit formation is stimulated by growth regulators produced by the seeds
• Fruit


  • Fruits are designed to protect the seed(s) and to help in seed dispersal
  • Some fruits are succulent or fleshy (eg tomatoes, grapes) and some are dry (eg popcorn grains, pea pods)
• Changes in the flower after fertilisation

  1. Before Fertilisation:

  2. Ovule

  3. Integuments

  4. Egg

  5. After Fertilisation:

  6. Seed

  7. Testa (seed coat)

  8. Zygote -> Embryo

  9. Polar nuclei
• Parts of a seed

  • Plumule
  • Radicle
  • Cotyledon
  • Endosperm
• Monocotyledon


  Seed with one cotyledon (seed leaf)
• Dicotyledon


  Seed with two cotyledons (seed leaves)
• Classification of seeds


  • Number of cotyledons
  • Presence of endosperm