Chapter 16 Reproduction in Plants Lesson 2 - Pollination

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  • 1. Pollination
  • 2. Pollination
    • Definition:
    • The transfer of pollen grains from the anther to the stigma
  • 3. Self-pollination vs Cross-pollination
    • Self pollination – transfer of pollen grains to stigma of same flower or different flower of the same plant
    • Cross pollination - pollen grains transferred to flower in another plant of the same kind
  • 4. Pollination
    • Usually effected by insects OR wind
    • Characteristics of insect-pollinated and wind-pollinated flowers differ
    Insect pollination
  • 5. In the table below list the possible differences between both wind and insect pollinated flowers 6) 5) 4) 3) 2) 1) Wind-pollinated flower Insect-pollinated flower Characteristic
  • 6. Usually absent Often present to attract insects 2) Nectar Flowers do not have scent Flowers are fragrant or sweet-smelling 3 ) Scent absent May be present 7) Nectar guides (marking that guide insects to nectar) Protrude + large & feathery  large s.a. to catch pollen floating in air Usually small and compact, not feathery and do not protrude; sticky so that pollen grains setting on them are not easily displaced 6) Stigmas Usually have long, slender filaments that sway in the slightest wind  pollen grains easily shaken out from anthers May not be pendulous 5) Stamens Abundant; small, smooth, dry, light  buoyant & easily blown about by wind Fairly abundant; large, sticky and heavy, rough surfaces to cling onto insects’ bodies 4) Pollen Usually small, dull-coloured and scentless (unattractive to insects) Usually large, brightly coloured and scented to attract insects.If flower small  form an influorescence 1) Flowers Wind-pollinated flower Insect-pollinated flower Characteristic
  • 7. Advantages of self-pollination
    • Only one parent is required
    • Offspring inherits its genes from parent plant. Hence beneficial qualities are more likely to be passed down to the offspring
    • It does not depend on external factors e.g. insects or wind for pollination
    • Anthers are close to the stigmas of the same flower hence there is a high possibility that self –pollination will occur
    • Less pollen and energy is wasted is self-pollination compared to cross pollination
  • 8. Disadvantages of self-pollination
    • Less varieties of offspring are produced as the offspring’s genes are similar to those of the parent plant, therefore the species is less adapted to changes in the environment
    • Continued self-pollination may lead to offspring becoming weaker, smaller and less resistant to diseases
  • 9. Features favouring self-pollination
    • Flowers are bisexual with anthers and stigmas maturing at the same time
    • Stigma is situated directly below the anthers
    • In certain plants with bisexual flowers, some flowers never open ( cleistogamous flowers). Only self-pollination can occur in these flowers
  • 10. ***Advantages of cross-pollination
    • Offspring may have inherited beneficial qualities from both parents
    • Abundant and more viable seeds tend to be produced (i.e. seeds are capable of surviving longer before germination)
    • More varieties of offspring can be produced (greater genetic variation)
    • -> increases chance of survival of species to changes in the environment
  • 11. Disadvantages of cross pollination
    • Two parent plants are required
    • Depends on external factors e.g. insects or wind for pollination
    • Lower probability that cross pollination will occur compared to self-pollination (because it involves transfer of pollen grains from the anther of one plant to the stigma of another plant)
    • More energy and pollen is wasted as compared to self-pollination
  • 12. Adaptations of plants to favour cross-pollination (genetic variability)
    • Dioecious plants bear either male or female flowers so that self-pollination is impossible e.g. paw paw
    • Maturation of anthers and stigmas at different times (bisexual flowers) e.g. custard apple
    • Stigmas of bisexual flowers may be situated a distance away from the anthers (less chances for self-pollination)
  • 13. Structure and Pollination of an Insect-pollinated Flower (pg. 303-304) e.g. Clitoria
  • 14. Characteristics of Clitoria
    • Butterfly-shaped flowers
    • Complete
    • Bisexual
    • Bilaterally-symmetrical
  • 15. Calyx
    • Is green
    • 5 sepals (at free end of calyx)
    • 2 leaves that enclose the base of the calyx = epicalyx
    Corolla
    • Brightly coloured with 5 petals of differing shape and size
    • Consists of
    • i) large purple petal
    • ii) 2 lateral wing petals
    • iii) 2 small yellowish-green keel petals
  • 16. Androecium
    • Definition:
    • The male (stamen) parts of the flower
    • 10 stamens with long filaments
    • 9 stamens fused together with 1 free stamen
    • Nectar secreted collects at bottom of stamen trough
    • Can only be reached by an insect with long proboscis e.g. bee or butterfly
  • 17. Gynoecium
    • Definition :
    • The female portion of the flower consisting of the ovary, stigma (a sticky surface to which pollen grains attach and germinate) and style (which connects the stigma to the ovary)
    • Consists of single carpel
    • Ovary long and narrow with a single row of ovules
    • Style is long, curved structure and is hairy (situated below stigma)
  • 18. Pollination mechanism in Clitoria
    • Can be
    • 1) insect -pollinated OR
    • 2) self -pollinated (because flower is inverted)
    • Insect pollination (cross-pollination) :
    • - bees force its way b/w 2 wing petals and move in to collect nectar
    • - back forces keel petals upwards exposing stigma and anthers which brush the hairy back of the insect
    • - pollen grains on the insect’s back (from another flower the insect had visited earlier) adhere to the sticky stigma
    • - when insect leaves, keel springs back to original position and enclose the stamens and stigma
  • 19. Structure and Pollination of an Wind-pollinated Flower (pg. 305-307) e.g. Grass flowers ( Ischaemum muticum)
  • 20.  
  • 21. Characteristics of Ischaemum muticum
    • Wind -pollinated flowers
    • Usually small dull-coloured flowers (scentless and without nectar), massed in influorescences
    • Influorescence consists of short stalks bearing flowers (in pairs)
    • Each pair of flower is enclosed and protected by bracts (leaf-like structures) -> forming a spikelet (occurs in pairs)
    • The lower spikelet is sessile while the upper one is stalked and smaller
    • Base of spikelet is a pair of glumes (non-flowering bracts that protect the 2 flowers in a spikelet)
  • 22. Characteristics of Ischaemum muticum
    • Lower flower is unisexual - consists only of 3 stamens with long filaments
    • Upper flower is bisexual – consists of an ovary + 2 long feathery stigmas, 3 stamens + 2 lodicules at base of ovary
    • When lodicules swell, they force the 2 flowering bracts slightly apart so that stigmas and anthers can emerge
  • 23. Adaptations of Ischaemum to wind pollination
    • Mature stamens have long and pendulous filaments
    • Filaments protrude out of bracts, expose mature anthers to wind
    • Delicate filaments sway in the slightest breeze
    • Dust-like pollen sheken free and carried away by wind
    • Mature stigmas do not hand freely but project out of the bracts (as they are large + feathery -> large s.a. to receive pollen floating around)