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Pollination
Pollination <ul><li>Definition: </li></ul><ul><li>The transfer of pollen grains from the anther to the stigma </li></ul>
Self-pollination vs Cross-pollination <ul><li>Self pollination  – transfer of pollen grains to stigma of same flower or di...
Pollination <ul><li>Usually effected by insects OR wind </li></ul><ul><li>Characteristics of insect-pollinated and wind-po...
In the table below list the possible differences between both wind and insect pollinated flowers 6) 5) 4) 3) 2)  1) Wind-p...
Usually absent Often present to attract insects 2)  Nectar  Flowers do not have scent Flowers are fragrant or sweet-smelli...
Advantages of self-pollination <ul><li>Only one parent is required </li></ul><ul><li>Offspring inherits its genes from par...
Disadvantages of self-pollination <ul><li>Less varieties of offspring are produced as the offspring’s genes are similar to...
Features favouring self-pollination <ul><li>Flowers are bisexual with anthers and stigmas maturing at the same time </li><...
***Advantages of cross-pollination <ul><li>Offspring may have inherited beneficial qualities from both parents </li></ul><...
Disadvantages of cross pollination <ul><li>Two parent plants are required </li></ul><ul><li>Depends on external factors e....
Adaptations of plants to favour cross-pollination (genetic variability) <ul><li>Dioecious plants  bear either male or fema...
Structure and Pollination of an Insect-pollinated Flower  (pg. 303-304) e.g.  Clitoria
Characteristics of Clitoria <ul><li>Butterfly-shaped flowers </li></ul><ul><li>Complete </li></ul><ul><li>Bisexual </li></...
Calyx <ul><li>Is green  </li></ul><ul><li>5 sepals (at free end of calyx) </li></ul><ul><li>2 leaves that enclose the base...
Androecium <ul><li>Definition: </li></ul><ul><li>The  male  (stamen) parts of the flower  </li></ul><ul><li>10 stamens wit...
Gynoecium <ul><li>Definition :  </li></ul><ul><li>The  female  portion of the flower consisting of the ovary, stigma (a st...
Pollination mechanism in Clitoria <ul><li>Can be </li></ul><ul><li>1)  insect -pollinated  OR </li></ul><ul><li>2)  self -...
Structure and Pollination of an Wind-pollinated Flower  (pg. 305-307) e.g. Grass flowers ( Ischaemum muticum)
 
Characteristics of  Ischaemum muticum <ul><li>Wind -pollinated flowers </li></ul><ul><li>Usually small dull-coloured flowe...
Characteristics of  Ischaemum muticum <ul><li>Lower flower is unisexual - consists only of 3 stamens with long filaments  ...
Adaptations of Ischaemum to wind pollination  <ul><li>Mature stamens have long and pendulous filaments </li></ul><ul><li>F...
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Chapter 16 Reproduction in Plants Lesson 2 - Pollination

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Chapter 16 Reproduction in Plants Lesson 2 - Pollination

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

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