Pollination is the transfer of pollen grains from the anther to the stigma. It can occur through self-pollination within a flower or plant or cross-pollination between plants. Flowers have adapted traits for wind or insect pollination, with wind-pollinated flowers generally having small, dry pollen and insect flowers having nectar, scent and bright colors. Cross-pollination provides genetic diversity but requires two parents, while self-pollination only requires one but can lead to inbreeding over time. Plants use various mechanisms like separate male and female plants or maturation timing to encourage outcrossing.

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)

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)