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POLLINATION.pptx
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- 2. The processof transfer of pollengrains from the anther to the stigma of flower is called pollination Essential for fertilization and development of embryo Depending on the source of pollen, pollination is of 3 types Autogamy Geitonogamy Xenogamy
- 3. AUTOGAMY Transfer ofpollen grains from the anther to the stigma of the same flower Conditions for autogamy: Flower must be bisexual Synchrony in the pollen release and stigma receptivity.The anther and pistil mature simultaneously Anther and stigma lie close to each other Some plants such as Viola (common pansy), Oxalis, and Commelina produce two types of flowers – chasmogamous flowers , flowers with exposed anthers and stigma, and cleistogamous flowers which do not open at all Autogamy is the only method of pollination in cleistogamous flowers. In such flowers, the anthers and stigma lie close to each other. When anthers dehisce in the flower buds, pollen grains come in contact with the stigma to effect pollination. Cleistogamous flowers produce assured seed-set even in the absence of pollinators cleistogamy is advantageous or disadvantageous to the plant? Why? Ans: inbreeding depression
- 5. GEITONOGAMY Transfer ofpollen grains from the anther to the stigma of another flower of the same plant. geitonogamy is functionally cross-pollination involving a pollinating agent But genetically it is similar to autogamy since the pollen grains come from the same plant XENOGAMY/ CROSS POLLINATION/ ALLOGAMY
- 6. Outbreeding devices /Conditions for Xenogamy Majority of flowering plants produce hermaphrodite flowers and pollen grains are likely to come in contact with the stigma of the same flower. Continued self-pollination result in inbreeding depression Devices to prevent self pollination and to increase cross pollination are: In some species, pollen release and stigma receptivity not synchronized Either the pollen is released before the stigma becomes receptive or stigma becomes receptive much before the release of pollen the anther and stigma are placed at different positions so that the pollen cannot come in contact with the stigma of the same flower Plant monoecious- unisexual flowers- prevent autogamy Eg; Maize,Caster Plant dioecious- male & female flowers different plant- prevent both autogamy and geitonogamy Eg; Datepalm, papaya self-incompatibility- Genetic mechanism that prevents the germination of pollengrains on the stigma of same flower/ another flower of the same plant.
- 7. POLLINATING AGENTS Externalagents which help in pollination 2 types- Abiotic agents- Wind, Water Biotic agents- Insects, birds, reptiles, mammals ABIOTIC AGENTS: The contact of pollengrains with stigma is a chance factor both in wind & in water pollination. So only small no: of plants use abiotic agents for pollination.
- 8. WIND POLLINATION (Anemophily) Common method Special features Produce large no: of pollengrains Pollen grain are light, dry & non sticky-transported in wind currents Sometimes they have wing like structures : eg; Pinus Stigma is large, feathery –trap air borne pollengrains Flowers normally have a single ovule in the ovary Flowers are arranged as infloresense : eg; corn cob Eg: Grasses, maize, cannabis
- 9. WATER POLLINATED (Hydrophily) rare in flowering plant , limited to about 30 genera, mostly monocotyledons. In lower plant groups such as bryophytes & pteridophytes water is the medium of transport of male gamates. for some bryophytes and pteridophytes, their distribution is limited because of the need for water for the transport of male gametes and fertilisation. Special features Pollengrains are light & protected from decaying- mucilaginous covering Stigma is sticky and unwetable due to waxy coating Eg: Vallisneria, zostera, hydrilla
- 10. In vallisneria,the female flower reach the surface of water by the long stalk and the male flowers or pollen grains are released on to the surface of water, reach female flower through water current. After pollination female flower sinks down. In Zostera ( Sea grasses), female flowers remain submerged in water and the pollen grains are released inside the water.They are long and ribbon like. They coil around female flowers and pollination takes place. All aquatic plants do not use hydrophily. Majority of aquatic plants flowers emerge above the level of water and are pollinated by insects or by wind Eg: Water hyacint
- 11. BIOTIC AGENTS Pollinationby animals – Zoophily Insects- Butterfly, bees, ants Birds- Sunbird, humming bird Reptiles- Garden lizard, geckolizard Mammals- lemurs, bats, rodents
- 12. INSECT POLLINATION (Entomophily) Flowers are large,if small they are grouped in inflorescence Flowers are brightly coloured, scented/ with foul odour ( flies, beetle pollinated) Produce nectar Pollengrains & stigma are sticky Nectar and pollen grains are the usual floral rewards Eg; Jasmine, Sunflower.
- 13. BIRDS POLLINATION (Ornithophily) Flowers are large & funnel shaped Brightly coloured Produce large amount of nectar Pollen grains are sticky Animal pollinated flowers give certain rewards to the pollinators.Explain it? Ans: The flowers provide nectar & pollengrains as food Some species provide safe place for laying egg, Eg; Amorphophalis & Yucca A species of moth and the plant Yucca– cannot complete their life cycles without each other. The moth deposits its eggs in the locule of the ovary and the flower, in turn, gets pollinated by the moth. The larvae of the moth come out of the eggs as the seeds start developing. YUCCA & Moth
- 14. Importance of pollination Pollination leads to fertilization, production of seeds and fruits Cross pollination- genetic recombination- new species Cross pollination- disease resistant, high yielding plant varieties Productivity can be increased by the availability of suitable pollinating agents Seeds and fruit formed after fertilization- source of nutrients for animals including man Essential for the perpetuation of species