Q.Write a note on: Allogamy.
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Pollination and Its Mechanisms
Pollination is the transfer of pollen grains (carrying the male gametes) from the anther to the stigma. Self-pollination (autogamy) occurs within the same flower; geitonogamy is between flowers of the same plant; cross-pollination (xenogamy) transfers genetically different pollen between plants.
Pollination is mediated by agents: wind (anemophily), water (hydrophily), insects (entomophily), birds (ornithophily), snakes (ophiophily) and bats. Floral adaptations match the agent — e.g. exposed anthers and stigmas suit chasmogamous (open) flowers, while cleistogamous flowers never open and ensure self-pollination. …
Pollination can be classified by whether pollen moves within the same plant or between genetically different plants, and this distinction has direct consequences for the genetic variation seen in the resulting offspring. …
Allogamy (cross-pollination / xenogamy in the strict sense) is the transfer of pollen between flowers of genetically different plants, promoting genetic variation in the offspring.
Pollination can broadly be of two kinds based on the source of pollen: autogamy (self-pollination), where pollen from a flower's own anther reaches its own stigma (or a different flower of the same plant, called geitonogamy), and allogamy (cross-pollination), where pollen is transferred from the anther of a flower on one plant to the stigma of a flower on a different, genetically distinct plant of the same species. Since allogamy brings together male and female gametes from two genetically different individuals, it results in greater genetic recombination and variation in the offspring compared to self-pollination, which is evolutionarily advantageous because it improves a population's adaptability. Plants have evolved numerous mechanisms to encourage allogamy and discourage self-pollination, including dicliny (unisexual flowers), dichogamy (anthers and stigma of the same flower maturing at different times), herkogamy (physical separation of anther and stigma), he …
Showing the 12 most recent of 34 on this concept.
- CBSE 2026Set EG1 markMCQQ.Which of the following characteristics of flower is suitable for insect pollination?(a) Light weighted pollen grains(b) Coloured attractive corolla(c) Multiple ovule(d) Small pollen grains
›Reveal solutionSolution
A brightly coloured, attractive corolla is an adaptation for insect pollination — option (b).
Pollination strategy shapes flower structure. Wind-pollinated flowers make large amounts of small, light, dry pollen and are usually dull/inconspicuous. Insect-pollinated (entomophilous) flowers must advertise themselves and reward the visitor, so they show:
- large, brightly coloured attractive corolla (petals),
- fragrance and nectar, …
- CBSE 2026Set A1 markMCQQ.Which of the following is the pollinating agent of Ophrys?(a) Wasp(b) Humming bird(c) A species of bee(d) Bat
›Reveal solutionSolution
Ophrys is pollinated by a species of bee that is deceived into pseudocopulation.
The orchid Ophrys uses a special strategy called sexual deceit. One petal of its flower bears an uncanny resemblance in size, colour and markings to the female of a particular species of bee. When the male bee 'sees' this petal, it is deceived into thinking it is a female and attempts to copulate with it (pseudocopulation). During this act, the flower's pollen gets deposited on the b …
- CBSE 2026Set BOTANY1 markMCQQ.An example of contrivance of self-pollination is _____.(a) cleistogamy(b) herkogamy(c) dicliny(d) heterostyly
›Reveal solutionSolution
Cleistogamy (flowers that never open) is a contrivance that guarantees self-pollination, unlike herkogamy, dicliny, and heterostyly, which are devices that favour cross-pollination.
Plants have evolved several floral mechanisms (contrivances) that either promote self-pollination (autogamy) or prevent it and favour cross-pollination (xenogamy). Among the given options:
- Cleistogamy: flowers such as those of Commelina, Viola, and Oxalis never open at all. Since the anthers and stigma lie close together inside a closed flower, self-pollination is inevitable and guaranteed, with no chance of contamination by foreign pollen. This is the surest device for self-pollination.
- Herkogamy: the anther and stigma are physically separated within the same flower (spatial hindrance), which discourages self-pollination and favours cross-pollination. …
- CBSE 2026Set ANNUAL1 markMCQQ.Water pollinated plant that grow in fresh water is(a) Zostera(b) Vallisneria(c) Eelgrass(d) Mangrove
›Reveal solutionSolution
Vallisneria is a fresh-water hydrophilous (water-pollinated) plant; Zostera and eelgrass are marine sea-grasses, and mangroves are not water-pollinated.
Pollination by water (hydrophily) is rare, confined to about 30 genera, mostly monocots growing in fresh or marine water. Common examples: Vallisneria and Hydrilla (fresh water), and Zostera (sea-grass/eelgrass, a marine species). Since the question asks specif …
- CBSE 2025Set ANNUAL1 markQ.Write the name of a wind-pollinated plant.
›Reveal solutionSolution
Maize (Zea mays) is a common example of a wind-pollinated (anemophilous) plant.
Wind-pollinated (anemophilous) plants produce enormous numbers of small, light, non-sticky pollen grains and typically bear well-exposed, often feathery, stigmas that trap airborne pollen efficiently. Their flowers are usually small, dull-coloured and without fragrance or nectar since no pollinator needs to be attracted. Be …
- CBSE 2025Set F1 markMCQQ.By which of the following is water hyacinth pollinated?(a) Water(b) Insect(c) Wind(d) Both (B) and (C)
›Reveal solutionSolution
Water hyacinth is insect-pollinated (entomophilous), not water-pollinated.
Though water hyacinth (Eichhornia crassipes) is an aquatic plant, its flowers are raised above the water surface and are large, brightly coloured and showy — features that attract insects. Pollination therefore occurs through insects (entomophily). True water-pollinated (hydrophilous) plants such as …
- CBSE 2025Set ANNUAL1 markQ.Write the agent of pollination in Hydrilla plant.
›Reveal solutionSolution
Hydrilla, a submerged aquatic plant, relies on water as the pollinating agent, a phenomenon called hydrophily.
In plants like Hydrilla and Vallisneria that grow submerged in water, pollen grains are released into the water and are carried passively by water currents to reach the stigma of another flower, accomplishing pollination. This mode of abiotic …
- CBSE 2025Set ANNUAL1 markMCQQ.A farmer noticed that his apple trees were not bearing as much fruits as expected, despite having plenty of flowers. He observed that the bee population in his orchard had decreased significantly this season due to recent pesticide usage. Which type of pollination is likely being affected in this case, and what could be a possible solution ?(a) Wind pollination - Reducing pesticide use will allow wind to effectively pollinate the flowers.(b) Water pollination - Increasing irrigation will help water carry pollen between flowers.(c) Insect pollination - Reducing pesticide use and introducing bee hives could improve fruit production.(d) None of the above.
›Reveal solutionSolution
Apples depend heavily on insect (entomophilous) pollination by bees; killing off the bee population with pesticides directly reduces pollination and hence fruit yield.
Many fruit crops, including apple, are largely insect-pollinated — bees visit flowers to collect nectar/pollen and, in doing so, transfer pollen from anther to stigma, enabling fertilisation and fruit/seed formation. Plenty of flowers but few fruits is a classic sign of pollination failure, not a lack of flowering itself. Pesticide use is well known to kill or repel pollinating insects like bees, cutting off this essential service. The practical fix is to reduce/manage pesticide application (e.g., spray at times when bees are inac …
- CBSE 2025Set ANNUAL1 markQ.Which type of pollination occurs in Vallisneria?
›Reveal solutionSolution
Vallisneria is a classic example of pollination by water (hydrophily), and specifically of surface pollination (epihydrophily).
Vallisneria is a submerged, dioecious aquatic plant. Its male flowers break off from the plant and float freely on the water surface. The female flowers reach the surface of water by the elongation of their long spirally-coiled stalks. Pollen grains from the male flowers, floating on the water surface, come into contact with the stigma of the female flowers that lies at the water surface, effecting pollination. Because the pollen travels ON the surface film of water (not submerged in it), this specific ty …
- CBSE 2025Set ANNUAL1 markQ.What is autogamy?
›Reveal solutionSolution
Autogamy is self-pollination confined to a single flower, requiring synchrony between anther dehiscence and stigma receptivity.
Autogamy is a type of self-pollination in which pollen from the anther of a flower is transferred to the stigma of that very same flower. It requires that the anther and stigma of the flower mature (become receptive/dehisce) at the same time and are positioned close enough to allow pollen transfer, and it can even occur without the involvement of any external pollinating ag …
- CBSE 2025Set ANNUAL1 markQ.Why do pollen grains produce in large numbers in anemophilous flower?
›Reveal solutionSolution
Wind is an unreliable, non-directed pollinating agent, so anemophilous flowers must produce vast quantities of pollen to ensure that at least some reaches a receptive stigma.
In anemophilous (wind-pollinated) flowers (e.g. maize, grasses), pollen grains are carried passively by air currents. Wind does not "aim" pollen at a stigma the way an animal pollinator can; pollen is dispersed in all directions, and only an extremely small fraction by chance lands on the stigma of a flower of the same species. To offset this very low probability of successful transfer, such flowers evolve to produce pollen grains in enormously large numbers, ensuring that, statistically, enough pollen reaches the stigmas for successful pollination and seed-set. Such flowers usually also have other adaptations for wind pollination — light, non-sticky pollen, well-exposed stamens, large often feathery stigma …
- CBSE 2025Set ANNUAL1 markMCQQ.Choose the type of pollination in which attractants and rewards are required :(a) Hydrophily(b) Anemophily(c) Cleistogamy(d) Entomophily
›Reveal solutionSolution
Entomophily (insect pollination) requires the flower to offer attractants and rewards because insects must be actively lured to visit.
Pollination modes differ in how the pollen reaches the stigma:
- Hydrophily (water pollination) and Anemophily (wind pollination) are abiotic — pollen is passively carried by the medium, so the flower needs no colour, scent or reward, only huge pollen output and exposed stigmas.
- Cleistogamy is self-pollination inside a flower that never opens, so no pollinator or reward is involved at all. …
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