NEET Exam  >  NEET Notes  >  Biology Class 12  >  Pollination

Pollination | Biology Class 12 - NEET PDF Download

Pollination

Pollination is defined as the process of transfer of pollen grains from the anther to the stigma of the same flower or of a different flower of the same species.

➢ Types of Pollination

1. Self-Pollination or Autogamy: If the pollen grains are transferred from an anther to the stigma of the same flower, or different flowers of the same plant is called Self-pollination or Autogamy.
2. Cross-Pollination or Allogamy: When the pollen grains are transferred to the stigma of other flowers of the same species is called Cross-pollination or Allogamy. It takes place in between two different flowers.

Cross-pollination is of two types:
(i) Geitonogamy: When pollination takes place in between the two flowers of the same plant then it is called geitonogamy. From the genetical point of view, geitonogamy is self-pollination because all flowers of the same plant are genetically identical. But ecologically, it is considered as cross-pollination.
(ii) Xenogamy: When the pollination takes place in between the two different flowers of two different plants of the same species then it is called xenogamy. This is real or true cross-pollination. Genetically, as well as ecologically, it is cross-pollination.

Question for Pollination
Try yourself:Transfer of a pollen grain to the stigma of the same plant is called
View Solution

➢ Contrivances or Adaptation for Self-Pollination

(i) Monocliny (Bisexuality): It means flowers are bisexual.
(ii) Homogamy: When both the sex organs of a flower mature at the same time. It is called homogamy. It increases the chances for self-pollination.
Examples: Mirabilis, Catharanthus.
(iii) Cleistogamy: In some plants, a bisexual flower is formed which never opens throughout life. Such flowers are called cleistogamous flowers, such as Commelina, Viola, Oxalis, Juncus, Drosera. Commelina plant has two types of flowers. One type of flowers are cleistogamous and another are chasmogamous flowers.
A special type of cleistogamy is found in the flowers of a legume plant. The sex organs are closed in a structure which is formed by the joining of some petals. It is called the keel. This keel never opens. So only self-pollination takes place in these plants.

(iv) Bud Pollination: This pollination occurs in the bud stage before the opening of flowers.
Example: Pisum, Wheat, Rice.

Contrivances for Cross Pollination 

(i) Dicliny (Unisexuality): The presence of unisexual flowers confirms cross-pollination. Self-pollination never takes place in these flowers. It means allogamy becomes compulsory.
Examples: Morus, Palms, Date Palms, Cucumber, Cucurbita, Carica.

Unisexual flowers perform cross-pollination (dicliny)Unisexual flowers perform cross-pollination (dicliny)(ii) Dichogamy: In many bisexual flowers of the plants, stamens and carpels of a flower do not mature at the same time.
Dichogamy is of two types:
(a) Protandry: The anther of a flower mature earlier than carpels, is called protandry. Many plants of Angiosperms are cross-pollinated only because of protandrous condition.
Examples: Salvia, Sunflower, Cotton.
(b) Protogyny: The carpels of the flower mature earlier than stamens. It occurs in a few plants.
Examples: Ficus bengalensis, Saraca indica, Ficusreligiosa, Aristolochia, most of the plants of Cruciferae and Rosaceae family.

(iii) Chasmogamy or Anthesis: Opening (blooming) of the floral bud in the form of a flower is called anthesis.

(iv) Herkogamy: In some plants, morphological barriers are formed in between the anther and stigma of the same flower, so self-pollination cannot occur and pollen grains from the anther are unable to reach the stigma of the same flower. In this condition, only cross-pollination is possible.
Examples: Gloriosa, Calotropis and Caryophyllaceae family.

(v) Heterostyly: There is a difference between the length of the filaments of stamens and the length of style in flowers of some plants. Some of the plants having long stamen and short style and some of the plants bear long style and short filament. Due to this reason, self-pollination can not possible in these plants.
Examples: Primrose, Linum, Primula.

(vi) Self sterility or self-incompatibility or intraspecific incompatibility: In this condition, the pollen grains of the flower cannot germinate on the stigma of the same flower. This condition is called self sterility. This is a parental (Genetical) characteristic feature which is controlled by genes.
Examples: Petunia, Malva, Thea, Passiflora, Vitis, Apple (Malus).
Incompatibility involves many complex mechanisms associated with interactions of pollen and stigmatic tissues. If the incompatibility is due to the genotype of the sporophytic /stigmatic tissues, it is termed sporophytic incompatibility on the other hand, if it is due to the genotype of the pollen, it is termed gametophytic incompatibility.
This may be due to the prevention of pollen germination, retardation of growth, de-orientation of pollen tube or even failure of nuclear fusion. It is controlled by genes with multiple alleles (s-allele). Enlarged pollen tube turns upwards and degenerates in style.

(vii) Prepotency: Growth of its pollen tube of the self-pollinated pollen grain is very slow and growth of the pollen tube of the cross-pollinated pollen grain is very fast so the pollen tube of cross-pollinated pollen grains reaches earlier inside the ovule. This is termed prepotency.
Examples: Apple, Grapes.

➢ Methods of Cross-Pollination

1. Anemophily 

  • When the pollen grains are transferred from one flower to another flower through the air is called anemophily and the flower is known as anemophilous flowers.
    Example: Cereal plants - Maize etc.
    Wind Pollination (Anemophily)
    Wind Pollination (Anemophily)
  • Anemophily is also found in all Gymnosperms. The anemophilous plants produce an enormous amount of pollen grains. The pollen grains are very small, lightweight and dry and their stigma is hairy or bushy and mucilaginous (sticky). Yellow clouds are formed in the sky during the wind pollination in Pinus.
  • These yellow clouds are formed due to the pollen grains are called "Sulphur Showers".
  • Anemophilous flowers are neither attractive nor have fragrance. They do not have nectar glands.
  • Anemophilous flowers are generally unisexual.
  • Examples: Sugar cane, Bamboo, Coconut, Cannabis, Grasses, Date palms, Typha, Oak, Hazel, Cucumber, Papaya, Cotton, Tobacco, Eucalyptus, etc.
  • Potamogeton and Myriophyllum are aquatic plants but are anemophilous.
  • The maximum loss of pollen grains takes place only in this pollination. It is a completely non-directional process.

2. Hydrophily 

  • When pollination brings by water, it is known as hydrophily.
  • It is of two types:
    (i) Epihydrophily: When the pollination takes place on the surface of the water, it is called epihydrophily.
    Examples: Vallisneria and Ruppia.
    (ii) Hypohydrophily: When the pollination takes place inside the water, it is called hypohydrophily.
    Examples: Ceratophyllum, Najas Zostera and Hydrilla Specific gravity is found in pollen grains so they remain suspended in water.

3. Zoophily

  • When pollination brings by animals, it is called zoophily. Generally in zoophilous plants, flowers are very large, attractive and maximum number of nectar glands are present (more than entomophilous).

ZoophilyZoophilyDifferent types of Zoophily are:

(i) Entomophily 

  • This pollination takes place with the help of insects and is known as entomophily. Most of the insect pollination is (80%) only by Honey bees. 
  • Most of the entomophilous plants are ornamental plants. Ornamental plants utilize their maximum energy in this pollination and develop different types of adaptation for the attraction of insects. These flowers are attractive in colour. They possess a special fragrance. Nectar glands are also present.
    Example: Rose, Lemon. 
  • The pollen grains of insect-pollinated flowers become sticky due to the presence of pollen kitt. The surface of the stigma of flowers is rough. Some of the plants develop a special adaptation for insect pollination.
  • In the Mussaenda plant, an advertising flag is present for the attraction of insects.
  • The lever mechanism or turn pipe mechanism is found in Salvia for pollination. The flowers of Salvia have bilabiate corollate tube. The connective of stamen is long. The anterior anther lobe of the connective is fertile while the posteriorly lobe is sterile.
  • When the insect lands on the lower lip, the fertile lobe automatically brings down to touch the back of the insect and thus depositing the pollen grains on the back of the insect.
  • Some of the flowers have attractive bracts i.e. bright and coloured e.g. Bougainvillea.
  • The Yucca plant has develops an obligate symbiotic relationship with an insect- the Pronuba moth. The pollination in "Yucca takes place only by the Pronuba moth. This insect lays eggs in the ovary of the flower. The life cycle of both depends on each other.
  • "Trap door mechanism" is found in species of Ficus (Peepal) for pollination (Blastophaga insect) because Hypanthodium type of inflorescence is present.
  • In Aristolochia "Flytrap mechanism" is found for pollination. This flower is known as the "Pitfall flower". Ophrys speculum flower pollinated by Wasp (Colpa aurea) by means of pseudo-copulation. The appearance and odour of the flower-like female wasp (Mimicry).
  • In Centaurea plant pollination takes place by "piston mechanism".
  • In Rafflesia, the pollination is brought about by Carrion flies and dispersal of seeds by Elephant.
  • Nymphaea, Nelumbo and Alisma are also entomophilous plants while they are hydrophytes.

(ii) Ornithophily

  • The process of pollination is taken place by birds is known as ornithophily.
    Examples: Sunbird or hummingbird in Bignonia plant and by Honeybird in Strelitzia, Callistemon (Bottlebrush), Bombax (Silk cotton tree) Butea monosperma.

(iii) Chiropterophily

  • If the pollination brings through the bats (Pteropus) is called chiropterophily. These flowers are big in size.
    Examples: Anthocephalus kadamba, Bauhinia, Kigelia plants, Adansonia, Musa.

(iv) Myrmecophily

  • This pollination brings about by Termites and Ants.
    Examples: Prosopis (kikar), Acacia (Mimosoideae family), Mango and some members of Rubiaceae family. 
    Pollination | Biology Class 12 - NEET
    Myrmecophilous Aphids being Tended by Ants

(v) Malacophily or Malmacophily

  • This pollination is brought about by Snails.
    Examples: Aspidistra lurida and Chrysanthemum plants.

Some other Type of Zoophily:

  • Erythrina (Coral tree) plant visited by Crows and Squirrels.
  • In Arisaema or Cobra Plant pollination by a snake called "Ophiophily".
  • Night flowering plants are pollinated by Moths. They are highly scented. Their flower generally white coloured.
  • Orchids are pollinated by Wasps/Snails.
  • The favourable colour of Honey bees is yellow, but they are blind to red colour.
  • Larger animals such as some primates (lemurs), arboreal (tree-dwelling) rodents, or even reptiles (gecko lizard and garden lizard) have also been reported as pollinators in some species.

Question for Pollination
Try yourself:Pollination by insect is called:
View Solution

➢ Difference Between Self and Cross-Pollination

Pollination | Biology Class 12 - NEET

➢ Out Breeding Devices


  • The 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.
    Outbreeding Devices
    Outbreeding Devices
  • Flowering plants have developed many devices to discourage self-pollination and to encourage cross-pollination. In some species, pollen release and stigma receptivity are not synchronized. Either the pollen is released before the stigma becomes receptive or the stigma becomes receptive much before the release of pollen. 
  • In some other species, the anther and stigma are placed at different positions so that the pollen cannot come in contact with the stigma of the same flower. Both of these devices prevent autogamy
  • The third device to prevent inbreeding is self-incompatibility. This is a genetic mechanism and prevents self-pollen (from the same flower or other flowers of the same plant) from fertilizing the ovules by inhibiting pollen germination or pollen tube growth in the pistil. 
  • Another device to prevent self-pollination is the production of unisexual flowers. If both male and female flowers are present on the same plant such as castor and maize (monoecious), it prevents autogamy but not geitonogamy
  • In several species such as papaya, male and female flowers are present on different plants, that is each plant is either male or female (dioecy). This condition prevents both autogamy and geitonogamy.
The document Pollination | Biology Class 12 - NEET is a part of the NEET Course Biology Class 12.
All you need of NEET at this link: NEET
158 videos|393 docs|239 tests

FAQs on Pollination - Biology Class 12 - NEET

1. What is pollination?
Ans. Pollination is the process by which pollen grains from the male reproductive organs of a flower, called the stamen, are transferred to the female reproductive organs, known as the pistil. This transfer of pollen is essential for the fertilization and reproduction of flowering plants.
2. How does pollination occur?
Ans. Pollination can occur through various mechanisms, including wind, water, and animals. In animal pollination, which is the most common form, insects, birds, bats, and other animals carry pollen from one flower to another as they visit them in search of nectar or other rewards. This transfer of pollen enables the plants to reproduce.
3. Why is pollination important?
Ans. Pollination is crucial for the survival of many plant species and for maintaining biodiversity. It allows for the transfer of genetic material between plants, leading to the production of seeds and fruits. Pollination also plays a vital role in the production of food crops, as many fruits, vegetables, and nuts depend on pollinators for their production.
4. What are the different types of pollinators?
Ans. Pollinators can be classified into various groups, including insects (bees, butterflies, moths, flies), birds (hummingbirds), bats, and even some small mammals. Each group of pollinators has specific characteristics and behaviors that make them effective in transferring pollen between flowers.
5. What are the threats to pollination and pollinators?
Ans. Pollination and pollinators face several threats, including habitat loss, pesticide use, climate change, and diseases. These factors can disrupt the delicate balance between plants and their pollinators, leading to declines in pollinator populations and affecting the reproduction of many plant species. Conservation efforts are crucial to protect pollinators and ensure the continuation of pollination services.
158 videos|393 docs|239 tests
Download as PDF
Explore Courses for NEET exam

How to Prepare for NEET

Read our guide to prepare for NEET which is created by Toppers & the best Teachers
Signup for Free!
Signup to see your scores go up within 7 days! Learn & Practice with 1000+ FREE Notes, Videos & Tests.
10M+ students study on EduRev
Download the FREE EduRev App
Track your progress, build streaks, highlight & save important lessons and more!
Related Searches

Objective type Questions

,

mock tests for examination

,

past year papers

,

ppt

,

practice quizzes

,

Viva Questions

,

Important questions

,

Exam

,

Pollination | Biology Class 12 - NEET

,

Sample Paper

,

MCQs

,

Previous Year Questions with Solutions

,

pdf

,

Pollination | Biology Class 12 - NEET

,

video lectures

,

Extra Questions

,

Pollination | Biology Class 12 - NEET

,

shortcuts and tricks

,

study material

,

Summary

,

Semester Notes

,

Free

;