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Sexual Reproduction in Flowering Plants

Pollination

Pollination is the transfer of pollen grains from the anther of one flower to the stigma of the same or another flower. It is said to be the first process of sexual fertilization in flowering plants. Pollen grains contain the male gamete and are present in the anthers of the flower.

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Types of Pollination

Pollination can be of two types:

  • Self- Pollination
  • Cross-Pollination

Let us understand more about each type of pollination a little in detail.

Self- Pollination

Pollination

Image Source: newtonsapple

When the pollen is transferred from the anthers of a flower to the stigma of the same flower, it is called as self- pollination. This form of pollination is common in hermaphrodite or dioecious plants which contain both male and female sexual parts on the same flower.

In self-pollinating plants, there is less dependence on the external factors to cause pollination. These plants depend on wind or other smaller insects that visit the flower regularly. In self- pollinating flowers, the anthers, and stigma are of similar lengths to facilitate the transfer of pollen. Self – pollination can be further divided into two types:

  • Autogamy– In this type of self-pollination, the pollen is transferred from the anthers of one flower to the stigma of the same flower.
  • Geitonogamy– In this type of self- pollination, the anthers are transferred from the anthers of one flower to the stigma of another flower but on the same plant.

Advantages of self – pollination

  • In self- pollination, there is no diversity in the genes and therefore the purity of the race is maintained.
  • The plants do not depend on external factors for pollination and even smaller quantities of pollen grains produce have a good success rate in getting pollinated.
  • Self- pollination ensures that recessive characters are eliminated.

Disadvantages of self- pollination

  • Since there is no mixing up of genes, there are no new characters or features that are introduced into the lineage of the offsprings.
  • Self- pollination is said to reduce the vigor and vitality of the race as there are no new features introduced.
  • Without new characters introduced, the resultant offsprings’ immunity to diseases reduces.

Cross-Pollination

In this type of pollination, the pollen is transferred from the anthers of one flower to the stigma of another flower. In this case, the two flowers are genetically different from each other. Cross-pollination is always dependant on another agent to cause the transfer of pollen. The agents of pollination include birds, animals, water, wind, and insects. Based on the agent of pollination, cross-pollination can be of different types:

  • Hydrophilous Flowers-These flowers are pollinated by water means. The flowers are often very small and inconspicuous to other agents. They do not have any fragrance or too much color on their petals. The pollen is adapted to be able to float in water.
Pollination

Image Source: drgpbiology

  • Zoophilous flowers– In this type of pollination, the pollinating agents are animals like human beings, bats, birds etc. The zoophilous flowers have pollen that is designed to stick on to the body of the animal so that they can be easily carried from one flower to another.
  • Anemophilous flowers– These flowers are pollinated by the agency of wind. These flowers, like zoophilous flowers, are small and inconspicuous. Another important feature of flowers that are wind pollinated is that they are very light so that they are easily carried by the wind. The pollen grains are very light, non-sticky and sometimes winged.
  • Entomophilic flowers– These flowers are pollinated by insects. These flowers are often attractive to look at with bright petals and are fragrant to attract the insect visitors to them. They often have broad stigmas or anthers to allow the insect to perch on it. Many of the insect-pollinated flowers also secrete nectar which attracts bees, butterflies or other similar insects to the flowers. The pollen grains in these flowers are often spiny or have extensions that help them to stick on to the body of the insects.

Image Source: brainkart

  • Ornithophilous flowers– These flowers are pollinated by birds. Very few flowers and birds show this form of pollination.

Advantages of cross-pollination

  • Cross-pollination is beneficial to the race of the plant as it introduces new genes into the lineage as a result of the fertilization between genetically different gametes
  • Cross-pollination improves the resistance of the offsprings to diseases and changes in the environment.
  • The seeds produced as a result of cross-pollination are good in vigor and vitality.
  • If there are any recessive characters in the lineage, they are eliminated as a result of genetic recombination.
  • It is the only way unisexual plants can reproduce.

Disadvantages of cross-pollination

  • There is a high wastage of pollen grains that need to be produced to ensure fertilization occurs.
  • There are high chances that the good qualities may get eliminated and unwanted characteristics may get added due to recombination of the genes.

Solved Example for You

Q1: What is pollination caused by birds called?

  1. Entomophily 
  2. Ornithophily
  3. Anemophily
  4. Zoophily

Sol. The correct answer is the option ”b”. Ornithophily is the pollination caused by birds. 

FAQ’s for You

Q1. List the different types of pollination depending upon the source of the pollen grain.

Answers: Pollination can be classified into three different types based on the source of pollen grains. They are:

i) Autogamy: It is defined as the transfer of pollen grains from the anther to the stigma of the same flower in the same plant.
ii) Geitonogamy: It is defined as the transfer of pollen grains from the anther of one flower to the stigma of another flower on the same plant.
iii) Xenogamy: This type of pollination brings genetically different types of pollen grains to the stigma of the flower.

Q2. What is pollination? State its significance.

Answers: Pollination refers to the transfer of pollen grains from the anther of a flower to the stigma of the same or a different flower. Pollination is a significant process as it helps in fertilisation by bringing the male gamete (male pronucleus) closer to the female (egg) and allowing their fusion. It, therefore, helps in the production of seeds and fruits and thereby help in reproduction as the seeds formed helps in generation of new offsprings. Cross-pollination (in which the pollen grains of one flower are transferred to the stigma of a different flower) helps in the introduction of new variations in plants.

Q3. Pollination is best defined as?

Answers: Pollination can be best defined as the transfer of pollen from the male anther of a flower to the female stigma to produce new offspring. It is carried out by various means like birds, water, wind etc. It helps in fertilization and also creates variation.

Q4. Pollination is a characteristic of
A. Angiosperms
B. Pteridophytes
C. Bryophytes
D. None of the above

Answers: Pollination is a process in which pollen is transferred to the female reproductive organs of seed plants, thereby enabling fertilization and reproduction through growth of the pollen tube and eventual release of sperm. Both gymnosperms and angiosperms undergo pollination, although the mechanism for angiosperms is much faster and more complex. A successful angiosperm pollen grain (gametophyte) containing the male gametes is transported to the stigma, where it germinates and its pollen tube grows down the style to the ovary. Pteridophytes and bryophytes pollination does not occur.
Therefore, the correct answer is option A.

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