Anjali Mishra Content Writer-SME
Content Writer-SME
Pollination in plants refer to a method through which pollen grains are transferred from the anther of one plant to the stigma of the other plant. This leads to development of seeds that further grow into a complete plant. There are two types of pollination in biology class 12: self pollination and cross pollination.
- Pollination marks the begining of sexual reproduction in flowering plants.
- The seeds of the flowering plants carry the genetic information of the parent plant and grow into a new plant.
- The act is mediated by both biotic and abiotic agents, commonly called pollinating agents.
What is Pollination?
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Pollination is a process of transferring pollen grains from the anther which is the male part of a flower to the stigma (female part). In this process, the plants produces seeds for the next generation. For successful pollination, the same species of flower are required.
- The process of pollination is further classified into two type- self pollination and cross pollination.
- In some plants, this process is mediated by pollinating agents such as birds, animals, air, or insects.
- While in few plant species, self-pollination is preferred in which there is no such requirements of pollinating agents.
Process of Pollination
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There are three stages in pollen germination. These are hydration, activation and pollen tube emergence. The pollen grain is strictly dehydrated so that it is easily transported from flower to flower. After rehydration, germination takes place.
- Hydration permits the pollen grain's plasma membrane to reform into an effective osmotic membrane.
- Activation engages the development of filament throughout the cytoplasm of cells.
- The pollen tube grows as the hydration and activation goes on.
- In flowering plants, the anthers generate microspores by meiosis.
- This causes mitosis to create male gametophytes.
- On the other hand the ovules produce megaspores by meiosis.
- When a pollen grain sticks to the stigma, it germinates and develops a pollen tube.
- When the tube arrives at the egg sac, two sperm cells go into the female gametophyte and fertilization takes place.
Types of Pollination
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Flowering plants completely depend on pollination methods for reproduction. There are two types of pollination –
- Self Pollination
- Cross-Pollination
Self Pollination
It is a primary type of pollination and needs a single flower. Self Pollination happens when pollen grains directly fall from anther into the stigma of the flower. This method is smooth and it causes reduction in genetic diversity as the flower's sperm and egg cells impart some genetic information.
- External carriers or pollinating agents are not required for self pollinated plants.
- Homogamy (maturation of male and female gamete at the same time) is an important biological phenomena required for self pollination.
Advantages and Disadvantages of Self- Pollination
Advantages of sel-pollination is as follows.
- Self Pollination confirms that recessive characters are extracted.
- In self pollination, the wastage of the pollen grains is less than cross pollination.
- In this case, purity of race is retained as there is no diversity in the genes.
- In self pollination, there are no external factors like wind, water etc.
- Self pollination lower quantity of pollen grains is a successful pollination process.
The main disadvantage of self pollination is that mixing up of genes does not happen.
- There is a reduction of vigour and vitality of the race.
- Among the offsprings, there is also the reduction of immunity to diseases.
Cross-Pollination
It is an intricate type of pollination that makes the transfer of pollen grains from the anther of the flower into the stigma of another flower. In this process, there is an increase in genetic diversity as different flowers share and combine genetic information to make unique offspring.
Types of Cross Pollination
In the process of cross pollination, there needs the help of biotic and abiotic factors like - water, wind , insects, birds, animals etc.
Pollination by wind: Some flowers use wind pollination. This type of Pollination happens as plants lack flowers with nectar. The male parts of the anemophilous flowers produce very large quantities of pollen and the stigma and the female reproductive parts of a flower are very large, sticky and feathery. Some examples of wind-pollinated plants are palm, maize, coconut, grasses etc.
Pollination by Animals: Animals take an important role in the reproduction of plants. They assist in seed dispersal. Animals move to different locations at the time for eating fruits of plants. This action helps in spreading the seeds and through this process new plants are born.
Artificial Pollination: Artificial Pollination is made by human beings. This process is also named anthropophily. If there are problems in the pollination by biotic and abiotic agents, the artificial process of pollination is followed by spreading pollen grains over the female flowers. In this process, hybridisation techniques are used.
Advantages and disadvantages of Cross-Pollination
Advantages of cross-pollination are listed below.
- Here the qualities of seeds are good in vigour and vitality.
- Unisexual plants can reproduce by the process of cross pollination.
- As a result of genetic recombination the recessive characters are eliminated.
- Through this process the baby plant's immunity level increases.
- Cross pollination makes new genes as there is mainly fertilisation between genetically different gametes.
Disadvantages of cross-pollination is as follows.
- There is huge wastage of pollen grains.
- At the time of genetic recombination, there are chances of removal of good qualities and additions of unwanted features in new generations.
Environmental Impacts
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Nowadays, pollinator decline is noticed on a large scale. This causes an inconvenience in plant regeneration. In the reproduction process plant - animal interaction is very necessary and as it lacks, there is a huge threat in biodiversity and ecosystem.
- Some causes of pollinators’ decline are use of pesticides, habitat destruction, parasitism, climate change etc.
- Some more destructive forms are selective logging, fragmentation, and conversion to secondary forest habitat.
- Climate change causes a pollinator crisis which affects the crops production.
- Insecticides like affect the bees and it is intensely detrimental for the population of pollinators.
Things to Remember
- Pollination is the process of transferring pollen from anther to stigma.
- It can be further categorized into two types; Self-pollination and cross-pollination.
- The meaning of pollinators are the agents that mediate the process of pollination such as are wind, water, birds and insects.
- Pollination is a first step in sexual reproduction of flowers that leads to fertilization and development of seed.
- Genetic variation is the end result of cross pollination whereas self pollination promotes genetic uniformity.
Previous Years Questions
- Meiosis takes place in...[NEET 2013]
- The sexual reproduction is absent in….[NEET 1995]
- For union between stock and scion in grafting which one is the first to occur….[NEET 1990]
- Which one of the following plants reproduces vegetatively by epiphyllous buds?
- Vegetative propagation in mint occurs by…
- Hydra reproduces by budding. This is an example of...
- A clone is ......… [KCET 2011]
- Animals which possess cleidoic eggs exhibit….[KCET 2011]
- Which among these is not a post fertilization event ?...[KCET 2016]
- Type of asexual reproduction found in Hydra is..[KEAM]
- Which of the following is having longitudinal binary fission ?….[KEAM]
- In grafting, the stock and scion should be joined….
- Banana is vegetatively propagated by… [AMUEEE 2012]
- Vegetative propagation by leaves is seen in… [JKCET 2010]
- Vegetative propagation in water hyacinth takes place by...[AMUEEE 2013]
- A slender, prostrate subaerial branch of the stem which creeps along….
Sample Questions
Ques. What are pollinators? (1 mark)
Ans. Pollinators are agents that move pollen from one plant to another. It is done when they are on nectar or pollen.
Ques. Mention the names of pollinators. (1 mark)
Ans. Names of some pollinators are butterflies, birds, bees, bats etc.
Ques. What role do the pollinators play? (1 mark)
Ans. The pollinators move pollen from the male part to the female part of the plant. Pollinators are very important parts to produce seeds, fruits in some plants.
Ques. What attracts pollinators to a plant? (1 mark)
Ans. Nectar, pollen, color, scent etc attract pollinators to a plant.
Ques. What kinds of bees pollinate crops? 1 mark)
Ans. Managed and wild bees can pollinate crops. In most commercial farms, the European honey bees are the main pollinators.
Ques. What are the advantages of self pollination? (3 marks)
Ans. Self pollination has following advantages.
- Low quantity of pollen grain can successfully fertilize the egg.
- No wastage of pollen grains.
- It confirms that recessive characters are extracted.
- In this case, purity of race is retained as there is no diversity in the genes .
Ques. why is the diversity of pollinators important? (1 mark)
Ans. Richness of species and pollinators strengthen effective crops. It also confirms the enhancement of quantity and quality of crops.
Ques. What do you mean by pollen- pistil interaction and how is it mediated? (Foreign 2014)
Ans. Pollen- pistil interaction refers to a chain or group of events that takes place due to the falling of pollen over the stigma and the formation of pollen tube and its entry into the ovule. It is basically a phenomenon of acceptance or rejection of pollen grains by the pistil (stigma) which is mediated by chemical components of pollen grains and interacting with that of pistil.
Ques. Differentiate between xenogamy and geitonogamy? (Delhi 2014c)
Ans. Xenogamy is the process by which pollen grains are transfered from anther of one flower to stigma of another flower of a different plant. While, geitonogamy is the transfer of pollen grains from the anther of one flower to the stigma of another flower on the same plant.
Ques. How do the pollen rains of Vallisneria protect themselves? (All India 2012)
Ans. The pollination of Vallisneria takes place by means of water, therefore in this case, the pollen grains are covered by mucilaginous coating that protects them.
Ques. Name the type of flower that favours cross-pollination. (All India 2009)
Ans. The type of flower that favours cross-pollination is Chasmogamous flowers which are similar to the other species with exposed anthers and stigma.
Ques. Explain: in angiosperms, zygote is diploid while whereas primary endosperm cell is triploid. (All India 2013)
Or, Mention the reasons for the difference in ploidy of zygote and primary endosperm nucleus in an angiosperm. (Delhi 2010)
Ans. In the angiosperms or the flowering plants, one of the male gametes fuses with egg cell which results in the formation of zygote. Thus, zygote is diploid. Whereas, primary endosperm cell is triploid because the nucleus of the second male gamete fuses with the two haploid polar nuclei or diploid secondary nucleus of the centrl cell to form a triploid primary endosperm nucleus. The central cell is now called primary endosperm cell.
Ques. Write one advantage and one disadvantage of cleistogamy. (All India 2012)
Ans. The advantage and disadvantage are as follows:
Advantage – Cleistogamous flowers produce assured seed-set even in the absence of pollinators.
Disadvantage – Cleistogamous flowers are invariably autogamous therefore, there is no chanse of cross-pollination.
Ques. Why should a bisexual flower be emasculated and bagged before artificial pollination? (Foreign 2010)
Ans. Emasculation in a bisexual flower is required in order to prevent the contamination of stigma with self pollen grains. Bagging is done to prevent contamination of stigma of the emasculated flower with any other unwanted pollen grains. This is the reason why a bisexual flower should emasculated and bagged prior to artificial pollination.
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