What is Fertilisation?
Fertilisation in plants is the joining (fusion) of male and female gametes to form a diploid zygote. This process is a crucial part of sexual reproduction and usually occurs after pollination has successfully transferred pollen grains from the anther (male part) to the stigma (female part). In flowering plants (angiosperms), fertilisation was first discovered by Ralph B. Strasburger in 1884.
Fertilisation Process in Plants
Pollination: In many flowering species, pollination in plants is carried out by animals such as honeybees, birds, bats, and butterflies. Wind and water can also serve as natural pollinating agents. Once the pollen grain lands on the stigma, it starts to germinate.
Pollen Tube Formation: After germination, the pollen grain develops a pollen tube, which grows through the style to reach the ovary.
Entry into the Ovule: The pollen tube enters the ovule through a small opening called the micropyle. Upon reaching the embryo sac, the pollen tube bursts, allowing the male nucleus to be released.
Fusion of Gametes: One male gamete fuses with the egg (female gamete), forming the diploid zygote. This zygote later divides and develops into an embryo.
Seed Formation: After fertilisation, the ovule matures into a seed, which protects the growing embryo. Eventually, seed dispersal happens through various agents like wind, water, or animals, ensuring that plants can colonise new habitats.
Types of Fertilisation
Depending on how the pollen tube enters the ovule, fertilisation can be divided into three types:
Porogamy:
The most common type in angiosperms.
The pollen tube enters the ovule directly through the micropyle.
Chalazogamy:
Observed in plants belonging to the genus Casuarina.
The pollen tube enters the ovule through the chalaza (the region opposite the micropyle).
Mesogamy:
Commonly seen in certain Cucurbit plants (such as pumpkins, ridge gourds, and bitter gourds).
The pollen tube enters the ovule through its middle region or through the integuments.
Double Fertilisation
Double fertilisation is unique to angiosperms. In this mechanism:
One male gamete fuses with the egg cell to form the zygote.
The other male gamete unites with two polar nuclei in the embryo sac to form the triploid endosperm.
The endosperm provides essential nutrients to the developing embryo, making double fertilisation highly efficient for plant growth and reproduction.
Significance of Fertilisation
Genetic Variation: Since fertilisation involves the fusion of male and female gametes, it introduces genetic diversity in the offspring.
Seed and Fruit Formation: Successful fertilisation leads to the formation of seeds and often the development of fruit around the seed.
Continuation of the Species: By producing new seeds that undergo seed dispersal, plants can spread to different regions and maintain their populations over generations.
Efficient Nutrient Use: Double fertilisation ensures that endosperm (the food source) is only created after the egg is fertilised, preventing wastage of resources.
Quick Quiz (With Answers)
Question: Which scientist discovered fertilisation in flowering plants in 1884?
Answer: Ralph B. Strasburger
Question: In double fertilisation, which cell fuses with the two polar nuclei?
Answer: The second male gamete (sperm cell)
Question: What is the role of endosperm in seed development?
Answer: It provides essential nutrients to the developing embryo.
Related Topics
FAQs on Fertilisation in Plants
1. How is fertilisation in plants different from fertilisation in animals?
Fertilisation in plants often involves pollination through external agents like wind or insects before the fusion of gametes, whereas in animals, fertilisation usually occurs through direct mating. Additionally, plants exhibit double fertilisation (in angiosperms), which does not occur in animals.
2. Why is double fertilisation essential for angiosperms?
Double fertilisation leads to the formation of both the zygote and the nutrient-rich endosperm. This ensures efficient use of resources and provides a ready food supply for the developing embryo.
3. What happens after fertilisation in plants?
After fertilisation, the zygote develops into an embryo, and the ovule matures into a seed. Eventually, seed dispersal takes place, helping the plant species to spread and grow in new areas.
4. Can fertilisation occur without pollination?
No. In flowering plants, fertilisation typically requires pollination first, so that the male gametes (pollen) can reach the female gametophyte (ovule).
5. Does seed dispersal directly affect fertilisation?
Seed dispersal occurs after fertilisation has produced the seed. While it does not affect the act of fertilisation itself, it is crucial for the next generation’s success and the plant’s survival across different habitats.
