Pollination and Fertilization

Pollination and Fertilization

Pollination

Pollination is the process that takes place when pollen grains go to the stigma of the pistil from the anthers of the stamens. Pollination occurs in two distinct ways, which are described below:

i) Self-pollination: Self-pollination is a process that occurs when a pollen grain travels to the stigma from the anther of one flower. Generally, self-pollination happens in bisexual flowers.

(ii) Cross-pollination: Cross-pollination occurs when pollen grains present in the flower’s anther are transported to the stigma found in a flower. This may happen in the same plant or of a different plant of the same species with the help of an external agent, such as water, wind, insects, animals, or birds.

Fertilization

Fertilization is the process in which the male and female gametes unite to generate a new cell (called a zygote).

When pollen is released on the pistol's stigma, it starts to germinate. A lengthy pollen tube develops from the pollen grain over time and travels through the style to the female gametes in the ovary. The male gametes pass down the pollen tube, and the pollen tube penetrates the ovary's ovule.

Male gametes are expelled from the pollen tube at its tip rupturing. The ovule in the ovary is where the male and female gametes meet and fuse to create the fertilized egg cell, or zygote.

The zygote transforms into an embryo, which is a component of the seed that grows into a new plant.

Fruit and Seed Development

Once fertilized, the ovary will transform into a fruit, and the ovule will mature into a seed. The flower's outer layers, including the sepals, stamen, and petals wither and eventually fall off as the flowering matures. 

In addition to stigma and style, just the ovary remains on the receptor. The zygote within the ovary is nourished by the ovule and develops into an embryo by cell division. A portion of the ovule transforms into the seed coat or seed coating.

The matured ovary of a flower is the fruit, which safeguards the seed 

Seed Dispersal

The ovule is the component of the plant that gives rise to the seed. A seed will have an embryo inside of it, which will be protected by the seed coat. Plants generate an abundance of seeds and when these seeds fall to the ground, they begin to grow. 

If a huge number of seeds land in the same location, they would not get sufficient space, water, or light to grow into a healthy plant. Thus, the seeds are transported by external agents to distant locations.

The process by which seeds are dispersed to various locations (far from their parents) is known as dispersion. The seeds and fruits are distributed by many agents, including wind, water, birds, and some animals. Occasionally, seed distribution occurs spontaneously by the explosion or bursting of fruits.

Seed Dispersing Agents

Wind, air, water, animals, birds, and people are the agents of seed dispersal. The following describes each of the external agents which play a role in pollination:

Dispersion through wind or air

Some seeds, like those of the maple and drumstick trees, have wings that help them fly, while others, like those of the madar and oak trees and the cottonseed, have hairs that help them cling to the wind and be dispersed. The wind may readily transport and disseminate these seeds outside of their normal environment.

Dispersion through Water

Water disperses the seeds of certain plants with an outer fibrous or sponge-like coating. The seeds of lotus, chestnut (singhara), water lily, and coconut are disseminated via water because they have the capacity to float in water and drift with their current. The coconut fruits possess a fibrous exterior that allows them to float in water and be moved to distant locations by moving water.

The role of birds in dispersal is significant

The birds consume both fruits and seeds, which have a tough exterior coating. The seeds are transported to another location by the excrement of birds. The digestive enzymes included in the digestive tract of birds aid in breaking the hard seed coat, and when the seeds are expelled with the feces, they sprout; for instance, neem seeds are distributed by the feces of birds.

Distribution by Animals

Some seeds contain spikes or spines that attach themselves to the hair or skin of ruminant animals. When these animals go to a distant location, the seeds are disseminated (when the animals rub their bodies), e.g. the fruit of Xanthium and Urena plants are coated with countless hooks that cling to the animal's hair and are dispersed along with it. In addition to the fruits, the seeds are also disseminated.

Dispersion through Fruit Explosion or Bursting

Occasionally, when fruits grow, a strain develops inside their walls. This causes an abrupt shock that causes fruits to split apart, enabling seeds to disperse far from their parent plants. The seeds of certain plants, like the castor plant, are dispersed far from the parent plant when the fruit explodes with a jolt and is hurled out with enormous force in all directions. Likewise, the fruit of balsam is disseminated by the explosion process.

The Germination of a Seed

The embryo of a plant is contained in a seed, and it does not begin to develop until the right circumstances are met. Seed germination is the process through which seeds start to grow from its seed. When a seed germinates, the seed coat breaks, and a root called radicle and a branch called plumule begin to develop downwards and upwards, respectively. This results in plant seedlings.

The seedling develops into a new plant with accelerated growth. As the plant begins to mature, it develops flowers, which in turn generate seeds and fruits. This cycle proceeds to create offspring to ensure the survival of a species.

FAQ:

Q1. What is the role of external agents in the pollination process?

Ans. The external sources or pollination agents such as water, wind, insects, animals, birds., etc., are primarily responsible for the pollination process.

Q2. Are all fruits juicy in nature?

Ans. No, some fruits are plump and juicy, such as mango, apple, and orange, whereas others, such as almonds and walnuts, are hard and dry.

Q3. What are the advantages of seed dispersal?

Ans. Given below are various advantages of the seed dispersal method. 

  • The spreading of seeds prevents the overpopulation of young plants near their parents.
  • It prevents the plants from competing with their own seedlings for sunshine, water, and nutrients.
  • One of the advantages of seed dispersion is that it allows the plant to develop in new settings, resulting in a greater probability of survival and a broader spread.

To know more about the pollination and fertilization method in plants, check out our videos. 

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