Fertilization in Plants: Definition, Process, Types, Steps and Diagram
Plant fertilisation is an essential reproductive process when the male gamete (sperm cell) of the pollen grain unites with the female gamete (egg cell) of the ovule. After fertilisation, the zygote is formed, which develops to form an embryo, the start of a new plant life cycle. Fertilisation guarantees genetic continuity and diversity, allowing plants to propagate and evolve over generations.
This Story also Contains
- What Is Fertilisation In Plants?
- Types Of Fertilisation
- Mechanisms Of Fertilisation in Plants
- Process Of Fertilisation in Plants
- Post-Fertilization Changes
- Recommended video on "Fertilisation in Plants"
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In angiosperms, fertilisation is also a component of a differentiated process known as double fertilisation. One of the male gametes fuses with the egg cell (syngamy) and the other fuses with two polar nuclei to create endosperm (triple fusion), which feeds the growing embryo. This effective mechanism ensures the simultaneous growth of the embryo and its food, thus increasing the chances of successful seed development.
What Is Fertilisation In Plants?
In flowering plants, fertilisation is a process by which the combination of male and female gametes results in to production a zygote. This is instantly followed by pollen grains of the anther bag sticking to the plant stigma. It will now initiate the development of seeds and fruits. Fertilisation is a necessary condition for any floral reproductive success. It finally leads to the production of genetically diverse offspring that facilitate the adaptability and evolution of plant species.
Secondly, it helps the production of seed and fruit, hence the propagation of plant species, providing a way of maintaining ecosystems and agricultural production. The process of fertilisation is initiated by the germination of the pollen grain on the stigma and proceeds in the growth of a pollen tube extending through the style to the ovule. A single male gamete fuses with the egg cell, and the second with two polar nuclei to produce the endosperm. Thus, seeds initiate an event of double fertilisation that develops into a new plant.
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Types Of Fertilisation
In angiosperms, fertilisation starts when the pollen tube brings in male gametes into the ovule. The path of the pollen tube in penetrating the ovule differs among species and is the basis for varying forms of syngamy: porogamy, chalazogamy, and mesogamy. These have been categorised based on point of entry, whether micropyle, chalaza, or integuments and have differing structural and functional importance in the process of fertilisation. Knowledge of these types of fertilisation shows the diversity and flexibility of angiosperm reproductive strategies. The types of fertilisation are discussed below-
| Type of Fertilisation | Path of Pollen Tube Entry | Point of Entry | Commonality | Examples |
|---|---|---|---|---|
| Porogamy | Pollen tube enters the ovule through the micropyle | Micropyle | The most common type of fertilisation | The majority of angiosperms (e.g., Lily) |
| Chalazogamy | Pollen tube enters through the chalaza, opposite the micropyle | Chalaza (basal part of ovule) | Rare occurrence | Casuarina, Pistacia |
| Mesogamy | Pollen tube enters the ovule through the integuments or funiculus | Integuments or funiculus | Less common | Cucurbita, Petunia |
Mechanisms Of Fertilisation in Plants
Pollination in flowering plants can occur through various natural agents that help transfer pollen from the anther to the stigma, making sure that there is fertilisation. These agents are classified into biotic (living) and abiotic agents of fertilisation (non-living) types. Both of them are discussed below:
| Type of Pollination Agent | Examples | Mechanism | Common Features |
|---|---|---|---|
| Biotic Agents | Entomophily - Pollination by Insects(bees, butterflies), Ornithophily - Pollination by Birds (hummingbirds), Chiropterophily - Pollination by Bats | Pollinators visit flowers for nectar and unintentionally transfer pollen. |
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| Abiotic Agents | Wind, Water | Pollen is transferred through air or water without the involvement of animals. |
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Process Of Fertilisation in Plants
Fertilisation in flowering plants is a specialised procedure that starts with the germination of pollen grains on the stigma. This results in the production of a pollen tube that passes through the style to the ovule. On penetration through the micropyle, the pollen tube discharges two male gametes, which trigger a special event called double fertilisation.
One of the male gametes combines with the egg cell to produce the zygote (syngamy), and the other combines with two polar nuclei to produce the triploid endosperm (triple fusion). This double fertilisation is characteristic of angiosperms and the development of the embryo and its food tissue.
| Process | Explanation | Outcome |
|---|---|---|
| Pollen Grain Germination | A mature pollen grain lands on the stigma of the same species and begins to germinate. | Formation of the pollen tube begins. |
| Growth of Pollen Tube | The pollen tube grows through the tissues of the style toward the ovary. | The pollen tube reaches the ovule. |
| Entry of Pollen Tube into Ovule | The pollen tube enters the ovule through the micropyle. | Delivers two male gametes (sperm cells). |
| Double Fertilization | Unique to angiosperms, both male gametes take part in fertilisation. | Leads to syngamy and triple fusion. |
| Syngamy (Sperm + Egg Fusion) | One sperm cell fuses with the egg cell. | Formation of a diploid zygote (future embryo). |
| Triple Fusion (Sperm + Polar Nuclei Fusion) | The second sperm fuses with two polar nuclei in the central cell. | Formation of a triploid endosperm, nutritive tissue. |
Post-Fertilization Changes
The post-fertilisation changes are explained below-
- Zygote Formation – The fertilised egg cell (zygote) develops by mitotic divisions into the embryo.
- Embryo and Seed Development – The ovule develops into a seed with the embryo, endosperm, and hard seed coat.
- Endosperm Formation – The triploid endosperm nucleus divides to produce a nutritive tissue that helps in embryo development.
- Development of Ovary into Fruit – The ovary develops into a fruit that covers, guards, and aids in seed dispersal.
- Seed and Fruit Ripening – Seeds ripen with stored food, and fruits can become fleshy or dry depending on the type of plant.
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Frequently Asked Questions (FAQs)
Fertilization leads to genetic variation in plants since their genetic materials are mixed from two different parent plants by cross-pollination, which usually results in offspring with different genetic compositions and thus improved adaptability.
Following fertilization, the ovules change into seeds, and the ovary changes into a fruit. This fruit protects the seeds and contributes to their dispersion to ensure living plant species from that family.
The pollen tube develops from the pollen grain on the stigma to the ovule in the ovary and forms a channel for the sperm cells to travel into the embryo sac to contact the egg cell and polar nuclei for fertilization.
In flowering plants, double fertilization is achieved to build the zygote and the endosperm at the same time. While the zygote forms an embryo, the endosperm develops nutrients to make the seed viable and helps in plant reproduction.
In self-pollination, takes place pollen transfer inside one flower or one plant. The offspring will therefore be genetically similar. In cross-pollination, there takes place inter-transfer of pollen between different plants. Offsprings are expected therefore to have much variation from one another.