Sexual Reproduction In Plants: Features and its Process

What is Sexual Reproduction?

Sexual reproduction in plants is a biological process in which a male and a female gamete combine to form a genetically variable offspring. Such reproduction is necessary for maintaining genetic diversity within populations of plants and thus adjusting to changes in the environment.

In contrast to asexual reproduction, which simply produces a genetically identical clone of the parent, sexual reproduction introduces variation that may benefit survival and evolution. This diversity is key to underpinning the long-term survivability of ecosystems and impacts agriculture and horticulture by providing a means of developing new varieties with desirable traits.

Pollination

It means the process of transferring pollen grains from the male anther to the female stigma of plants. In general, it is divided mainly into two types: self-pollination and cross-pollination. The first case refers to a process within the same flower or any flowers of a plant that is going to ensure genetic constancy. On the other hand, the latter refers to those events that take place between different plants and give rise to genetic variation.

Definition And Types Of Pollination

The types of pollination are:

Self-Pollination

Self-pollination occurs when the pollen from the same flower or another flower of the exact plant fertilises the ovules. Though in the process, it is efficient it makes sure that the plant will reproduce in the complete absence of any pollinating agent.

Cross-Pollination

Cross-pollination is a process where there is a transfer of pollen to another plant's stigma. The process increases the amount of genetic variation and, hence, enhances the resistance of the plant towards pathogenic diseases or even response towards changes in the environment.

Agents Of Pollination

Wind

Plants that are wind-pollinated produce large amounts of light-weight pollen to be easily carried by the wind for a considerable distance. Examples include grasses and many trees.

Water

Plants adapted to water pollination, like some aquatic plants, depend on the flowing water, at least for some time, to carry the pollen to other plants.

Animals (Insects, Birds, Bats)

Major animal pollinators are insects, especially bees and butterflies, and some birds and bats. In searching for nectar from one flower to another, they pick up pollen and drop it where it is needed, hence pollinating.

Importance Of Pollination

Pollination leads to the development of fruits and seeds. It means reproduction in plants, which in turn leads to biodiversity, agriculture, and food production.

Fertilisation

The process of fertilisation in plants includes the following steps: pollen germination on the stigma, growth of the pollen tube in the style, and finally, the fusion of male and female gametes in the ovule.

Process Of Fertilisation

The process of fertilisation includes:

Germination of Pollen Grain

After a pollen grain settles on a compatible stigma, it takes up water and the nutrients that stimulate its germination and a pollen tube.

Growth of Pollen Tube

The pollen tube grows down the style following the chemical signals and finally reaches the ovule. It takes along the male gamete into the ovule to get fertilised.

Fusion of Male and Female Gametes

A male gamete fuses with an egg cell in the ovule to form a zygote and another one joins with two polar nuclei to form endosperm, which acts as nutrition to the developing embryo.

Significance Of Double Fertilisation In Angiosperms

Double Fertilisation of Angiosperms Produces the Zygote and the Endosperm That Nourishes the Developing Embryo.

Post-Fertilisation Events

After double fertilisation, the zygote develops into the embryo, and the triploid endosperm forms the embryonic nutritive tissue.

Formation Of Seed And Fruit

After fertilisation, the ovary of the flower develops into a seed, and the surrounding ovary wall forms the fruit. The fruit protects the seeds as well as aids in their dispersal.

Structure Of Seed

A seed mainly consists of three parts, which are, embryo, endosperm and seed coat. The embryo is the future plant, the endosperm provides nourishment, and the seed coat protects the seed.

Embryo

A young plant inside the seed that develops into a new plant upon germination.

Endosperm

Reserve of food for the embryo. It will supply nutritive factors to the growing plant at the time of germination.

Seed Coat

The seed coat is the outer protective layer that prevents the embryo and endosperm from mechanical damage and desiccation.

Types Of Seeds (Monocot And Dicot)

The seeds can be differentiated concerning the number of cotyledons. In that direction, monocots—like grasses and lilies—are endowed with a single cotyledon and dicots—like beans and sunflowers—with two.

Seed Dispersal Mechanisms

The seeds disperse by several mechanisms as a means to avoid competition, thereby enhancing the chance of survival.

Wind

Wind-borne seeds are mostly light in weight and may have wings or other features that may carry them easily by the wind, like the seeds of dandelion.

Water

Water-borne seeds can float and they are mostly often carried for great distances by streams, rivers or sea currents, such as coconut seeds.

Animals

Animal-borne seeds are mostly embedded with fleshy fruits, which easily appeal to animals. Once the animals consume the fruit, they spread the seeds in the form of droppings.

Explosive Mechanisms

Some plants possess seed pods that abruptly open and then suddenly throw out their seeds. An example is the touch-me-not plant.

Adaptations For Sexual Reproduction

The key adaptations of flowers are highlighted below, which enhance the probability of effective pollination and fertilisation.

Adaptations In Flowers

Attractants (Color, Scent)

The colouring of the petals and fragrances in flowers are attractants to the pollinators. The chances of pollination are maximised.

Structural Adaptations

The plants may have some structural features on flowers, that favour pollination, such as nectar guides and modified anthers and stigmas that will touch the relevant pollinators.

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