Sexual Reproduction

Most of the evolved organisms on the planet, like plants and animals and various multicellular organisms, display sexual reproduction. This is often considered the superior method of reproduction because of variation and evolution that occurs. Let us discuss sexual reproduction in plants and animals.

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Sexual Reproduction

As you all know, sexual reproduction is characterized by the fusion of male and female gametes. When compared to asexual reproduction, sexual reproduction is considered as a better mode as there is a variation in the population, along with the evolution of species. Genetically speaking, sexual reproduction involves both the processes of mitosis and meiosis.

Something unique that is observed is that even though plants, animals, and fungi are quite different from each other in aspects such as morphology, physiology, anatomy etc., all these organisms display sexual reproduction. The whole process also is quite elaborate and complex, involving many stages. Let us learn more about the sexual reproduction in plants and animals.

Sexual Reproduction in Plants

Plants have to complete the vegetative phase to reach a certain stage of growth and maturity. It is only after this period that they can reproduce sexually. The higher order plants, the reproductive phase of the plant is characterized by the flowering. This flowering phase in plants can vary from plant to plant.

In the Sexual reproduction in plants, the reproductive part of a plant is the flower. The male and female gametes are produced by flowers. Flowers mainly have petals, sepals, stamen, and pistil. Stamen is the male reproductive part and has anther and filament. The anther produces and stores the pollen.

The pistil is the female reproductive part and has the stigma, style, and ovary. The style connects the stigma to the ovary. When both the stamen and the pistil are seen in the same flower, then they are called bisexual flowers. Otherwise, when separate, they are called unisexual flowers.

Pollination, which is the process of transferring the pollen to the stigma, can occur in two ways. It can be either through self-pollination or cross-pollination. In this way, the male gametes are transferred to the stigma of the flower, from where they reach the ovary.

Fertilisation occurs in the ovary, when the male gametes fuse with the female gametes, resulting in the formation of the zygote. This zygote divides further and develops into an embryo. The ovary gets transformed into the fruit. This is how Sexual reproduction in plants occurs.

Sexual Reproduction in Animals

There are different stages that animals, including humans, go through. The juvenile phase is the phase of growth and development till the animal reaches its maturity, after which it can reproduce sexually. In different animals, there are some cyclical changes that occur during reproduction.

In animals such as cows, dogs, deer, sheep etc., it is called the Oestrus cycle and in mammals like humans, apes, and monkeys, it is called the Menstrual cycle. Old age often signifies the end of the reproductive phase.

Stages of Sexual Reproduction

There are three distinct events that occur here, which can be categorized as Pre- fertilization, Fertilisation and Post fertilization.

Pre-Fertilization

This is a stage that occurs prior to the fertilization. The two events that occur at this stage are gametogenesis and the transfer of gametes. In gametogenesis, the gametes – male and female are formed. Gametes are haploid cells and are distinct in males and females.

The male gametes are called the sperms and the female gametes are the ova or eggs. The female gametes are non-motile while the male gametes are motile. Transfer of gametes occurs when the male gamete gets transferred, after which fertilization occurs.

Fertilization

The fusion of gametes is the most crucial step in the process of sexual reproduction. This fusion of male and female gametes is called fertilization or syngamy. As a result of this fertilization, a diploid zygote is formed. Fertilization can be external or internal. Some exceptions to this fertilization process are some lizards, turkeys, honeybees, where the female gamete undergoes development without fertilization and forms a new organism. The name of such a phenomenon is parthenogenesis.

Post Fertilization

All the events that occur after the formation of the zygote are called the post-fertilization events. The zygote divides through mitosis and develops into an embryo. This development of the embryo from the zygote is called embryogenesis. Cell differentiation also occurs at this stage, where specialized tissues and organs are formed.

Depending on where the zygote develops, animals are classified as viviparous and oviparous animals. In oviparous animals, development takes place outside the body. Examples are reptiles, birds etc. When the fertilized eggs are laid in a safe place, after a period of incubation, they hatch into young ones. In viviparous animals such as human beings, development occurs inside the body. After some specific gestation period, young ones are born.

Solved Questions For You

Q: What are bisexual flowers? How are they different from Unisexual flowers?

Ans. Bisexual flowers are flowers where both the stamen and the pistil are present in the same flower. In other words, the male reproductive part and the female reproductive part are in the same flower. Examples of bisexual flowers are the following flowering plants – Hibiscus rosasinensis, Pisum sativum, Petunia hybrida etc.

In Unisexual flowers, either the male reproductive part i.e. the stamen is present or the female reproductive part is the pistil is present. Examples are Papaya plant, Mulberry plant etc. In unisexual plants, only the female plant bears the fruits and not the male plant.