Sexual and Asexual Reproduction

Reproduction is the biological process by which an individual organism or offspring is produced from their parents. This is essential for the species’ continuation.

 Modes of Reproduction:

Animals reproduce through 2 modes of reproduction. These are (1) Sexual reproduction, and (2) Asexual reproduction.

Sexual Reproduction:

•       Sexual reproduction is the fusion of male and female gametes.
•       Males and Females have different reproductive parts.
•       These parts produce gametes that fuse to form a zygote.
•       The zygote develops into a new individual.

 Male Reproductive Organs: 

Penis

The external genitalia of a man. It consists of three erectile tissue cylindrical spaces. The two bigger ones, the corpora cavernosa, are next to each other, and the third is the sinus, which covers the urethra and is termed the corpus spongiosum.

Scrotum

It’s a thick-skinned sac that protects and encircles the testes. It houses the testicles (commonly known as testes) as well as a number of nerves and blood arteries. The testes have a “temperature control system” in the scrotum. The testes must be kept at a temperature that is somewhat colder than body temperature for proper sperm development.

Testicles (testes)

These are oval organs in the scrotum that are roughly the size of big olives and are connected at both ends by a tissue called the spermatic cord. The majority of males have two testes. The testes are in charge of producing testosterone, which is the principle male sex hormone, as well as sperm.

Female Reproductive Organs: 

Vagina

The vagina connects the cervix (the bottom section of the uterus) to the outside of the body. The birth canal is another name for the tube that connects the womb to the outside world.

Uterus

The uterus is a pear-shaped organ that holds a growing baby. The uterus is divided into two parts: 

Cervix, (in the bottom of the uterus) it opens into the vaginal canal

Corpus (main body of the uterus), it in-houses the foetus.

Fallopian tubes

These tubes are encased in fimbriae, tiny projections that sweep over the ovaries, picking up released eggs and delivering them to the infundibulum for uterine supply.

Fertilisation: The fusion of a sperm and an ovum is the first step in the process of reproduction. When sperms meet an egg, one of the sperms may fuse with the egg.

The nuclei of the sperm and the egg fuse to form a single nucleus that results in the formation of a fertilised egg or zygote during fertilisation. Based on the place of fusion, fertilisation is of two types:

•   Fertilisation inside the female body is called internal fertilisation. E.g.- human beings, hens, cows, and dogs.
•   Fertilisation outside the female body is called external fertilisation. E.g.- aquatic animals such as frogs, fish, starfish, etc.

Test-tube Babies:

• In some women, oviducts are blocked due to which sperms cannot reach the egg for fertilisation.
•   In such cases, released egg and sperms are collected and kept together for a few hours for IVF or in vitro fertilisation i.e., fertilisation outside the body.
•   Once fertilisation occurs the development of the zygote is allowed for about a week, and then it is placed in the mother’s womb.
•     Complete development of the baby takes place in the uterus.
•     Babies born through this technique are called test-tube babies.

Development of Embryo:

Fertilisation results in the formation of a zygote which then begins to develop into an embryo.

In Humans:

•       Division of zygote repeatedly occurs and gives rise to a ball of cells.
• Ball of cells then develops into different tissues and organs of the body. The developing  structure is termed an embryo.
•       Development of the embryo occurs while it is embedded in the wall of the uterus.
•       The development of the embryo continues in the uterus that gradually develops body parts such as hands, legs, head, eyes, ears, etc.
•       The stage of the embryo in which all the body parts can be identified is called a foetus.
•       When the development of the foetus is complete, the mother gives birth to the baby.

In Hens:

Fertilisation is internal in hens but they lay eggs. It takes about 3 weeks for the embryo inside the eggshell to develop into a chick. Development of the chick occurs inside the eggshell. When the chick is completely developed it bursts open the eggshell.

In Animals (external fertilisation):

The embryo develops outside the female body. The embryos continue to grow under the egg coverings. Eggs hatch when the embryo develops. Animals laying eggs are called oviparous animals such as hens, frog whereas animals that give birth to young ones are called viviparous animals such as human beings.

Young Ones to Adults:

The growth of individuals born or hatched from the eggs continues to grow till they become adults. In human beings, body parts like those present in adults are present from the time of birth. But in some cases, the young ones look different from the adults and have the following lifecycle:

Silkworm: egg → larva or caterpillar → pupa → adult, Frog: egg → tadpole (larva) → adult

The features that are present in the early stage of life are not found in adults. This stage of transformation of the larva into an adult through several changes is called metamorphosis.

Asexual Reproduction:

In this reproduction, a single parent is involved and is called asexual reproduction. Types of asexual reproduction include Budding, Binary fission, etc.

Budding: In hydra, buds develop into a new individual by the process of budding.

Fragmentation

Organisms like spirogyra and planaria use fragmentation as a mechanism of asexual reproduction. Each component of the parent body evolves into a new creature.

Regeneration

The ability to produce a new organism from a lost bodily component is known as regeneration. Hydra and planaria are examples of organisms that regenerate.

Spore Formation

Another method of asexual reproduction is spore generation. In unfavourable circumstances, the organism generates sporangium, which are sac-like structures that carry spores.

Vegetative propagation

Plants reproduce asexually by means of their vegetative organs, such as leaves, roots, stems, and buds. This process is known as vegetative propagation.

Binary Fission: Animal reproduces through the asexual mode of reproduction by dividing into two individuals. 

•       The process begins with the division of the nucleus into two nuclei.
•       Nuclear division is followed by the division of the body into two, each receiving a nucleus.
•       Thus, a parent amoeba produces two new amoebae.

Cloning: Clones are created with the application of modern genetic technology. The production of an exact copy of a cell or a complete organism is called cloning. On 5th July 1996, Dolly was the first mammal to be cloned.

Conclusion

Reproduction is the process through which genetic material is passed down from one generation to the next. As a consequence, new members of a species or creatures are born. Furthermore, organisms reproduce in order to maintain races. As a result, this aids in their population growth and survival on this planet.