What is reproduction

Reproduction in animal of Class 8

what is reproduction ?

Reproduction is the ability of living organisms to produce new organisms similar to them. It is one of the important characteristic of life.

Reproduction is one of the most characteristic features of living organisms. Life would not exist on Earth if plants and animals did not reproduce to make their offspring. By reproducing, a living organism can be sure that there is another individual of its kind to take its place when it dies. In this way a species of organism guarantees its survival.

IMPORTANCE OF REPRODUCTION:

  • It is an important characteristic of living organisms.
  • It is an essential life process which helps in survival of species.
  • It helps in maintaining continuity of the race and group immortality.

TYPES OF REPRODUCTION:

This can be of two types:

  • ASEXUAL REPRODUCTION: Production of offspring by a single parent without the formation and fusion of gametes is called as asexual reproduction. It is more primitive type of reproduction. It ensures rapid increase in number.

Occurrence:

Asexual reproduction occurs in protozoans and some animals such as sponges, coelenterates, certain worms and tunicates. It is absent among the higher invertebrates and all vertebrates.

Another method of asexual reproduction is observed in the microscopic organism, amoeba. Amoeba is a single-celled organisms. It begins the process of reproduction by the division of its nucleus into two nuclei. This is followed by division of its body into two, each part receiving a nucleus. Finally, two amoebae are produced from one parent amoeba. This type of asexual reproduction in which an animal reproduces by dividing into two individuals is called binary fission.

Characteristics:

  • This is the uniparental reproduction (one parent is involved).
  • No formation and fusion of gametes occurs.
  • It involves mitosis.
  • New organisms are produced from somatic part of parent body, e.g. Amoeba, Paramecium, Sponges (Scypha), Coelenterata (Hydra, Tubularia.) etc.

Types of Asexual Reproduction:

Asexual reproduction takes place in the following principal ways:

Fission: It is the simplest form of reproduction in which unicellular organism either divides into two or many organisms.

  • It is also divided into two types:
  • Binary fission: It is a type of reproduction in which nuclear division is followed by the appearance of a constriction in the cell membrane, which gradually deepens inward and divides the cytoplasm into two parts, each with one nucleus. Finally two daughter cells are formed. e.g. Amoeba

binary fission

  • Multiple fission: Sometimes the nucleus divides several times, into many daughter nuclei. The daughter nuclei arrange at the periphery of the parent cell, and a bit of cytoplasm around each daughter nuclei is present. Nucleus develops an outer membrane. Finally the multinucleated body divides into many daughter cells. e.g. Plasmodium.

Budding: Formation of a daughter individual from a small projection which is called as bud, arising on the parent body is called as budding.

Budding is also of two types:

  • Exogenous budding: [External budding] In this, bud arises from the surface of parent body. e.g., Hydra.

budding

hydra budding

In each hydra, there may be one or more bulges. These bulges are the developing new individuals and they are called buds. In hydra too the new individuals develop as outgrowths from a single parent. Since new individuals develop from the buds in hydra, this type of asexual reproduction is called budding.

  • Endogenous budding: [Internal budding] In this, bud arises inside or within the parent body. e.g., Sponges.

note

During the process of budding, the bud remains attached to the parent body so as to derive it's nutrition from the parent but as it matures, it get's detached from the parent body.

Fragmentation: It is a type of reproduction or the regeneration ability of the organism to replace their lost part. In this process an entire new organism can grow from certain pieces or cells of the parent organisms. e.g. Flatworm.

Spore formation: It is a process of reproduction most commonly found in fungi, some cocci and bacillus bacteria. During this process a structure called as sporangium is formed. In this structure nucleus divides several times and each nucleus with a little trace of cytoplasm forms a spore. These spores are then liberated out and develop into a new hyphae, e.g. Rhizopus.

SEXUAL REPRODUCTION: In animals, males and females have different reproductive parts or organs. Like plants, the reproductive parts in animals also produce gametes that fuse to form a zygote. It is the zygote which develops into a new individual. This type of reproduction beginning from the fusion of male and female gametes is called sexual reproduction.

Characteristics:

  • This reproduction involves two parents so it is biparental reproduction.
  • It involves formation and fusion of gametes.
  • In it meiosis occurs during gametogenesis and mitosis occurs after zygote formation. e.g. Human beings, birds etc.

Viviparous and Oviparous Animals:

Some animals give birth to young ones while some animals lay eggs which later develop into young ones. The animals which give birth to young ones are called viviparous animals. Those animals which lay eggs are called oviparous animals.

Basic Process of Reproduction involves:

  • Gametogenesis: It is the process of formation of haploid male gamete (sperm) and female gamete (ovum). Sperm production occurs in testis and ovum production occurs in ovary.
  • Fertilization: The fusion of haploid gametes i.e. sperm and ovum to form diploid zygote is called as fertilization. This is the diploid phase.
  • Embryogenesis: Zygote undergoes mitosis and form embryo which develops into the foetus.
  • Parturition: Birth of developed young one is called as parturition.

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