Reproduction in Animals Class 8 Notes - Chapter 9

According to the CBSE Syllabus 2023-24, this chapter has been renumbered as Chapter 6.

Introduction to Reproduction

• Reproduction is the process of giving rise to offspring.
• Reproduction is essential for the continuation of a species.
• There are two modes of reproduction:

1. Sexual reproduction
2. Asexual reproduction

Asexual reproduction

The type of reproduction in which only a single parent is involved is called asexual reproduction.

• There is no mixing of genetic information.
• For example, buds in Hydra

Sexual reproduction

The type of reproduction, which involves two parents to give rise to an offspring is called sexual reproduction.

• The males and females have different reproductive parts or organs.
• These organs produce the male and female gametes, which fuse together to form the offspring.
• Genetic information from both parents is inherited.
•  For example, humans

To know more about Modes of Reproduction, visit here.

Fission

It is a type of asexual reproduction in which a single-celled organism divides into two.

• Division of a nucleus is followed by the division of other cell organelles in the cytoplasm and finally the cytoplasm.
• Thus, two cells are produced from one parent cell.
• Example: Amoeba.
• Amoeba reproduces by binary fission, which is dividing into two cells.

If one parent cell gives rise to many daughter cells, this type of fission is called multiple fission.

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Budding

• A bud starts as an outgrowth of the parent body.
• As this bud grows, it becomes a new individual organism.
• In some organisms, the buds remain attached to the parent’s body (example: yeast)
• In some organisms, it detaches from the parent body and develops into a completely mature individual (hydra).
• This type of reproduction is called budding.

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Cell Division

• Reproduction essentially involves cell division.
• Without cell division, life will not propagate.
• The two types of reproductive processes involve two different types of cell divisions.

Cell division is the process in which a parent cell divides into two or more daughter cells.

Cell division provides more cells:

• For growth
• Regeneration
• Repair and damage control
• Gamete formation

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There are two types of cell division:

1. Mitosis
2. Meiosis

Mitosis

Mitosis is a process where a single cell divides into two identical daughter cells.

• DNA replication occurs once, followed by a single division.
• The number of chromosomes is maintained in this type of division.
• This type of division happens in asexual reproduction.
• It is also used for growth, repair and regeneration of tissues.

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Meiosis

This is a cell division in which a single cell divides into four haploid cells.

• DNA replication occurs once followed by two divisions.
• The number of chromosomes are halved in meiosis.
• Meiosis takes place in sex organs to produce haploid gametes.
• Thus, the gametes have only half the number of chromosomes in them.

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Sexual Reproduction in Humans

To know more about Male and Female Reproductive System, visit here.

Male reproductive system

• The male reproductive system consists of a pair of testes, a pair of sperm ducts and a penis.
• The testes are located outside the male body.
• Sperms are produced in testes.
• Sperms are the male gametes.

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Testosterone

• Testosterone is the primary male sex hormone and is produced by the testes.
• Testosterone is responsible for the development of sex organs, the production of sperm and also the development of secondary sexual characteristics.

Sperms

• Sperms are the male gametes produced by testes in humans.
• Millions of sperms are produced by the testes in a day.
•  Each sperm is a single, microscopic cell having a head, a middle piece and a tail as its parts.
• The head contains a nucleus with a single set of chromosomes.
• The middle piece contains a large number of mitochondria that provide energy during active movement.
• Sperm is a motile gamete which moves through the female reproductive tract with the help of the tail.

Female reproductive system

• The female reproductive system consists of a pair of ovaries, a pair of fallopian tubes (oviducts) and a single uterus.
• Ova are produced by ovaries.
• Fallopian tubes (oviducts) carry the ova from the ovaries to the uterus.
• Uterus holds the growing embryo/foetus and thus helps in holding the pregnancy.

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Oestrogen

• Estrogen or oestrogen, is the primary female sex hormone secreted by ovaries.
• It is responsible for the development of female reproductive organs, secondary sexual characteristics, development of female gamete, i.e. Ovum and maintenance of menstrual cycle.

Ovum

• The ovary produces the female gametes known as ovum or ova (plural).
• In human beings, a single mature egg or ovum is released into the oviduct/fallopian tube by the respective side ovary every month.
• The ovum is a single cell and is much larger than the sperm.
• It is non-motile and is carried to the uterus by the oviduct.

Fertilization

Fertilization is the process of fusion of the male gamete with the female gamete.

• Both the gametes containing haploid (single) sets of chromosomes fuse and thus maintain the diploid (double) number of chromosomes.
• The fertilized ovum is now called a zygote.
• In human fertilization takes place in the fallopian tube, and then the zygote is carried to the uterus.
• Inside the uterus, it undergoes repeated divisions and grows and becomes an embryo.

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For more information on Reproduction in Animals, watch the below video

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