How Do Organisms Reproduce CBSE Class 10 Science Notes Chapter 8

CBSE Class 10 Science Revision Notes for Chapter 8 How do Organisms Reproduce are given below in a pointwise format. The notes are based on the current syllabus for Class 10 Science and are the best study resource for board exam preparation. With these notes, you can revise the whole chapter of How do Organisms Reproduce in just 15 minutes. The notes include all the important points, definitions and diagrams for your complete understanding.

Class 10 Science CBSE Chapter 8 How do Organisms Reproduce includes topics like sexual reproduction, asexual reproduction and reproduction in flowering plants, fission and fusion, sexual reproduction in animals, changes in the body at puberty, birth control methods, etc. You can revise every topic in detail with our online free revision notes for CBSE Class 10 Science.

Free Revision Notes for Class 10 Science How do Organisms Reproduce

The ability to produce a new organism is known as reproduction. There are two types of reproduction-asexual reproduction and sexual reproduction.

Do organisms create exact copies of themselves?

Reproduction at its most basic level involves making copies of the blueprints of body design.
The chromosomes in the nucleus of a cell contain information for the inheritance of features from parents to the next generation in the form of DNA (Deoxyribo Nucleic Acid) molecules.
The DNA in the cell nucleus is the information source for making proteins. If the information is changed, different proteins will be made. Different proteins will eventually lead to altered body designs.
The cells use chemical reactions to build copies of their DNA. This creates two copies of the DNA in a reproducing cell, and they will need to be separated from each other.
To ensure that, a cell divides itself into two cells, each cell containing its own DNA and cellular apparatus.
Now, both these cells will be identical, but we cannot say that copying of the DNA will be 100% identical.
There might be some variations in the chemical reaction which means organisms cannot create exact copies of themselves.

Different types of Reproduction

There are mainly two types of reproduction- asexual reproduction and sexual reproduction.

Asexual Reproduction

It is a mode of reproduction involving a single parent. There are different modes of asexual reproduction-

Fission is defined as the splitting of the organisms into two halves and each half gives rise to a new organism. For example, Amoeba, bacteria. The most common type of fission is binary fission. It is a division of organisms such as bacteria into two or more parts. Binary fission can be irregular (division can take place in any plane), longitudinal (division occurs longitudinally), transverse (division occurs transversely) and can also be oblique (division occurs obliquely).

Fig.1. Binary fission in Amoeba

Fragmentation is another mode of asexual reproduction in which organism breaks into pieces and each piece give rise to a new organism. For example, Spirogyra, Planaria.

Fig.2. Fragmentation in Planaria

Regeneration is the ability to form new organisms from body parts. Cut or broken part generates a new organism. For example, Hydra, Planarians

Fig. 3. Regeneration in Hydra

Budding is defined as an outgrowth from the body of the organism. This outgrowth then detaches from the body and forms a new independent organism. For example, Hydra and Yeast.

Fig .4. Budding in Hydra

Vegetative reproduction is another method of asexual reproduction. In this form of reproduction, stem, root and leaves are used to form plants when provided with suitable conditions. Layering and cutting are the two common methods used for vegetative propagation. For example, banana, rose, jasmine etc. The plant produced through vegetative propagation is genetically identical to the parent plant.

Cutting involves the rooting of the severed piece of the plant.

Layering involved rooting the piece of the plant and then severing it.

Grafting occurs when two plant parts are joined together such as stem and root. The stem of the plant to be grafted is known as the scion, and the root is called the stock. (NTSE)

Fig.5. Vegetative Propagation

Spore formation is another method of asexual reproduction that involves specific reproductive parts such as hyphae in Rhizopus and blob-on-a stick structure in Rhizopus are involved in reproduction.

Fig.6. Spore formation in Rhizopus

Sexual Reproduction

Sexual reproduction involved two different parent organisms involving a female and a male parent.

Significance of Sexual Reproduction

Sexual reproduction is the source of variation. The mixing of two organisms gives rise to new recombinants or variants. Sexual reproduction involves the mating of germ cells also known as gametes. These gametes are haploid, that is, they have a half set of chromosomes. These gametes are formed through the process of meiosis. When male gametes and female gametes each with a haploid set of chromosomes combine they will form a diploid zygote. Zygotes undergo repeated divisions to form a new organism.

In humans, the male gamete is small and motile whereas the female gamete is large and non-motile.

Sexual Reproduction in Flowering Plants

The flower is the reproductive structure found in angiosperms. The flower consists of sepals, petals, stamens and pistils.

Fig.7. Structure of flower

A flower is said to be unisexual if it contains either stamens or pistils whereas if both stamens and pistils are present, it is known as bisexual. Papaya and watermelon are unisexual whereas Hibiscus and mustard are bisexual.

Pistil/carpel is the female reproductive structure that consists of a swollen basal ovary, middle elongated style and terminal stigma. The ovary contains ovules and each ovule bears an egg cell. Stamen is the male reproductive part and it consists of the anther and the stigma. The anther contains pollen grains that fuse with a female gamete, that is, egg cells. Fusion leads to zygote formation which forms a new plant.

Transfer of pollen grains from the anther to the stigma of the flower is known as pollination. When the pollen and the stigma are of the same flower, it is known as self-pollination. When pollen from one flower lands on the stigma of another flower it is known as cross-pollination.

Gametogenesis

The formation of gametes is known as gametogenesis. The male gamete is pollen grains whereas the female gamete is present inside the ovary. The ovary contains an ovule. Ovule contains the female gametophyte. Ovule also consists of outer layers known as integuments, nucellus and female gametophyte. Male and female gametes are produced and they are haploid in nature. There are two types of gametes- homogametes and heterogametes. When male and female gametes cannot be differentiated morphologically. They are known as homogametes. For example, gametes in Cladophora, Algae. When male and female gametes can be differentiated morphologically, they are known as heterogametes.

Post Fertilisation Events

The most important post-fertilization structure is the embryo and seeds. Zygote forms the embryo. Zygote first forms a pro-embryo which later converts into a mature embryo. Seeds are the result of sexual reproduction. Ovules mature into seeds whereas the ovary develops into fruits.

Double Fertilisation

In flowering plants, one sperm fertilises the egg cell, whereas the other sperm fuses with the two polar nuclei forming the endosperm. This is known as double fertilisation as two fertilisation events are taking place. The zygote divides to form 7 celled and 8 nucleated embryo sacs. Out of these 7 cells and 8 nuclei, there are two synergids with egg cells, 3 antipodals and two polar nuclei. Two polar nuclei fuse with one sperm and the other sperm fuse with the egg cell to form the zygote.

Fig.8. Double fertilisation

Reproduction in Human Beings

Humans reproduce sexually. When girls and boys attain puberty (reproductively active) there occur lots of changes in their bodies. The development of hair in armpits and genital regions is common to both males and females. Girls have increased breast size, darkening of skin and tips of nipples etc. Some changes such as thick hairy facial growth, voice changes occur in males.

Male Reproductive System

The male reproductive system comprises a pair of the testis, glands, accessory ducts, and male genitalia.

The testis is the site where male gametes or germ cells are produced. They are located outside the abdominal cavity in a sac-like structure known as the scrotum. This is to maintain the lower temperature required for the formation of sperm. Testis produces the male hormone testosterone needed for the development of secondary sexual characteristics in males such as the formation of beard and moustaches and also in the development of sperm.

Vas deferens is a duct that transports sperm to the urethra, which is a common passage for both urine and sperm ejaculation.

Prostate glands and seminal vesicles are also found in males to nourish and for easy transport of sperm in the female genital tract. Cowper’s gland produces mucus-like fluid that neutralises the acidity of the female vagina. All these secretions along with sperm form the semen.

Fig.9. Male Reproductive System

The formation of male gametes or sperm in testes is known as spermatogenesis. Sperms are haploid in nature. Seminiferous tubules are the site for spermatogenesis.

Testis produces a male hormone known as testosterone needed for the male secondary sexual characteristics as well as for spermatogenesis.

Female Reproductive Tract

The female reproductive system consists of a pair of ovaries, uterus, cervix, vagina, and external genitalia.

Female eggs or ova are produced in the ovaries. The formation of ova in the ovaries is known as oogenesis. The ovary produces female hormones such as oestrogen, progesterone. These hormones are needed for female sexual development and well as for pregnancy. The fallopian tube carries ova from the ovary to the womb. Two oviducts joined to form the uterus. Uterus then opens into Vagina via the cervix.

Fig.10. Female Reproductive System

Sperm enter into the female vagina at the time of sexual intercourse. Then the sperm reaches the fallopian tube where it fuses the ova to form a zygote. This is known as fertilisation. Then the zygote divides to form an embryo. The embryo gets implanted into the uterus. The embryo development occurs in the uterus to form the foetus.

Mother supplies nutrition to the growing foetus via the placenta. The placenta helps in the exchange of nutrients, gases and the removal of excretory products. The development of a child inside the womb of the mother takes place for about 9 months. Then the rhythmic uterine contraction leads to the delivery of the baby outside the female body.

Fig.11. Human Placenta

If the egg is not fertilised, the uterine lining is shed off in the form of fluid known as menstrual fluid. The discharge occurs from the vagina as blood and mucus. This is known as menstruation. It lasts for about 2 to 8 days.

Reproductive Health

It is defined as the state of well being in terms of safe sex, reproductive fitness as well as the absence of any reproductive diseases. Unsafe sex leads to different diseases which are known as sexually transmitted diseases.

Some of the sexually transmitted diseases are as follows-

Gonorrhoea is caused by bacteria
Syphilis is caused by bacteria
AIDS (acquired immunodeficiency syndrome) is caused by a virus HIV(human immunodeficiency virus)

In-vitro Fertilisation (IVF)

IVF is an infertility treatment method. In this case, the egg is fertilised with sperm outside the female body. Ovum is removed from the female body and is allowed to fertilise with sperm outside the body in In-vitro conditions.

Birth Control Methods

For a country like India where the population is increasing continuously, there is a need for birth control methods.

Condoms and diaphragms are barrier methods for birth control. They prevent the binding of sperm to the ovum.
The chemical method of birth control includes oral pills and vaginal pills.
Intrauterine contraceptive devices are also there to prevent the implantation of embryos in the uterus.
Surgical methods include vasectomy in males and tubectomy in females. Vasectomy is done by cutting the Vas deferens and then tying them up. Tubectomy involves cutting and tying a small portion of oviducts.

Fig. 12. Birth Control Methods

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