Reproduction: Importance of Reproduction and Types of Reproduction

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The process of production of new organisms from the existing organisms of the same species is known as reproduction.

OR

  • The biological process by which an organism produces another organism like itself is known as reproduction.
  • The existing organism is called parent and new organisms produced by them are known as offspring.

Importance of Reproduction

  • It is essential for the survival of species on earth.
  • It ensures the continuity of life on earth.

Types of Reproduction

There are mainly two types of reproduction:

  • Asexual reproduction
  • Sexual reproduction.
Types of Reproduction

Difference between Sexual and Asexual Reproduction

Difference between Sexual and Asexual Reproduction

Asexual Reproduction

It is a mode of reproduction involving single parent.

There are different modes of asexual reproduction:

Modes of Asexual Reproduction

Fission

The mode of asexual reproduction in which a unicellular parent organism splits up into two or more daughter cells. It is of two types-

Binary Fission

The parent organism splits to form two daughter cells. E. g. , Amoeba, paramecium, leishmania etc.

Binary Fission in Amoeba

Multiple Fission

The parent organism splits to form many daughter cells at the same time. E. g. , plasmodium.

Budding

In budding a small part of the body of the parent organism grows out as a โ€˜budโ€™ which then detaches and becomes a new organism. E. g. , Hydra, yeast etc.

Budding in Hydra

Fragmentation

The mode of asexual reproduction in which organism breaks into pieces and each piece give rise to a new organism. E. g. , spirogyra.

Fragmentation in Spirogyra

Spore Formation

Spores are small bulb like structures which are covered by thick walls. Under favorable conditions, they germinate and produce new organism. E. g. , Rhizopus.

Spore Formation in Rhizopus

Regeneration

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

Regeneration: Organism from the Body Parts

Vegetative Propagation

In many plants new plants develop from old parts of plant such as-

  • Stem: e. g. , Sweet potato
  • Root: e. g. , Potato, ginger, onion etc.
  • Leaves: e. g. , Bryophyllum

Artificial Methods of Vegetative Propagation

  • Grafting: 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. e. g. , Mango.
  • Layering: Layering involved rooting of the piece of the plant and then severing it. E. g. , Jasmine.
  • Cutting: Cutting involves the rooting of the severed piece of the plant. E. g. , rose.

Sexual Reproduction

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

Sexual Reproduction

Sexual Reproduction in Flowering Plants

Flower is the reproductive structure found in angiosperms. Flower consists of sepals, petal, stamens, and pistils

  • Sepals: Green structures that protect the inner parts when the flower is in bud stage.
  • Petals: Colorful and attract the insects for pollination.
  • Stamens: Male reproductive parts and produce pollen grains that contain male gametes. Each stamen has two parts โ€” Filament i.e.. , stalk and Anther i.e.. , swollen top part which has large number of pollen grains.
  • The carpel is the female reproductive part and produces ovules that contain female gametes.

It has three parts:

  • Stigma: Top sticky part and receives pollen grains during pollination.
  • Style: The middle long part and
  • Ovary: The swollen part and contains ovules. Each ovule has an egg cell i.e.. , female gamete.
Longitudinal Section of Flower
Female and Male Reproductive Organ of a Plant
  • The flowers may be bisexual i.e.. , having both stamens and carpels for example; Mustard, China Rose (Hibiscus) .
  • The flower may be unisexual i.e.. , having either stamens or carpels for example; Papaya, Watermelon.

Pollination

The process of transfer of pollen grains from anthers to the stigma of a flower is known as pollination.

Pollination is of two types:

  • Self-pollination (autogamy) and
  • Cross-pollination (allogamy) .

Explanation:

  • In self-pollination, transfer of pollen grains takes place from anthers to the stigma of the same flower or another flower of the same plant.
  • In cross-pollination, pollens are transferred from anthers to the stigma of another flower.

Many pollinating agents play their roles in cross-pollination. Examples: water, wind, insects etc.

Fertilization

Fertilization is the process of fusion of male and female gamete to form a zygote during sexual reproduction. Pollination is followed by fertilization in plants.

The events are:

  • Pollen grains land on the stigma of the ovary.
  • Pollen tubes grow out of the pollen grains, travel through the style, and reach the ovary, through micropyle.
  • Pollen tube has two male germ cells.
  • Each ovule has two polar nuclei and a female germ cell (egg) .
  • Pollen tube releases two male germ cells inside the ovule, one of them fuses with female germ cell and forms a zygote which grows into embryo, the fusion is known as syngamy. The other male germ cell fuses with two polar nuclei, the process is known as triple fusion. So, in flowering plants two fusions take place during fertilization. It is known as double fertilization.
  • After fertilization, ovary becomes fruit and ovules turn into seeds. All other parts wither away.
Double Fertilization

Reproduction in Human Beings

Human beings show sexual reproduction.

  • Male parent produces male gametes called sperms. Sperms have tail and are therefore, motile. They are produced in large numbers in the testes. There is no food stored in the sperms
  • Female parent produces female gametes called ova. Ovum is bigger, non-motile and only one ovary produces one ovum in one month. Ova contain stored food.
  • Sexual maturation: The period of life at which production of germ cells i.e.. , sperms and ova start in the body. This period of sexual maturation is known as puberty.

Changes During Puberty

In Boys and Girls Both

  • Thick dark hair starts growing in parts of the body such as arm pits and genital area.
  • Thinner hair appears on legs, arms, and face.
  • Skin becomes oily and pimples may appear on the face etc.
In Boys

Beard and mustache start appearing, voice begins to crack, reproductive organs develop and start producing sperms.

In Girls

Breast size begins to increase, skin of the nipples darkens, menstruation starts.

The act of mating between the male and female partner is termed as copulation.

Male Reproductive System

Male reproductive system comprises of

  • A pair of testes
  • Glands
  • Vas deferens
  • Penis.
    • 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 scrotum. This is to maintain lower temperature required for the formation of sperm. Testis produces male hormone testosterone needed for the development secondary sexual characteristics in males such as formation of beard and moustaches and in the development of sperm.
    • Prostate glands and seminal vesicles are also found in males to nourish and for easy transport of sperm in the female genital tract.
    • Vas deferens is a duct that transport sperm to urethra, which is a common passage for both urine and sperm ejaculation.

All this secretion along with sperm form the semen.

Female Reproductive System

It consists of the following components:

  • 1 pair of ovaries,
  • 1 pair of fallopian tubes or oviducts,
  • A uterus,
  • A vagina

Explanation:

  • Ovaries: Ovary produces female hormones such as oestrogen, progesterone. These hormones are needed for female sexual development and well as for pregnancy. Female egg or ova are produced in ovaries.
  • Fallopian Tubes: It is the site of fertilization between the male and the female gametes and formation of the zygote early embryo.
  • Uterus: The inner lining of the uterus is richly supplied with blood vessels and is known as endometrium. The narrow end of the uterus is called cervix. The embryo formed in the fallopian tube comes down at endometrium and develops for the next nine months till the baby is delivered.
  • Vagina: The uterus opens into the vagina through the cervix. The vagina is a muscular tube through which the baby is delivered at the end of nine months. It also serves as the canal for receiving the semen at the time of copulation.

Fertilization of Egg

When Egg is Fertilized?

  • The fertilized egg called zygote is planted in uterus and develops into an embryo.
  • The embryo gets nutrition from the motherีšs blood with the help of a special tissue called placenta. It provides a large surface area for the exchange of glucose, oxygen, and waste material.
  • The time period from fertilization up to the birth of the baby is called gestation period. It is about9 months.

When Egg is Not Fertilized?

  • The uterus prepares itself every month to receive fertilized egg.
  • The lining of the uterus becomes thick and spongy, required to support the embryo.
  • When fertilization had not taken place, this lining is not needed any longer. This lining breaks and comes out through vagina as blood and mucus. - This cycle takes around 28 days every month and called menstruation.
  • The beginning of menstruation at puberty is known as menarche. The stoppage of menstruation when the woman is 45 - 55 years of age is called menopause.

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