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HOW DO ORGANISMS REPRODUCE?

  • Have you wondered what would have happened if organisms never reproduced? Then we would not have existed in this world right!! Reproduction is an essential process that helps in the survival of species on earth. We will learn the different types of reproduction that occur in plants and animals. There are two modes of reproduction seen in organisms and, they are:
  1. Asexual Reproduction
  2. Sexual Reproduction
  • How different organisms reproduce is determined by their bodily design.

ASEXUAL REPRODUCTION

A type of reproduction in which a single organism produces a new generation. There are different types of asexual reproduction:

Fission

  • Fission or cell division takes place in unicellular organisms.
  • There are two types of fission, and they are (i) Binary fission and (ii) Multiple fission.
  • In binary fission, the organism divides into two equal halves giving two individuals. Eg: Amoeba and Leishmania.
  • Whereas, in multiple fission, the unicellular organisms divide into many offspring. Eg: Plasmodium.

binary fission in amoeba

Binary_fission_in_Leishmania

Multiple_fission_in_Plasmodium

Fragmentation

    • Fragmentation occurs in muti-cellular organisms with simple body designs.
    • In fragmentation, the organism on maturation breaks into smaller pieces or fragments.
    • These fragments then grow into new offspring. Eg: Spirogyra

Regeneration

    • In regeneration, an individual organism breaks into many pieces and these pieces grow into a complete organism. Eg: Hydra and Planaria

Budding

    • During budding, the organism develops a small extension from its body called a bud. This bud then forms a tiny organism that gets detached on becoming a fully matured one. Eg: Hydra

Vegetative Propagation

    • Plants use this mode of reproduction.
    • In vegetative reproduction, certain parts of plants like the stem, root, and leaves grow into new plants.
    • Plants like sugarcane, roses, or grapes use vegetative propagation techniques like grafting and budding for agricultural purposes.
    • In Bryophyllum, the buds formed on its leaf margin fall on the soil and a new plant is produced. 

Advantages of Vegetative Propagation

      • Plants grown using this method give flowers and fruits earlier than those formed from seeds.
      • Plants that have lost the ability to produce seeds like banana, orange, rose, and jasmine can be grown through vegetative propagation.
      • All plants grown through this process are genetically similar to the parent plant.

Spore Formation

      • In certain multicellular organisms, there are tiny blob-on-a-stick structures. These blobs are called sporangia.
      • The sporangia are found on a thread-like structure known as hyphae.
      • The sporangia contain cells or spores that develop into new organisms when they come in contact with a moist surface. Eg: Rhizopus

SEXUAL REPRODUCTION

It is a type of reproduction in which a new organism is produced by two organisms i.e., a male and female. 

Sexual Reproduction in Flowering Plants

  • In plants, the reproductive parts are situated on the flower. There are two types of flowers:
        • Unisexual- flowers that contain either stamen or pistil. Eg: Papaya, watermelon
        • Bisexual- flowers that contain both stamen and pistil. Eg: Hibiscus, mustard
  • The reproductive parts of a flower are the stamens and pistils. They contain the germ-cells. The male reproductive part of a flower is the stamen. The stamen consists of anther and filament. The stamen contains the pollen grains.
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Pollination

The transfer of pollen grains from the anther to the stigma is known as pollination.

  • There are two types of pollination-
        • Self-pollination- when the transfer of pollen from the stamen of one flower to the stigma of the same flower or other flowers of the same plant happens, it results in self-pollination.
        • Cross-pollination- when the transfer of pollen from the stamen of one flower to the stigma of a flower on other plants of the same species happens, it results in cross-pollination.
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Fertilisation

  • The fusion of male and female germ cells is called fertilisation in plants. During pollination, the pollen grains reach the stigma. The pollen contains the male germ cells. The ovary consists of ovules and these ovules contain the female germ-cells (egg cells).
  • For fertilisation the male germ-cells have to fuse with the female germ cells in the ovule. A tube grows from the pollen grains through which the male germ cells travel and reach the egg cells in the ovary. Thus, fertilisation takes place and a zygote gets formed. After fertilisation the zygote forms an embryo inside the ovule. The ovule develops a thick covering and transforms into a seed over time.
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Germination

  • The process by which the seed develops into a plant is called germination.
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REPRODUCTION IN HUMAN BEINGS

The Male Reproductive System

  • The most important reproductive organ in males is the testes. The two major roles of testes are:
        • They produce sperms.
        • They produce the sex hormone testosterone.
  • The testes are situated in the scrotum outside the abdominal cavity. This is because the formation of sperm needs a lower temperature than the normal body temperature. The sperm produced by the testis are transferred through the vas deferens which joins to a tube coming from the urinary bladder. The urethra acts as a common duct for sperms and urine. The prostate gland and seminal vesicle are present along the route of vas deferens. They add their secretion so that the sperm could move easily through this fluid. This fluid also gives nutrition.

The Female Reproductive System

  • The most important reproductive organ in females is the ovaries. The ovaries produce the female germ-cells or eggs. The female sex hormones- estrogen and progesterone are released by the ovaries. The other major organs of the female reproductive system are the oviduct or fallopian tube, the uterus, the vagina, and the cervix. The egg is transferred from the ovary to the womb through the fallopian tube. The development of the foetus occurs in the uterus.

So how is a child born?

  • During sexual intercourse, the sperm enters through the vagina. The sperm then travels and reaches the fallopian tube, where they may come in contact with the egg. The egg gets fertilized and forms a zygote. Further, the zygote divides and forms a ball of cells called an embryo.
  • The embryo is placed in the uterus lining, where it grows and develops organs to become a foetus. To nourish the growing embryo, the lining of the uterus thickens and is supplied with blood. There is a disc implanted in the wall of the uterus known as the placenta. The placenta helps the embryo receive nutrition from the mother’s blood. It consists of villi that give a large surface area for glucose and oxygen to move from the mother to the embryo.
  • The waste materials produced by the embryo are removed through the placenta by moving them to the mother’s blood. It takes around nine months for the child to develop inside the mother’s body. Finally, the muscles in the uterus contract, and the baby is born.

Menstruation

  • What happens when the egg is not fertilized? Every month the ovary releases one egg. Every month, the uterus also prepares itself to receive a fertilised egg. The lining of the uterus thickens to nourish the embryo. If fertilisation does not occur, the lining of the uterus breaks.
  • The cyclic process of bleeding through the vagina due to the removal of the uterus lining is known as mensuration. It takes place every month and lasts for 2 to 8 days.

Reproductive Health

  • Reproductive health is important for avoiding sexually transmitted diseases (STDs) and unplanned pregnancy.  Contraceptives-methods used to prevent pregnancy and STDs. There are different types of contraceptives:
    • Condoms- The coverings used on the penis or vagina to prevent the sperm from reaching the female reproductive system are called condoms.
    • Contraceptive pills- Drugs are taken orally to prevent fertilisation. They change the hormonal balance of the body. Taking these pills prevents the release of eggs and, hence fertilisation does not occur.
    • Copper-T- it is placed in the uterus to avoid pregnancy.
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Surgical methods- In males, the vas deferens are blocked to prevent sperm transfer. In females, the fallopian tube is blocked so that the egg does not reach the uterus.