How Do Organisms Reproduce ?

  • Reproduction is the biological process by which new individual organisms (offspring) are produced from their parents. Reproduction is a fundamental feature of all known life. Each individual organism exists as the result of reproduction.
  • The inheritance of features from parents can be transferred to their offsprings through chromosomes present in the nucleus of the cell.
  • Basic event in reproduction is the creation of a DNA copy.
  • Some changes in DNA copying produces variations in organisms known as mutations.
  • Vegetative propagation in plants is also an example of asexual reproduction. New plants can be grown from different vegetative parts of the plants like roots, stems, leaves etc.
  • Some plants like Bryophyllum develops adventitious buds on their leaves which develops into new plants.
  • Modified tuberous roots like sweet potato can be propagated vegetatively when planted in soil.
  • Artificial methods of vegetative propagation includes cutting, layering, grafting etc.
  • The parts of a flower are calyx, corolla, androecium and gynoecium.
  • Calyx is the outermost whorl of a flower which is a collection of sepals mostly green in colour and they are protective in function.
  • Corolla is the collection of petals, they are brightly coloured and helps in attraction of insects for pollination.
  • Androecium is a collection of stamens which are the male reproductive organs of a flower. A stamen consists of anther and filament. Anther contains pollen sacs in which pollen grains are produced. Pollen grains contain male gametes.
  • Gynoecium is a collection of carpels which are the female reproductive organs of a flower.
  • A carpel consists of stigma, style and ovary
  • The ovary contains ovules which contains the female gametes.
  • Double fertilisation is a complex fertilisation mechanism in flowering plants. This process involves the fusion of a female gametophyte (megagametophyte, also called the embryo sac) with two male gametes (sperm).
  • Ovules grow into seeds and ovaries grow into fruits after fertilisation.
  • Gonads are primary sex organs in humans. Testes are male gonads which produces sperms whereas ovaries are female gonads which produce eggs.
  • Testes are found within sac like structures called scrotum. Vas deferens or sperm ducts carry sperms from testis.
  • Ovaries produce eggs. The fertilisation of egg with sperms occurs at oviduct. After fertilisation zygote is formed which develops into embryo that grows in uterus to a full term baby in about 280 days which is called gestation period.
  • If fertilisation does not occur the egg disintegrates and along with blood and mucus it comes out through the vagina. This cycle occurs every month in females known as menstrual cycle.
  • To avoid rapid growth of population some preventive measures are taken which is called birth control.
  • The infectious diseases which spread from an infected person to healthy ones through sexual contact are called Sexually Transmitted Diseases or STDs. Examples are AIDS, syphilis, gonorrhea.
  • 1. Asexual reproduction: The process of producing offsprings which involves a single parent without the formation of gametes is called asexual reproduction.
  • 2. Spore: A spore is a single-celled or multi-celled reproductive structure which gets separated from its parent and under the favourable conditions gives rise to a new individual.
  • 3. Seed: A seed is the reproductive unit of a plant from which a new plant grows.
  • 4. Vegetative propagation: It is mainly seen in plants and is an asexual mode of reproduction where a new plant grows from different parts of plant like roots, stem, leaves etc., rather than from a seed.
  • 5. Tissue culture: The production of new plants from a small piece of plant tissues or cells removed from the growing tips of a plant in a suitable growth medium is called tissue culture.
  • 6. Pollination: The process of transfer of pollen grains from anthers of stamens to the stigma of carpel within the same flower or different flower of same plant or to any other flowers of different plants but of same species is called pollination.
  • 7. Double fertilisation: The process by which a male gamete fuses with an egg
  • to form zygote and the second male gamete unites with two polar nuclei to form endosperm is called double fertilisation.
  • 8. Primary sex organs: They are the gonads i.e., testes and ovaries which produce gametes and secrete sex hormones.
  • 9. Gametes: The special cells involved in sexual reproduction to produce the offsprings are called gametes or sex cells.
  • 10. Puberty: The age at which sex hormones are produced, reproductive organs become matured and have the capacity to give rise to new individuals and there is development of secondary sexual characters in both males and females.
  • 11. Fertilisation: The process of fusion of male and female gametes to produce the zygote is called fertilisation.
  • 12. Gestation period: It is the time from fertilisation till the birth of the new born.
  • 13. Parturition: The delivery of full term baby from the uterus of mother after the end of gestation period is called parturition.