Reproduction in Organisms Short Notes PDF in English for Class 12, NEET, AIIMS and Medical Exams

Reproduction in Organisms Short Notes PDF: Find below the important notes for the chapter, Reproduction in Organisms as per the NEET Biology syllabus. This is helpful for aspirants of NEET and other exams during last-minute revision. Important notes for NEET Biology- Reproduction in Organisms Short Notes PDF cover all the important topics and concepts useful for the exam.

Reproduction in Organisms Short Notes

Reproduction in Organisms Short Notes PDF

Reproduction is one of the important biological process by which every living organism gives rise to new organisms similar to themselves. It is the means of multiplication and perpetuation of species because the older individual of each species undergo senescence and then dies.

Basic features of reproduction are:

  • Replication of DNA
  • Cell division (only mitotic, or both mitotic and meiotic).
  • Formation of reproductive bodies or units.
  • Development of reproductive bodies into offspring.

Types of Reproduction

Based on the participation of one or two organisms, reproduction can be of following two types:

  • Asexual reproduction
  • Sexual reproduction

Asexual Reproduction

In asexual reproduction, the new individuals are produced by any means other than the fusion of gametes, or Reproduction in which new individuals are formed without meiotic division and fusion of gametes is called asexual reproduction.
  • Asexual reproduction is also known as apomixis.
  • Apomixis term was suggested by Winkler.
  • Rate of reproduction is faster in asexual reproduction.
  • Asexual reproduction is common among single-celled organisms and in plants and animals with simple organisations.

Characteristics of Asexual Reproduction

  • A single parent produces offspring, that is, asexual reproduction is uniparental.
  • Gametes are not formed.
  • Cell divisions are only mitotic.
  • The new individuals formed are usually genetically identical to the parent. Variability, if it occurs, is restricted to mutation only.
  • Multiplication occurs rapidly.
  • The offsprings are often formed in large numbers.

Types of Asexual Reproduction

  • Binary Fission: The term “fission” means “to divide”. During binary fission, the parent cell divides into two cells. The cell division patterns vary in different organisms, i.e., some are directional while others are non-directional. Amoeba and euglena exhibit binary fission. It can be following types:
    • Simple binary fission: When division occurs in any plane but it is always right angle to the elongated dividing nucleus, e.g. Amoeba.
    • Longitudinal binary: fission When division occurs along the longitudinal axis, e.g. Euglena, Vorticella.
    • Oblique binary fission: When division occurs at an angle to the transverse axis, e.g. Ceratium, Gonyaulax.
    • Transverse binary fission: When division occurs along the transverse axis of the individual, e.g. Paramecium, diatoms, bacteria, Planaria.
    • Multiple fission: The division of the parent body into many daughter organisms, e.g. Amoeba, Plasmodium, Monocystis (all Protozoa).
  • Budding: Budding is the process of producing an individual through the buds that develop on the parent body. Hydra is an organism that reproduces by budding. The bud derives nutrition and shelter from the parent organism and detaches once it is fully grown.
  • Fragmentation: Fragmentation is another mode of asexual reproduction exhibited by organisms such as spirogyra, planaria etc. The parent body divides into several fragments and each fragment develops into a new organism.
  • Vegetative Propagation: Asexual reproduction in plants occurs through their vegetative parts such as leaves, roots, stem, and buds. This is called vegetative propagation. For example, potato tubers, runners/stolon, onion bulbs, etc., all reproduce through vegetative propagation.
  • Spore Formation: Spore formation is another means of asexual reproduction. During unfavourable conditions, the organism develops sac-like structures called sporangium that contain spores. When the conditions are favourable, the sporangium burst opens and spores are released that germinate to give rise to new organisms.
  • Regeneration: Regeneration is the power of growing a new organism from the lost body part. For eg., when a lizard loses its tail, a new tail grows. This is because the specialized cells present in the organism can differentiate and grow into a new individual. Organisms like hydra and planaria exhibit regeneration.

Vegetative Propagation in Plants

Plants belonging to this category propagate by a part of their body other than a seed. The structural unit that is employed in place of seed for the propagation of new plants is called propagule. In angiosperms any part of the plants – roots, stems and leaves can be used for vegetative propagation. Generally methods of vegetative propagation have been further divided into two types – Natural and Artificial.

  • Natural Vegetative Propagation: The technique of propagation in which a portion gets detached from the plant body and functions as propagule naturally is called natural vegetative propagation. It can be done by roots, underground stems, creepers and leaves. The plants propagated vegetatively are given below:
    • Stem: Runners grow horizontally above the ground. The buds are formed at the nodes of the runners.
    • Roots: New plants emerge out of swollen, modified roots known as tubers. Buds are formed at the base of the stem.
    • Leaves: Leaves of a few plants get detached from the parent plant and develop into a new plant.
    • Bulbs: Bulbs have an underground stem to which the leaves are attached. These leaves are capable of storing food. The centre of the bulb contains an apical bud that produces leaves and flowers. Shoots are developed from the lateral buds.
  • Artificial Vegetative Propagation: This is a type of vegetative reproduction carried out by humans on the fields and laboratories. The most common types of vegetative reproduction occurring artificially include:
    • Cutting
    • Grafting
    • Layering
    • Tissue Culture

Merits of Vegetative Propagation:

  • It is good for the multiplication of seedless plants, e.g., banana, sugarcane; pineapple and seedless orange and grape.
  • It is the fastest method of reproduction, e.g., potato crop requires more than one year with the help of seeds, however, it takes only 3 to 4 months with the help of tubers. Similarly, lily takes 4 to 7 years through seeds, however, 1 to 2 years by bulbs.
  • By grafting, desirable quality of fruit/flower/seed can be obtained.
  • Disease free plants can be cultured by micropropagation and micrografting.
  • Plants with long seed dormancy or poor seed viability or poor seeds can be propagated vegetatively. E.g., Cynodon dactylon (Lawn. Doob or Bermuda grass).
  • Good quality and better yield varieties can be preserved for a long duration in offsite collection, herbarium, botanical gardens, etc.
  • It gives 100% genetic similarity to their parents i.e., clone.

Advantages of Asexual Reproduction

  • Only one parent is needed.
  • The population can increase rapidly when the conditions are favourable.
  • It is more time and energy efficient as you don’t need a mate.
  • It is faster than sexual reproduction.

Disadvantages of Asexual Reproduction

  • It does not lead to genetic variation in a population.
  • The species may only be suited to one habitat.
  • Disease may affect all the individuals in a population.

Sexual Reproduction

Sexual reproduction is a mode of reproduction involving the fusion of haploid female gamete (egg cell) and haploid male gamete (sperm cell). The fusion of these gametes occurs at fertilization resulting in the formation of a diploid zygote. The zygote develops into an individual organism that is genetically distinct from the parent organisms. This is in contrast to asexual reproduction where an organism reproduces without involving gametes and the resulting offspring is a clone of the parent.

Difference between Sexual Reproduction and Asexual Reproduction

Sexual Reproduction Asexual Reproduction
It takes place by the fusion of male and female gametes. In this, the organism arises from a single organism.
The offsprings produced are not identical to the parents. The offsprings produced are identical to the parents and are known as clones.
It is found in higher invertebrates and all the vertebrates. It is found in lower organisms.
It is a slow process. It is faster compared to sexual reproduction.

 

 

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