Reproduction in Organisms - Notes | Class 12 | Part 1: Asexual Reproduction

• Reproduction is a process in which an organism produces young ones (offspring) similar to itself.
• The period from birth to the natural death of an organism is known as its lifespan.
• No individual is immortal, except unicellular organisms. There is no natural death in unicellular organisms.

Life Spans of Some Organisms

Organism	Lifespan	Organism	Lifespan	Organism	Lifespan
Rose	5-7 years	Butterfly	1-2 weeks	Tortoise	100-150 yrs
Rice plant	3-7 months	Fruit fly	2 weeks	Crow	15 yrs
Banyan tree	400+ yrs	Parrot	140 yrs	Cow	22 yrs
Banana tree	2-3 yrs	Crocodile	60 yrs	Elephant	50-70 yrs
Dog	22 yrs	Horse	40-50 yrs

Asexual Reproduction

• It is the production of offspring by a single parent.
• It is seen in unicellular organisms, simple plants & animals.
• The offspring are identical to one another and to their parent. Such morphologically and genetically similar individuals are known as clones.

Types of Asexual Reproduction

Fission:

• The parent cell divides (cell division) into two or more individuals. E.g., Protists and Monerans. Fission is 2 types:
  • Binary fission: Division of parent cell into two individuals. E.g., Amoeba, Paramecium.
  • Multiple fission: Division of parent cell into many individuals. E.g., Plasmodium, Amoeba.

  Under unfavorable conditions, Amoeba withdraws its pseudopodia and secretes a 3-layered hard covering (cyst) around itself, called encystation. Under favorable conditions, encysted Amoeba undergoes multiple fission to produce many minute amoebae or pseudopodiospores. The cyst wall bursts, and spores are liberated to grow into many amoebae. This is called sporulation.

  

Budding:

• A bud appears and grows in the parent body. After maturation, it detaches to form a new individual. E.g., Hydra, Sponge, Yeast.

  

Fragmentation:

• The body breaks into distinct pieces (fragments), and each fragment grows into an adult capable of producing offspring. E.g., Hydra.

Vegetative Propagation:

• Production of offspring from vegetative propagules in plants. Vegetative propagules are units of vegetative propagation.

  Examples of vegetative propagules:

  • Buds (‘eyes’) of the potato tuber.
  • Rhizomes of banana & ginger. Buds & rhizomes arise from the nodes of modified stems. The nodes come in contact with damp soil or water and produce roots and new plants.
  • Adventitious buds of Bryophyllum. They arise from the notches at margins of leaves.
  • Bulbil of Agave.
  • Offset of water hyacinth.
  • Runner, sucker, tuber, bulb, etc.

Other Asexual Reproductive Structures:

• E.g., zoospores (microscopic motile structures in some algae and protists), conidia (Penicillium), and gemmules (sponge).

  

Asexual reproduction is the common method in simple organisms like algae and fungi. During adverse conditions, they can shift to sexual reproduction.

Higher plants reproduce asexually (vegetative) & sexually. Most animals show only sexual reproduction.

Select a Topic 👇

1. Asexual Reproduction 2. Sexual Reproduction 3. Events in Sexual Reproduction

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