Reproduction: it  is a process of formation of new offspring from their pre existing parent.

  1. Q) Why reproduction is important?

1)Continuation of life

2)Perpetuation of species

3)Replacement of dead individual

4)introduction and transfer of variation

Do organisms create copies of themselves?

DNA functions as a blue print of life as it contain information not only about building and running cellular machinery but also organization of cells into tissues, tissues into organs, organs into organ level. DNA  carry  chromosomes which is responsible to inherits parents characters.

If we talk about eukaryotic organism they posses sexual reproduction in which chromosomes is surrounded by nuclear envelop, DNA replication give rises to variation in sexual reproduction

While in Asexual method of reproduction we do not observe any variation hence they produce same copy of individual to parents.

Importance of Variations

1)Pre adaptation

2)Individuality

3)Improvement of varieties

4)Evolution

Types of Reproduction

There are two types of reproduction Asexual and Sexual reproduction.

Asexual mode of reproduction

It is the process of formation of new individuals from specialized or unspecialized parts of a single parent without any fertilisation(fusion of two gametes)

All the individuals formed through asexual reproduction are genetically similar. They represents clone of the parent and are called remets.

Basic  Features

  • Single parent
  • No fusion of gametes
  • Division are usually mitotic
  • Rapid multiplication

The common modes of asexual reproduction are fission, budding, fragmentation, regeneration, spore formation and vegetative reproduction.

 

Fission

It is a mode of reproduction in which a parent undergoes division to form two or more individual it is mainly occurs in unicellular organisms.

1.Binary Fission:  when the unicellular individuals has become mature, it divides  to form two similar individuals. It occurs under favourable conditions, In this method parents gets disappear to form two new daughters.

E.g  Amoeba, Euglena, Leishmania.

 Fig : Binary Fission in amoeba  

2) Multiple Fission : it is mode of multiplication in which one unicellular parent divides and splits internally to form a number of daughter individuals. It occurs in protozoans and some unicellular algae. It can occurs in both favourable and unfavourable conditions.

 Fig : multiple fission

 Difference between binary fission and multiple fission

Binary Fission Multiple Fission
1)      It gives rises to two individuals

2)      It occurs under favourable condition

3)      Nucleus of the parent cell divides only once to form two daughters

4)      Cytoplasm undergoes cleavage after each nuclear division

5)      E.g : amoeba, paramecium

1)      it forms several individuals

2)      it occurs both under favourable and unfavourable condition

3)      nucleus of parent undergoes repeated division to form a number of daughter nuclei

4)      cytoplasm does not divide after every nuclear division

5)      e.g: plasmodium, amoeba

 

2)Budding:  it is the formation of an outgrowth from an organism which separates to produce a new individual,

e.g : Yeast, Hydra

a single yeast cell may produce 1-3 buds which may further bear buds.

 Fig: budding of yeast

3) Fragmentation: it is the process of breaking up of the body of an organism into two or more parts called fragments. Each fragments grow into new individuals.

e.g:  algae, fungi, bryophytes, marine ribbon worm

Fig: Fragmentation in Spirograph

4) Regeneration: it is the ability to repair injured parts and replace the one lost through accident

It is first seen by Trembly(1740) in case of hydra.

Regeneration is due to presence of special reserve or stem cells and dedifferentiation of differentiated cells.

e.g  Planeria

Fig: Regeneration of planeria

5) Spore formation or Sporulation: Spores are very minutes unicellular asexual reproductive bodies which get dispersed and form new individuals.

It occurs in bacteria, protest, algae and fungi.

Some of aquatics spore are motile and called zoospores

e.g: Rizopus, Ulothrix etc

Fig : Sporulation in Rizopus

3) Vegetative Propagation : it is the process of formation of new plants from the vegetative parts of the plants like leaves, roots, stems, buds ,etc.

e.g: Potato, Bryophyllum

 Fig: vegetative propagation of potato

 

 Fig: Leaves of Bryophyllum

Artificial method of vegetative propagation

1)Cuttings: they are small pieces of stems, roots and leaves which cut off from the plants and used as vegetative propagules.

e.g: Sugercane

2)Layering :  a soft one year old basal branch is defoliated fot a few cm in roughly the middle. The defoliated part is a given a small cut (V –shaped). The injured and defoliated part is pegged down and covered with soil.

e.g: jasmine, gotee grapes etc

3)Grafting: it is a technique of joining shoot system of one plant over the stump of another related  plant so as to form a composite plant that grows as a single plant.

The  plant which provide shoot system is called Sicon. While the one which provides root system is known as stock.

e.g: Orange Grapes etc

Advantages of vegetative propagation

  • Uniform Yield
  • Seedless plants
  • Good qualities
  • Survival rate
  • Introduction in new areas

Disadvantages of vegetative propagation

  • Overcrowding
  • Vegetative propagules cannot be stored for long.
  • Diseases
  • Absence of variation
  • Reduction of vigour.

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