- Reproduction is defined as a biological process in which an organism gives rise to young ones (offspring) similar to itself.
- Reproduction at its basic level involves creation of the copy of DNA
- DNA present in the chromosome of the cell is the information source for making proteins.
- If the information is changed, different proteins will be made, and would lead to altered body designs.
- The two DNA’s need to be separated, for the copy of DNA to have an organised cellular structure, DNA copying is accompanied by creation of additional cell apparatus.
- Since no bio-chemical reaction is absolutely reliable, therefore the copying of DNA will have some variations each time.
- DNA copies generated will be similar to each other and not identical.
- Some of the variations may even be drastic enough for the new DNA generated not would not be able to work with the cellular apparatus and would eventually lead to death of the new cell.
- The consistency of DNA copying during reproduction is important for maintenance of body design features that allow the organism to use a particular niche .
- Reproduction is linked to stability of population of species.
IMPORTANCE OF VARIATION in Reproduction
- Population of organisms fill well-defined places or niches in the ecosystem, using their ability to reproduce.
- Variation in DNA copying can ensure the survival of some individuals among a population, in case of changes in a particular niche in which the population is suited to survive in.
- Variation is useful for survival of species over time.
- Asexual reproduction:A sexual reproduction involves production of Offsprings by single parents.
- There is no involvement of specialized gamete cell .
- Offspring are genetically identical to their parents
Types of Asexual Reproduction
- In unicellular organisms, fission is the mode of reproduction used to create new individuals.
- In simple unicellular organisms fission can take place in any plane, such as in amoeba.
- In organisms showing somewhat more organisation of body, it occurs in a definite orientation in relation to the structure, for example leishmania having a whip-like structure present in one end.
- Some single-celled organisms simply divide into many daughter cells simultaneously using multiple fission, for example plasmodium.
- Yeast can put out small buds that separate and grow further
- Multicellular organisms with simpler body design use fragmentation as a method of reproduction, for example in spirogyra, which breaks up into smaller pieces upon maturation.
- These fragments grow into new individuals.
- Not all multicellular organisms can use cell by cell division for reproduction as they are not simply a random collection of cells, and have organised body designs and structures,
- In multicellular organisms reproduction via a single cell-type which is capable of growing, proliferating and making other cell types under right circumstances.
- Many fully differentiated organisms have the ability to give rise to new individuals from their body parts.
- For example , if hydra or planaria is cut or broken into any number of pieces each piece grows into a complete organism this is known as regeneration
- It is not the same as reproduction, since organisms would not depend on being cut up to be able to reproduce.
- Organisms such as hydra use regenerative cells for reproduction in process of budding.
- In hydra a bud develops as an outgrowth due to repeated cell division at one specific site
- These buds develop into tiny individuals and detach themselves from parent body when fully mature.
- There are many plants in which parts like roots, stems and leaves can develop into new plants in appropriate conditions, this property is used in vegetative propagation method such as layering or grafting
- Plants raised by vegetative propagation can bear fruits and flowers earlier than those reproduced by seeds.
- Plants raised by vegetative propagation are genetically similar enough to the parent plant to have all its characteristics.
- In rhizopus tiny blob-on-a-stick structures called sporangia containing spores that can develop into new rhizopus are involved in reproduction.
- The spores have thick walls that protect them until they come into contact of another moist surface and being to grow.