Class 12 Chapter 1, Reproduction in Organisms

Class 12 Chapter 1, Reproduction in Organisms

 

Meaning of Reproduction 

Reproduction is the formation of a new individual of the same kind. It can be defined as "a biological process in which an organism gives rise to young ones (offspring) similar to itself". It is an important characteristic feature of all living organisms. Word reproduction' consists of two words - 're' (again) and production. Thus, reproduction literally means "to produce again". Only a pre-existing individual can produce new individual again (of its own kind). It signifies that new individual can arise only from a pre-existing individual. Perpetuation of organisms on this earth is possible only because of reproduction.

TYPES OF REPRODUCTION IN ORGANISMS

Animals have great diversity and therefore they are adapted for various modes of reproduction. Primitive and unicellular animals reproduce mainly by binary fission. Among multicellular organisms, the primitive forms.

1. Asexual Reproduction: 

asexual reproduction, only one In individual is used as parent. • The individual does not produce gametes by meiosis • Due to the absence of meiosis, the ploidy (number of chromosomes) remains unchanged through out the reproductive process.

• Since, there is no gamete formation, fertilization is also absent.

The newly formed individual (offspring) is the exact carbon copy of its parent. Therefore, it can simply be called as a clone.

Asexual reproduction is found only in lower and primitive animals such as protozoans, sponges and coelenterates etc. 

Protozoa

2. Sexual Reproduction

It is an advance mode of reproduction, which is exhibited by majority of the animals. These animals show differentiation of sex. In this reproduction one/two individual are used which have male and female reproductive organ. If any one individual is used, then it must possess both male and female reproductive organs. Such animals are called bisexual or hermaphrodite, e.g., Earthworm, Leech etc. But in most of the animals, male and female individuals are separate (.e. they are uni-sexual) The most striking feature of sexual reproduction is the production of specialized haploid cells, called gametes. • During reproductive process, male and female gametes fuse to form zygote. This fusion is known s fertilization. In case of sexual reproduction, the offspring (new individuals) are not the carbon copies of their parents,

Hence, 

they are not the clones. They can better be called as hybrids. • Sexual reproduction is found in almost all types of animals from protozoans to mammals. Some protozoans in which sexual reproduction is present are - Plasmodium, Monocystis and Trypanosoma etc.