Reproduction in Organisms
Asexual reproduction in organisms
• All species are able to live generation after generation due to the process of reproduction.
• There are two types of reproduction depending upon whether one or two organisms participate in the process:
a) Asexual Reproduction and
b) Sexual Reproduction.
• Only one parent is involved in asexual reproduction.
• The fusion of gametesand fertilisation does not occur and the offspring formed by asexual reproduction are identical and are calledclones.
• Fission is the most common type of asexual reproduction, which takes place in unicellular organisms. It results in the formation of two daughter cells that are identical to the parents.
• Some other methods of asexual reproduction in animals include budding, regeneration, fragmentation, spore formation and parthenogenesis.
• In uniparental condition, only one of the parents transfers chromosomes to the progeny.
• Two types of asexual reproduction takes place in plants, which include vegetative propagation and apomixis. Various units of vegetative reproduction in plants are runner, rhizome, sucker, tuber, offset and bulb.
• Grafting is another process in which a cut stem of one plant is taken as a graft and firmly attached to the rootstock of another plant.
• In apomixis, the seed is developed without fertilisation. It can be either obligate apomixis or facultative apomixis.
Sexual reproduction in organisms
• Sexual reproduction is characterised by the formation of male and female gametes, which fuse to form a zygote that further develops into a new organism. It is mostly found in higher animals.
• All organisms need to attain a certain stage of growth and maturity in order to reproduce sexually. This period of growth is called juvenile phase in animals and vegetative phase in plants.
• Three apparent phases are found in annual and biennial plants namely vegetative, reproductive and senescent.
• The end of juvenile phase in animals is followed by morphological and physiological changes in the reproductive phase.
• Animals can be either seasonal breeders or continuous breeders.
• Cyclic changes are exhibited by the females of placental animals during the reproductive phase.
• Flowers are thereproductive organs of the flowering plants.
• Events of sexual reproduction can be divided intothree categories: pre-fertilisation, fertilisation and post-fertilisation events.
• Pre-fertilisation events includegametogenesis and gamete transfer.
• Post-fertilisation events include zygote formationand embryogenesis.
• Plants can either be monoeciousordioecious. The flowers may be bisexual or unisexual. Their gametes are haploid and are formed by the process of meiosis.
• One of the most essential events in sexual reproduction is the transfer of male gametes. In case of unisexual animals,it occurs either by the process of copulationor by simultaneous release.
• In angiosperms, the transfer of gametes occur by the pollination. The process of fertilisation or syngamy is followed by pollination. Fertilisationincludes the fusion of male and female gametes.Syngamy leads to the formation of zygote. Embryogenesis is the process of development of embryo from the zygote.
• After fertilisation, in angiosperms, the ovary develops into fruit and the ovules mature into seeds.