The period from birth to the natural death of an organism represents its life span. Life span may be as short as a few days or as long as thousand years. Whatever be the life span, death of every individual is certainty. Number of organisms should reduce due to death but there is a process in living organism that ensure continuity, i. Reproduction is defined as a biological process in which an organism give rise to young one similar to itself.
It ensure continuity of species of a particular organisms. Asexual reproduction is the process by which an organism creates a genetically similar or identical copy of itself without a contribution of genetic material from another individual. This method is found in those organism in which single individual is capable of producing offspring.
Why asexual offspring are termed as clone? Asexual organism produce offspring without involvement of two organism, fusion of gamete and crossing over, As a result, the offspring that are produced are not only identical to one another but are also exact copies of their parent. These offspring are genetically and morphologically identical and known as clone. Asexual reproduction is common among single-celled organisms, and in plants and animals with relatively simply organizations.
Asexual reproduction is the primary form Asexual reproduction definition yahoo messenger reproduction for single celled organisms such as the archaebacteria, eubacteria, and Protista. Many plants and fungi reproduce asexually as well. There are following modes of asexual reproduction:. In this type of method a cell divides into two halves and each rapidly grows into an adult. The nucleus divides first and the cytoplasm next. Due to both these division the mother cell splits into two equal sized daughter halves or cells.
On the basis of cytoplasmic division Binary fission are of three types:. New individuals form by mitosis. Initially a small outgrowth of the parent's body develops. It then separates from the mother to lead a free life. There are two types of budding: Exogenous budding The bud grows externally on the surface of parent body.
Yeast and Endogenous budding The buds are formed within the parent's body. They are called gemmules. Gemmules are small group of cells in a protective covering.
The body of the parent breaks into distinct pieces, each of which can produce an offspring. Hydra, some marine worms. Members of the Kingdom Fungi and simple plants such as algae reproduce through special asexual reproductive structures. Asexual Reproduction in plants usually termed as vegetative "Asexual reproduction definition yahoo messenger" or vegetative propagation.
In this type of reproduction plant used vegetative parts like root, stem and leaf for production of offspring. In such methods of vegetative propagation, a portion of the plant gets detached from the mother plant and develops into a new independent platn under suitable environmental conditions.
The detached parts may be roots, stems, leaves or flowers. The capacity for regeneration in higher plants can be used for production of new individuals. Some common method of artificial methods of vegetative propagation are cutting, layering and grafting. What is Terror of Bengal? Water hyacinth is an aquatic plant that grows well in water bodies like ponds and rivers. This plant was introduced in India because of its beautiful flowers and shapes of leaves.
This plant can propagate vegetatively by producing runner called offset.
It can spread all over the water body. It was known as "Terror of Bengal" as it grow fast and difficult to get rid of. It also drained O 2 from the water, as a result of which,
Asexual reproduction definition yahoo messenger led to the death of fishes. Sexual reproduction is a process that creates a new organism by combining the genetic material of two organisms. Sexual reproduction involves formation of the male and female gametes, either by the same individual or by different individuals of the opposite sex.
These gametes fuse to form the zygote which develops to form the new organism. Sexual reproduction is an elaborate, complex and slow process as compared to asexual reproduction.
In sexual reproduction the offspring receive a set of genome from each of the parents. Because of it offspring are not identical to the parents or amongst themselves. There are three main phase in sexually reproductive organism —. All organisms have to reach a certain stage of growth and maturity in their life, before they can reproduce sexually.
That period of growth Asexual reproduction definition yahoo messenger called the Juvenile phase. It is known as vegetative phase in plants. The end of Juvenile or vegetative phase which marks the beginning of the reproductive phase.
The female of placental mammals exhibits cyclical changes in the activities of ovaries and accessory ducts as well as hormones during the reproductive phase. In non-primate mammals like Asexual reproduction definition yahoo messenger, sheep, rats, deer, dogs, tiger, etc. Where as in primates like monkeys, apes, and human it is called Menstrual Cycle. After attainment of maturity all sexually reproductive organisms follow a regular sequence. These regular sequences may be grouped into three stage —.
These include all the events of sexual reproduction before the fusion of gametes. There are two main pre-fertilization events — gametogenesis and gamete transfer.
The process of formation of haploid gametes is known as gametogenesis. There are two type of gametes — male and female gamete. Gametes are haploid cells. Cell division during gamete formation Organisms belonging to monera, fungi, algae and bryophytes have haploid plant body so they produce haploid gametes by mitosis.
But organisms belonging to pteridophytes, gymnosperms, angiosperms and most of the animals including human beings, the parental body is diploid. These organisms produce haploid gametes by meiosis reductive division. After their formation, male and female gametes must be physically brought together to facilitate fusion. Successful transfer and coming together of gametes is essential for the most critical event in sexual reproduction.
The fusion of male and female gametes is known as syngamy and formation of a diploid zygote is known as fertilisation. Fertilisation are of two types on the basis "Where does syngamy occur". Two types are external fertilisation
Asexual reproduction definition yahoo messenger internal fertilisation.
If the fusion of male and female gamete occurs in external medium or outside the body of the organism, then gametic fusion is known as external fertilization. In most aquatic organisms such as algae, fishes and some amphibians show external fertilization. These organisms show great synchrony between the sexes and release of large number of gametes into the medium in order to enhance the chances of syngamy.
Frog and bony fishes show external fertilization. If the fusion of male and female gamete occurs inside the body of the organism, then gametic fusion is known as internal fertilisation.
Terrestrial organisms, fungi, higher animals such as reptile birds, mammals and bryophytes, and higher plants such as pteridophytes, gymnosperms and angiosperms show internal fertilisation.
A major disadvantage of external fertilization is survival of offspring because the offspring are exposed in front of predators.
In all these organisms, egg
Asexual reproduction definition yahoo messenger formed inside the female body where they fuse with the male gamete. In these organism male gamete is motile and has to reach the egg in order to fuse with it.
In seed plants non motile male gamete are carried to female gamete by pollen tube. Parthenogenesis is a special form where an ovum develops into a new individual without being fertilised by the sperm. Parthenogenesis could be haploid as in honey bees, ants, bees and wasps or diploid as in aphidsdepending on the number of chromosomes present in the ovum. The organisms produced by parthenogenesis are identical to the mother.
Events in sexual reproduction after the formation of zygote are called post-fertilisation events. Zygote and Embryogenesis are two main terms to study under Asexual reproduction definition yahoo messenger events. After the fusion we got diploid zygote by fertilisation process.
In external fertilisation zygote is formed in external medium and in internal fertilisation zygote is formed inside the body of the organisms. Zygote is the vital link that ensures continuity of species "Asexual reproduction definition yahoo messenger" organism of one generation and the next.
Every sexual reproducing organism including human beings begin life as a single cell zygote. The process of development of embryo from the zygote is known as embryogenesis. During embryogenesis, zygote undergoes mitosis cell division and cell differentiation. Cell division increase the number of cell in the developing embryo, cell differentiation helps to form specialised tissues and organs to form an organism.
Animals can be grouped into two categories based on how and where the development of the zygote takes place. Seed S and Pericarp P. I love to learn and teach biology.
By this blog I want to increase my knowledge and share my knowledge with others. Feel free to ask what ever you want to ask related to biology, I try my best to help you.  Agamospermy in plants: An embryo arises from tissue surrounding the embryo asexual reproduction, while parthenogenesis is mainly applied to animals.
In asexual reproduction only one gamete develops into the adult. Bacterial conjugation, the transfer of DNA between two bacteria, A more stringent definition is agamogenesis which Asexual reproduction definition yahoo messenger to reproduction without the.