Reproduction in Organisms
In simple language, the definition of reproduction is “The process by which living organisms produces their own kind or offspring for the continuity of their species is known as reproduction.” It is one of the most important characteristics of organisms. In this process, the genetic material transmits from the parental generation to the next generation.
There are two types of reproduction-
In this type of reproduction, gamete formation does not take place. No gamete formation and fertilization are found in this type of reproduction.
- In this type of reproduction, offspring are produced by a single organism.
- This type of reproduction found in lower organisms or unicellular organisms.
- In this type of reproduction, the offspring is identical to the parent.
- Less variation is found in this type of reproduction.
Asexual reproduction is divided as–
Binary fission, budding, fragmentation, regeneration, and sporogenesis, vegetative propagation.
- Fission– In this type of asexual reproduction having various forms as fission, binary fission, and multiple fission.
- Binary fission– In it, the cell splits into two equal halve during cell division. Each cell contains a copy of its parent cell. fission is observed in many lower organisms like protozoa and bacteria. Ex. Amoebae, leishmania (cause kala-azar)
- The malarial parasite, Plasmodium, reproduces by dividing into many daughter cells simultaneously by multiple fission.
- Budding- In this type of reproduction, a small bud develops as an outgrowth of body in the result of repeated cell division. Very soon it separates and grows into a new individual. Example- Hydra.
- Fragmentation– In this type of reproduction, the organism simply breaks into several small individuals after maturation. Example- Spirogyra.
- Regeneration- If an organism can be cut into the various parts and each part gets regenerated i.e. Each piece grows in to complete organism; the process is called regeneration. Ex. Planaria
- Sporogenesis– It is a very simple type of reproduction found even in some multicellular also by spore formation. These spores are the thread-like structure, having a tiny blob-like structure that gets involved in reproduction. Example- Rhizopus.
- Vegetative propagation-It is also an asexual process of preproduction, In plants, vegetative propagation takes place through runner, rhizome, sucker, tuber, offset, bulb these are called vegetative propagules. Ex- Bryophyllum.
In this type of reproduction, offspring is produced by the formation of gametes and subsequent fusion of gametes. During fertilization, the male and female gametes unite to form a zygote which develops into a mature organism. Most animals and higher plants reproduce their progeny by sexual reproduction.
- In sexual reproduction, two parents are involved as male and female.
- In this type of reproduction, diversity is found on a large scale, as two offspring cannot be similar, variation occurs in parent and offspring also.
- The germ-cells from two individuals combine during sexual reproduction to form a new individual in sexual reproduction.
The flower is the reproductive part of a plant. In papaya, the flower is unisexual which contains either stamen or pistil and it may be bisexual as in mustard, hibiscus. Parts of flower – sepals, petals, stamens, and pistil.
Calyx – consisting of sepals, Corolla – consisting of petals, Androecium – consisting of stamens, Gynoecium or pistil – consisting of carpels. Stamens and pistil found in flower are the reproductive parts which contain the germ-cells.
- Stamen is the male reproductive part of the flower and it produces pollen grains that are yellowish in colour.
- The pistil is present in the center of a flower and it is the female reproductive part.
- The pistil is made up of three parts – first, the swollen bottom part is the ovary, second, the middle elongated part is the style, and third, the terminal part which may be sticky is the stigma.
- the ovary contains an ovule and there is one egg in each ovule.
Pollination– Transfer of pollen grains from the anther to the stigma of a flower it may follow various ways. for example- Pollination by wind, Pollination by insects (Entomophily), Pollination by Water (Hydrophily), Pollination by Animals (Zoophile)
Pollination may be of two types- Self-pollination and Cross-pollination
- Self-Pollination-Transfer of the Pollen grains to stigma of the same or from another flower on the same plant. Ex. pea and gram
- Cross-Pollination-Transfer of Pollen grains from a flower to the stigma of another flower of another plant of the same species Ex. palm and maize
Fertilization– After the pollen coms on a suitable stigma, it has to reach the female germ-cells which are in the ovary. For this, a tube grows out of the pollen grain and travels through the style to reach the ovary.
- Each pollen grain forms a small tube-like structure called a pollen tube which emerges through the germ pore.
- The pollen tube grows through the tissues of the stigma and style and finally enters the ovule through the micropyle.
- Here two types of fusion, syngamy and triple fusion take place in an embryo sac, the process is termed double fertilization. After triple fusion, the triploid primary endosperm cell develops into an endosperm.
- It Gives stimulus for the growth of the ovary, leading to fruit formation.
After fertilization– Events found are the development of endosperm and embryo and maturation of the ovule into seed and ovary into a fruit. i.e. ovule makes seed and ovary make fruits.
The seed contains the future plant or embryo which develops as a seedling under appropriate conditions and the process is known as germination
***Tissue culture– In tissue culture, new plants are grown by removing tissue or separating cells from the growing tip of a plant. These cells get placed in an artificial medium where they divide rapidly to form a small group of cells or callus. Then the callus is transferred to another medium containing hormones for growth and differentiation. The plantlets are then placed in the soil so that they can grow into mature plants.
*** You can also read- reproduction in human beings in detail.