Reproduction

Reproduction :- Reproduction is the biological process by which organisms give birth or give rise to a new organism. This process is seen in all living organisms- both plants  and   animals.

Types of Reproduction :- Basically there are two types in Reproduction :-

1)Asexual reproduction :- Asexual reproduction involves a single parent. It results in offspring that are genetically identical to each other and to the parent. All prokaryotes and

some eukaryotes reproduce this way. There are several different methods of asexual reproduction. They include binary fission, fragmentation, and

budding.

* Budding:- Budding occurs when a parent cell forms a bubble-like bud. The bud stays attached to the parent cell while it grows and develops. When the bud is fully developed, it breaks away from the parent cell and forms a new organism.

* Binary fission :- Binary fission occurs when a parent cell splits into two identical daughter cells of the same size.

* Multiple fission :- Multiple fission is the process of asexual reproduction  in which instead of 2 daughter cells, many daughter cells are produced from the parent cell. In this, the nucleus undergoes repeated division to produce a large number of nuclei. Each nucleus along with little bit of cytoplasm forms a membrane around it.

* Fragmentation :- It is a form of asexual reproduction in which an organism split fragments.

* Regeneration :- The process of developing lost parts of an organism is called Regeneration.

* Parthenogenesis :- reproduction from an ovum without fertilization, especially as a normal process in some invertebrates and lower plants.

* Vegetative Propagation :- producing new plants from vegetative parts of old plant with human interface.

E.g :- 1)Sweet potato,

           2)Banana,

           3)Bryophyllum, etc

* Spore formation :- This involves the development and propagation of spores which give rise to a new organism. 

E.g :- fungi

Types of Artificial propagation :- 

1)Grafting :- Grafting is an  artificial  method of asexual reproduction used to produce plants combining favorable stem characteristics with favorable root characteristics. The stem of the plant to be grafted is known as the scion, and the root is called the stock.

2)Cutting :- Cutting is removing a portion of the stem and fixing it in the soil to allow the growth of roots and buds growing into shoots.

3)Layering :- Layering is a means of plant propagation in which a portion of an above-ground stem grows roots while still attached to the parent plant and then detaches as an independent plant. Layering has evolved as a common means ofvegetative propagation of numerous species in natural environments.

4)Tissue Culture :- Using tissue culture, sometimes called micropropagation, tiny fragments of plants are treated with plant hormones in a sterile growing medium. The hormones stimulate the growth of a callus, from which a new seedling can grow. This method is used to produce large numbers of identical seedlings.

Sexual Reproduction :- Sexual reproduction is a type of reproduction that involves the production of an offspring by the fusion of male and female gametes.In Sexual Reproduction, male and female gametes are formed to produce an offspring. These gametes are either formed by the same individual or by different individuals of the opposite sex.

This process is usually slow and complex compared to asexual reproduction. The organisms so produced are genetically diverse. Thus, they can evolve along with the changing climatic conditions. Humans and many multicellular organisms exhibit a sexual mode of reproduction.

Reproduction in plants :- Plants reproduce by sexual and asexual means. Vegetative reproduction is the main mode of plant reproduction. Roots such as a corm, stem tuber, rhizomes and stolon undergo vegetative propagation.

Sexual reproduction in plants takes place through pollination in which the pollen grains from the anther of a male flower transfer to the stigma of the female flower. 

Few plants produce seeds without fertilization and the process is called apomixis. Here, the ovule or the ovary gives rise to new seeds.

The reproductive parts of plants are flowers, Stamen being male reproductive part and pistil being the female reproductive part. If one of these reproductive parts are present in a flower, it is said to be a unisexual flower. Example: papaya. If both Stamen and Pistil are present in flowers they are called bisexual flowers. Example: rose.

Pollen grains form the male gametes. The pistil consists of style, stigma, and the Ovary. The ovary consists of one or more ovules. Ovules are where female gametes or the egg is formed. Female and male gametes fuse to form a zygote.

Pollination

When pollen is transferred from the anther to the stigma of a flower through carriers such as insects it is called pollination. It can be a case of self-pollination if pollen lands on the stigma of the same flower or another flower of the same plant. If pollen grains land on the stigma of a flower of a different plant, but of the same kind, it is called cross-pollination.

Fertilization

A zygote is formed as a result of the fusion of gametes which later develops into the embryo. Fruits and seeds are formed post-fertilization. Ripened ovary goes on to become a fruit. Ovules give rise to seeds which contain the embryo in a protective covering.

Reproduction in animals :- 

The process in which the male and female gametes fuse together to form a new individual is called sexual reproduction. Let us have a brief account of the human reproductive organs and their role in reproduction.

Reptoductive Organs :-

 The male reproductive organs comprise a pair of testes, sperm ducts, and a penis. The sperms are produced by the testes. The sperms are very small in size with a head, a middle piece, and a tail.

The female reproductive system comprise a pair of ovaries, oviducts, and the uterus. The eggs (ova) are produced by the ovaries. The development of the baby takes place in the uterus. A mature egg is released into the oviduct every month.

Process of Sexual Reproduction in Animals

Fertilization :-

 The semen contains millions of sperms. A single sperm fuses with the ova during fertilization. The nuclei of the egg and the sperm fuse together to form a single nucleus. Thus, a zygote is formed.

Fertilization is of two types:

• Internal Fertilization

The fertilization that takes place inside the body of the female is known as internal fertilization. For eg., humans, cows, dogs, etc. This method is more prevalent in terrestrial animals. However, some aquatic animals also adopt this method. This may take place by direct introduction of sperms by the male in the female reproductive tract, or the male deposits the sperms in the environment which is picked up by the female in her reproductive tract.

They are three ways by which offsprings are produced by internal fertilization:

1. Oviparity– The fertilized eggs are laid outside, where they receive nourishment from the yolk.

2. Ovoviviparity– The fertilized eggs are retained in the female’s body where they receive nourishment from the yolk. The eggs are laid right before they are hatched.

3. Viviparity– The offsprings are born directly instead of hatching from the eggs. They receive nutrition from the mother. This can be seen in mammals.

• External Fertilization

The fertilization that takes place outside the female is called external fertilization. For eg., frogs, fish. Most fertilization takes place during the process of spawning. The environmental signals such as water temperature trigger spawning.

Embryo Development

The zygote divides repeatedly to form a ball of cells. This is known as the developing embryo. These cells differentiate into respective tissues and organs. The embryo gets implanted in the uterine wall. This process is known as implantation.

When all the body parts of the embryo start being visible, it is called a foetus. The child is developed after nine months in humans.

Viviparous and Oviparous Animals

Oviparous and viviparous animals are two different groups of animals, which are classified on the basis of fertilization. The main difference between oviparous and viviparous animals are listed below:

Oviparous	Viviparous
Meaning
Egg-laying animals	Animals that give birth to the young ones
Fertilization
Either internal or external	Fertilization is internal
Nutrients to the developing embryo
Provided by the egg yolk	Provided by the mother through the placenta
Development of zygote
There is very little or no development of the embryo inside the mother.	The embryo develops entirely inside the mother.
Survival chances
There are fewer chances of survival since the eggs are laid outside the body	The young one is protected inside the mother and so the chances of survival are more.
Examples
Insects, hens, fish, amphibians.	Humans, dogs, cats, horses, etc.