There are two main methods of reproduction - sexual and asexual.
First we will go over asexual methods of reproduction in different organisms and then we will explore the process of sexual reproduction and fertilisation in human beings.
The main difference between sexual and asexual reproduction is ofcourse- that only one parent is needed in asexual reproduction, whereas in sexual reproduction a female and male parent is needed.
All information about an organism's internal and external structure is stored in the chromosomes.
A chromosome is a long DNA molecule.
DNA - Deoxyribo Nucleic acid carries genetic instructions for the development, functioning and reproduction of all living organisms.
Whether reproduction is sexual or asexual, it will involve replication/ splitting up of DNA.
Below you can see a diagramatic representation of DNA.
A sequence of DNA's is known as a gene. Chromosomes can cotain hundreds of genes.
Genes contain the code to create protiens.
These protiens then lead to formation of a single cell which then further divides into a group of cells.
A group of specialised cells is called a tissue.
And finally tisues combine to form organs.
You are already familiar with the process of binary fission in amoeba. Many bacteria and protozoa simply split into equal halves during binary fission.
Below you can the process of fission in an organism called Leishmania. In leishmania, the fission occurs vertically.
In multicellular organisms, with simple body structures simple reproductive methods work.
In organisms like planaria, reproduction involves generating a full new organism through its own body parts.
Planaria can split itself in many pieces. Each of these pieces then develop into seperate individuals.
In organisms like Hydra, reproduction takes place through a process called budding.
In budding, hydra makes use of regenerative cells. The process begins with the formation of a bud/outgrowth at a specific site.
This outgrowth is formed due to repeated cell division.
This bud then develops into tiny individuals and then detach from the parent body once they are fully matured.
In plants, reproduction can be sexual or asexual.
There are two main forms of asexual reprduction- vegetative reproduction or apomixis.
In vegetative reproduction new plants are formed without the production of seeds or spores.
Methods like grafting, layering and micropropogation are some of the methods used for artifical asexual reproduction in plants.
Fungis like rhizopus reproduce through spores.