$\displaystyle \small \bullet$ Reproduction is a biological process in which an organism gives rise to young ones (offspring) similar to its own kind.
$\displaystyle \small \bullet$ It enables the continuity of the species, generation after generation as older individuals undergo senescence and ultimately they die.
$\displaystyle \small \bullet$ Four basic processes of reproduction are- DNA replication, cell division, formation of reproductive units and development of new individuals.
$\displaystyle \small \bullet$ Lifespan: The period from birth to natural death of an organism is called lifespan.
$\displaystyle \small \bullet$ Life span of organisms varies from few days to thousands of years.
$\displaystyle \small \bullet$ The life span of an organism is not correlated with their body size.
$\displaystyle \small \bullet$ Every living organism, which takes birth, is certainly die at the end of its life span.
$\displaystyle \small \bullet$ Some unicellular organisms are immortal as they do not have natural death. In process of binary fission they lose their identity and become daughter cells. Ex: Amoeba, Euglena, Paramecium, etc.


Types of Reproduction
1. Asexual Reproduction
2. Sexual Reproduction

ASEXUAL REPRODUCTION
$\displaystyle \small \bullet$ Offsprings produced by single parent without involvement of gamete formation.
$\displaystyle \small \bullet$ Offsprings produced are genetically and morphologically similar to each other and to the parent, i.e. they are clones.
$\displaystyle \small \bullet$ Characteristics of Asexual reproduction
1. A single parent is involved in the reproduction.
2. Gametes are not formed.
3. No fertilization in the asexual reproduction.
4. There is no meiotic division and only mitotic division.
5. Daughter organisms are genetically similar to the parents.
6. Multiplication occurs rapidly.

Types of Asexual Reproduction
Fission: In this, the parent cell divides (cell division) into two or more individuals. Ex. Protists and Monerans.
Binary Fission: It is the division of parent cell into two individuals. Ex. Amoeba, Paramecium.
Multiple fission: It is the division of parent cell into many individuals. Ex. Plasmodium, Amoeba.
Budding: (torulation) An outgrowth or bud develops, grows, constricts at the base and separates from the parent body, e.g. yeast and Hydra. The complex budded condition is called torala stage.
Sporulation: Occurs by tiny, single-celled, thin-walled spores that are extremely resistant to environmental extremes. The spores form new individuals. It commonly occurs in Monera, Protista, Fungi and Algae. Ex. Zoospores are produced in Chlamydomonas. Conidia are produced in Penicillium.
Fragmentation: It is a form of asexual reproduction where an organism splits into fragments. Each of these fragments develops into mature fully grown individual followed by mitosis. It occurs in some algae (Spirogyra), fungi, some annelids and sea stars.
Gemmules: These are the asexual reproducing structure in sponges.
Conidia of Penicillium
Vegetative propagation:
 $\displaystyle \small \circ$ The process in which part of the plant body used to develop new individuals is called vegetative propagation.
 $\displaystyle \small \circ$ The fragment of the plant body function as propagule. The plant parts are capable of giving rise to new offsprings.
 $\displaystyle \small \circ$ Examples for vegetative propagules:  
 $\displaystyle \small \circ$ Buds (‘eyes’) of the potato tuber.
 $\displaystyle \small \circ$ Rhizomes of banana & ginger.
 $\displaystyle \small \circ$ Buds & Rhizomes arise from the nodes of modified stems.
 $\displaystyle \small \circ$ The nodes come in contact with damp soil or water and produce roots and new plants.
 $\displaystyle \small \circ$ Adventitious buds of Bryophyllum. They arise from the notches at margins of leaves.
 $\displaystyle \small \circ$ Bulbil of Agave.
 $\displaystyle \small \circ$ Offset of water hyacinth.
 $\displaystyle \small \circ$ Runner, sucker, tuber, bulb etc.
Water hyacinth: One of the most invasive weeds found growing wherever there is standing water. It drains oxygen from the water, which leads to the death of fishes. It is also referred to as ‘terror of Bengal’.
$\displaystyle \small \bullet$ Asexual reproduction is the common method in simple organisms like algae and fungi. During adverse conditions,they can shift to sexual method.
$\displaystyle \small \bullet$ Higher plants reproduce asexually (vegetative) & sexually. But most of the animals show only sexual reproduction.