** The period from birth to the natural death of an organism is called life span.
**Life span vary from few days to thousand years.
**Life span of an organism does not related with their sizes.Example:Size of crow and parrot are nearly same but their life span show wide differences.
**Life span of some organisms:
Elephant : 65years
Dog : 20-30 years
Cow. : 20-25 years
Horse : 25-39 years
Crow : 15 years
Parrot. : 140 years
Fruitfly : 1 month
Butterfly. : 1-2 weeks
Tortoise : 100-150 years
Crocodile : 60 years
Rose. : 5-7 years
Banana. :25 years
Banyan. : 300-500 years
Rice. :6 months
Reproduction
**A biological process in which an organism give rise to young ones (offspring) similar to itself.
**There is a cycle of grow, mature and death.
**It enables the continuity of the species ,generation after generation.
**There are two ways of reproduction:
1)Sexual(2parents participate;fusion of male and female gametes occur)
2) Asexual( single parent;no fusion of gametes)
Asexual
Clone: Morphological and genetically similar individuals.
**Asexual reproduction is common among single celled organisms, in plants and animals with relatively simple organization.
**In Monera and protista , parent cell divides into 2 individuals(Cell division is itself a mode of organization).
**In Amoeba and paramecium via. binary fission.
. fig:. Amoeba (binary fission)
In yeast via.budding(unequal division
In fungi and simple plants via. Special asexual reproductive structures like Zoospores(microscopic motile structure)
Fig : Chlamydomonas zoospores
Other Common asexual structures are: Conidia (Penicillium)
. Fig:. Penicillium (Conidia)
Buds
. Fig:. Budding in Hydra
Gemmules
. Fig: Gemmule(in sponge)
In plants,term vegetative reproduction most commonly used instead of asexual reproduction.Unit of vegetative structures are: runner, rhizome (Banana and ginger),sucker, offset,bulb,adventitious buds(Bryophullum).
Fig: Bulbil of Agave
. Fig: Rhizome of ginger
Terror of Bengal: Scourage of water bodies.A plant called as '
Water Hyacinth' growing very fastly
vegetatively in
standing water and
drains oxygen from it which leads death of fishes.It is introduced in India due to its
beautiful flowers and shapes of leaves.It grows such a faster rate cause very difficulty to get rid off from it.
**Eyes of potato is their bud.
**When nodes come in contact with damp soil or water,it produce new plants.
Sexual
**Elaborate,complex and slow.
Juvenile phase: Period of growth.Called as vegetative phase in plants.
**Bamboo species flower only once in their life time;generally after 50 -100years ,produce large number of fruits and die.
**Strobilanthus kunthiana (neelakuranji) flower once in 12 years.Its mass flowering turned large tracks of hilly areas in Kerala, Karnataka and Tamil Nadu into blue stretches.
**Birds in nature lay eggs seasonally but in captivity (in poultry farms) lay eggs throughout the year.In case of poultry,layying egges is not related with reproduction but it is a commercial exploitation for human welfare.
**The females of placental mammals exhibit cyclic changes in ovary and accessory ducts as well as hormones during reproductive phase.In non-primate like sheep,cows,rats,deers, dogs,tiger etc.cycle is called oestrus cycle .While in primates like monkeys,apes and humans cycle is called menstrual cycle.
**Seasonal breeders: Cycle only during favourable seasons in their reproductive phase.
Continuous breedees : Reproductively active throughout the reproductive phase.
*End of the reproductive phase is a parameter of old age /senescence . Old age ultimates death.
Events in Sexual reproduction:
1)Pre fertilization events
2) fertilization
3)post fertilization events
Pre fertilization events
All the events of sexual reproduction prior to the fusion of gametes.Two main pre -fertilization events are:Gametogenesis and Gamete transfer.
Gametogenesis : It is the process of formation of two types of gametes-male and female.Gametes are haploid in nature.
Isogametes: Also called homogametes. Male and female gametes are similar in appearance;not possible to categorise into male and female gametes.
Heterogametes: Male and female gametes are lu distinct/differentiated .Male gamete is called antherozoid/sperm and female gamete is called egg/ovum.
Monoecious/Homothallic : male and female are present in same organism. Term used in plants and fungi.In animals, term used is bisexual. Example: Cucurbits,Coconut ,Chara,Earthworm,Tapeworm,Leech,Sponge.
Dioecious/Heterothallic: Male and female are present in different condition.In animals ,term used is unisexual. Example:papaya ,Date palm, Cockroach.
**In flowering plants,unisexual male flower is staminate while unisexual female flower is pistillate.
Cell division during gamete formation:
Gametes are of two types in all heterogametic species ; male and female.
Gametes are halpoid though plant body from which they arise may be either haloid or diploid .
* A haploid parent produces gametes by mitotic division. Organisms belonging to Monera,fungi , algae and bryophytes have haploid plant body.
*
A diploid parent produces gametes by meiosis (reductional division). Organisms belonging to pteridophytes, gymnosperms, angiosperms and most of the animlas have diploid parent body.In these organisms, specialised cells called
meiocytes undergo meiosis.
Gamete transfer : It is the process of physically bringing together of male and female gametes after the formation.
**In majority , male gamete is motile and female gamete is stationery. Exception- few fungi and algae,both gametes are motile.
** In several simple plants like algae, bryophytes and pteridophytes ,water is the medium through which gamete transfer takes place.A large number of gametes fail to reach the female gametes .Hence ,to compensate this loss, number of male gametes produces is several thousand times higher than number of female gametes produced .
** In seed plants,pollen grains are the carrier of male gametes and ovule have the egg.Pollen grains transferred from the anther to stigma by various means called pollination in cross fertilization but in self fertilization there is no need of pollination.
Fertilization
The process of fusion of gametes is called syngamy. Syngamy results the formation of zygote. The term fertilization is often used for this process.
However, the term fertilization and syngamy are frequently used interchangeably.
** In some organisms like rotifers , honeybees 🐝, and even some lizards 🦎 and birds (turkey) ,the female undergoes development to form new organisms without fertilization.The phenomenon is called parthenogenesis.
** Fertilization occur via two ways : outside the body (external ) and inside the body (internal ).
Post fertilization events
Events in the sexual reproduction after the formation of zygote are called post fertilization events.
Zygote : Zygote is the vital link that ensures continuity of species between organisms of one generation and the next.
** Every sexually reproducing organism including human beings begin life as a single cell called zygote.
** Zygote us formed in the external medium (water) in external fertilizing organism and inside the body in internal fertilizing organism.
Embryogenesis: It is the process of development of embryo from the zygote.
During embrogenesis ,zygote undergoes cell division and cell differentiation. Cell division increase the number of cells in the developing embryo and cell differentiation helps group of cells to undergo certain modifications to form specialized tissues and organs to form an organism.
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