Class- 12th Biology, Chapter-1, Reproduction in organism, Lecture-1

Lifespan  - Each and every organism can live only for a certain period of time.The period from birth to the natural death of an organism represents its life span. It may vary from a day to thousand's of years.

Life span of few organisms are as follows:- 

Elephant 75 years

Rose 10 years

Dog 15 to 20 years

Butterfly 1 to 2 weeks

Crow 15 years

Banana tree 25 years

Cow 25 years

Parrot 140 years

Crocodile 60 years

Horse 50 years

Fruit fly one month

Rice plant 4 months

Tortoise 100 to 150 years

Banyan tree 300 to 500 years

Mayfly one day (shortest lifespan)

# lifespan of organisms are not necessarily correlated with their sizes.

example -the sizes of crows and parrots are not very different yet their lifespan shows a wide difference.

#Whatever be the lifespan,  death of every individual organism is a certainty, i.e. no individual is immortal except single celled organisms.

#In single celled organisms death does not occur because their single celled body divides by binary fission producing two identical daughter individual. Here no dead body is found so they are considered as immortal.

Phases of lifespan

1. Juvenile phase - It is the pre-reproductive phase during which only vegetative growth takes place.

2. Reproductive phase - During this phase the reproductive organs develop and become function.

3. Aging or senescence- This phase is characterized by gradual deterioration of vital capacity is the terminal stage of ageing before death is called senescence.

4. Death- It is the end of life of an organism.