Biology REPRODUCTION: INTRODUCTION

### KEY TOPICS

star Life Span
star Reproduction
star Modes of Reproduction

### LIFE SPAN

color{blue} ul(mathtt ("Life Span")) : The period from birth to the natural death of an organism is its life span.

color{green} ✍️ color{green} mathbf("KEY CONCEPT")

● Each and every organism can live only for a color{Violet}"certain period of time".

● The period from birth to the natural death of an organism represents its color{Violet}"life span".

● The life span of some organisms may be as short as a few days or as long as a few thousand years.

● Between these two extremes are the life spans of most other living organisms.

● The life spans of organisms are not necessarily color{Violet}"correlated with their sizes".

● E.g.: the sizes of crows and parrots are not very different yet their life spans show a wide difference.

● Also no individual is immortal, except single-celled organisms.

● Therefore, the processes in living organisms that color{Violet}"ensures their continuity" of their species in spite of their limited lifespan is reproduction.

### REPRODUCTION

color{blue} ul(mathtt ("Reproduction")) : Reproduction (procreation or breeding) is the biological process by which new individual organisms (offsprings) are produced from their parents.

color{green} ✍️ color{green} mathbf("KEY CONCEPT")

● Reproduction is defined as a biological process in which an organism gives rise to color{Violet}"young ones" (offspring) similar to itself.

● The offspring color{Violet}"grow, mature" and in turn produce color{Violet}"new offspring".

● Thus, there is a color{Violet}"cycle" of birth, growth and death.

● Reproduction enables the color{Violet}"continuity of the species", generation after generation.

● Reproduction is a color{Violet}"fundamental feature" of all known life (except infertile organisms); each individual organism exists as the result of reproduction.

### MODES OF REPRODUCTION

color{blue} ul(mathtt ("Asexual Reproduction")) : When offspring is produced by a single parent with or without the involvement of gamete formation, the reproduction is asexual.

color{blue} ul(mathtt ("Sexual Reproduction")) : When two parents (opposite sex) participate in the reproductive process and also involve fusion of male and female gametes( which contain half the number of chromosomes of normal cells and are created by meiosis) , it is called sexual reproduction.

color{green} ✍️ color{green} mathbf("KEY CONCEPT")

● There is a large diversity in the biological world leading to each organism evolving its own mechanism to multiply and produce offspring.

● The organism’s color{Violet}"habitat", its color{Violet}"internal physiology" and several other factors are collectively responsible for how it reproduces.

● Based on whether there is participation of one organism or two in the process of reproduction, it is of color{Violet}"two types".

● When offspring is produced by a single parent with or without the involvement of gamete formation, the reproduction is color{Violet}"asexual".

● By asexual reproduction, an organism creates a color{Violet}"genetically similar" or identical copy of itself.

● When two parents (color{Violet}"opposite sex") participate in the reproductive process and also involve fusion of color{Violet}"male and female gametes" (which contain half the number of chromosomes of normal cells and are created by meiosis) , it is called color{Violet}"sexual reproduction".

● Sexual Reproduction produces offspring whose genetic characteristics are derived from those of the two parental organisms and show color{Violet}"genetic and phenotypic variation" from their parents.