Labelled diagram of the longitudinal section of a flower.

Various methods of contraception are in use. They are:a. Physical barriers: These methods provide a barrier to the fusion of gametes by physical means. Example: Condom.

Unicellular organisms have a simple cellular structure. They reproduce by simple methods of reproduction like binary fission, multiple fission, budding etc.

Every organism has a fix life span. They grow, mature and eventually die. If there is no reproduction organism will eventually die and the concerned species will become non-existent.