What is the main cause of variations among organisms during sexual reproduction?

Which of the following organisms does not reproduce by binary fission?

Name two simple organisms having the ability of regeneration.

Which of the following statements are true for flowers?
$(i)$ Flowers are always bisexual
$(ii)$ They are the sexual reproductive organs
$(iii)$ They are produced in all groups of plants
$(iv)$ After fertilization they give rise to fruits

Which of the following is the correct sequence of events of sexual reproduction in a flower?

The spherical bacteria of the species $Neisseria$ $gonorrhoeae$ are responsible for which sexually transmitted disease in humans?