Which disease is caused by the bacterium $Treponema$ $pallidum$?

Describe sexually transmitted diseases (STDs) and mention the ways to prevent them.

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

Leaves of $Bryophyllum$ fallen on the ground produce new plants. Why?

Offspring formed as a result of sexual reproduction exhibit more variations because

In human females,an event that reflects the onset of the reproductive phase is: