Which of the following organisms reproduces only once in its lifetime?

What is the viability period of pollen grains in members of the families $Rosaceae$,$Leguminosae$,and $Solanaceae$?

Which of the following plants produces both chasmogamous and cleistogamous flowers?

Choose the correct options for the following statements:
$1$. Autogamy is genetically xenogamy.
$2$. Pollination occurs by air in grass.
$3$. Placenta is arranged in the inner wall of the ovary.
$4$. It is possible to store pollen grains in liquid nitrogen at $-196^oC$.

Provide information about pre-fertilization structures and events in flowering plants.

Bisexual flowers which never open,demonstrate