In angiosperms,two non-motile male gametes are produced by the division of the:

In a microsporangium,which layer is generally having more than one nucleus?

The microsporangium of gymnosperms is homologous to which part of angiosperms?

Which is an incorrect statement?
$I$. Each cell of sporogenous tissue in anther is capable of giving rise to a microspore tetrad.
$II$. The pollen grain represents the male gametophyte.
$III$. Pollen grains are usually triangular and $10-15 \mu m$ in diameter.
$IV$. Sporopollenin is one of the most resistant organic materials,which can be destroyed only by strong acids and alkalis.

Pollen grains are generally . . . . . . in outline measuring . . . . . . micrometers in diameter.

How many microsporangia are present in a typical angiosperm anther?