The male reproductive organ of a flower consists of:

Assertion: If pollen mother cells have $42$ chromosomes,the pollen has only $21$ chromosomes.
Reason: Pollens are formed after meiosis in pollen mother cells.

Given below are two statements.
Statement $I$: Generally,anthers in angiosperms are dithecous,having two pollen sacs in each lobe.
Statement $II$: Each sporangium produces pollens from sporogenous tissues by the process of sporogenesis.
In light of the above statements,select the correct answer from the options given below.

In angiosperms,the wall surrounding all four microspores of a microspore tetrad is made up of which substance?

How many pollen mother cells are involved in the formation of $8$ pollen tetrads?

Draw the diagram of a microsporangium and label its wall layers. Write briefly about the wall layers.