At which stage of pollen grain development are the male gametes formed?

If the cells of the root in a wheat plant have $42$ chromosomes,then the number of chromosomes in the cell of a pollen grain is:

Describe the location and function of the $Endothecium$ and $Tapetum$.

Pollen grains are generally spherical,measuring about

How many layers is the pollen grain wall composed of?

Arrange the following in the correct developmental sequence related to microsporogenesis:
$A$. Microspore tetrads
$B$. Sporogenous tissue
$C$. Pollen grains
$D$. Pollen mother cells
Choose the correct answer from the options given below: