Through which cell of the embryo sac does the pollen tube enter the embryo sac?

What does the filiform apparatus do at the entrance into the ovule?

$A$: Filiform apparatus guides the pollen tube into the synergids.
$R$: It is a special cellular thickening at the micropylar tip to secrete chemotropic stimulus.

Which one of the following is not associated with pollen-pistil interaction?

Name the part of the gynoecium that determines the compatible nature of the pollen grain.

The compatibility and incompatibility of the pollen-pistil interaction is determined by