The entry of pollen tube in the embryo sac is guided by:

The correct answer is Option (3) → Synergids through filiform apparatus

Option (1) Pollen pistil interaction — Incorrect. Pollen–pistil interaction takes place on the stigma and style: the pistil recognises compatible pollen and lets its tube grow. Inside the ovule, the entry of the tube into the embryo sac is guided by the filiform apparatus of the synergids.

Option (2) Presence of germ pores — Incorrect. Germ pores let the pollen tube out of the pollen grain.

Option (3) Synergids through filiform apparatus — Correct. The synergids have special cellular thickenings at the micropylar tip called the filiform apparatus. It plays an important role in guiding the pollen tube into the synergid of the embryo sac.

Option (4) Interaction between the chemical components of the pollen and pistil — Incorrect. The chemical interaction between pollen and pistil is the pollen–pistil interaction, which decides acceptance on the stigma. It does not guide the tube into the synergid; the filiform apparatus does.

NCERT Extract:
Pollination – “… Pollen tube, after reaching the ovary, enters the ovule through the micropyle and then enters one of the synergids through the filiform apparatus (Figure 1.12d, e). Many recent studies have shown that filiform apparatus present at the micropylar part of the synergids guides the entry of pollen tube.”