Step 1: Understand the role of the micropyle.
The micropyle is a small opening in the ovule that the pollen tube enters. Sperm cells use this opening to reach and fertilize the egg cell within the embryo sac.
Step 2: Role of other components.
- Antipodal Cells: Located at the opposite end of the embryo sac, these cells do not direct pollen tube entry.
- Filiform apparatus: Found within synergid cells, this structure aids in guiding the pollen tube into the ovule but is not directly involved in its entry.
- Synergids: These cells attract the pollen tube, but their primary role in fertilization occurs after the pollen tube has entered.
Step 3: Conclusion.
The micropyle is the direct entry point for the pollen tube into the embryo sac.
Final Answer: \[\boxed{\text{The correct answer is Micropyle.}}\]