Take on and Take part

Take on verb - To enter into contest or conflict with.

Take part and take on are semantically related In some cases you can use "Take part" instead a verb "Take on".

Take part verb - Share in something.

Take on and take part are semantically related in play topic. Sometimes you can use "Take on" instead a verb phrase "Take part", if it concerns topics such as compete in sport, go up against in contest.