Take on means you are about to start something or challenge someone. "I'm about to take on this video game boss." Take over means you are replacing someone or something. "I'll take over driver duties at the next service station." Take over also means to conquer. "I'm going to take over the world!"

Hmm, they're slightly different. To take over is to start doing what someone else was doing e.g. '''My brother took over the cooking as i went to the store'', and to take on is to usually accept responsibility of something e.g. '' I can't take on any more work today''. However, it can have more meanings such as employing someone ( we can't take on anymore staff) or fighting/ competing against someone ( Italy will be taking on France for tonight's football match) Hope that helped ^^