The introductory three-word phrase "And now for..." is often used as an idiomatic, attention-grabbing expression to alert the audience that something significant about to happen.
For example, toward the conclusion of his act, a magician might say:
"And now for my final trick..."
The comedy troupe Monty Python would often interject:
"And now for something completely different."
as an transition between sketches; they even used that quote as a title for a compilation film.
One could argue that the for could often be omitted, but that might require a comma in the written version, or perhaps a brief pause in the spoken version:
"And now, my conclusion..." (vs. "And now for my conclusion...")
Sure, the speaker's sentence could be rearranged and shortened some:
Now, the coolest part of the animal cell (totally objectively speaking, of course) is its power plants.
but you've asked enough questions about these videos to know that speakers don't always word things in the most succinct way when speaking off-the-cuff.