movement is also a possible answer for the question, why is behavior is better answer ?
as there are no contrasting words, the idea before the comma must match the idea after it, physical form and cellular organization are both hinting towards shape or construction of a thing (hence , structure works for blank(i)) and as idea before comma is same as idea after the comma we’re reusing the word function in blank(ii).
Also, there are no words in the question that is pointing towards movement .