In Germany with little sister, occupied by ordinary division of cells (7)

'division of cells' is the definition.
'mitosis' can be an answer for 'division' (type of cell division). I am not sure about the 'of cells' bit.

'in germany with little sister occupied by ordinary' is the wordplay.
I cannot quite see how this works, but
'sister' could be 'sis' (synonyms) and 'sis' is present in the answer.
'ordinary' could be 'o' (abbreviation e.g. O-Levels) and 'o' is located in the answer.
The remaining letters 'mit' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?