Diffusions through membranes for very big Hebrew leader (7)

I believe the answer is:

osmoses

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'diffusions' is the definition.
(I know this)

'membranes for very big hebrew leader' is the wordplay.
I cannot quite see how this works, but
'big' could be 'os' and 'os' is present in the answer.
'hebrew' could be 'moses' (Moses is an example) and 'moses' is present in the answer.
This accounts for all the letters.
This explanation may well be incorrect...

'through' acts as a link.

Can you help me to learn more?

(Another definition for osmoses that I've seen is " Causes change gradually".)

I've seen this clue in the Sydney Morning Herald.

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