Ionization of Zinc in galvanic cells

[B4ssHunter]

what exactly ionizes zinc in the galvanic cell or the daniell cell ?
i mean zinc atoms in the galvanic cell are ionized into Zn ++ and 2 e- .
then the electrons move through the conductor to the copper bar , my question is why does zinc ionize when connected in a battery ? when the circuit is turned off , the ionization stops , why's that ?

 

[Borek]

What happens in the other half cell?

 

[B4ssHunter]

it is forced to be reduced i suppose

 

[Borek]

So there is a charge transfer between both half cells?