Yes, the reaction can be catalyzed using a base because no group needs to leave after the nucleophile attack.

No, the reaction can not be catalyzed using a base because aldehydes or ketones are sensitive toward bases.

Yes, the reaction can be catalyzed using a base because the mechanism starts with the deprotonation of the aldehyde or ketone.

No, the reaction can not be catalyzed using a base because the mechanism must start with the protonation of the carbonyl carbon.