Where the appropriate word size is selected for the operand?
It's worse than that.  the 16 bits from memory may be aligned across two memory rows meaning that two reads are performed 

exactly what happens depends on which 32 bit processor you are considering.  80386 doesn't have cache and, so would just discard the unwanted bits, more modern CPUs will cache the fetched data, so the mov instruction may cause 0,1,or 2 memory read cycles depending on cache hits and alignment.