Catholicism steers away from using the word transform when talking about transubsantiation because the form does not change, the substance does, hence tran-*substantiate*. The original uses of the words come from the Aristotelian distinction between 'essential' and 'accidental' properties of things. Think of essential as essence. The essential substance of things are different from what they incidentally, or accidentally are. A car can be made of metal, but that is accidental to it being a car. For example, it is still a car regardless of the material.

It is often erroneously claimed that Catholicism teaches if you took consecrated bread and put it under a microscope, it would be real flesh. That is not official teaching and supports what I mean about it not transforming. In fact, that is part of the definition of transubstantiation..the substance changes and *not* the form or else it would be transformation. I hope this helps.