To genetically transform an entire organism, you must insert the new gene into every cell in the organism. which organism is better suited for total genetic transformation—one composed of many cells, or one composed of a single cell?

The answer would be a single celled organism.

Explanation:

Even though transforming genetically any organism is not an easy task, as it requires the whole organism to be changed, it's more practical to do in a unicellular organism. For example, bacteria mutate very easily due to its ability to incorporate new genes by horizontal transfer. Anyway, unicellular organisms have mechanisms to avoid strange genetic material to get into their DNA, that's why scientists have to use such tools as vectors and more.

weathering is the answer.