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.

the abdomen (less formally called the belly, stomach, tummy or midriff) constitutes the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. the region occupied by the abdomen is termed the abdominal cavity. the stomach secretes acid and enzymes that digest food. ridges of muscle tissue called rugae line the stomach. the stomach muscles contract periodically, churning food to enhance digestion. the pyloric sphincter is a muscular valve that opens to allow food to pass from the stomach to the small intestine.