Final answer:
Statement 4, that single-unit smooth muscle is composed of individual cells, is NOT true because these cells are interconnected by gap junctions, allowing them to contract as a single unit.
Step-by-step explanation:
The question asks which statement is NOT true of single-unit smooth muscle. The options list several features of single-unit smooth muscle, and the correct answer will be the one that does not accurately describe this type of muscle. Single-unit smooth muscle is indeed found in the walls of hollow organs such as the intestines, stomach, and urinary bladder (1), contracts involuntarily (2), and is controlled by the autonomic nervous system (3). However, the statement that it is composed of individual cells (4) is not true in the sense that these cells are not independent; they are joined by gap junctions and contract as a coordinated unit. Therefore, option 4 is the statement that is NOT true of single-unit smooth muscle.