Final answer:
The characteristic present in both skeletal and cardiac muscle but not in smooth muscle is striations. Additionally, cardiac muscle uniquely features intercalated discs, while smooth muscle has no striations and a single nucleus with a tapered shape.
Step-by-step explanation:
The characteristic of skeletal and cardiac muscle, but not smooth muscle, is the presence of striations. Both skeletal muscle cells and cardiac muscle cells have these striations due to the highly organized arrangement of contractile proteins, actin and myosin, within the cells. Additionally, both these types have sarcomeres with a banding pattern visible under a microscope. Smooth muscle, however, lacks these striations and has a more uniform appearance. Furthermore, cardiac muscle cells are unique in that they have intercalated discs, specialized structures not found in skeletal or smooth muscles, that facilitate electrical impulse conduction between cells, enabling the heart to contract efficiently.
While skeletal muscle cells are multinucleated and have their nuclei situated peripherally, cardiac muscle cells typically have a single, centrally located nucleus. Smooth muscle cells also have a single nucleus but differ in being non-striated and tapering at the ends. All muscle types have mitochondria, and thus, this is not a differentiating feature. Therefore, the correct answer to the question, 'Which of the following is a characteristic of skeletal and cardiac muscle, but not smooth muscle?' is option 3) Striations.