Final answer:
Muscle tissues under a microscope would show hypertrophy and increased mitochondria and myoglobin in active individuals, while sedentary individuals' muscles might exhibit atrophy. Skeletal muscle can be distinguished by striations and multiple nuclei per fiber.
Step-by-step explanation:
If you were to look under a microscope at muscle tissue from an active versus a sedentary individual, you would likely observe several adaptations. In an active individual, the muscle fibers might show evidence of hypertrophy, an increase in cell diameter due to the addition of structural proteins.
These muscles often contain more mitochondria and have higher levels of myoglobin, especially in muscles used for endurance exercise. Myoglobin enhances oxygen delivery within the muscle, supporting sustained aerobic activity.
Conversely, in a sedentary individual, you might see signs of atrophy, where muscle fibers have reduced in size due to the loss of structural proteins. The quantity of mitochondria and myoglobin may also be lower, reflecting decreased demands for aerobic respiration and energy production.
Additionally, under the microscope, skeletal muscle can be distinguished from smooth muscle by the presence of striations, which are regular patterns created by the arrangement of actin and myosin proteins. Skeletal muscle fibers are also typically multinucleated, whereas smooth muscle cells have a single nucleus and lack striations.