The words underlined above are the main variables of the experiment, the factors that changed. Label them below: • Magnification is the variable. • The cell organelles seen is the variable.

Abird flies by moving its wings up and down. which two systems are most directly responsible for the movement of a bird's wings? a. skeletal and muscular systems b. respiratory and muscular systems c. skeletal and digestive systems d. respiratory and digestive systems