Aprotein channel is a transport protein that a. always moves substances against a concentration gradient. b. pumps ions out of a cell. c. serves as a tunnel for specific substances. d. always requires energy from the cell.

Which statement best explains why cells were observed in more detail using a compound microscope than a simple microscope? a compound microscope has greater magnification ability than a simple microscope. the compound microscope was invented before the simple microscope. a compound microscope is much easier to manufacture than a simple microscope. compound microscopes were more common than simple microscopes.