Final answer:
Red blood cells are flat discs for easy movement, nerve cells are long for communication, and muscle cells have different shapes for their specific functions.
Step-by-step explanation:
Red blood cells (RBC) are flat discs that can easily move through blood vessels and deliver oxygen throughout the body. Nerve cells are long and stringy, allowing them to form a communication network with other cells. Muscle cells have different shapes based on their type - skeletal muscle cells are long and cylindrical, cardiac muscle cells are striated with intercalated disks, and smooth muscle cells are spindle-shaped. These shapes are specifically adapted to perform the unique functions of each cell type.