Q Louis Sullivan described architectural design as “form follows function.” For example, a window is designed to add light to a space without heat transport. A door is designed to allow access to a space. Windows and doors have different functions and so take different forms. Biological systems are not designed, but selected from random trials by interaction with the environment. Apply Sullivan’s principle to explain the relationship of function and form for each pair of cellular structures below. 1. Plasma membrane and endoplasmic reticulum 2. Mitochondrion and chloroplast 3. Rough endoplasmic reticulum and smooth endoplasmic reticulum 4. Flagella and cilia 5. Muscle cells and secretory cells