Final answer:
Two biological structures with rotating parts are ATP synthase and bacterial flagella (A), with ATP synthase involved in energy production and bacterial flagella functioning in mobility.
Step-by-step explanation:
Two types of biological structures that contain rotating parts are ATP synthase and bacterial flagella. ATP synthase is a complex enzyme that plays a critical role in the production of ATP (adenosine triphosphate), the energy currency of the cell. It is found in the inner membrane of mitochondria and is composed of the Fo and F1 subunits. The Fo portion is embedded in the membrane, while the F1 portion protrudes into the mitochondrial matrix. The F1 portion, which includes a rotating element, is essential for the synthesis of ATP as it undergoes conformational changes during rotation.
Similarly, bacterial flagella are composed of the protein flagellin and are attached to a rotary motor in the cell membrane. This motor spins the flagellum, allowing bacteria to move through liquid environments. Unlike eukaryotic flagella, which move by bending, bacterial flagella rotate like a propeller.
Thus, both ATP synthase and bacterial flagella showcase the fascinating capacity for rotational movement in biological structures, so the answer is A.