In order to answer why the cell would need aquaporins when the plasma membrane is permeable to water, we need to understand the make-up of water and the cell membrane. The water molecule is polar with its H+ and OH- ions. Cell membranes are selectively permeable.
Anatomy of the Auricle. The auricle or pinna is a relatively large appendage on the side of the head. It is prominent in most people and plays a very important role in hearing â it directs sound waves into the ear canal. The auricle is composed of cartilage which is covered by skin.
Collagen and Cartilage. Cartilage is a rather firm rubber material that covers the extremities of bones in normal joints. The primary function of cartilage is to reduce joint friction and, since cartilage can change shape when compressed, serve as a shock absorber for the bones.