it separates the inside of the cell from the environment outside and it controls substances moving in and out of the cell (selectively permeable)
The type of joint that allows bones to move backward and forward in only one direction is the hinge joints. Ball and socket are the joints that allows movement in all directions. Gilding joints are type of joints that are the vertebral disks that allow twisting, turning, and sliding. Hinge joints are formed between two or more bones where the bones can only move along one axis to flex or extend. They include the ankle, elbow and knee joints.
<span>Simply because cells need both these types of molecules for proper function.</span>
