It is needed by all living things and every living cell to carry out life processes, such as breaking down and building up molecules, and transporting many molecules across cell membranes. The form of energy that living things need for these processes is chemical energy, and it comes from food.
Answer:
(a) Allow movement in only one plane/direction (that is extension or flexion)
(b) The skeletal system also produces blood cells in their bone marrow
C.75 of the cell's mass is water