Share. By Regina Bailey. Definition: The cell membrane is a thin semi-permeable membrane that surrounds the cytoplasm of a cell, enclosing its contents. Its function is to protect the integrity of the interior of the cell by allowing certain substances into the cell, while keeping other substances out.t also serves as a base of attachment for the cytoskeleton in some organisms and the cell wall in others. Thus the cell membrane also serves to help support the cell and help maintain its shape. The cell membrane is primarily composed of a mix of proteins and lipids.
Continued from page 1. Periods and Groups. Elements in the periodic table are arranged in periods (rows) and groups (columns). Atomic number increases as you move across a row or period. Periods. Rows of elements are called periods. The period number of an element signifies the highest unexcited energy level for an electron in that element.
Well usually elements in a periodic table are arranged into groups based on a set of repeating properties. However, Mendeleev arranged the elements in his periodic table in â¦ order of increasing atomic mass. Mendeleev arranged the elements in the increasing order of atomic masses and repeating periodic properties.They were arranged by the element's atomic mass. (lowest to highest) He arranged the elements in the increasing order of their atomic masses and repeating periodic properties.+ 31 others found this useful.mitri Mendeleev discovered scandium, gallium, technetium, and  germanium. He also predicted the existence of more elements and  developed the modern periodic table.