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.
in the table the elements are placed in the order of their atomic numbers starting with the lowest number the atomic number of an element is the same as the number of electrons or protons in that particular atom in the periodic table the elements are arranged into periods and groupsa row of elements across the table is called a period each period has a number from 1 to 7period 1 has only 2 elements in it hydrogen and helium period 2 and period 3 both have 8 elementsn the table the elements are placed in the order of their atomic numbers starting with the lowest number the atomic number of an element is the same as the number of electrons or protons in that particular atom in the periodic table the elements are arranged into periods and groups