The cell membrane is a double membrane made of that have their water-soluble heads facing the interior and exterior of the cell.

Phospholipids.

Explanation:

Phospholipids are the lipids that have both polar and nonpolar components in their structure. They have a glycerol molecule to which a phosphate group is bonded. This makes their polar head. Two fatty acid chains are also linked to the glycerol of phospholipids which in turn make their nonpolar tails. The membranes have two layers of phospholipids. The polar heads of the two layers face the surroundings watery medium. On the other hand, the non-polar tails of phospholipids of a bilayer are oriented towards the inner core of the membrane.

primary succession occurs in essentially lifeless areas regions in which the soil is incapable of sustaining life as a result of such factors as lava flows, newly formed sand dunes, or rocks left from a retreating glacier. secondary succession occurs