Final answer:
All living organisms are made of cells that possess a semi-permeable membrane primarily made up of phospholipids, forming a protective and selective barrier for the cell.
Step-by-step explanation:
All living organisms are made up of one or more cells that have semi-permeable membranes composed mostly of phospholipids.
The cell membrane, also known as the plasma membrane, plays a critical role in protecting and enclosing the cell's inner contents. This membrane is predominantly made up of a double layer of phospholipids, forming what is called a phospholipid bilayer. Each phospholipid molecule is composed of a hydrophilic (water-loving) head that is attracted to water, and hydrophobic (water-fearing) tail that repels water. These properties allow the cell membrane to form a barrier that is selectively permeable, controlling the entry and exit of substances, and thus, maintaining the cell's internal environment. This selective permeability is crucial for processes such as nutrient absorption, waste removal, and the regulation of ion flow, which are essential for the cell's survival and function. Furthermore, the presence of other molecules like cholesterol and proteins within the cell membrane adds to its fluidity and functionality, permitting communication and transport through various mechanisms. Hence, the semi-permeable membrane composed mostly of phospholipids is a fundamental feature of all living cells.