Final answer:
Biological membranes are selectively permeable, allowing them to control which substances enter and leave a cell. They use passive and active transport mechanisms to maintain a state of homeostasis, with selectivity based on membrane structure and function.
Step-by-step explanation:
Biological membranes are selectively permeable, regulating the cell's molecular traffic. They control which molecules or ions can enter or leave the cell, thereby aiding in maintaining homeostasis. These membranes utilize both passive and active transport processes to regulate the movement of substances such as water, ions, and polar molecules. During passive transport, materials move by simple diffusion or by facilitated diffusion through the membrane, down their concentration gradient, without the need for cellular energy. Active transport processes require energy, often in the form of ATP, to move substances against their concentration gradient.
Due to their selective permeability, plasma membranes prevent harmful materials from entering cells and essential materials from leaving. Substances that are crucial to cell function may be transported actively, which is an energy-consuming process. Membranes possess specific structures, such as small pores or transport proteins, that determine their permeability properties. Understanding the functioning of cell membranes is an interdisciplinary subject, involving biology, chemistry, and physics.