Membranes are thin layers that separate different environments or substances. They can be found in various forms, such as biological membranes that surround cells, or synthetic membranes used in filters. In living organisms, membranes play a crucial role in controlling what enters and exits cells, helping maintain balance and function. In addition to biological membranes, there are also membranes used in technology, like those in water purification systems. These membranes can filter out impurities, allowing clean water to pass through while blocking harmful substances. Overall, membranes are essential for both life and many modern applications.