No, not all biological membranes are regulated solely by osmosis. While osmosis is a crucial process in maintaining cell volume and regulating the movement of water across membranes, it's not the only mechanism involved in membrane regulation.

Here's why:

* Active transport: Many biological membranes use active transport to move molecules against their concentration gradient, requiring energy input. This is vital for maintaining specific ion gradients, bringing in nutrients, and removing waste products.

* Facilitated diffusion: Some molecules cross membranes with the help of membrane proteins, a process called facilitated diffusion. This process is still passive, meaning it doesn't require energy, but it relies on specific protein channels or carriers to facilitate movement.

* Endocytosis and exocytosis: These processes involve the movement of large molecules or particles across membranes via the formation and fusion of vesicles. They are active processes requiring energy.

Therefore, while osmosis is important, it's just one of many mechanisms that contribute to the complex regulation of biological membranes.