selectively permeable membrane

Architectural surface acts like a membrane. It controls all the movement of objects passively and actively. The control system has 3 modes: - deflect - absorb - extract The envelope of a building can deflect air like what airplane or car design does. It also absorbs air for better interior ventilation. It extracts air or sucks out air from the interior to outside for particular functions. Similar to cell membrane, Substances need to pass through the membrane to enter or leave the cell and they do so in a number of ways. Some of these processes require no energy i.e. they are passive, while others require energy - they are active, while others require energy i.e. they are active. Passive processes include: a) diffusion and b) osmosis, while active processes include: c) active transport, d) phagocytosis, e) pinocytosis and f) exocytosis. Illustration above: a semi permeable cell membrane which controls which substances pass through it. Reference: _ http://en.labs.wikimedia.org/wiki/Anatomy_and_Physiology_of_Animals/The_Cell