Michael Denton, a biologist from Australia, describes the cell through the following analogy:
“To understand the reality of cellular function, let’s enlarge the cell a million times until its diameter reaches 20 km and it looks like a spaceship the size of a large city. We would see a structure of unparalleled complexity and adaptability. There would be millions of openings on the spaceship’s surface, the ship’s portholes. If we entered through one of these openings, we would discover a world with astonishing technologies.”
Let’s rework this analogy for our purposes: take the example of a molecule trying to enter into a cell to accomplish a specific action. It moves in the arteries’ blood stream, until it reaches the exit leading it to the appropriate cell. When this substance nears the cell, it first searches for a door which will open as though reacting to a detector”. The cell’s doors function selectively: each molecule reaching a door is “scanned” to reveal any danger it may represent for the cell; the doors only open for useful molecules. If a harmful element, like a virus, tries to enter through one of these many entrances, it is immediately detected and the doors remain firmly closed.