approximately 2.2 billion years ago which gas was first added in large amounts to earth atmosphere from life forms that evolved
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Yeah yeah so :D,
Large polar molecules can only cross the membrane with the help of protein named channel protein and carrier protein.
So, this both proteins act like a gate, the large molecules enter the protein and the protein let the large molecules in to the membrane. (see the picture so that you can understand more, its carrier protein)
the only difference between channel protein and carrier protein is, channel proteins has fixed shape while carrier protein can flip.
