It does ave something about the exchange of gas,they give out oxygen this is trapped in the wrapping and the mixture of the three gasses in the air,oxygen,carbondioxide and hydrogen causes thr fruits to ripen.<br />
Crikey it is 30 years since I studied this sort of stuff,there is a name for this exchange however I can not think og it off thr top of my hrad.
The ethylene gas that the ripening fruit produce is trapped around the fruit.
Bananas too. Gas or something.
Tomatoes, too. Something about a gas they emit as they ripen, I think. The bag keeps the gas from escaping and increases the speed of ripening. Sounds reasonable, anyway.