http://en.wikipedia.org/wiki/Gas_exchange [2]
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/G/GasExchange.html [3]
http://people.eku.edu/ritchisong/301notes6.htm [4]
http://www.enotes.com/homework-help/what-process-gas-exchange-human-body... [5]
https://www.google.co.in/search?q=Evidence+for+evolution&ie=utf-8&oe=utf... [6]
http://www.britannica.com/EBchecked/topic/499530/human-respiratory-syste... [7]
Links
[1] https://hootsgo.org/?q=node/6335
[2] http://en.wikipedia.org/wiki/Gas_exchange
[3] http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/G/GasExchange.html
[4] http://people.eku.edu/ritchisong/301notes6.htm
[5] http://www.enotes.com/homework-help/what-process-gas-exchange-human-body-467185
[6] https://www.google.co.in/search?q=Evidence+for+evolution&ie=utf-8&oe=utf-8&gws_rd=cr&ei=xSqiVMywAcGWuATWmYLgCQ#q=gas+exchange+in+humans&revid=1392397201
[7] http://www.britannica.com/EBchecked/topic/499530/human-respiratory-system/66150/The-respiratory-pump-and-its-performance
[8] http://www.mrothery.co.uk/exchange/exchange.htm