Yosemite: replace desktop with Launchpad
There is probably no way to switch Desktop and Launchpad like it's in iOS.

But you can at least remove all icons from the desktop. This way it looks clean and you can focus on the Launchpad.

To remove the icons, run this command in the Terminal.app (paste it then run it by hitting Enter):

defaults write com.apple.finder CreateDesktop -bool false; killall Finder


For more information, check out the source: http://osxdaily.com/2009/09/23/hide-all-desktop-icons-in-mac-os-x/