photos on screensaver and background

I have just updated to Yosemite 10.10.3 and want to have my photos as my background and screen saver as I had before. I have gone into the screen saver tab in System Preferences and tried to set up my photos. I have selected 'choose folder' but am unable to select iphotos. This happened when I first downloaded Mountain Lion in 2012 and I had to set up a separate folder of photos on my desktop, but was solved when I used Yosemite. Does anyone know how I can use my photos again for my background and screensaver?