ISO.. some image quality thing for cameras. But to make it simple,
low ISO --> Quality of image higher, sharper but lighting is lower, darker.
high ISO--> Quality of image lower, more distorted, but lighting is higher, better in dark places.
(as seen in the pics above)
as you see, from ISO 200-->1600, the aperture is low, f/2.8 (more light can enter) and at ISO 3600, aperture is higher, f/8.0 (lesser light can come in) which proves a higher iso captures more light which forces the aperture to drop. and from 200-->1600, the shutter speed increases. which also gives the same conclusion, faster shutter, less light, slower shutter, more light. these are the effects of ISO towards the aperture and shutter speed, but also the quality of the image.