Answer to Question 1
Spondylosis refers to an age-related degenerative disease of the spine.
Spondylolysis refers to the degeneration or deficient development of a part of the spine, often the pars interarticularis, that leads to spondylolisthesis.
Spondylolisthesis refers to the forward slippage of a vertebral body over the vertebral body directly below it.
Answer to Question 2
After the cartilage covering the joints wears away, the bone surface becomes hard and polished, somewhat like ivory. The surfaces of the joint become misaligned and the joint becomes unstable.