Answer:
in medieval art, it wasn't very well proportioned, didn't use the golden mean, and didn't have a lot of blending/ shading. mostly dealt in religious (Christian) subject matter. pagan (Roman/Greek) subjects discouraged by the church.
in renaissance, art was more refined. the invention of oil paint allowed better blending and shading. proportion was better, rediscovery of the golden mean. people fascinated by Roman and Greek art/ architecture. artists allowed to go to dissections to learn about the human body. pagan subject matter now explored (example) the birth of Venus. there was also nudity (not allowed by the church in medieval times)