TCP requires some buffers to be reserved at reciever side for its seq no., ack no. adv window. Thatswhy it is called connection oriented. By connection oriented ,we simply means that some buffers need to be reserved at reciever side.
But in UDP, we does not need anything.it is 1 request/1 reply. Infact it is like when we ask time to any stranger, we don't ask his details or his name, we are just interesting in knowing what the time is.