Hey there!
Let's start with the first blank. The ozone layer starts in the stratosphere and is made of ozone gases made to protect the Earth from the Sun's harmful UV rays. If the ozone layer wasn't there (not to mention the rest of the atmosphere), we would be exposed to that kind of radiation. Thereofe, "Ultra violet rys would not be blocked by the ozone layer."
For the next one, a lot of levels of substances in the air would change, like UV and oxygen- as there would be more radiation from the lack of protection and all the oxygen would escape.
Hopefully this helps!