1. In this case, we usually don't use "the." However, we often say "the police." It's a little bit strange. There is no underlying idea. It's just tradition. Here are some more weird examples: the ocean the library the bank the hospital the bathroom In some cases, it is because there is only one ("the sun" "the bathroom"). Sometimes, there are historical reasons. For example, in old times, most towns only had one bank. Therefore, we say "the bank." Now, there are tons of banks, but the language hasn't changed! 2. Correct. 3. Correct. In this case, we can't use "the" because it is not a group of sea turtles. It is "all sea turtles." In English, you have to guess. Is it "all firefighters" or "some firefighters"? Here are two examples: Firefighters work long hours. FIrefighters cleared the area. Usually, the meaning is clear. If we add "the," it is usually the second time that we mention the noun: Police, firefighters, and paramedics arrived. The fIrefighters cleared the area. Of course, if we add more information, we can use "the": The firefighters who extinguished the blaze were awarded the city's highest honor. Now, it is a specific group of firefighters: "The firefighters who extinguished the blaze."

You only use "the" in both of these situations if you are talking about a specific group of firefighters or turtles. I think these statements are meant to talk about sea turtles and firefighters in general so I wouldn't use "the."