If no oxygen is present, pyruvic acid breaks down to form lactic acid. you can feel the effects of lactic acid if you exercise very hard. one way to produce lactic acid is to do a "wall sit," supporting yourself against a wall in a sitting position. try doing this for a few minutes. what do you feel in your thigh muscles?

You would feel thigh muscle pain.

Explanation:

Lactic acid occurs when the muscle gets energy without oxygen and can cause immense pain in the muscle. This occurs when the muscle is subjected to extreme exertion, which the muscle is not used to. This pain comes with a feeling of muscle fatigue and intense burning.

If you did the wall sit position your thigh muscles would be making an intense effort to maintain that position. There would probably be the release of lactic acid into the muscles of your thigh causing pain, fatigue and a burning sensation.

answer/// the nucleoid region contains dna; ///

i think i can answer even without the example. over time with environmental changes, sometimes a group of animals will adapt to better survive. take a moth for example. if the trees the moths use to camouflage themselves from predators, started to die or change colors themselves, the moths may, overtime of course, change color too. its just adapting to its surroundings. hope i was of any : )