Which statement about endotherms and ectotherms is correct?

1. endotherms are regulators while ectotherms are conformers
2. endotherms have higher energetic demands compared to ectotherms.
3. endotherms spend more energy on internal temperature regulation compared to ectotherms.
4. endothermy is more common among animal phyla than ectothermy.
5. at the cellular level, endotherms cells always produce more atp and more heat.

3.  Endotherms spend more energy on internal temperature regulation compared to ectotherms.

Explanation:

Ectotherms, are considered  as cold-blooded animals (reptiles and amphibians),  and are organisms that don't have the ability to generate enough heat to keep themselves warm. Endotherms, in contrast, do possess the ability to generate their own body heat.

Endotherms also called warm blooded animals  (mammals) have the ability to regulate their body temperature by themselves. If the endotherms are in a cold place their body increases the metabolism and generates more heat. This will compensate for the cold outside.

the answer is lactic acid from anaerobic respiration. the acid in lactic acid is what creates sore and burning muscles. if you think about how acid burns that will give you a clue for questions like this.