They're multiple ways to categorize nearly everything in biology. The value of an individual categorization scheme depends on the perspective of the user. The Classification of organisms is a hard task causes many organisms to have their differences and similarities, whereby making it very complicated in classifying organisms.
If you're referring to one mammal in particular, then it should be the mitosis of body cells. Body cells do not perform meiosis as that is only for gamete production, therefore, it only happens in sex cells. In contrast, body cells will create identical copies of themselves so the organism can grow through mitosis. I hope that helps!
The circulatory system and respiratory system are protected by your skin, muscles, and ribs.
