Natural selection is the correct answer
The respiratory system works directly with the circulatory system to provide oxygen to the body. Oxygen taken in from the respiratory system moves into blood vessels that then circulate oxygen-rich blood to tissues and cells.
<span>Animals are generally more scared of humans than humans scared of them. Mice and other familiar animals run when they sense danger. The faster they run, the more danger they likely feel. Even humans have a natural instinct to flee when sensing danger.</span>
The two cycles of the matter are the carbon and nitrogen cycle. Both of them are biogeochemical cycles, it means that the chemicals spend a portion of the cycle in living things and non-living things. They are also common in that they both recycle nutrients that are essential to all organisms.
They are different in the manner that they cycle. Nitrogen is huge, 78% of the air around us is nitrogen. It cannot be used by plants or animals. Once the nitrogen is used by the plant and make its way to the animal, it can be released to decomposition.
Carbon has no requirement in processing by bacteria prior to plants and animals being able to use. Plants take carbon dioxide and make it sugar, animals eat the sugar. Some of it is released carbon dioxide that we exhale.
Yes, short answer, I can not give you the specifics (consult your biology textbook)
