Mitochondria, using oxygen available within the cell convert chemical energy from food in the cell to energy in a form usable to the host cell.
chlorophyll density, water, carbon dioxide
Answer: They teach us about the evidence of evolution
Explanation: According to https://flexbooks.ck12.org, "Structures that have lost their use through evolution are called <u>vestigial structures</u>. They provide evidence for evolution because they suggest that an organism changed from using the structure to not using the structure, or using it for a different purpose."