Answer:
DNA, it controls all cell activities
Explanation:
its the central part of the cell that contains dna and rna and is responsible for growth and reproduction
So many new species were being discovered, it was impossible to arrange them all in a hierarchy based on relative complexity of species.
The respiratory and circulatory systems work with each other in this manner, the respiratory system will obtain oxygen then the circulatory system brings the oxygen to different parts of the body then it also takes carbon dioxide from different tissues of the body and bring carbon dioxide to lungs then the respiratory system takes carbon dioxide outside the body during exhalation
viruses i think again sorry if this is wrong
