There are four different types of nucleotides in DNA, and they differ from one another by the type of base that is present: adenine (A), thymine (T), guanine (G), and cytosine (C). A base on one of the chains that makes up DNA is chemically bonded to a base on the other chain.
Relative dating determines how old it is
They are basically the next step up from atoms. They are smaller living organisms. (might not be helpful but it's a start)
Respiratory and circulatory systems work hand in hand to expel wastes. respiratory system removes CO2 and the circulatory uses the blood as a medium to move excess salts and water from source to sink.
