The best description out of the two stated is "mixtures".
A pure substance is something which is composed of only one kind of primary unit, whether it be elements (comprised of just one type of atom), or compounds (comprising just one type of molecule or ionic species).
Living organisms comprise a number of different types of atoms and molecules. Take a simple plant cell, it contains many different compounds, including water, cellulose and hemicellulose. So this is certainly a mixture of many pure substances.