Ventilation systems are needed in a <span>multicellular organism to actually obtain oxygen and give out carbon dioxide. Without this ventilation system, it would be very difficult for multicellular organisms to survive. It has been also observed that surface diffusion is not enough for a multicellular organism to breath.</span>
C. To live in a group with other organisms
The answer is primary structure. The protein's primary structure pertains to the amino acids' linear sequence in the chain. Usually, the protein's structure is combined together with a covalent bond that is produced while the process of biosynthesis is present.
