Mark are used in proteins within the body have two functions structure in transport sarah disagrees which significant function of proteins did mark admit from his list

Proteins are large complex compounds made up of one or more polypeptide chains.  

They play various roles in living organisms such as:

Transport: They help in transport of material across the cell membrane by forming carriers and channels across the lipid bilayer.Structural role: They are called building block of the body as they provide structure and strength to all the cells. For example, keratin protein is found in nails, hair, and skin, collagen is a protein found in connective tissue et cetera. Immunological role: Antibodies or immunoglobulins are primarily protein in nature which helps our body to fight against a pathogen. Biochemical reactions: In living organisms, proteins in the form of enzymes help in escalating the biochemical reactions taking place in an organism. For example, RuBisCO. Chemical messenger: Proteins also occur as chemical messengers in the form of hormones such as insulin et cetera.

Thus, Mark did not add immunological role, role in biochemical reaction, and role as chemical messenger of proteins.