Which of the following is true of integral membrane proteins? a) they lack tertiary structure. b) they are loosely bound to the surface of the bilayer. c) they are usually transmembrane proteins. d) they are not mobile within the bilayer. e) they serve only a structural role in membranes.

C) They are usually transmembrane

Explanation:

Integral membrane proteins (intrinsic protein) are known to be a type of membrane protein that is attached permanently to the biological membrane. Also, they are made up of significant proteins that are encoded in the genome of the organism. Furthermore, trans-membrane proteins allow the transportation of specific substances across the membrane and they undergo significant changes in order to move substances across or through the membrane.

oxygen +1 most likely