This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
On weight basis, the percentage of proteins contain in a cell membrane is: 
Select and explain. 
A. 70%, B. 30%, C. 50%, D. 80%
C: 50%
Answer: C: 50% 
Explanation: Proteins are major constituents of membranes (~50% by weight in the plasma membrane). Integral proteins are directly incorporated within the lipid bilayer itself, whereas peripheral proteins exhibit a looser association with one of the two membrane surfaces, paicularly the inner. Ref: (2013). Chapter 2. The Cytoplasm. In Mescher A.L. (Eds), Junqueira's Basic Histology: Text & Atlas, 13e.