Paper 2 · Cell Structure and Membranes
Fig 1.1 shows a diagrammatic model of a cell surface membrane. Name the structure labelled Q.
Model answer
hydrophilic channel
Also accepted: protein pore, protein channel
Explanation: Q is a protein that spans the bilayer and forms a water-filled passage through the otherwise hydrophobic interior of the membrane. This lets polar or charged substances, such as ions, cross the membrane without dissolving in the lipid tails, which is why Q is identified as a hydrophilic channel (protein pore/channel).
Derived from ZIMSEC Biology Paper 2, November 2008, Q16
