The structure of the cell membrane is a

Analyze the question: It asks about the arrangement of lipids and proteins in the cell (plasma) membrane.

Concept: The cell membrane was first described by the Davson-Danielli model (the "sandwich" model), which is the model most WASSCE questions of this type refer to. It says:

• The core is a phospholipid bilayer (two layers of lipid molecules). The hydrophilic (water-loving) heads face outward, and the hydrophobic (water-fearing) tails face inward.
• Proteins coat the outer and inner surfaces of this lipid bilayer, like the bread in a sandwich.

The later Singer-Nicolson fluid mosaic model modifies this. In it, proteins are embedded in or float across the lipid bilayer rather than forming continuous layers. In both models, the lipid bilayer is the central framework.

Step-by-step evaluation of the options:

• A. Double layer and a double protein layer: This is vague and does not show the lipid bilayer at the centre. Wrong.
• B. Middle bi-layer of protein with a lipid layer on either surface: This reverses the arrangement, because the bilayer in the middle is lipid, not protein. Wrong.
• C. Middle bi-layer of lipid with a protein layer on either surface: This matches the Davson-Danielli structure exactly. Correct.
• D. Protein layer with two inner lipid layers: This has only one protein layer, but proteins are found on both sides. Wrong.

Answer: The correct option is C.

Exam tip: Remember "Lipid in the Middle, Protein on the Sides", like a sandwich with the filling (lipid) between two slices of bread (protein). If an option places protein in the middle, you can eliminate it right away.