Question

Select out of the following the correct statement regarding cell membrane.

• A. Na and K ions move across the cell membrane by passive transport.
• B. Proteins make up 60 to 70% of the cell membrane.
• C. Fluid mosaic model of the cell membrane was proposed by Singer and Nicolson.
• D. Lipids are arranged in a bilayer with polar heads towards the inner part.

Hint:

Think about which membrane model is taught as the standard, and which direction lipid heads actually face.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks which one statement about the structure and working of the cell membrane is factually correct. We need to check each option against what we know about membrane composition and models.

Step 2: Key Formula or Approach:
The cell membrane is described by the fluid mosaic model, and its transport of ions is mostly active rather than passive. We check each option one by one against these facts.

Step 3: Detailed Explanation:
Option 1 says Na and K ions cross the membrane by passive transport. This is not correct as the main stated fact, because Na and K ions are kept at very different concentrations inside and outside the cell by the Na-K pump, which uses ATP and moves ions against their gradient. That is active transport, not passive.
Option 2 says proteins make up 60 to 70% of the membrane. Protein content actually varies a lot between different membranes, from as low as 20% to as high as 80% depending on the cell type, and there is no fixed rule that it is always 60 to 70%. So this statement is not a safe general fact.
Option 3 says the fluid mosaic model was proposed by Singer and Nicolson. This is a well established and correct fact. Singer and Nicolson gave this model in 1972, describing the membrane as a fluid lipid bilayer in which proteins float and move like a mosaic pattern.
Option 4 says lipids are arranged in a bilayer with polar heads towards the inner part. This is wrong because in a lipid bilayer the polar, water loving heads face outward on both sides, towards the watery cytoplasm and the watery outside environment. The non polar, water hating tails face inward, away from water.

Step 4: Final Answer:
Only option 3 states a fact that is always true, so the fluid mosaic model given by Singer and Nicolson is the correct statement about the cell membrane.