Select of correct statement from the following regarding cell membrane
" Or"
Who proposed "fluid mosaic model" for plasma membrane

Options

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

Explanation

To answer the question regarding the cell membrane and the fluid mosaic model, we will evaluate each of the provided statements step by step.

### Step 1: Evaluate the first statement
**Statement:** Sodium and potassium ions move across the cell membrane by passive transport.

**Analysis:** This statement is incorrect. Sodium and potassium ions typically move across the cell membrane through active transport mechanisms, such as the sodium-potassium pump, which requires ATP to function.

**Hint:** Remember that passive transport does not require energy, while active transport does.

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### Step 2: Evaluate the second statement
**Statement:** Proteins make up 60% to 70% of the cell membrane.

**Analysis:** This statement is also incorrect. Proteins actually make up more than 70% of the cell membrane according to the fluid mosaic model, indicating that they are a major component of the membrane structure.

**Hint:** Consider the composition of the cell membrane and the significance of proteins in its structure.

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### Step 3: Evaluate the third statement
**Statement:** Lipids are arranged in the bilayer with polar heads towards the inner part.

**Analysis:** This statement is incorrect. In the fluid mosaic model, lipids are arranged in a bilayer with the polar (hydrophilic) heads facing outward towards the aqueous environment and the non-polar (hydrophobic) tails facing inward, away from water.

**Hint:** Visualize the structure of the lipid bilayer to understand the orientation of polar and non-polar regions.

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### Step 4: Evaluate the fourth statement
**Statement:** The fluid mosaic model of the cell membrane was proposed by Singer and Nicholson.

**Analysis:** This statement is correct. The fluid mosaic model was indeed proposed by scientists Singer and Nicholson in the early 1970s, describing the structure of the plasma membrane.

**Hint:** Recall the names of the scientists associated with significant biological models and theories.

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### Conclusion
After evaluating all the statements, we find that the correct statement regarding the cell membrane is the fourth one: "The fluid mosaic model of the cell membrane was proposed by Singer and Nicholson."

**Final Answer:** The correct answer is option D.

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