Direction: In the following questions, a statement of assertion (A) i...
Each cell is bound by an extremely delicate, thin, elastic, selectively permeable, living membrane called plasma membrane. It is selectively permeable as it allows some molecules to pass through more easily than others.
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Direction: In the following questions, a statement of assertion (A) i...
Assertion: Plasma membrane is selectively permeable.
Reason: Plasma membrane allows some molecules to pass through it more easily than others.
The correct answer is option A, which states that both the assertion and the reason are true and the reason is the correct explanation of the assertion. Let's understand why.
Explanation:
The plasma membrane is a vital component of all cells. It surrounds the cell and acts as a barrier between the cell's internal environment and the external environment. It is selectively permeable, which means it allows some substances to pass through while restricting the passage of others.
Plasma Membrane:
The plasma membrane is composed of a phospholipid bilayer, which consists of two layers of phospholipid molecules. The phospholipids have a hydrophilic (water-loving) head and a hydrophobic (water-repelling) tail. This arrangement creates a barrier that controls the movement of substances in and out of the cell.
Selective Permeability:
The selective permeability of the plasma membrane is essential for maintaining homeostasis and regulating the internal environment of the cell. It allows the cell to control the entry and exit of substances, ensuring that only necessary molecules enter the cell and waste products are removed.
Reason:
The reason given for the assertion is that the plasma membrane allows some molecules to pass through it more easily than others. This is true because of the structure of the phospholipid bilayer. The hydrophilic heads of the phospholipids face outward, towards the watery extracellular and intracellular environments, while the hydrophobic tails face inward, creating a nonpolar region in the center of the bilayer.
Passage of Molecules:
This arrangement allows small, nonpolar molecules, such as oxygen and carbon dioxide, to pass through the plasma membrane easily through simple diffusion. However, larger or polar molecules, such as glucose or ions, face more difficulty crossing the membrane. They require specialized transport proteins or channels to facilitate their movement.
Explanation of Reason:
Therefore, the reason provided is a correct explanation of the assertion. The selective permeability of the plasma membrane is a result of its structure and allows for the regulation of the movement of molecules in and out of the cell.
In conclusion, the plasma membrane is selectively permeable, allowing some molecules to pass through more easily than others. This property is crucial for cellular function and is a result of the structure of the phospholipid bilayer that makes up the membrane.
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