AIIMS 2003 Botany Cell Membrane Assertion Reason Question

To answer the question regarding the assertion and reason about cell membranes, let's break down the concepts involved.

Assertion: A cell membrane shows fluid behaviour.

Explanation:
The fluid mosaic model of the cell membrane, proposed by Singer and Nicolson in 1972, describes the cell membrane as a dynamic and fluid structure. In this model, the membrane is composed of a phospholipid bilayer with embedded proteins that can move laterally within the layer. This fluidity is crucial for various cellular processes, including the movement of substances across the membrane, cell signaling, and membrane fusion.

Reason: A membrane is a mosaic or composite of diverse lipids and proteins.

Explanation:
The term "mosaic" refers to the diverse composition of the cell membrane, which consists of various types of lipids (such as phospholipids and cholesterol) and proteins (integral and peripheral). This diversity contributes to the fluid nature of the membrane. The presence of different fatty acid chains in the phospholipids and the variable shapes and sizes of proteins allows for flexibility and movement. Additionally, cholesterol molecules help to maintain membrane fluidity, especially at varying temperatures.

Conclusion on the Options:

Option A: (a) Both Assertion and Reason are true and Reason is the correct explanation of Assertion.
This option is correct. Both the assertion and the reason are true, and the reason explains why the cell membrane exhibits fluid behavior. The diverse composition of lipids and proteins directly contributes to the fluidity of the membrane.

Option B: (b) Both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
This option is incorrect. While both the assertion and reason are indeed true, the reason accurately explains the assertion.

Option C: (c) Assertion is true but Reason is false.
This option is incorrect. The assertion is true, and the reason is also true. Therefore, it cannot be correct to say the reason is false.

Option D: (d) Both Assertion and Reason are false.
This option is incorrect as both the assertion and the reason are true.

Summary:

• The correct answer is A, because both the assertion and reason are true, and the reason provides a valid explanation for the assertion regarding the fluid behavior of the cell membrane due to its mosaic nature.
• Other options are incorrect based on the evaluation of the truthfulness of the assertion and reason.

This understanding of the fluid mosaic model is essential for grasping various biological processes and mechanisms at the cellular level, which will be helpful not only for NEET/JEE but also for further studies in biology and biochemistry.