AIIMS 2006 Chemistry Osmosis Assertion Reason Question

To understand the question and its components, we need to delve into the principles of osmosis and the behavior of red blood cells (RBCs) in different solutions.

Explanation of the Assertion

Assertion: If red blood cells were removed from the body and placed in pure water, pressure inside the cells increases.

When red blood cells are placed in pure water, which is a hypotonic solution (having a lower concentration of solutes compared to the inside of the cells), water enters the cells through osmosis. Osmosis is the process where water moves across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration in order to equalize concentrations on both sides of the membrane.

As water enters the cells, it causes the internal pressure (or turgor pressure) to increase, which can eventually lead to the cells swelling and possibly bursting (in a process known as hemolysis). Therefore, the assertion is true.

Explanation of the Reason

Reason: The concentration of salt content in the cells increases.

This statement is misleading in the context of the assertion. When red blood cells are placed in pure water, the external environment has no salt (or a very low concentration), and thus, water enters the cells to dilute the higher concentration of solutes (including salts) inside the cells. As water enters, the overall concentration of salt inside the cells does not increase; rather, it decreases because the volume of the cell increases due to the influx of water.

Conclusion on Correct Answer

Given this analysis:

• The assertion is true because the pressure inside the cells does indeed increase when they are placed in pure water.
• The reason is false because the concentration of salt content in the cells does not increase; it actually decreases as water enters the cells.

Thus, the correct answer is C) Assertion is true but Reason is false.

Why Other Options are Incorrect

• A) Both Assertion and Reason are true and Reason is the correct explanation of Assertion: This option is incorrect because the reason is false.
• B) Both Assertion and Reason are true but Reason is not the correct explanation of Assertion: This is incorrect because the reason is actually false.
• D) Both Assertion and Reason are false: This is incorrect since the assertion is true.

Relevant Concepts

1. Osmosis: The movement of water across a semipermeable membrane from a region of lower solute concentration to a region of higher solute concentration.
2. Hypotonic Solution: A solution that has a lower concentration of solutes compared to another solution (in this case, the interior of the RBCs).
3. Turgor Pressure: The pressure of the fluid inside the cell against the cell wall, which increases as water enters the cell.

This comprehensive breakdown of the assertion and reason allows us to understand the osmotic behavior of red blood cells in response to different environments.