Understanding Human RBCs in a Detergent Solution

This question asks what happens when human red blood cells (RBCs) are placed in a 2% detergent solution. To understand this, we need to consider how cell membranes interact with different types of solutions and substances like detergents.

Human red blood cells are living cells with a cell membrane. This membrane acts as a barrier between the inside of the cell and its external environment. The behavior of the RBCs in a solution depends on the properties of the solution and how they affect the cell membrane and water balance.

The Effect of Solutions on Red Blood Cells

Red blood cells are sensitive to the concentration of solutes in the solution surrounding them. Water moves across the cell membrane by a process called osmosis, from an area of lower solute concentration to an area of higher solute concentration.

• Isotonic Solution: If the solute concentration outside the cell is the same as inside, there is no net movement of water, and the RBC maintains its normal shape.
• Hypotonic Solution: If the solute concentration outside the cell is lower than inside, water moves into the cell. This causes the RBC to swell and can lead to it bursting (lysis) because animal cells like RBCs do not have a rigid cell wall to withstand the internal pressure.
• Hypertonic Solution: If the solute concentration outside the cell is higher than inside, water moves out of the cell. This causes the RBC to lose volume and shrink. The shrunken, wrinkled appearance of RBCs in a hypertonic solution is called crenation.

Analyzing the 2% Detergent Solution Scenario

The question specifies a 2% detergent solution. Detergents are amphipathic molecules, meaning they have both water-loving and water-repelling parts. They interact strongly with cell membranes, which are lipid bilayers.

Based on the provided outcome for this scenario, placing human RBCs in a 2% detergent solution causes a specific reaction related to water movement and cell volume.

Outcome: RBCs Shrink in 2% Detergent Solution

According to the scenario presented, when human red blood cells are placed in a 2% detergent solution, they will shrink.

Shrinking occurs because water moves out of the red blood cells. This happens when the external solution has a higher concentration of solutes compared to the inside of the cell, creating a hypertonic environment relative to the RBC's cytoplasm. The difference in solute concentration drives the osmotic movement of water out of the cell across the selectively permeable cell membrane. As water leaves, the cell volume decreases, resulting in the characteristic wrinkled or crenated shape of a shrinking RBC.

Therefore, the presence of the 2% detergent in the solution creates conditions that lead to water exiting the RBCs, causing them to shrink.

Comparing Shrinking with Other Potential Outcomes

Let's look at why the other options are different from the outcome of shrinking:

• Swelling and becoming turgid: Turgidity is a term used for plant cells with cell walls that become firm when placed in a hypotonic solution. Animal cells like RBCs don't become turgid; they swell and may burst.
• Swelling and bursting: This happens when RBCs are placed in a hypotonic solution, causing water to rush in and the cell to lyse due to increased internal pressure.
• Lysis: This is the bursting or destruction of the cell membrane. While detergents are known to interact with cell membranes and cause lysis by disrupting the lipid bilayer, the specific outcome indicated in this scenario is shrinking.

Based on the outcome provided for human RBCs in a 2% detergent solution, the key effect described is the osmotic loss of water leading to shrinking, characteristic of being in a hypertonic environment.

Revision Table: RBC Responses to Different Environments

Additional Information: Cell Membrane Structure and Function

The cell membrane is crucial for regulating what enters and leaves the cell. It's primarily made of a phospholipid bilayer with embedded proteins.

• Phospholipid Bilayer: Forms the basic structure, acting as a barrier to most water-soluble molecules.
• Selective Permeability: The membrane controls the passage of substances, allowing some to pass freely (like water via osmosis), while others require transport proteins.
• Interaction with Detergents: Detergents can disrupt the structure of the cell membrane by interacting with the lipids and proteins, potentially affecting its permeability and integrity. However, in the context of this specific question's outcome, the primary observed effect is water movement leading to shrinkage.

Understanding how different solutions affect cell volume through osmosis is key to predicting the behavior of cells like human red blood cells.