Question

Red blood cells placed in distilled water will: a. swell as water moves into the cells by osmosis b. shrink as sodium moves out of the cells by diffusion c. swell as water moves into the cells by active transport d. shrink as proteins move out of the cell by diffusion e. remain unchanged because of homeostatic mechanisms

Short answer

Red blood cells will swell as water moves into the cells by osmosis (Answer: a).

Step-by-step solution

Understand Osmosis

Osmosis is the movement of water molecules from an area of lower solute concentration to an area of higher solute concentration through a semi-permeable membrane. Red blood cells have a semi-permeable membrane, allowing water to pass through.

Analyze the Situation

Distilled water is pure water with no solutes. The solute concentration inside the red blood cells is higher compared to distilled water.

Predict Water Movement

Since water moves from an area of low solute concentration (distilled water) to an area of high solute concentration (inside the red blood cells), water will move into the cells.

Determine Cell Response

As water enters the red blood cells, they will swell. This is because the cell membrane allows water to flow inward to balance the solute concentrations.

Eliminate Incorrect Options

Given that the cells will swell due to water movement by osmosis, eliminate options b (shrink as sodium moves out), c (swell by active transport), d (shrink as proteins move out), and e (remain unchanged).

Select the Correct Answer

The correct answer is that the red blood cells will swell as water moves into the cells by osmosis.

Key concepts

semi-permeable membrane

Red blood cells are surrounded by a semi-permeable membrane. This special type of membrane allows certain molecules like water to pass through while blocking others like proteins or ions.
Think of it like a selective gatekeeper that controls what can enter and exit the cell.
In the case of red blood cells, the semi-permeable membrane allows for the regulation of water and solute balance, which is crucial for cell survival and function.
When placed in different environments, the behavior of the membrane plays a key role in the cell's response, especially in the process of osmosis.

solute concentration

Solute concentration refers to the amount of dissolved substances within a solution. In biology, understanding solute concentration is important because it influences the movement of water across cell membranes.
In the exercise, red blood cells have a higher solute concentration inside them compared to the distilled water outside.
This difference in solute concentration sets the stage for osmosis, as water moves to balance the solute levels across the semi-permeable membrane.
It's important to remember:

• High solute concentration inside the cell means more 'stuff' dissolved in the water.
• Distilled water outside the cell has no solutes.
• Water moves toward areas with higher solute concentration to try to equalize the concentrations on either side of the membrane.

This movement drastically affects the cell's volume and shape.

water movement

The principle of water movement is central to the concept of osmosis. Water movement in cells follows the gradient of solute concentration.
In simpler terms, water travels from regions where there are fewer dissolved substances (low solute concentration) to regions where there are more dissolved substances (high solute concentration).
In the exercise, water moves from the distilled water (low solute) into the red blood cell (high solute) to balance the solute levels.
This process is crucial for maintaining cellular balance and function, and it's driven purely by the differences in solute concentration inside and outside the cell.
Key points:

• Water seeks to balance solute concentrations on both sides of the membrane.
• This movement happens naturally without needing energy from the cell.

This natural process ensures cells function correctly within different environments.

red blood cell swelling

When red blood cells are placed in distilled water, the osmotic process causes them to swell. This happens because water moves in to balance the higher solute concentration inside the cells.
As water enters the cells, the cell membrane stretches to accommodate the increased volume.
If too much water enters, the cells can swell significantly and might even burst in a process called hemolysis.
Key takeaways:

• The water influx is driven by the difference in solute concentration.
• The red blood cells swell as they absorb water to equalize the solute levels.
• Excessive swelling can damage or destroy the cells.

Understanding this concept is essential for grasping why red blood cells and other cell types behave differently in various environments.