The differences between isotonic, hypotonic, and hypertonic solutions

Full Answer Section

• Example: A common example of an isotonic solution is normal saline (0.9% sodium chloride) used in intravenous fluids.  

Hypotonic Solution

• Definition: A hypotonic solution has a lower concentration of solutes than the inside of a cell. This means there is a higher concentration of water outside the cell compared to inside.  
• Red Blood Cell: When a red blood cell is placed in a hypotonic solution, water moves into the cell due to osmosis. The cell swells up like a balloon as it gains water. If the cell gains too much water, it may eventually burst (a process called lysis).  
• Example: Distilled water is a hypotonic solution.  

Hypertonic Solution

• Definition: A hypertonic solution has a higher concentration of solutes than the inside of a cell. This means there is a lower concentration of water outside the cell compared to inside.
• Red Blood Cell: When a red blood cell is placed in a hypertonic solution, water moves out of the cell due to osmosis. The cell shrinks and shrivels up as it loses water (a process called crenation).  
• Example: A concentrated salt solution is a hypertonic solution.  

Key Points

• Osmosis: The movement of water across a semipermeable membrane (like a cell membrane) from an area of higher water concentration to an area of lower water concentration.  
• Solutes: Dissolved substances in a solution (e.g., salts, sugars).  
• Concentration Gradient: The difference in concentration of a substance between two areas.

In summary:

• Isotonic: No net water movement, cell stays the same.
• Hypotonic: Water moves in, cell swells and may burst.
• Hypertonic: Water moves out, cell shrinks

Sample Answer

Here's a breakdown of isotonic, hypotonic, and hypertonic solutions, along with how a red blood cell would react in each:

Isotonic Solution

• Definition: An isotonic solution has the same concentration of solutes (dissolved substances) as the inside of a cell. This means there is no net difference in water concentration between the inside and outside of the cell.  
• Red Blood Cell: When a red blood cell is placed in an isotonic solution, there is no net movement of water.
  Water molecules still move across the cell membrane, but the rate of water movement into the cell is equal to the rate of water movement out of the cell. The cell maintains its normal shape and volume.