Animal Cells Rely on Isotonic Environments For Stability
- Animal cells are highly sensitive to their environment because they lack the structural support of a cell wall.
- Water movement across the cell membrane can cause cells to swell, shrink, or remain stable depending on the surrounding solution.
Hypotonic Solutions Cause Cells To Swell and Burst
- In a hypotonic solution, the surrounding environment has a lower concentration of solutes than inside the cell.
- Water moves into the cell by osmosis.
- What happens: The cell swells as water enters, pressure increases, and without a cell wall, the cell membrane may rupture (a process called lysis).
Example
When red blood cells are placed in pure water, they swell and burst, leaving behind empty membranes called "red cell ghosts"
Hypertonic Solutions Cause Cells To Shrink and Crenate
- In a hypertonic solution, the surrounding environment has a higher concentration of solutes than inside the cell.
- Water moves out of the cell by osmosis.
- What happens: The cell loses water and shrinks. The cell membrane pulls away from the cytoplasm, creating a wrinkled appearance called crenation.
Hint
Remember: Hypertonic solutions cause cells to shrink, while hypotonic solutions cause them to swell.
Example
Red blood cells placed in a concentrated salt solution will shrink and develop a spiky appearance due to crenation.
Isotonic Solutions Is Where Cells Are Balanced and Stable
- In an isotonic solution, the concentration of solutes is equal inside and outside the cell.
- Water moves in and out at the same rate, maintaining equilibrium.
- Why is this important: Cells remain stable and functional, preventing swelling or shrinking.
Example
Intravenous (IV) fluids used in medical treatments are isotonic to human blood to ensure cells remain healthy.
Hint
- Cells thrive in stable environments.
- This is why your body works hard to maintain homeostasis.
Theory of Knowledge
How does the concept of isotonic solutions relate to the idea of balance in other systems, such as economic or ecological systems?
Adaptations in Unicellular Organisms
- Freshwater unicellular organisms, like Paramecium, live in hypotonic environments where water constantly enters their cells.
- Without adaptations like contractile vacuoles, they would burst.
- How contractile vacuoles work:
- Water enters the vacuole as solutes are pumped in, drawing water by osmosis.
- The vacuole contracts and expels excess water from the cell.Contractile vacuoles require energy to function.
Note
Contractile vacuoles require energy to function, highlighting the trade-off between survival and energy expenditure.
The Need to Maintain Isotonic Conditions
- Multicellular organisms must carefully regulate the solute concentration of their extracellular fluids to prevent cells from swelling or shrinking.
- Why is this critical:
- Swelling or shrinking can disrupt cellular processes and organ function.
- Organs like the brain are particularly sensitive to changes in water balance.
Self review
- Can you explain what happens to a cell in hypotonic, hypertonic, and isotonic solutions?
- How do contractile vacuoles help unicellular organisms survive in freshwater environments?
