2.4.7 Osmosis in Animal Cells

Osmosis and Animal Cell Structure:

1. Cell Membrane:

• The partially permeable membrane allows the movement of water molecules in and out of the cell.

2. Water Potential:

• Water moves from a region of higher water potential to lower water potential.
• The solute concentration of the surrounding solution influences the direction of water movement.

Effects of Osmosis on Animal Cells:

3. Hypotonic Solution (Higher Water Potential Outside the Cell):

• Water enters the cell by osmosis.
• The cell swells and may burst (lysis) because it lacks a cell wall to resist the pressure.
• Example: Red blood cells in distilled water undergo haemolysis.

4. Isotonic Solution (Equal Water Potential):

• No net movement of water occurs.
• The cell retains its normal shape and volume.
• This is the ideal condition for animal cells, such as blood cells in plasma.

5. Hypertonic Solution (Lower Water Potential Outside the Cell):

• Water leaves the cell by osmosis.
• The cell shrinks and becomes crenated (shrunken with a wrinkled appearance).
• Example: Red blood cells in a concentrated salt solution.

Practical Investigation:

• Aim: To observe the effects of osmosis on animal cells.
• Method:
  1. Place red blood cells in solutions with different water potentials (distilled water, isotonic saline, hypertonic saline).
  2. Observe the changes under a microscope.
• Results:
  • Hypotonic: Cells swell and burst.
  • Isotonic: Cells maintain their shape.
  • Hypertonic: Cells shrink and become crenated.

Importance of Osmosis in Animal Cells:

6. Maintains Homeostasis:

• Osmosis regulates the balance of water and electrolytes in tissues and cells.
• Prevents extreme changes in cell volume, which could impair function.

7. Fluid Balance:

• Osmosis ensures proper hydration of tissues.
• Regulated by the kidneys, which adjust water and solute levels in the blood.

8. Transport and Function:

• Proper water balance is essential for processes such as nerve impulses and muscle contractions.