2.4 Cells Have an Optimum pH

Cells Have an Optimum pH

• Importance of H+ Ions

  • H+ ions (protons) play a critical role in living systems.

  • Imbalance in H+ concentration can disrupt molecular shapes and cellular functions, potentially leading to cell death.

• Source of H+ Ions

  • Pure water can spontaneously dissociate into H+ and OH- ions:

    • H₂O ⇌ H+ + OH-

  • In pure water, concentrations of H+ and OH- ions are equal (neutral solution).

Acids and Bases

• Acids

  • Substances that increase the concentration of H+ ions in a solution, lowering the pH.

  • Examples:

    • Hydrochloric acid (HCl)

    • Vinegar and lemon juice

  • Reaction with water: HCl → H+ + Cl-

• Bases

  • Substances that increase the concentration of OH- ions or decrease H+ ions, raising the pH.

  • Common bases include:

    • Baking soda

    • Sodium hydroxide (NaOH): NaOH → Na+ + OH-

• Neutralization

  • When mixed, acids and bases neutralize each other:

    • Acid releases protons; base absorbs H+ or releases OH-.

pH Scale

• Measuring Acidity and Basicity

  • pH scale ranges from 0 to 14:

    • 7 is neutral (pure water).

    • pH < 7 indicates acidic solutions.

    • pH > 7 indicates basic solutions.

  • Strongly acidic solutions are closer to 0; strongly basic solutions are closer to 14.

H+ Concentration and pH Relationship

High H+ Concentration

• 10⁰ HCl (strong acid) has the highest H+ concentration.

• Acids have lower pH values:

  • Stomach acid (pH 1.6-1.8)

  • Lemon juice (pH 2.0)

  • Cola and similar drinks (pH 3.0)

  • Coffee (pH 5.0)

Neutral pH=7

• Examples of Neutral and Alkaline Solutions:

  • Pure water (pH 7.0)

  • Blood and tears (pH 7.35-7.45)

  • Pancreatic juice (pH 7.5-8.0)

Alkaline (Basic) Solutions

• Basic substances have higher pH values:

  • Baking soda (pH 8.1)

  • Laundry detergent (pH 9.0)

  • Ammonia (pH 11.5)

  • Bleach (pH 12.5)

• pH Changes and Organisms

  • Each pH unit on the scale represents a tenfold change in H+ concentration.

  • Organisms have specific pH requirements and use buffers to maintain homeostasis against pH fluctuations.