Rucete ✏ Campbell Biology In a Nutshell
Unit 1 THE CHEMISTRY OF LIFE — Concept 3.3 Acidic and Basic Conditions Affect Living Organisms
Understanding how acids and bases behave in aqueous solutions is fundamental to biology. This section explores how even the smallest fluctuations in pH can dramatically influence life—both at the cellular level and across ecosystems.
1. Acids, Bases, and Hydrogen Ions
In water, acids donate hydrogen ions (H⁺) while bases reduce H⁺ concentration either by accepting H⁺ or releasing OH⁻. Examples:
- Strong Acid: HCl → H⁺ + Cl⁻
- Strong Base: NaOH → Na⁺ + OH⁻
- Weak Base: NH₃ + H⁺ ⇌ NH₄⁺
- Weak Acid: H₂CO₃ ⇌ HCO₃⁻ + H⁺
Strong acids and bases dissociate completely, while weak ones remain in equilibrium.
2. The pH Scale
The pH scale compresses a wide range of H⁺ concentrations into a simple 0–14 scale:
- pH < 7 → Acidic
- pH = 7 → Neutral
- pH > 7 → Basic
Each step equals a tenfold difference in H⁺ concentration. pH 3 is 1,000× more acidic than pH 6.
3. Buffers: Nature’s pH Stabilizers
Life is pH-sensitive. Human blood must stay near pH 7.4. Buffers help by reversibly absorbing or releasing H⁺ ions.
Example: The Carbonic Acid–Bicarbonate Buffer
- If blood is too basic, carbonic acid donates H⁺.
- If too acidic, bicarbonate absorbs H⁺.
This buffer system protects the body from sudden pH changes.
4. Ocean Acidification: A Global Buffer Crisis
Oceans absorb ~25% of CO₂ from burning fossil fuels. CO₂ reacts with water to form carbonic acid, releasing H⁺:
This lowers ocean pH and reduces carbonate ions (CO₃²⁻), which are essential for calcification in marine organisms:
Ca²⁺ + CO₃²⁻ → CaCO₃ (calcium carbonate)
With fewer CO₃²⁻ ions, corals and shellfish struggle to build skeletons. A predicted 40% drop in carbonate by 2100 may threaten entire marine ecosystems.
In a Nutshell
- Acids increase [H⁺], bases decrease it.
- The pH scale shows 10× changes per unit.
- Buffers keep pH stable in organisms.
- Ocean acidification from CO₂ threatens marine life by lowering pH and reducing calcification.
Even small pH shifts ripple through cells and ecosystems. This chemistry is essential not just in labs—but for life itself.