buffers

1. pH, Buffers & Biological
Significance
• Bridge Course for UG Microbiology Students

2. Learning Objectives
• • Define pH and buffer.
• • Explain the importance of pH in biological
systems.
• • Understand the concept of buffers and how
they work.
• • Describe key biological buffer systems and
their significance.

3. What is pH?
• • Definition: pH = -log[H+]
• • Range: 0 (acidic) to 14 (basic), with 7 being
neutral.
• • Examples:
• - Stomach acid ~ pH 1.5
• - Blood ~ pH 7.4
• - Soap ~ pH 10

4. Importance of pH in Biology
• • Enzyme activity is pH-dependent
• • Cellular function requires optimal pH
• • Imbalance can lead to diseases (e.g.,
acidosis, alkalosis)
• • pH homeostasis is essential for survival

5. What are Buffers?
• • Definition: A buffer is a solution that resists
changes in pH upon addition of small amounts
of acid or base.
• • Components: Weak acid and its conjugate
base (or vice versa)
• • Mechanism: Neutralizes added H+ or OH-

6. Buffer Action - Example
• • Acetic Acid Buffer:
• - CH3COOH CH3COO⁻ + H⁺
⇌
• - On adding acid: CH3COO⁻ + H⁺ →
CH3COOH
• - On adding base: CH3COOH + OH⁻ →
CH3COO⁻ + H2O

7. Biological Buffers
• • Key Systems:
• - Bicarbonate buffer system (H2CO3 /
HCO3⁻)
• - Phosphate buffer system (H2PO4⁻ /
HPO4²⁻)
• - Protein buffer systems (e.g., Hemoglobin)
• • Example: Bicarbonate buffer maintains
blood pH

8. Henderson-Hasselbalch Equation
• • Equation: pH = pKa + log ([A⁻]/[HA])
• • Application: Used to calculate pH of a buffer
• • Example: pKa = 4.76, [A⁻] = 0.1M, [HA] =
0.1M
• • Answer: pH = 4.76

9. Biological Significance of Buffers
• • Maintain cellular and extracellular pH
• • Facilitate metabolic reactions
• • Transport of gases (e.g., CO₂ buffering in
blood)
• • Protect proteins from denaturation

10. Recap and Quick Quiz
• Quick Questions:
• 1. What is the pH of neutral water?
• 2. Name one biological buffer system.
• 3. What happens to pH when strong acid is
added to a buffer?

11. Activity – pH Testing Demo
• • Use pH paper or digital pH meter
• • Test substances: lemon juice, soap solution,
tap water
• • Record and compare observations
• • Discussion: Were predictions accurate?

12. Assessment
• Short Answer Questions:
• • Define buffer with an example.
• • Explain how bicarbonate buffer works in the
body.
• MCQs:
• • What is the pH of blood?
• • Which of the following is a buffer?

13. Thank You
• Thank you! Keep exploring the chemistry of
life.