Buffers in biological systems MCQs With Answer

Buffers in biological systems MCQs With Answer are essential for B. Pharm students to master pH regulation, acid–base balance, and formulation stability. This concise, keyword-rich introduction covers buffer definition, Henderson–Hasselbalch concepts, pKa relevance, physiological buffers (bicarbonate, phosphate, proteins, hemoglobin), buffer capacity, and pharmaceutical implications such as drug ionization and stability. Understanding buffer selection, preparation, and the impact of dilution, temperature, and ionic strength is vital for pharmacology, biochemistry, and formulation science. These MCQs emphasize clinical and practical applications, linking theory to lab and therapeutic contexts. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is the primary role of buffers in biological systems?

• To catalyze biochemical reactions
• To maintain a stable pH despite addition of acids or bases
• To transport oxygen in blood
• To store energy as ATP

Correct Answer: To maintain a stable pH despite addition of acids or bases

Q2. The Henderson–Hasselbalch equation relates pH to which two parameters?

• pH and temperature
• pH and buffer capacity
• pH, pKa and ratio of conjugate base to acid
• pH and ionic strength

Correct Answer: pH, pKa and ratio of conjugate base to acid

Q3. A buffer is most effective at a pH that is close to which value?

• Twice the pKa
• Equal to the pKa of the buffering acid
• One unit below the pKa
• One unit above the pKa

Correct Answer: Equal to the pKa of the buffering acid

Q4. Which physiological buffer system is the main extracellular buffer in humans?

• Hemoglobin buffer system
• Bicarbonate-carbonic acid buffer system
• Phosphate buffer system
• Protein buffer system

Correct Answer: Bicarbonate-carbonic acid buffer system

Q5. In Henderson–Hasselbalch equation, pH = pKa + log([A-]/[HA]), what does [A-] represent?

• Concentration of undissociated acid
• Concentration of conjugate base
• Concentration of water
• Concentration of hydrogen ions

Correct Answer: Concentration of conjugate base

Q6. Buffer capacity is defined as:

• The ratio of acid to base in a buffer
• The amount of acid or base needed to change pH by one unit
• The pH at which the buffer is neutral
• The total ionic strength of the solution

Correct Answer: The amount of acid or base needed to change pH by one unit

Q7. Which buffer system is most important for intracellular pH regulation?

• Bicarbonate buffer
• Phosphate buffer
• Plasma proteins
• CO2 dissolved in plasma

Correct Answer: Phosphate buffer

Q8. The pKa of a buffer is 7.2. For optimal buffering at physiological pH 7.4, which statement is true?

• Buffer will be ineffective because pH is greater than pKa by 2 units
• Buffer will provide good buffering since pH is within ±1 unit of pKa
• Buffer is only effective at pH equal to 7.2
• Buffer capacity is maximal at pH 9.2

Correct Answer: Buffer will provide good buffering since pH is within ±1 unit of pKa

Q9. Which of the following is a Good’s buffer commonly used in biological formulations?

• Sodium chloride
• Tris (tris(hydroxymethyl)aminomethane)
• Hydrochloric acid
• Glucose

Correct Answer: Tris (tris(hydroxymethyl)aminomethane)

Q10. In the bicarbonate buffer system, increased CO2 in blood will cause:

• Alkalosis due to HCO3- consumption
• No change in pH
• Acidosis due to increased H2CO3 and H+ formation
• Hyperventilation to increase CO2

Correct Answer: Acidosis due to increased H2CO3 and H+ formation

Q11. Which component of hemoglobin helps it act as a buffer?

• Iron in heme group
• Histidine residues with imidazole side chains
• Polypeptide backbone carbonyls
• Disulfide bonds

Correct Answer: Histidine residues with imidazole side chains

Q12. During titration of a weak acid with a strong base, the pH at the half-equivalence point equals:

• pKa of the weak acid
• pH 7.0 always
• Twice the pKa
• Zero

Correct Answer: pKa of the weak acid

Q13. Which factor decreases buffer capacity?

• Higher total concentration of buffer components
• Ratio of acid to base near 1:1
• Dilution of the buffer solution
• Choosing a pKa close to desired pH

Correct Answer: Dilution of the buffer solution

Q14. Phosphate buffer in plasma primarily exists in which forms at physiological pH?

• H3PO4 and H2PO4-
• H2PO4- and HPO4(2-)
• PO4(3-) and H3PO4
• Only PO4(3-)

Correct Answer: H2PO4- and HPO4(2-)

Q15. Which statement about pKa and drug ionization is correct?

• Weak acids are ionized at pH below pKa
• Weak bases are ionized at pH above pKa
• Ionization affects solubility and absorption of drugs
• pKa has no effect on drug formulation

Correct Answer: Ionization affects solubility and absorption of drugs

Q16. The isohydric principle states that:

• All buffer systems in a solution have the same pKa
• Different buffering species in equilibrium maintain the same H+ concentration
• Buffers cannot coexist in biological fluids
• Buffer capacity is independent of concentration

Correct Answer: Different buffering species in equilibrium maintain the same H+ concentration

Q17. Which experimental condition shifts the pKa of a buffering compound significantly?

• Changing solvent ionic strength and temperature
• Keeping temperature constant
• Using ultrapure water only
• Adding equimolar salt with no ionic effect

Correct Answer: Changing solvent ionic strength and temperature

Q18. A solution containing 0.1 M acetic acid and 0.1 M sodium acetate will have high buffer capacity around which pH?

• pH 2.4
• pH 4.76
• pH 7.0
• pH 10.0

Correct Answer: pH 4.76

Q19. Which buffer is commonly used in intracellular fluids and has pKa around 6.8?

• Bicarbonate buffer
• Phosphate buffer
• Tris buffer
• Acetate buffer

Correct Answer: Phosphate buffer

Q20. In pharmaceutical formulations, why are buffers used?

• To change drug color
• To maintain pH for drug stability and solubility
• To neutralize active drug
• To increase viscosity only

Correct Answer: To maintain pH for drug stability and solubility

Q21. Which of the following increases buffer capacity most effectively?

• Increasing concentration of both acid and conjugate base
• Decreasing total buffer concentration
• Using a buffer with pKa far from target pH
• Adding organic solvents

Correct Answer: Increasing concentration of both acid and conjugate base

Q22. What happens to buffer pH when a small amount of strong acid is added?

• pH increases dramatically
• pH decreases slightly due to neutralization by conjugate base
• No change at all
• Buffer converts to pure acid

Correct Answer: pH decreases slightly due to neutralization by conjugate base

Q23. Which buffer component participates in ammonia transport and pH regulation in kidney?

• Albumin
• Phosphate
• Tris
• Acetate

Correct Answer: Phosphate

Q24. The Henderson–Hasselbalch equation is most reliable when:

• The acid is strong
• The buffer components are highly dilute
• There is a well-defined weak acid/conjugate base pair and activity coefficients ~1
• Temperature varies widely

Correct Answer: There is a well-defined weak acid/conjugate base pair and activity coefficients ~1

Q25. Which is a major limitation when using phosphate buffers in parenteral formulations?

• Strong odor
• Possible precipitation with divalent cations and incompatibilities
• Too high buffer capacity
• Unstable pKa

Correct Answer: Possible precipitation with divalent cations and incompatibilities

Q26. Which statement about blood buffering is true?

• Only bicarbonate buffers blood pH
• Hemoglobin both transports O2 and buffers H+ in red blood cells
• Plasma proteins have no buffering role
• Buffering is not important for enzymatic function

Correct Answer: Hemoglobin both transports O2 and buffers H+ in red blood cells

Q27. Which parameter must be adjusted when preparing a buffer to a precise pH in lab?

• Final volume only
• Ratio of conjugate base to acid and ionic strength
• Boiling point
• Evaporation rate

Correct Answer: Ratio of conjugate base to acid and ionic strength

Q28. A buffer solution contains 0.05 M HA and 0.05 M A−. If 0.005 mol strong base is added to 1 L, what happens to pH qualitatively?

• Large increase in pH
• Small increase in pH because buffer neutralizes base
• pH drops to 1
• Solution becomes non-buffering

Correct Answer: Small increase in pH because buffer neutralizes base

Q29. Which buffer system plays a significant role in the urine for acid excretion?

• Bicarbonate buffer only
• Phosphate buffer and ammonium buffer
• Hemoglobin buffer
• Glycogen buffer

Correct Answer: Phosphate buffer and ammonium buffer

Q30. For a weak base buffer, Henderson–Hasselbalch can be written in terms of pKb. Which form is equivalent?

• pOH = pKb + log([B]/[BH+])
• pH = pKb + log([B]/[BH+])
• pH = pKb – log([B]/[BH+])
• pKa = pKb + 7

Correct Answer: pOH = pKb + log([B]/[BH+])

Q31. Which of these factors does NOT directly affect buffer capacity?

• Total concentration of buffer components
• Ratio of acid to conjugate base
• Temperature affecting pKa slightly
• Color of the solution

Correct Answer: Color of the solution

Q32. When designing a formulation to maintain drug stability at pH 5.0, which buffer would be appropriate?

• HEPES (pKa ~7.5)
• Acetate buffer (pKa ~4.76)
• Tris (pKa ~8.1)
• Phosphate (pKa ~2.1)

Correct Answer: Acetate buffer (pKa ~4.76)

Q33. Which statement describes buffer dilution effect on pH?

• Dilution always changes pH by 1 unit
• Dilution does not change pH significantly if ratio [A-]/[HA] remains constant
• Dilution converts buffer to acid
• Dilution increases buffer capacity

Correct Answer: Dilution does not change pH significantly if ratio [A-]/[HA] remains constant

Q34. The major extracellular buffer that responds rapidly to respiratory changes is:

• Hemoglobin
• Bicarbonate buffer regulated by lungs and kidneys
• Phosphate buffer only in cells
• Albumin exclusively

Correct Answer: Bicarbonate buffer regulated by lungs and kidneys

Q35. Which buffer is preferred for cell culture media because of minimal interaction with metal ions and biological systems?

• Glycine
• HEPES
• Hydrochloric acid
• Sodium hydroxide

Correct Answer: HEPES

Q36. In metabolic acidosis, which buffering system compensates over hours to days?

• Lung ventilation changes
• Renal bicarbonate reclamation and H+ secretion
• Immediate hemoglobin buffering only
• Skin buffering

Correct Answer: Renal bicarbonate reclamation and H+ secretion

Q37. Which equation estimates buffer capacity (β) qualitatively?

• β = 2.303 × total buffer concentration × ( [A-][HA] / ([A-] + [HA]) )
• β = pH × pKa
• β = [H+] / [OH-]
• β = molecular weight of buffer

Correct Answer: β = 2.303 × total buffer concentration × ( [A-][HA] / ([A-] + [HA]) )

Q38. Which buffer would be least suitable for a formulation exposed to refrigerated storage due to pKa temperature sensitivity?

• Phosphate (stable pKa)
• Tris (pKa highly temperature-dependent)
• Acetate (relatively stable)
• Citric (relatively stable)

Correct Answer: Tris (pKa highly temperature-dependent)

Q39. What is the effect of ionic strength on buffer pKa and activity coefficients?

• Ionic strength has no effect
• Increased ionic strength alters activity coefficients and apparent pKa
• Ionic strength only affects color
• Activity coefficients are constant at all ionic strengths

Correct Answer: Increased ionic strength alters activity coefficients and apparent pKa

Q40. Which of the following is an advantage of using zwitterionic buffers in biological assays?

• They strongly chelate metal ions
• They minimize interactions with enzymes and metal ions and have stable pKa
• They change color with pH
• They are highly reactive with proteins

Correct Answer: They minimize interactions with enzymes and metal ions and have stable pKa

Q41. The buffering action of proteins primarily arises from which groups?

• Side chains of ionizable amino acids like histidine, lysine, glutamate
• Nonpolar residues like leucine
• Peptide bonds only
• Carbohydrate moieties

Correct Answer: Side chains of ionizable amino acids like histidine, lysine, glutamate

Q42. Which buffer pair would be most suitable to maintain pH 7.4 in a biological assay?

• Acetate/Acetic acid
• Phosphate/H2PO4- (pKa ~7.2) or HEPES (pKa ~7.5)
• Formate/Formic acid
• Citrate/Citric acid only

Correct Answer: Phosphate/H2PO4- (pKa ~7.2) or HEPES (pKa ~7.5)

Q43. What is the equivalence point pH when titrating a weak acid with a strong base?

• Always pH 7
• Greater than 7 due to conjugate base hydrolysis
• Less than 7
• Exactly equal to pKa

Correct Answer: Greater than 7 due to conjugate base hydrolysis

Q44. In buffer selection for parenteral drug products, which consideration is critical?

• Buffer must change color on exposure
• Buffer pH should be compatible with drug stability and patient physiology, and avoid incompatibilities
• Buffer should have strong smell
• Buffer must be highly reactive with container materials

Correct Answer: Buffer pH should be compatible with drug stability and patient physiology, and avoid incompatibilities

Q45. A buffer composed of a weak acid with pKa 3.8 will be effective in which pH range?

• pH 0–1
• pH 2.8–4.8
• pH 7–9
• pH 10–12

Correct Answer: pH 2.8–4.8

Q46. Which is true about the bicarbonate buffer equation relating pH, pKa, and concentrations in blood?

• pH = pKa + log([H2CO3]/[HCO3-])
• pH = pKa + log([HCO3-]/0.03×pCO2) where 0.03 is solubility coefficient for CO2
• pH is independent of pCO2
• Bicarbonate does not participate in Henderson–Hasselbalch

Correct Answer: pH = pKa + log([HCO3-]/0.03×pCO2) where 0.03 is solubility coefficient for CO2

Q47. In designing a buffer for enzyme assays, why avoid buffers that chelate divalent cations?

• Chelation increases buffer pH
• Chelation may inhibit metalloenzymes or remove essential cofactors
• Chelation enhances enzyme activity always
• Chelation reduces buffer capacity only

Correct Answer: Chelation may inhibit metalloenzymes or remove essential cofactors

Q48. How does temperature generally affect buffer pKa?

• pKa is constant with temperature
• pKa can shift with temperature; effect depends on the enthalpy of dissociation
• Temperature only affects color
• pKa becomes zero at high temperature

Correct Answer: pKa can shift with temperature; effect depends on the enthalpy of dissociation

Q49. What is the practical implication of buffer capacity being highest when [A-] ≈ [HA]?

• Buffer should be highly diluted
• Prepare buffers with acid and conjugate base concentrations approximately equal for maximal resistance to pH change
• Buffers should be prepared with only acid
• Buffer capacity is irrelevant in formulations

Correct Answer: Prepare buffers with acid and conjugate base concentrations approximately equal for maximal resistance to pH change

Q50. In acid-base physiology, respiratory compensation primarily affects which parameter to restore pH?

• Renal HCO3- reabsorption
• Plasma protein concentration
• pCO2 through changes in ventilation
• Extracellular phosphate concentration

Correct Answer: pCO2 through changes in ventilation

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com