All Free Biochemistry MCQs with Answers

• A. Serotonin
• B. Thyroxine
• C. Triidothyronine
• D. Parathyroid hormone

Explanation: Calcitonin lowers blood calcium mainly by inhibiting osteoclast-mediated bone resorption, opposing the calcium-raising action of…

• A. 1 : 1
• B. 30 : 1
• C. 15 : 1
• D. 20 : 1

Explanation: The bicarbonate buffer equation is pH = 6.1 + log([HCO3−]/[H2CO3]); at pH 7.4, the ratio is 10^1.3, approximately 20:1.

• A. Hydrolase
• B. Oxidase
• C. Peroxidase
• D. Dehydrogenase

Explanation: The respiratory burst begins when NADPH oxidase is activated in phagocytes, producing superoxide from molecular oxygen.

• A. 3 - 4 mg%
• B. 1 - 3 mg%
• C. 0.5 - 1 mg%
• D. 4 - 5.5 mg%

Explanation: Normal total blood bilirubin is approximately 0.2–1.2 mg/dL, commonly rounded in exam texts to about 0.5–1 mg%.

• A. Proteins
• B. K+
• C. Cl
• D. Na+

Explanation: Sodium is the principal extracellular cation and therefore the main electrolyte in ECF.

• A. Any of the above
• B. Reduction
• C. Conjugation
• D. Oxidation

Explanation: Detoxification reactions include oxidation, reduction and conjugation. Oxidation or reduction modifies a compound, while conjugation…

• A. Cytochrome
• B. Cytochrome C
• C. Cytochrome P450
• D. Cytochrome A

Explanation: Cytochrome P450 is a family of microsomal enzymes that carries out many drug oxidation and other phase I biotransformation reactions.

• A. 100-140 mgs/100 ml
• B. 260-360 mgs/100 ml
• C. 80-250 mgs/100 ml
• D. 150-250 mgs/100 ml

Explanation: A traditional reference range for total serum cholesterol is approximately 150–250 mg/dL, making that the closest listed range.

• A. Phosphosphingosides
• B. Phosphoinositides
• C. Glycerophosphatides
• D. Glycerosphingosides

Explanation: Niemann-Pick disease types A and B result from sphingomyelinase deficiency, causing sphingomyelin, a phosphosphingoside, to accumulate in…

• A. >135 mmol/L
• B. < 135 mmol/L
• C. < 160 mmo/L
• D. < 100 mmo/L

Explanation: Hyponatremia means a serum sodium concentration below 135 mmol/L. Values above this threshold are not hyponatremic, while below 100 mmol/L…

• A. Carbohydrates
• B. Micronutrients
• C. Fats
• D. Fibres

Explanation: Parenteral nutrition supplies carbohydrates, lipid-based fats, amino acids, water, electrolytes, vitamins and trace elements…

• A. 1-4 Bodansky units
• B. 1000-4000 Bodansky units
• C. 0.1-0.4 Bodansky units
• D. 100-400 Bodansky units

Explanation: The classical normal serum alkaline-phosphatase range is approximately 1 to 4 Bodansky units, making 1 to 4 the matching option.

• A. 300 to 320
• B. 280 to 295
• C. 350 to 375
• D. 200 to 250

Explanation: Normal plasma or serum osmolality is approximately 280 to 295 mOsm/kg, often rounded similarly in questions using mOsm/L.

• A. Kidney
• B. Liver
• C. Spleen
• D. Bone marrow

Explanation: Heme is broken down mainly by macrophages of the reticuloendothelial system, especially those in the spleen, forming biliverdin and then…

• A. 1-2 mgm%
• B. 7-9 mgm%
• C. 40-50 mgm%
• D. 2.5 - 4.5 mgm%

Explanation: Normal adult serum phosphate is approximately 2.5 to 4.5 mg/dL, also written as mg%.

• A. Potassium
• B. Protein
• C. Urea
• D. Phosphate

Explanation: Potassium is the principal intracellular cation and, with its accompanying anions, contributes greatly to intracellular osmolality.

• A. Myocardial infarction
• B. Muscular dystrophy
• C. Alcoholic cirrhosis
• D. Brain tumours

Explanation: CK-3 corresponds mainly to the CK-MM isoenzyme found in skeletal muscle, so it rises in muscular dystrophy and other skeletal-muscle…

• A. 4-6 mg/dl
• B. 9-11 mg/dl
• C. 19-21 mg/dl
• D. 20-30 mg/dl

Explanation: Normal total serum calcium is approximately 8.5-10.5 mg/dL, making 9-11 mg/dL the closest listed range.

• A. 2.8-3.8 meq/L
• B. 6-7.2 meq/L
• C. 5-5.8 meq/L
• D. 3.8-5 meq/L

Explanation: Normal serum potassium is roughly 3.5-5.0 mEq/L, with many references giving 3.8-5.0 mEq/L.

• A. Transferrin
• B. Ferritin
• C. Hemoglobin
• D. Ceruloplasmin

Explanation: Transferrin is the main plasma protein that binds and transports iron. Ferritin stores iron mainly inside cells, while haemoglobin carries…