Medical Biochemistry II PAPER A (MBMB 2200) – 16 MCQs | Kenya MBChB

16 Year 2: Clinical Biochemistry exam questions on Medical Biochemistry II PAPER A (MBMB 2200) for medical students. Includes MCQs, answers, explanations and wr

This MCQ set contains 16 questions on Medical Biochemistry II PAPER A (MBMB 2200) in the Year 2: Clinical Biochemistry unit. Each question includes the correct answer and a detailed explanation for active recall and exam preparation.

Q1: The probability that disease is present when a test result falls outside reference interval is called the test's

  1. A. Specificity
  2. B. Sensitivity
  3. C. Positive predictive value
  4. D. Efficiency
  5. E. Negative predictive value

Correct answer: C – Positive predictive value

Positive predictive value (PPV) represents the probability that a patient actually has the disease when the test result is positive (outside reference interval). It depends on both test characteristics and disease prevalence. ---

Q2: The molecule that serves as the major source of readily available fuel for neurons and blood cells is

  1. A. Fat
  2. B. Glucose
  3. C. Acetyl CoA
  4. D. Cellulose
  5. E. Glycogen

Correct answer: B – Glucose

Glucose is the primary energy source for neurons and red blood cells. Neurons have limited ability to use alternative fuels, and RBCs lack mitochondria, making glucose essential for their ATP production via glycolysis. ---

Q3: Ammonia is an effective and important urinary buffer for which of the following reasons

  1. A. Its production in the kidney decreases during chronic acidosis
  2. B. The walls of the renal tubules are impermeable to NH3
  3. C. The walls of the renal tubules are impermeable to NH4+
  4. D. Its acid base reaction has a low pKa
  5. E. None of the above

Correct answer: C – The walls of the renal tubules are impermeable to NH4+

NH3 diffuses into tubular fluid where it combines with H+ to form NH4+. The tubular membrane is impermeable to NH4+, effectively trapping it in urine and facilitating acid excretion. ---

Q4: Which of the choices below is not a fate of carbohydrate taken into the body

  1. A. ATP production
  2. B. Lipogenesis
  3. C. Amino acid synthesis
  4. D. Conversion to a nucleic acid
  5. E. Glycogenesis

Correct answer: D – Conversion to a nucleic acid

While carbohydrates can provide ribose for nucleic acid synthesis, they are not directly converted to nucleic acids. The other options are all direct metabolic fates of carbohydrates. ---

Q5: The amount of potassium excreted by the kidney will decrease if

  1. A. Distal tubular flow increases
  2. B. Circulating aldosterone levels increase
  3. C. Dietary intake of potassium increases
  4. D. Na+ reabsorption by the distal nephron decreases
  5. E. The excretion of organic ions increases

Correct answer: B – Circulating aldosterone levels increase

Aldosterone promotes Na+ reabsorption and K+ secretion in the distal nephron. However, when aldosterone levels increase, it also enhances overall K+ conservation mechanisms, leading to decreased K+ excretion. ---

Q6: Dietary fats are important because they

  1. A. Keep blood pressure normal
  2. B. Help the body absorb fat-soluble vitamins
  3. C. Contribute significantly to the health of the skin
  4. D. Help prevent the common cold
  5. E. None of the above

Correct answer: B – Help the body absorb fat-soluble vitamins

Dietary fats are essential for absorption of fat-soluble vitamins (A, D, E, K) in the intestine. These vitamins require lipid micelles for proper absorption. ---

Q7: An increase in the concentration of plasma potassium causes increases in

  1. A. Release of renin
  2. B. Secretion of aldosterone
  3. C. Secretion of ADH
  4. D. Release of natriuretic hormone
  5. E. Production of angiotensin II

Correct answer: B – Secretion of aldosterone

Hyperkalemia directly stimulates aldosterone secretion from the adrenal cortex, which promotes K+ excretion in the distal nephron to restore K+ homeostasis. ---

Q8: When proteins undergo deamination, the waste substance found in the urine is mostly

  1. A. Acetyl CoA
  2. B. Ketone bodies
  3. C. Urea
  4. D. Creatinine
  5. E. Ammonia

Correct answer: C – Urea

Protein deamination produces ammonia, which is converted to urea in the liver via the urea cycle. Urea is the major nitrogenous waste product excreted in human urine. ---

Q9: Glomerular filtration rate would be increased by

  1. A. Constriction of the afferent arteriole
  2. B. A decrease in afferent arteriolar pressure
  3. C. Compression of the renal capsule
  4. D. A decrease in the concentration of plasma protein
  5. E. A decrease in renal blood flow

Correct answer: D – A decrease in the concentration of plasma protein

Decreased plasma protein concentration reduces oncotic pressure, decreasing the force opposing filtration and thereby increasing GFR. ---

Q10: Lipogenesis occurs when

  1. A. There is a shortage of fatty acids
  2. B. Glucose levels drop slightly
  3. C. Excess proteins are transported through the cell membrane
  4. D. Starvation
  5. E. Cellular ATP and glucose levels are high

Correct answer: E – Cellular ATP and glucose levels are high

Lipogenesis (fat synthesis) occurs during fed state when energy (ATP) and substrate (glucose) are abundant, allowing conversion of excess carbohydrates to fat for storage. ---

Q11: The greatest amount of hydrogen ion secreted by the proximal tubule is associated with

  1. A. Excretion of potassium ion
  2. B. Excretion of hydrogen ion
  3. C. Reabsorption of calcium ion
  4. D. Reabsorption of bicarbonate ion
  5. E. Reabsorption of phosphate ion

Correct answer: D – Reabsorption of bicarbonate ion

About 80-90% of filtered bicarbonate is reabsorbed in the proximal tubule via H+ secretion, making bicarbonate reabsorption the major mechanism of proximal H+ secretion. ---

Q12: Oxidative deamination takes place in the

  1. A. Liver
  2. B. Muscles
  3. C. Kidneys
  4. D. Blood
  5. E. Brain

Correct answer: A – Liver

The liver is the primary site of oxidative deamination where amino acids are deaminated to produce ammonia, which is then converted to urea. ---

Q13: Urinalysis is comprised of all of the following except

  1. A. Macroscopic analysis
  2. B. Dipstick testing
  3. C. Microscopic analysis
  4. D. Chemical analysis
  5. E. All of the above

Correct answer: E – All of the above

This is a trick question. Urinalysis includes all listed components: macroscopic (physical), chemical (dipstick), and microscopic analysis. ---

Q14: Glycogen is formed in the liver during the

  1. A. Pre-absorptive state
  2. B. Post absorptive state
  3. C. Absorptive state
  4. D. Starvation period
  5. E. Period when the metabolic rate is lowest

Correct answer: C – Absorptive state

Glycogenesis (glycogen synthesis) occurs during the absorptive state when glucose is abundant after eating, allowing storage of excess glucose as glycogen. ---

Q15: Urine that is not tested immediately or refrigerated before testing will give inaccurate results due to all of the following except

  1. A. Increased acidity
  2. B. Dissolution of cells and casts
  3. C. Reduced clarity due to crystallization of solutes
  4. D. Overgrowth of contaminating microorganisms
  5. E. None of the above

Correct answer: A – Increased acidity

Urine typically becomes more alkaline (not acidic) upon standing due to bacterial conversion of urea to ammonia. The other changes all occur with delayed testing. ---

Q16: Which of the following is a normal consequence of the activation of the heat-promoting center

  1. A. Release of epinephrine
  2. B. Sympathetic sweat gland activation
  3. C. Increase in ADH production
  4. D. Vasodilation of cutaneous blood vessels
  5. E. Vasoconstriction of cutaneous blood vessels

Correct answer: E – Vasoconstriction of cutaneous blood vessels

Heat-promoting center activation causes vasoconstriction of skin blood vessels to conserve body heat by reducing heat loss

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