Daily Olympiad: Biology - Human Physiology [20260511] – 6 Practice Problems & Printable PDF

1. Which sequence correctly represents the conduction pathway of electrical impulses in the heart?

A. SA node → Bundle of His → Purkinje fibers → AV node B. AV node → SA node → Bundle of His → Purkinje fibers C. SA node → AV node → Bundle of His → Purkinje fibers D. Bundle of His → AV node → SA node → Purkinje fibers

Solution

Correct: C

The sinoatrial (SA) node acts as the pacemaker, initiating the impulse. The electrical signal then travels to the atrioventricular (AV) node, which delays the impulse briefly. From there, the impulse moves through the bundle of His, splits into the right and left bundle branches, and finally reaches the Purkinje fibers for rapid ventricular depolarization.

2. Which of the following factors is the primary driving force for the diffusion of oxygen across the alveolar-capillary membrane?

A. Partial pressure gradient of oxygen B. Oxygen-carrying capacity of blood C. Surface area of the alveoli D. Diffusion coefficient of oxygen

Solution

Correct: A

Oxygen diffuses across the alveolar membrane due to the partial pressure gradient (alveoli to capillaries). The other factors (surface area, diffusion coefficient) influence the rate but not the primary direct mechanism.

3. During the countercurrent multiplication in the loop of Henle, which segment is impermeable to water but actively transports salts?

A. Proximal convoluted tubule B. Descending limb C. Ascending limb D. Distal convoluted tubule

Solution

Correct: C

The ascending limb of the loop of Henle is impermeable to water and actively transports Na⁺ and Cl⁻ out of the filtrate via secondary active transport. The descending limb is water-permeable but not salt-reabsorbing, while the PCT and DCT have different reabsorption roles.

4. Which enzyme secreted by the stomach is responsible for breaking down dietary protein into polypeptides?

A. Lipase B. Pepsin C. Amylase D. Trypsin

Solution

Correct: B

Pepsin is secreted as pepsinogen by gastric chief cells and activates in low pH to break down proteins into polypeptides. Trypsin is pancreatic and acts in the duodenum.

5. An inhibitory postsynaptic potential (IPSP) is caused by an increase in the permeability of postsynaptic neurons to:

A. Na⁺ ions B. K⁺ ions C. Ca²⁺ ions D. Cl⁻ ions

Solution

Correct: D

IPSP hyperpolarizes the postsynaptic neuron, typically via Cl⁻ ion influx (e.g., GABA/glycine receptors) or K⁺ efflux. This inhibits action potential propagation.

6. A patient presents with reduced basal metabolic rate, weight gain, and cold intolerance. Which hormone deficiency is most likely?

A. Luteinizing Hormone (LH) B. Thyroid-Stimulating Hormone (TSH) C. Cortisol D. Insulin

Solution

Correct: B

These symptoms align with hypothyroidism. Hypothalamic-pituitary feedback would elevate TSH if the issue is primary thyroid dysfunction. A deficit in TSH itself would be less likely to cause cold intolerance.

Daily Olympiad: Biology - Human Physiology [20260511]

1. Which sequence correctly represents the conduction pathway of electrical impulses in the heart?

2. Which of the following factors is the primary driving force for the diffusion of oxygen across the alveolar-capillary membrane?

3. During the countercurrent multiplication in the loop of Henle, which segment is impermeable to water but actively transports salts?

4. Which enzyme secreted by the stomach is responsible for breaking down dietary protein into polypeptides?

5. An inhibitory postsynaptic potential (IPSP) is caused by an increase in the permeability of postsynaptic neurons to:

6. A patient presents with reduced basal metabolic rate, weight gain, and cold intolerance. Which hormone deficiency is most likely?

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