USABO - USA Biology Olympiad Animal Physiology and Homeostasis Questions and Answers

Question 1

In the flippers of a seal swimming in icy water, which of the following best describes the function of the countercurrent heat exchanger?

Accepted Answer

Warm arterial blood flowing to the flipper transfers heat to the cold venous blood returning to the body core, reducing overall heat loss.

Answer

It concentrates solutes in the interstitial fluid to prevent the flipper from freezing.

Answer

It maximizes the diffusion of oxygen from the water into the blood vessels of the flippers.

Answer

It shunts cold blood directly back to the heart to be rapidly rewarmed by metabolic processes.

Question 2

A healthy individual consumes a large meal rich in carbohydrates. Which of the following represents the primary homeostatic response to the resulting increase in blood glucose?

Accepted Answer

Beta cells of the pancreas secrete insulin, promoting glucose uptake by cells and glycogenesis.

Answer

Alpha cells of the pancreas secrete glucagon, stimulating glycogenolysis.

Answer

The adrenal medulla secretes epinephrine, stimulating gluconeogenesis.

Answer

The posterior pituitary releases ADH, increasing water retention to dilute the blood glucose.

Question 3

An action potential is propagated unidirectionally along an axon, from the axon hillock to the terminal. What is the primary molecular mechanism that prevents the action potential from propagating backward?

Accepted Answer

The refractory period caused by the inactivation of voltage-gated sodium channels.

Answer

The hyperpolarization of the membrane following repolarization.

Answer

The immediate pumping of Na+ ions out of the cell by the Na+/K+ pump.

Answer

The selective permeability of the membrane to K+ ions during the resting state.

Question 4

During a period of intense exercise, the affinity of hemoglobin for oxygen changes to facilitate delivery to muscle tissues. Which of the following factors causes a 'right shift' in the oxygen-hemoglobin dissociation curve?

Accepted Answer

An increase in the partial pressure of CO2 and a decrease in blood pH.

Answer

An increase in blood pH and a decrease in temperature.

Answer

A decrease in the partial pressure of CO2 and an increase in 2,3-BPG.

Answer

A decrease in temperature and a decrease in blood pH.

Question 5

A patient is suffering from severe dehydration. How would the state of their urine and the level of Antidiuretic Hormone (ADH) compare to a normally hydrated individual?

Accepted Answer

Low volume of concentrated urine; high levels of ADH.

Answer

High volume of dilute urine; low levels of ADH.

Answer

Low volume of dilute urine; high levels of ADH.

Answer

High volume of concentrated urine; low levels of ADH.

Question 6

In the sliding filament model of muscle contraction, which of the following events directly triggers the 'power stroke' where the myosin head pivots and pulls the actin filament?

Accepted Answer

The release of inorganic phosphate (Pi) from the myosin head.

Answer

The binding of a new ATP molecule to the myosin head.

Answer

The hydrolysis of ATP into ADP and Pi by the myosin head.

Answer

The binding of Ca2+ to the myosin head.