IB Biology Quiz: Apply Gas Exchange
17 questions · exam conditions
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Apply Gas ExchangeQuestion 1 of 17

Carbon monoxide poisoning is life-threatening. Its primary mechanism of toxicity involves its interaction with hemoglobin. Which statement most accurately describes this interaction and its consequence?

CO binds irreversibly to the active site of carbonic anhydrase, preventing CO₂ transport and causing acidosis.
CO causes oxidation of the iron in hemoglobin to Fe³⁺, forming methemoglobin which cannot bind oxygen.
CO competes with oxygen for binding sites on hemoglobin, but also increases the affinity of the remaining sites for oxygen.
CO directly damages the alveolar-capillary membrane, leading to pulmonary edema and increased diffusion distance.
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IB Biology Quiz

IB Biology Quiz: Apply Gas Exchange

Practice Apply Gas Exchange in IB Biology with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.

What this quiz covers

This quiz focuses on Apply Gas Exchange, giving you a quick way to practice the rules, question types, and explanations that matter most for IB Biology.

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Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

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Question 1

Carbon monoxide poisoning is life-threatening. Its primary mechanism of toxicity involves its interaction with hemoglobin. Which statement most accurately describes this interaction and its consequence?

  1. CO binds irreversibly to the active site of carbonic anhydrase, preventing CO₂ transport and causing acidosis.
  2. CO causes oxidation of the iron in hemoglobin to Fe³⁺, forming methemoglobin which cannot bind oxygen.
  3. CO competes with oxygen for binding sites on hemoglobin, but also increases the affinity of the remaining sites for oxygen. (correct answer)
  4. CO directly damages the alveolar-capillary membrane, leading to pulmonary edema and increased diffusion distance.
Explanation: CO has an affinity for hemoglobin over 200 times that of O₂. It competitively inhibits O₂ binding, reducing the oxygen-carrying capacity. A more subtle and dangerous effect is that CO binding to one site on a hemoglobin molecule increases the binding affinity of the remaining sites for O₂. This shifts the oxygen dissociation curve to the left and makes it harder for the bound oxygen to be released to the tissues. Distractor A describes the action of certain inhibitors but not CO. Distractor B describes methemoglobinemia, caused by other agents. Distractor D is incorrect; CO is a systemic poison that does not cause direct lung injury.

Question 2

Pulmonary surfactant is a substance that prevents the collapse of alveoli. In cases of respiratory distress syndrome in premature infants, insufficient surfactant is produced. What is the primary biophysical reason for the resulting difficulty in breathing?

  1. The diffusion distance across the alveolar epithelium is increased, slowing down gas exchange.
  2. High surface tension of the fluid lining the alveoli creates a large pressure that opposes inflation. (correct answer)
  3. The elastic recoil of the lung tissue is lost, preventing passive expiration and trapping air.
  4. The partial pressure of oxygen in the inspired air is effectively lowered due to chemical reactions with the alveolar fluid.
Explanation: Surfactant is a complex of lipids and proteins that reduces the surface tension of the aqueous film lining the alveoli. Without it, the high surface tension of water would cause the small alveoli to collapse and require a very large pressure to re-inflate during inspiration. Distractor A is incorrect; surfactant does not change the thickness of the epithelial cells. Distractor C is incorrect; the problem is with inflation, not the loss of elastic recoil, which is more characteristic of emphysema. Distractor D is incorrect; the composition of inspired air is unchanged.

Question 3

The primary stimulus for changes in the rate and depth of breathing in a healthy person at rest is detected by chemoreceptors. Which event provides the most powerful and direct stimulus to the respiratory centre in the medulla?

  1. A significant drop in blood pO₂, detected by peripheral chemoreceptors in the aorta and carotid arteries.
  2. A slight increase in blood pCO₂, leading to a decrease in the pH of the cerebrospinal fluid. (correct answer)
  3. A rise in blood lactate concentration during anaerobic exercise, detected by central chemoreceptors.
  4. Voluntary signals originating from the cerebral cortex to increase the ventilation rate.
Explanation: The respiratory centre in the medulla is most sensitive to changes in the pH of the cerebrospinal fluid (CSF). CO₂ from the blood diffuses into the CSF, where it forms carbonic acid and lowers the pH. This provides the primary drive for breathing. Distractor A is incorrect because the response to low pO₂ is much less sensitive and only becomes a major factor at very low oxygen levels (e.g., high altitude). Distractor C is incorrect because lactate and H⁺ ions in the blood do not easily cross the blood-brain barrier to affect the central chemoreceptors directly, though they can stimulate peripheral ones. Distractor D refers to conscious control, not the primary homeostatic mechanism.

Question 4

Which sequence correctly describes the mechanism of a quiet inspiration in a human?

  1. Alveolar pressure drops, air flows in, diaphragm contracts, thoracic volume increases.
  2. Diaphragm and external intercostals contract, thoracic volume increases, alveolar pressure drops below atmospheric pressure, air flows in. (correct answer)
  3. Air flows in, thoracic volume increases, alveolar pressure drops, diaphragm and external intercostals contract.
  4. Thoracic volume increases, diaphragm and external intercostals relax, alveolar pressure drops below atmospheric pressure, air flows in.
Explanation: The correct causal sequence for inspiration is: 1) Contraction of respiratory muscles (diaphragm, external intercostals). 2) This increases the volume of the thoracic cavity. 3) The increase in volume leads to a drop in intra-alveolar pressure to below atmospheric pressure. 4) Air then flows down the pressure gradient into the lungs. All other options present an incorrect or illogical sequence of these events.

Question 5

The air inhaled at sea level has a partial pressure of oxygen (pO₂) of approximately 21 kPa. However, the pO₂ in the alveoli is only about 14 kPa. Which factor is the most significant contributor to this reduction?

  1. The rapid diffusion of oxygen from the alveoli into the pulmonary capillaries.
  2. The mixing of fresh inspired air with the residual volume of air that remains in the lungs after exhalation. (correct answer)
  3. The active transport of oxygen out of the alveoli by type II pneumocytes.
  4. The increased partial pressure of nitrogen gas in the alveoli, which displaces oxygen.
Explanation: The air in the lungs is never fully replaced with each breath. Fresh air (high pO₂) mixes with the functional residual capacity of air that remained from the previous cycle (lower pO₂, higher pCO₂). This mixing, along with the saturation of the air with water vapour, lowers the pO₂ of the alveolar gas mixture compared to the inhaled atmospheric air. Distractor A is the reason pO₂ in the capillaries rises, but it is the consequence, not the cause, of the alveolar pO₂. Distractor C is incorrect as gas exchange is passive. Distractor D is incorrect as the partial pressure of nitrogen actually decreases slightly in the alveoli.

Question 6

A pneumothorax is a condition where air enters the pleural cavity, the space between the chest wall and the lung. This leads to a collapsed lung because:

  1. the pressure in the pleural cavity becomes positive, actively compressing the lung tissue.
  2. the surface tension of the pleural fluid is eliminated, causing the lung to detach from the thoracic wall.
  3. the negative intrapleural pressure that holds the lung open is lost as it equilibrates with atmospheric pressure. (correct answer)
  4. the diaphragm is unable to contract due to the increased pressure within the thoracic cavity.
Explanation: The lungs are held open against their natural elastic recoil by the negative pressure (sub-atmospheric pressure) within the pleural cavity. If this cavity is breached and air enters, the intrapleural pressure equalizes with the atmospheric pressure. The loss of this negative pressure 'suction' allows the lung's inherent elasticity to cause it to collapse. Distractor A is incorrect; the pressure equalizes, it doesn't become highly positive. Distractor B is a contributing factor but the loss of the pressure gradient is the primary mechanism. Distractor D is incorrect; the diaphragm can still contract, but its movement will not inflate the collapsed lung.

Question 7

In large, active insects, the tracheal system is ventilated by rhythmic body movements. If this ventilation process is experimentally inhibited, what is the first consequence for gas exchange at the tissues?

  1. The partial pressure of CO₂ in the tissues will rise, leading to a drop in hemolymph pH.
  2. The fluid at the ends of the tracheoles will be drawn back, increasing the surface area for diffusion.
  3. Oxygen-carrying pigments in the hemolymph will release their stored oxygen to compensate.
  4. The concentration gradient for oxygen between the tracheoles and the muscle cells will decrease. (correct answer)
Explanation: Active ventilation in insects functions to replenish the air in the main tracheae, maintaining a high pO₂ deep within the body. If this process is stopped, respiring cells will continue to consume O₂, lowering the pO₂ at the ends of the tracheoles. This reduces the partial pressure gradient between the air in the tracheoles and the mitochondria in the cells, slowing the rate of oxygen diffusion to the tissues. Distractor A will also happen, but the drop in the O₂ gradient is the most immediate problem for aerobic respiration. Distractor B describes a mechanism to increase diffusion, which would not happen if ventilation is inhibited. Distractor C is incorrect as most insects do not use hemolymph or pigments for O₂ transport.

Question 8

A spirometer records a person's vital capacity as 4.8 L, tidal volume as 0.5 L, and breathing rate as 15 breaths per minute. During maximal exercise, their breathing rate increases to 45 breaths per minute and their tidal volume increases to 3.5 L. What is the approximate increase in their minute ventilation from rest to maximal exercise?

  1. 150.0 L·min⁻¹ (correct answer)
  2. 157.5 L·min⁻¹
  3. 7.5 L·min⁻¹
  4. 165.0 L·min⁻¹
Explanation: Minute ventilation = Tidal Volume × Breathing Rate. First, calculate resting minute ventilation: 0.5 L/breath × 15 breaths/min = 7.5 L·min⁻¹. Next, calculate exercise minute ventilation: 3.5 L/breath × 45 breaths/min = 157.5 L·min⁻¹. The question asks for the increase, so subtract: 157.5 L·min⁻¹ - 7.5 L·min⁻¹ = 150.0 L·min⁻¹. The vital capacity information is not needed for this calculation.

Question 9

An individual has a genetic disorder that results in the production of abnormally thick and sticky mucus lining their airways. How would this condition directly impede gas exchange?

  1. The mucus increases the surface tension in the alveoli, causing them to collapse during expiration.
  2. The mucus blocks nerve signals to respiratory muscles, preventing effective ventilation movements.
  3. The mucus chemically binds to oxygen molecules, reducing the partial pressure available for diffusion.
  4. The mucus layer increases the diffusion distance between the alveolar air and the pulmonary capillaries. (correct answer)
Explanation: According to Fick's law of diffusion, the rate of diffusion is inversely proportional to the thickness of the diffusion barrier. An abnormally thick layer of mucus increases the distance that oxygen must travel to reach the blood and that carbon dioxide must travel to be exhaled. This slows the rate of gas exchange. Additionally, the mucus can block smaller airways, preventing ventilation of some alveoli. A describes a surfactant deficiency. C is biochemically incorrect as mucus does not chemically bind oxygen. D is incorrect as this condition affects mucus secretion, not neural control.

Question 10

In the counter-current exchange system of fish gills, blood flows through the lamellae in the opposite direction to the water flowing over them. What would be the immediate consequence if the system were a concurrent flow (blood and water in the same direction)?

  1. The partial pressure of oxygen in the blood would reach equilibrium with the water at approximately 50% of the water's initial oxygen concentration. (correct answer)
  2. The blood would become fully saturated with oxygen, but over a much longer section of the lamella to achieve this.
  3. The diffusion gradient for carbon dioxide from blood to water would be maximized, improving its removal.
  4. The rate of diffusion of oxygen into the blood would be greatest at the end of the lamella, just before the blood exits.
Explanation: In a concurrent system, blood and water flow in the same direction. A steep diffusion gradient exists initially, but it rapidly decreases as both fluids approach equilibrium. Equilibrium would be reached when the pO₂ in both blood and water is equal, at about 50% of the initial water pO₂. This is far less efficient than counter-current flow, which maintains a gradient across the entire length of the lamella, allowing blood pO₂ to exceed 80% saturation. Distractor B is incorrect; full saturation is not possible. Distractor C is incorrect; the CO₂ gradient would also become less efficient. Distractor D is incorrect; the greatest diffusion rate would be at the beginning of the lamella where the gradient is steepest.

Question 11

Birds possess a unique respiratory system with unidirectional air flow across parabronchi, which is more efficient than the tidal flow in mammals. What feature of the avian system explains this enhanced efficiency?

  1. It allows gas exchange to occur during both inhalation and exhalation, continuously refreshing the gas exchange surface with oxygenated air. (correct answer)
  2. It utilizes a counter-current exchange mechanism between air in the parabronchi and the blood, similar to fish gills.
  3. It has a much larger total volume of air sacs compared to the lung volume of a similarly sized mammal, storing more oxygen.
  4. It completely lacks anatomical dead space because air from the trachea flows directly to the posterior air sacs.
Explanation: Due to the arrangement of air sacs, it takes two full respiratory cycles for a bolus of air to move through the avian system. This complex pathway ensures that air flowing over the gas exchange surfaces (parabronchi) is always fresh, oxygenated air moving in one direction, both during the first inhalation/exhalation and the second. This avoids the mixing of fresh and stale air that occurs in mammalian lungs, maintaining a steeper concentration gradient. B is incorrect; it's a cross-current exchange, not counter-current. C is true, but it's the flow system, not the storage volume, that is the key to efficiency. D is incorrect; dead space still exists in the trachea and primary bronchi.

Question 12

The Bohr effect describes the rightward shift of the oxygen-hemoglobin dissociation curve in response to increased pCO₂ or decreased pH. Where in the body is this effect most physiologically significant for gas exchange?

  1. In the alveoli, where high pH promotes the loading of oxygen onto hemoglobin.
  2. In the aorta, where high blood pressure enhances the binding of oxygen to hemoglobin.
  3. In the pulmonary artery, where low pO₂ causes the dissociation curve to shift right.
  4. In the systemic capillaries of exercising muscle, where high CO₂ promotes the unloading of oxygen from hemoglobin. (correct answer)
Explanation: The Bohr effect is most significant in metabolically active tissues. During exercise, muscle cells produce large amounts of CO₂ and lactic acid, which lowers the pH of the surrounding blood. This drop in pH (and increase in pCO₂) causes hemoglobin to decrease its affinity for oxygen, shifting the curve to the right and facilitating the release of a larger amount of oxygen to the tissues that need it most. In the alveoli (A), the opposite occurs (Haldane effect), where high O₂ and low CO₂ promote oxygen loading. C and D describe locations but not the mechanism of the Bohr effect.

Question 13

The oxygen dissociation curve of fetal hemoglobin is shifted to the left compared to that of adult hemoglobin. What is the physiological advantage of this property for gas exchange at the placenta?

  1. It allows fetal hemoglobin to release oxygen more readily to the developing tissues.
  2. It enables fetal hemoglobin to bind oxygen tightly at the low partial pressures present in the maternal blood of the placenta. (correct answer)
  3. It increases the total oxygen carrying capacity of fetal blood compared to adult blood.
  4. It facilitates the unloading of carbon dioxide from the fetal blood into the maternal circulation.
Explanation: A left-shifted curve indicates a higher affinity for oxygen. In the placenta, the pO₂ is relatively low. Fetal hemoglobin's higher affinity allows it to effectively 'pull' oxygen away from the mother's hemoglobin and become saturated, ensuring the fetus receives adequate oxygen. Distractor A is incorrect; a higher affinity means it releases oxygen less readily at a given pO₂ (this is overcome by the very low pO₂ in fetal tissues). Distractor C is incorrect; the shift affects affinity, not the carrying capacity per gram of hemoglobin. Distractor D is incorrect; the curve relates to oxygen binding, not directly to CO₂ transport.

Question 14

Emphysema is a lung disease where the walls of the alveoli break down and merge. How does this structural change most significantly impair gas exchange?

  1. It causes widespread inflammation and mucus production, which increases airway resistance.
  2. It thickens the respiratory membrane, which increases the diffusion path length for gases.
  3. It reduces the total surface area for diffusion and decreases the elastic recoil of the lungs. (correct answer)
  4. It paralyzes the cilia lining the bronchi, preventing the removal of trapped pathogens.
Explanation: The defining characteristic of emphysema is the destruction of alveolar walls. This merging of alveoli drastically reduces the total surface area available for gas diffusion. A secondary effect is the loss of elastin fibres, which reduces the lung's ability to recoil passively during expiration, making it difficult to exhale. Distractor A describes chronic bronchitis. Distractor B describes pulmonary fibrosis. Distractor D is a consequence of smoking but not the primary mechanism of impairment in emphysema itself.

Question 15

An athlete moves from sea level to train at high altitude. After several weeks of acclimatization, which physiological adaptation would be most effective in enhancing oxygen delivery to their muscles?

  1. A permanent increase in both the rate and depth of breathing to match the ventilation rate at sea level.
  2. A decrease in the affinity of hemoglobin for oxygen, permanently shifting the dissociation curve to the right.
  3. An increase in the concentration of red blood cells and hemoglobin circulating in the bloodstream. (correct answer)
  4. A significant increase in the total surface area of the alveoli in the lungs through tissue growth.
Explanation: The most significant long-term adaptation to high altitude is an increase in the oxygen-carrying capacity of the blood. The kidneys release erythropoietin (EPO), which stimulates the bone marrow to produce more red blood cells (and thus more hemoglobin). This allows the blood to carry more oxygen per unit volume, compensating for the lower pO₂. Distractor A is a short-term response; hyperventilation is not sustained indefinitely. Distractor B describes a change that may occur due to increased 2,3-BPG, but the increase in hemoglobin is the more critical adaptation. Distractor D is incorrect; the lung's surface area is anatomically fixed and does not increase during acclimatization.

Question 16

Which statement correctly distinguishes between the processes of gas exchange and cellular respiration?

  1. Gas exchange is the production of ATP using oxygen, while cellular respiration is the intake of oxygen from the environment.
  2. Gas exchange is the passive diffusion of gases across a respiratory surface, while cellular respiration is the series of metabolic reactions that generate ATP. (correct answer)
  3. Gas exchange occurs only in the lungs of vertebrates, while cellular respiration occurs in all living cells.
  4. Gas exchange involves active transport of O₂ and CO₂, while cellular respiration is a passive process.
Explanation: This question addresses a common point of confusion. Gas exchange is a physical process involving the movement of gases (O₂, CO₂) between an organism and its environment across a specialized surface (e.g., alveoli, gills), driven by partial pressure gradients (diffusion). Cellular respiration is a chemical process that occurs within cells (cytoplasm and mitochondria) to break down organic molecules and produce ATP, often using the oxygen obtained via gas exchange. Distractor A reverses the definitions. Distractor C is incorrect as gas exchange occurs in many organisms without lungs, and cellular respiration does not occur in all living cells (e.g., some obligate anaerobes). Distractor D is incorrect as gas exchange is passive and cellular respiration involves many active steps.

Question 17

Which of the following comparisons between the gas exchange systems of a mammal and an insect is correct?

  1. In both systems, ventilation is always a passive process driven by the organism's movement.
  2. The respiratory surface in insects is internal to prevent water loss, while in mammals it is external.
  3. Both systems utilize a hemoglobin-like pigment to increase the oxygen-carrying capacity of their transport fluid.
  4. The mammal's circulatory system is integral to gas transport from the exchange surface, whereas the insect's is not. (correct answer)
Explanation: A key difference is the role of the circulatory system. In mammals, oxygen diffuses from the alveoli into the blood, where it is transported by hemoglobin to the tissues. In insects, the tracheal system is a network of air-filled tubes that extends directly to the respiring cells, bypassing the need for the circulatory system (hemolymph) to transport gases. A is incorrect; ventilation is an active process in mammals and in active insects. C is incorrect; insects do not use hemoglobin for oxygen transport. D is incorrect; both respiratory surfaces are internal.