IB Biology Quiz: Apply Transport
19 questions · exam conditions
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Apply TransportQuestion 1 of 19

A plant is kept in a controlled environment. Which of the following combinations of conditions would result in the highest rate of transpiration?

High humidity, low temperature, and still air.
Low humidity, high temperature, and light wind.
High humidity, high temperature, and still air.
Low humidity, low temperature, and light wind.
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IB Biology Quiz

IB Biology Quiz: Apply Transport

Practice Apply Transport 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 Transport, 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

A plant is kept in a controlled environment. Which of the following combinations of conditions would result in the highest rate of transpiration?

  1. High humidity, low temperature, and still air.
  2. Low humidity, high temperature, and light wind. (correct answer)
  3. High humidity, high temperature, and still air.
  4. Low humidity, low temperature, and light wind.
Explanation: The correct answer is B. Transpiration is the evaporation of water from the plant, primarily through stomata. The rate is highest when the water potential gradient between the moist interior of the leaf and the surrounding air is steepest. Low humidity means the air is dry, increasing the gradient. High temperature increases the kinetic energy of water molecules, promoting evaporation. Light wind removes the boundary layer of humid air from around the stomata, maintaining a steep gradient. All other options include at least one factor that reduces the transpiration rate: high humidity (A, C) reduces the water potential gradient, low temperature (A, D) reduces the rate of evaporation, and still air (A, C) allows a humid boundary layer to form.

Question 2

A student uses a potometer to investigate the effect of an environmental factor on the transpiration rate of a plant cutting. They observe that the air bubble in the capillary tube does not move. Assuming the plant is alive and the apparatus is assembled, which procedural error is the most likely cause of this observation?

  1. The end of the shoot was cut at an angle instead of straight across before being placed in the potometer.
  2. The experiment was conducted in a room with very high humidity and no air movement.
  3. An air leak has occurred at a joint, allowing water to be drawn from the leak instead of the capillary tube. (correct answer)
  4. The student used distilled water in the potometer instead of a mineral salt solution.
Explanation: The correct answer is C. The potometer works by measuring the rate of water uptake, which is assumed to be equal to the rate of transpiration. The entire system must be airtight and full of water. If there is an air leak, the plant will draw in air or water from the leak instead of pulling the water column along the capillary tube, and therefore the bubble will not move. A is incorrect; cutting the stem at an angle is a correct procedure to maximize surface area for water uptake. B would result in a very low, but likely still measurable, rate of transpiration, not a complete stop. D is incorrect; using distilled water is standard and would not stop water uptake, as the driving force is transpiration pull, not root osmosis.

Question 3

What is the primary advantage of a four-chambered heart and double circulation, as found in a mammal, over the two-chambered heart and single circulation of a fish?

  1. It allows for a larger heart size relative to body mass, increasing the total volume of blood that can be pumped.
  2. It completely separates oxygenated and deoxygenated blood, allowing for more efficient gas exchange in the lungs.
  3. It allows blood to be pumped to the systemic circuit at a much higher pressure than the blood flowing through the gas exchange circuit. (correct answer)
  4. It eliminates the need for capillaries by allowing arteries and veins to connect directly, speeding up circulation.
Explanation: The correct answer is C. In a single circulatory system (fish), blood passes through the gills (gas exchange) and then directly to the rest of the body. The delicate gill capillaries cannot withstand high pressure, so blood flow to the body is sluggish and at low pressure. In a double circulatory system, blood returns to the heart after being oxygenated in the lungs. The heart can then pump this oxygenated blood to the body (systemic circuit) at very high pressure, allowing for rapid delivery of oxygen and nutrients to support a high metabolic rate. B is an advantage, but the maintenance of high systemic pressure is the more significant functional consequence that enables an active, endothermic lifestyle.

Question 4

Aphids feed by inserting a stylet into phloem sieve tubes. If a plant is supplied with CO₂ containing a radioactive isotope of carbon (¹⁴C), where would the radioactivity be detected first in the phloem sap extracted from an aphid feeding on the stem?

  1. In an aphid feeding on the roots, as sucrose is transported for storage.
  2. In an aphid feeding on the stem just below a young, developing leaf.
  3. In an aphid feeding on the stem just below a mature, photosynthesizing leaf. (correct answer)
  4. In an aphid feeding on a flower, as this is the primary metabolic sink.
Explanation: The correct answer is C. The radioactive ¹⁴C will be incorporated into glucose, and then sucrose, during photosynthesis in mature leaves (sources). This radiolabeled sucrose is then loaded into the phloem and transported to sinks. The highest concentration of newly synthesized, radioactive sucrose will therefore first be found in the phloem just downstream from its point of production. An aphid feeding on the stem just below a mature leaf is in the optimal position to tap into this flow first. A is a sink, but the sucrose would take time to travel there. B is incorrect because a young, developing leaf is a sink, not a source; it imports sugars rather than exporting them. D is a sink, but the transport path may be longer or more complex than to the stem directly below the source leaf.

Question 5

In the human circulatory system, both hydrostatic pressure and colloid osmotic pressure are critical for fluid exchange in capillary beds. Which statement correctly describes the net fluid movement at the venous end of a typical capillary?

  1. Hydrostatic pressure is higher than osmotic pressure, causing net filtration of fluid out of the capillary.
  2. Both pressures are negligible, so fluid movement is determined solely by active transport.
  3. Hydrostatic and osmotic pressures are equal, resulting in no net movement of fluid.
  4. Osmotic pressure is higher than hydrostatic pressure, causing net reabsorption of fluid into the capillary. (correct answer)
Explanation: The correct answer is B. At the arterial end of a capillary, blood hydrostatic pressure is high, forcing fluid out into the tissues (filtration). As blood moves through the capillary, hydrostatic pressure drops due to resistance and fluid loss. The colloid osmotic pressure (due to plasma proteins like albumin) remains relatively constant. At the venous end, the blood hydrostatic pressure has fallen to a level below the colloid osmotic pressure. This pressure gradient drives the net movement of fluid from the interstitial space back into the capillary (reabsorption). A describes the situation at the arterial end. C is incorrect as there is net movement. D is incorrect as pressure gradients, not active transport, drive bulk fluid movement.

Question 6

A patient is diagnosed with a condition where the sinoatrial (SA) node is non-functional. However, their ventricles still contract at a regular, but slower, rhythm of about 45 beats per minute. Which structure is most likely acting as the pacemaker for the ventricles?

  1. The Purkinje fibres stimulating the atria directly.
  2. The atrioventricular (AV) node initiating its own depolarization. (correct answer)
  3. The sympathetic nervous system overriding the heart's intrinsic control.
  4. The medulla oblongata sending direct, rhythmic signals to the ventricular muscle.
Explanation: The correct answer is B. The heart's conduction system has a hierarchy of pacemakers. The SA node is the primary pacemaker (intrinsic rate of ~70-80 bpm). If it fails, the atrioventricular (AV) node can take over, but its intrinsic rate is slower, typically 40-60 bpm. This matches the patient's symptoms. A is incorrect as Purkinje fibres are in the ventricles and do not stimulate the atria. C is incorrect because the sympathetic nervous system can increase the heart rate but does not generate the primary rhythm itself. D is incorrect because while the medulla regulates the rate, it does not create the beat-to-beat impulse; the control is intrinsic to the heart muscle.

Question 7

A plant has been genetically engineered to express faulty proton pumps (H⁺-ATPase) in the membranes of its phloem companion cells, such that the pumps are non-functional. What is the most likely outcome of this modification?

  1. Transpiration will increase because the xylem will overcompensate for the lack of phloem transport.
  2. The water potential in the xylem will become more negative, drawing more water from the soil.
  3. The cotransport of sucrose into companion cells will be inhibited, severely reducing translocation. (correct answer)
  4. The plant will switch to transporting glucose instead of sucrose in the phloem.
Explanation: The correct answer is C. Phloem loading in many plants is an active process that uses a proton pump (H⁺-ATPase) to pump H⁺ ions out of the companion cell, creating a strong electrochemical gradient. This gradient is then used to power the cotransport of sucrose (along with H⁺ ions) into the companion cell against its concentration gradient. If the proton pumps are faulty, this gradient cannot be established, and active loading of sucrose ceases. This prevents the buildup of solutes needed for the pressure-flow mechanism. A and B relate to xylem function, which is not directly affected by this specific molecular change in the phloem. D is incorrect; the plant's carbohydrate transport system is specific to sucrose.

Question 8

A person moves from sea level to a high-altitude location where the partial pressure of oxygen is significantly lower. After several weeks, which physiological adaptation would be most effective in improving oxygen transport to their tissues?

  1. A permanent increase in heart rate and breathing rate to maximize oxygen intake.
  2. A significant increase in the volume of blood plasma to allow blood to flow more easily.
  3. A decrease in the affinity of hemoglobin for oxygen to facilitate unloading in the tissues.
  4. An increase in the production of red blood cells, raising the oxygen-carrying capacity of the blood. (correct answer)
Explanation: The correct answer is B. Acclimatization to high altitude involves several changes, but the most significant long-term adaptation for oxygen transport is an increase in the number of red blood cells (erythrocytes) and thus the total amount of hemoglobin. This is stimulated by the hormone erythropoietin (EPO) from the kidneys. A higher red blood cell count increases the total oxygen-carrying capacity of the blood, compensating for the lower oxygen saturation in the lungs. A is a short-term response, not a sustainable long-term adaptation. C is incorrect; a higher affinity (left shift) would actually be more beneficial for loading the scarce oxygen in the lungs. D would dilute the red blood cells, reducing oxygen-carrying capacity per unit volume.

Question 9

A researcher applies a potent metabolic inhibitor that blocks all ATP synthesis to the companion cells in the leaves of a healthy plant. What is the most immediate and significant consequence for the plant's transport systems?

  1. The transpiration stream in the xylem will cease due to a lack of energy for the cohesion-tension mechanism.
  2. The loading of sucrose into the phloem sieve tubes will be severely impaired, halting translocation from the leaves. (correct answer)
  3. Water absorption by the roots will stop immediately because active transport of mineral ions into the root ceases.
  4. The stomata will close permanently, preventing gas exchange and stopping both transpiration and photosynthesis.
Explanation: The correct answer is B. The pressure-flow hypothesis for translocation relies on the active transport of sucrose from source cells into phloem companion cells and then into sieve tubes. This process requires ATP. A metabolic inhibitor that blocks ATP synthesis would directly stop this active loading, preventing the buildup of solute concentration needed to drive phloem flow. A is incorrect because the cohesion-tension mechanism driving transpiration is a passive process, relying on the physical properties of water and evaporation, not direct ATP input in the leaves. C is incorrect because while mineral uptake in roots requires ATP, this effect would not be as immediate or widespread as the halt in phloem loading at the source (leaves). D is incorrect as stomatal opening and closing is complex and not solely dependent on ATP in companion cells; while ATP is involved in guard cell function, the most direct effect of the specified inhibitor is on phloem loading.

Question 10

Which statement correctly explains why the walls of arteries are more muscular and elastic than the walls of veins?

  1. To allow the arteries to dilate and constrict to absorb and maintain the high pressure generated by ventricular contraction. (correct answer)
  2. To facilitate the exchange of substances with surrounding tissues, which requires strong, flexible walls.
  3. To prevent the backflow of blood as it returns to the heart under low pressure, a function supported by muscle contraction.
  4. To house the valves that direct blood flow, which require significant structural support from muscle and elastic tissue.
Explanation: The correct answer is A. Arteries carry blood away from the heart under high pressure. The thick elastic walls allow them to stretch and recoil with each heartbeat (pulse), which smooths blood flow and maintains pressure. The muscular layer allows for vasoconstriction and vasodilation to regulate blood flow and pressure. B is incorrect; this describes the function of capillaries, which have very thin walls (one cell thick) to facilitate diffusion. C describes a problem faced by veins (low pressure and backflow), which they solve with valves, not thick muscular walls. D is incorrect as arteries do not have valves (with the exception of the semilunar valves at the exit of the heart); veins have valves.

Question 11

In the pressure-flow model of translocation, what process is directly responsible for the high hydrostatic pressure generated within the sieve tubes at the source?

  1. The evaporation of water from the leaves, which pulls the phloem sap upwards.
  2. The active transport of sucrose into the sieve tubes, which causes water to enter by osmosis. (correct answer)
  3. The active transport of water into the phloem, which pushes the sucrose solution towards the sink.
  4. The passive diffusion of sucrose from companion cells, which draws water in from the xylem.
Explanation: The correct answer is B. At the source (e.g., a leaf), sucrose is actively transported into the phloem sieve tubes. This significantly increases the solute concentration inside the phloem. Due to this low water potential, water moves by osmosis from the adjacent xylem into the sieve tubes. This influx of water increases the volume of fluid in a fixed space, generating high hydrostatic (turgor) pressure, which forces the sap to flow towards areas of lower pressure (the sink). A describes transpiration pull in the xylem, not phloem pressure. C is incorrect as water is not actively transported. D is incorrect because sucrose loading is an active, not passive, process.

Question 12

Xerophytes are plants adapted to arid conditions. Many xerophytes have stomata located in deep pits on the leaf surface, often lined with fine hairs. How does this arrangement reduce water loss?

  1. It traps a layer of moist, still air, which reduces the water potential gradient between the leaf and the atmosphere. (correct answer)
  2. It increases the surface area for CO₂ absorption, allowing stomata to stay closed for longer.
  3. It physically blocks wind from entering the stomata, which would otherwise force water vapour out.
  4. It reflects excess sunlight, keeping the leaf cool and reducing the kinetic energy of water molecules.
Explanation: The correct answer is B. The rate of transpiration is driven by the difference in water potential between the inside of the leaf and the outside air. By having stomata in pits lined with hairs, a pocket of air is trapped. As water evaporates from the stomata, this trapped air becomes saturated with water vapour (high humidity). This reduces the steepness of the water potential gradient between the leaf interior and the air immediately outside the stomata, thereby slowing the net rate of diffusion and conserving water. A is incorrect as this structure does not increase surface area for CO₂ absorption. C is a partial explanation, but the primary mechanism is related to the water potential gradient, not just physically blocking wind. D describes a function of a shiny or waxy cuticle, not stomatal pits.

Question 13

What is the primary physiological advantage of the Bohr shift for an actively respiring tissue, such as a muscle during exercise?

  1. It decreases the affinity of hemoglobin for oxygen in the muscle, promoting efficient oxygen unloading where it is most needed. (correct answer)
  2. It increases the affinity of hemoglobin for oxygen in the lungs, maximizing oxygen uptake from the air.
  3. It increases the blood's capacity to transport carbon dioxide by converting it into carbonic acid more rapidly.
  4. It decreases the pH of the blood in the lungs, which facilitates the release of carbon dioxide from hemoglobin.
Explanation: The correct answer is B. The Bohr shift is a rightward shift in the oxygen-hemoglobin dissociation curve caused by increased CO₂ and H⁺ concentrations (lower pH). This shift signifies a decreased affinity of hemoglobin for oxygen. In actively respiring tissues, CO₂ and lactic acid levels are high, which induces the Bohr shift, causing hemoglobin to release its bound oxygen more readily. This ensures efficient oxygen delivery to the tissues with the highest metabolic demand. A is incorrect; the opposite conditions exist in the lungs (low CO₂, high pH), which causes a leftward shift, increasing affinity and promoting oxygen loading. C and D are incorrect descriptions of the primary advantage and location of the effect. The Bohr shift is about O₂ unloading, not CO₂ transport capacity or pH changes in the lungs.

Question 14

The transport of water through xylem vessels depends on the cohesive and adhesive properties of water. Which statement provides the most accurate explanation for these properties?

  1. Cohesion is the attraction between water molecules and the xylem wall, while adhesion is the attraction between water molecules themselves.
  2. Both cohesion and adhesion are results of the high specific heat capacity of water, allowing it to form an unbroken column.
  3. Cohesion is the result of covalent bonds within water molecules, while adhesion results from the hydrophilic nature of the xylem wall.
  4. Both cohesion and adhesion are results of hydrogen bonds; cohesion is between water molecules and adhesion is between water and the cellulose of the xylem wall. (correct answer)
Explanation: The correct answer is B. Water is a polar molecule, which allows it to form hydrogen bonds. Cohesion is the attraction between like molecules, so the hydrogen bonds between adjacent water molecules create a cohesive force. Adhesion is the attraction between unlike molecules. The cellulose and lignin in xylem walls are also polar, allowing hydrogen bonds to form between water molecules and the vessel wall. This adhesive force helps support the water column against gravity. A incorrectly swaps the definitions of cohesion and adhesion. C incorrectly attributes cohesion to strong covalent bonds instead of weak hydrogen bonds. D incorrectly links cohesion and adhesion to specific heat capacity, which is a thermal property, not an attractive force.

Question 15

Fetal hemoglobin (HbF) has a higher affinity for oxygen than adult hemoglobin (HbA). What is the functional significance of this difference in the context of the placenta?

  1. It ensures that the fetus can effectively pull oxygen from the maternal blood across the placental barrier. (correct answer)
  2. It allows fetal blood to carry more carbon dioxide away from the tissues than maternal blood can.
  3. It protects the fetus from low oxygen environments by storing excess oxygen in the blood.
  4. It causes the fetal oxygen-hemoglobin dissociation curve to shift to the right, promoting unloading in fetal tissues.
Explanation: The correct answer is A. In the placenta, fetal and maternal blood circulate close to each other but do not mix. Oxygen must diffuse from the maternal hemoglobin to the fetal hemoglobin. Because fetal hemoglobin has a higher affinity for oxygen, it can effectively bind oxygen at the lower partial pressures found in the placenta, essentially 'stripping' the oxygen away from the maternal hemoglobin. This creates a favorable gradient for oxygen to move from mother to fetus. B is incorrect as this property relates to oxygen, not CO₂. C is incorrect; it facilitates uptake, not storage. D is incorrect; a higher affinity corresponds to a leftward shift in the dissociation curve, not a rightward shift.

Question 16

In early spring, a deciduous tree that has been dormant over winter begins to grow new leaves. Which statement accurately describes the transport of sugars during this period?

  1. The mature leaves from the previous year act as the source, and the new leaves act as the sink.
  2. The new developing leaves are the source, performing photosynthesis to supply the rest of the tree.
  3. Carbohydrate storage organs, such as the roots, act as the source, and the developing leaves act as the sink. (correct answer)
  4. There is no phloem transport until the new leaves are mature enough to produce their own sugars.
Explanation: The correct answer is C. The roles of source and sink can change depending on the plant's developmental stage. In early spring, the tree has no leaves to perform photosynthesis. It relies on stored energy (starch) from the previous season, which is kept in storage organs like roots or stems. This starch is converted back to sucrose and loaded into the phloem. These storage organs act as the source. The new, growing leaves are not yet photosynthetically active and have high metabolic demands, so they are the primary sink. A is incorrect as the leaves are gone. B is incorrect as new leaves are sinks until they mature. D is incorrect as phloem transport is essential to fuel the initial growth.

Question 17

During intense physical activity, the partial pressure of CO₂ increases in the tissues. How is the majority of this excess CO₂ transported in the blood back to the lungs?

  1. Bound directly to the heme groups of hemoglobin, displacing oxygen.
  2. As dissolved CO₂ gas carried within the blood plasma.
  3. As bicarbonate ions (HCO₃⁻) in the blood plasma after conversion in red blood cells. (correct answer)
  4. Bound to the amino groups of hemoglobin, forming carbaminohemoglobin.
Explanation: The correct answer is C. While some CO₂ is transported dissolved in plasma (about 7%) and as carbaminohemoglobin (about 23%), the vast majority (about 70%) is transported as bicarbonate ions. Inside red blood cells, the enzyme carbonic anhydrase rapidly converts CO₂ and water into carbonic acid (H₂CO₃), which then dissociates into H⁺ and HCO₃⁻. The HCO₃⁻ is then transported out of the red blood cell into the plasma in exchange for a chloride ion (the chloride shift). A is incorrect because CO₂ does not bind to the heme groups; oxygen does. D is a valid but minor method of transport compared to bicarbonate ions.

Question 18

What is the role of the elastic fibres in the wall of the aorta?

  1. To contract actively like smooth muscle and propel blood towards the systemic circulation.
  2. To anchor the semilunar valve firmly, preventing it from inverting into the left ventricle.
  3. To prevent the aorta from bursting under the high pressure of blood ejected from the left ventricle.
  4. To allow the aorta to stretch during systole and recoil during diastole, maintaining blood pressure. (correct answer)
Explanation: The correct answer is B. During ventricular systole, a large volume of blood is ejected into the aorta under high pressure, causing its elastic walls to stretch. This stretching stores potential energy. During ventricular diastole, when the pressure from the heart drops, the stretched elastic walls recoil. This recoil converts the stored potential energy back into kinetic energy, pushing the blood forward and maintaining a relatively high pressure. This 'pressure smoothing' ensures continuous blood flow throughout the body. A describes the function of smooth muscle tissue, not elastic fibres. C is incorrect; while the aorta does withstand high pressure, the elastic fibres' primary function is pressure smoothing, not just structural support. D is incorrect; valves are anchored by fibrous rings at the base of the vessel, not by the elastic fibres in the wall.

Question 19

If the chordae tendineae attached to the cusps of the mitral (bicuspid) valve were surgically cut, what would be the most direct result during the cardiac cycle?

  1. Blood would be unable to enter the left ventricle from the left atrium during atrial systole.
  2. The valve would fail to close properly, causing regurgitation of blood into the left atrium during ventricular systole. (correct answer)
  3. The aortic valve would be forced open prematurely due to the unregulated flow from the left atrium.
  4. Blood would leak back into the left ventricle from the aorta during ventricular diastole.
Explanation: The correct answer is B. The chordae tendineae are 'heart strings' that anchor the cusps of the atrioventricular valves (mitral and tricuspid) to the ventricle walls. Their function is to prevent the valves from inverting or prolapsing into the atria when the ventricles contract at high pressure (ventricular systole). If they were cut, the valve would be pushed backward into the left atrium, allowing blood to flow back (regurgitation). A is incorrect because the valve opens passively when atrial pressure exceeds ventricular pressure; the chordae tendineae do not prevent opening. C is incorrect because the aortic valve's function is independent of the mitral valve's state and is controlled by the pressure differential between the left ventricle and the aorta. D describes aortic regurgitation, which is a problem with the aortic valve, not the mitral valve.