IB Biology Quiz: Understand Transport
20 questions · exam conditions
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Understand TransportQuestion 1 of 20

An aphid inserts its stylet into a plant stem and a sugary fluid flows into its digestive system without any effort from the aphid. Which plant tissue has the aphid's stylet most likely penetrated and why?

Xylem, because the negative pressure (tension) in the vessel forces the sap out.
Phloem, because the sap is under high positive pressure due to the pressure-flow mechanism.
Parenchyma, because these cells store large quantities of free sucrose that leaks out when punctured.
Epidermis, because this layer produces a sugary nectar to attract insects for defence.
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IB Biology Quiz

IB Biology Quiz: Understand Transport

Practice Understand 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 Understand Transport, giving you a quick way to practice the rules, question types, and explanations that matter most for IB Biology.

How to use this quiz

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

An aphid inserts its stylet into a plant stem and a sugary fluid flows into its digestive system without any effort from the aphid. Which plant tissue has the aphid's stylet most likely penetrated and why?

  1. Xylem, because the negative pressure (tension) in the vessel forces the sap out.
  2. Phloem, because the sap is under high positive pressure due to the pressure-flow mechanism. (correct answer)
  3. Parenchyma, because these cells store large quantities of free sucrose that leaks out when punctured.
  4. Epidermis, because this layer produces a sugary nectar to attract insects for defence.
Explanation: Aphids feed on the sugary sap in the phloem. The pressure-flow hypothesis describes how this sap is maintained under high positive hydrostatic pressure. When the aphid's stylet punctures a sieve tube element, this high pressure forces the sap out of the phloem and into the aphid's stylet, allowing for passive feeding. A is incorrect; xylem is under negative pressure (tension), so sap would not flow out; rather, air would be sucked in. C is incorrect; while parenchyma can store sugars, they are not under the high pressure characteristic of the transport system. D is incorrect; the epidermis does not function this way.

Question 2

In the human heart, the wall of the left ventricle is significantly thicker than the wall of the right ventricle. Which statement provides the most accurate functional explanation for this difference?

  1. The left ventricle must generate higher pressure to overcome the greater resistance of the systemic circuit compared to the pulmonary circuit. (correct answer)
  2. The left ventricle receives deoxygenated blood from the body, which requires more force to pump than the oxygenated blood in the right ventricle.
  3. The right ventricle pumps a larger volume of blood per beat (stroke volume) than the left ventricle, requiring a less muscular wall.
  4. The left ventricle's thicker wall allows it to expand more during diastole, accommodating more blood returning from the pulmonary veins.
Explanation: The left ventricle pumps blood to the entire body (systemic circuit), which is a high-pressure, high-resistance system. The right ventricle only pumps blood to the lungs (pulmonary circuit), which is a short, low-pressure, low-resistance system. Therefore, the left ventricle requires a more muscular wall to generate the necessary force. Distractor B is factually incorrect; the left ventricle receives oxygenated blood. Distractor C is incorrect; in a healthy heart, the stroke volume of both ventricles is equal over time. Distractor D incorrectly links wall thickness to expansion; a thicker, more muscular wall is less compliant (less able to expand) and is adapted for forceful contraction, not passive filling.

Question 3

[HL] A plant scientist develops a chemical that specifically and non-competitively inhibits the proton pumps in the membranes of phloem companion cells. If this chemical is applied to the leaves of a plant, what is the most likely immediate effect on translocation?

  1. The rate of transpiration in the xylem will increase to compensate for the reduced sugar transport.
  2. The hydrostatic pressure in the phloem sieve tubes of the leaves will decrease, reducing the pressure gradient. (correct answer)
  3. Sucrose will be actively transported into the phloem by other membrane proteins, leaving translocation unaffected.
  4. Water potential in the sieve tubes will become more negative, causing an influx of water from the xylem.
Explanation: Phloem loading is an active process. Proton pumps create a proton gradient that is used to co-transport sucrose into companion cells and then into sieve tubes. Inhibiting these pumps prevents the active loading of sucrose. This leads to a lower sucrose concentration in the phloem at the source (leaves), which in turn reduces the osmotic influx of water from the xylem. Consequently, the high hydrostatic pressure required to drive the pressure-flow mechanism is not generated, reducing the pressure gradient and slowing translocation. A is incorrect as xylem and phloem transport are largely independent systems in this context. C is incorrect as the proton co-transport mechanism is the primary way sucrose is actively loaded. D is incorrect as lower sucrose concentration makes the water potential less negative (closer to zero), which prevents water influx.

Question 4

The cohesion-tension theory explains water movement in the xylem. What is the primary role of adhesion in this process?

  1. To facilitate the evaporation of water from the surface of mesophyll cells.
  2. To provide the pulling force (tension) that draws the water column upwards.
  3. To help the water column resist the downward pull of gravity by sticking to the xylem walls. (correct answer)
  4. To ensure water molecules stick tightly to each other, forming an unbroken column.
Explanation: Adhesion is the force of attraction between unlike molecules. In the xylem, it refers to the attraction between water molecules and the polar cellulose/lignin in the xylem walls. This force helps to counteract gravity and support the water column, preventing it from breaking. A describes transpiration. B describes the role of transpiration creating tension. D describes cohesion, the attraction of water molecules to each other.

Question 5

The exchange of substances between blood in the capillaries and the surrounding tissue fluid is regulated by the balance between hydrostatic pressure and solute potential. Which statement correctly describes this process at the venule end of a capillary bed?

  1. Hydrostatic pressure is higher than the solute potential of the blood, forcing fluid out of the capillary.
  2. Solute potential of the blood is higher than the hydrostatic pressure, causing a net movement of fluid into the capillary. (correct answer)
  3. Hydrostatic pressure and solute potential are equal, resulting in no net movement of fluid.
  4. Hydrostatic pressure is negative, drawing fluid from the interstitial space into the capillary.
Explanation: At the arteriole end of a capillary, blood hydrostatic pressure is high, forcing fluid out. As blood flows through the capillary, hydrostatic pressure drops due to resistance and fluid loss. However, the solute potential (or osmotic pressure), mainly due to plasma proteins like albumin, remains relatively constant. At the venule end, the blood hydrostatic pressure has fallen to a point where it is now lower than the constant inward-pulling force of the blood's solute potential. This results in a net movement of fluid from the tissue fluid back into the capillary. Therefore, B is the correct description. A describes the situation at the arteriole end. C describes a theoretical equilibrium point. D is incorrect as hydrostatic pressure is always positive, though it decreases along the capillary.

Question 6

A ring of bark and phloem is removed from the trunk of a tree (girdling). After several weeks, a swelling is observed in the bark just above the removed ring. What is the most likely cause of this swelling?

  1. Accumulation of water transported up the xylem, which cannot pass the ring.
  2. Accumulation of sugars transported down the phloem, which are blocked by the ring. (correct answer)
  3. Increased cell division (callus formation) to repair the wound, stimulated by water from the xylem.
  4. Blockage of mineral ion transport from the leaves to the roots, causing them to accumulate.
Explanation: Phloem transports sugars (produced during photosynthesis) from the leaves (source) downwards to other parts of the plant like the roots (sink). Girdling removes the phloem. Therefore, the downward flow of sugars is interrupted at the ring. The sugars accumulate in the area just above the ring, increasing the solute concentration. This causes water to move into the cells by osmosis, leading to swelling. A is incorrect because the xylem is deeper inside the trunk and is not removed during girdling, so water transport upwards continues. C is a secondary effect, but the primary cause of swelling is osmotic pressure from sugar accumulation. D is incorrect as minerals are primarily transported upwards in the xylem from the roots.

Question 7

[HL] During the cardiac cycle, what event is the direct cause of the closure of the semilunar (aortic and pulmonary) valves?

  1. The pressure in the atria exceeds the pressure in the ventricles.
  2. The pressure in the ventricles drops below the pressure in the aorta and pulmonary artery. (correct answer)
  3. The ventricles begin to contract at the start of systole.
  4. The atrioventricular valves open to allow ventricular filling.
Explanation: The semilunar valves are located between the ventricles and the major arteries (aorta and pulmonary artery). They open when ventricular pressure exceeds arterial pressure, allowing blood to be ejected. They close when the ventricles relax (diastole) and ventricular pressure falls below the pressure in the arteries. This drop in ventricular pressure relative to arterial pressure causes back pressure that snaps the valve cusps shut, preventing backflow. A describes the condition for opening the AV valves. C describes the event that causes the AV valves to close and the semilunar valves to open. D is a consequence of ventricular pressure being lower than atrial pressure, not a cause of semilunar valve closure.

Question 8

[HL] A patient's electrocardiogram (ECG) shows a normal P wave, but the QRS complex is frequently absent. This indicates a malfunction in the signal transmission between which two structures?

  1. The atrioventricular (AV) node and the Purkinje fibres. (correct answer)
  2. The sinoatrial (SA) node and the atrial muscle.
  3. The left and right bundle branches within the septum.
  4. The Purkinje fibres and the ventricular muscle.
Explanation: The P wave represents atrial depolarization, initiated by the SA node. The QRS complex represents ventricular depolarization. A normal P wave means the SA node is firing correctly and the atria are contracting. An absent QRS complex means the signal is not being transmitted to the ventricles to cause their contraction. The atrioventricular (AV) node is responsible for receiving the signal from the atria and transmitting it to the ventricles via the bundle of His and Purkinje fibres. A failure in this transmission (an AV block) would result in the observed ECG pattern. A is incorrect because a P wave is present. C and D represent problems later in the ventricular conduction pathway, which might alter the shape of the QRS complex but would not typically cause it to be completely absent following a P wave.

Question 9

The lymphatic system is crucial for maintaining fluid balance. What would be the most immediate consequence of a blockage in the major lymphatic ducts?

  1. A rapid increase in blood pressure due to increased blood volume.
  2. A severe decrease in the transport of oxygen to the tissues.
  3. Failure of the blood to clot due to a lack of fibrinogen returning to the circulation.
  4. The accumulation of excess interstitial fluid in the tissues, a condition known as edema. (correct answer)
Explanation: The lymphatic system collects excess interstitial fluid (fluid that leaks from capillaries) and returns it to the bloodstream. If the lymphatic vessels are blocked, this fluid cannot be returned effectively. It therefore accumulates in the spaces between cells in the tissues, causing swelling, a condition called edema. A is incorrect; a blockage would prevent fluid from returning to the blood, which would tend to decrease, not increase, blood volume and pressure. C is incorrect as fibrinogen is a plasma protein that does not normally leave the capillaries in large amounts and is not primarily transported by the lymph. D is incorrect as the lymphatic system is not directly involved in oxygen transport.

Question 10

A patient is diagnosed with severe liver failure. Which of the following blood components would be expected to be at abnormally low levels as a direct consequence of this condition?

  1. Erythrocytes
  2. Haemoglobin
  3. Platelets
  4. Fibrinogen (correct answer)
Explanation: The liver is the primary site of synthesis for many plasma proteins, including clotting factors like fibrinogen. In severe liver failure, production of these proteins is impaired, leading to low fibrinogen levels and coagulation problems. Erythrocytes (A) and their main component haemoglobin (B) are produced in the bone marrow. Platelets (C) are cell fragments derived from megakaryocytes, also in the bone marrow. While liver disease can indirectly affect these, the most direct and primary effect is on plasma proteins.

Question 11

In early spring, a potato tuber that was stored over winter begins to sprout new stems and leaves. How are the tuber and new leaves functioning in terms of phloem translocation at this time?

  1. The tuber is the sink and the developing leaves are the source.
  2. Both the tuber and the developing leaves are functioning as sinks.
  3. The tuber is the source and the developing leaves are the sink. (correct answer)
  4. Both the tuber and the developing leaves are functioning as sources.
Explanation: A source is an area of the plant that produces or releases sugars (e.g., photosynthesizing leaves, storage organs). A sink is an area that uses or stores sugars (e.g., roots, fruits, developing leaves). In early spring, the new leaves are not yet photosynthesizing and require energy to grow, making them sinks. The potato tuber contains stored starch, which is converted to sucrose and transported to the growing leaves. Therefore, the tuber acts as the source. This is a classic example of source-sink reversal.

Question 12

[HL] During which phase of the cardiac cycle are all four heart valves closed simultaneously?

  1. Atrial systole and late ventricular diastole.
  2. Mid-ventricular diastole and passive ventricular filling.
  3. Ventricular ejection and atrial diastole.
  4. Isovolumetric contraction and isovolumetric relaxation. (correct answer)
Explanation: There are two phases when all four valves are closed. The first is isovolumetric contraction: after the atria contract and the AV valves close, the ventricles begin to contract, but the pressure is not yet high enough to open the semilunar valves. The second is isovolumetric relaxation: after ventricular ejection, the semilunar valves close, but the ventricular pressure is still higher than atrial pressure, so the AV valves remain closed. During both brief periods, ventricular volume does not change. A, C, and D all describe phases where at least one set of valves must be open to allow for blood movement (e.g., AV valves open for filling, semilunar valves open for ejection).

Question 13

Which statement correctly distinguishes the composition of blood in the pulmonary artery from blood in the aorta?

  1. Blood in the pulmonary artery has a higher concentration of carbon dioxide and a lower concentration of oxygen. (correct answer)
  2. Blood in the pulmonary artery has a higher concentration of glucose and a lower concentration of urea.
  3. Blood in the pulmonary artery has a lower concentration of plasma proteins and a higher red blood cell count.
  4. Blood in the pulmonary artery is at a higher pressure and has a higher concentration of oxygen.
Explanation: The pulmonary artery carries deoxygenated blood from the right ventricle to the lungs. This blood has returned from the body tissues where it has picked up carbon dioxide and given up oxygen. The aorta carries oxygenated blood from the left ventricle to the body. This blood has just returned from the lungs where it has released carbon dioxide and picked up oxygen. Therefore, pulmonary artery blood is high in CO₂ and low in O₂, while aortic blood is low in CO₂ and high in O₂. B is incorrect as glucose/urea levels are not primarily different between these two vessels. C is incorrect as plasma protein and cell counts should be similar. D is incorrect; aortic blood is at much higher pressure and has higher oxygen.

Question 14

Which of the following describes the initial event that triggers the process of blood clotting after a vessel is damaged?

  1. Platelets adhere to exposed collagen fibres and release clotting factors. (correct answer)
  2. Conversion of soluble fibrinogen into insoluble fibrin by the enzyme thrombin.
  3. Red blood cells aggregate at the site of injury to form a physical plug.
  4. Prothrombin is activated by plasma proteins to form the enzyme thrombin.
Explanation: The blood clotting cascade begins when the endothelial lining of a blood vessel is damaged, exposing underlying collagen fibres. Platelets in the blood recognize and adhere to these exposed fibres. This adhesion activates the platelets, causing them to change shape and release chemical clotting factors that initiate a cascade of reactions. A is the final step in forming the clot. C is incorrect; red blood cells are trapped by the fibrin mesh but do not initiate the process. D is an important step in the cascade but occurs after the initial platelet activation.

Question 15

Atherosclerosis involves the build-up of plaque in arteries. Which of the following is a direct consequence of this condition on blood circulation?

  1. A decrease in blood pressure due to reduced elasticity of the arterial walls.
  2. An increase in the lumen diameter, leading to a slower velocity of blood flow.
  3. An increase in blood pressure due to narrowing of the arterial lumen. (correct answer)
  4. A decrease in the risk of thrombosis as the plaque provides a smooth surface.
Explanation: Atherosclerosis causes the arterial lumen (the open channel) to narrow. According to principles of fluid dynamics, for a constant flow rate, a decrease in cross-sectional area leads to an increase in pressure and velocity. Therefore, the heart must pump harder to force blood through the narrowed arteries, resulting in higher blood pressure (hypertension). A is incorrect; while elasticity may decrease, the primary effect of narrowing is increased pressure. B is incorrect; the lumen diameter decreases, not increases. D is incorrect; the rough surface of atherosclerotic plaques actually promotes the formation of blood clots (thrombosis).

Question 16

Which sequence correctly describes the path of a red blood cell from the right atrium to the aorta?

  1. Right atrium → tricuspid valve → right ventricle → pulmonary artery → pulmonary valve → lungs → pulmonary vein → left atrium → mitral valve → left ventricle → aortic valve → aorta
  2. Right atrium → mitral valve → right ventricle → aortic valve → lungs → pulmonary artery → left atrium → tricuspid valve → left ventricle → pulmonary vein → aorta
  3. Right atrium → tricuspid valve → right ventricle → pulmonary valve → pulmonary artery → lungs → pulmonary vein → left atrium → mitral valve → left ventricle → aortic valve → aorta (correct answer)
  4. Right atrium → tricuspid valve → right ventricle → pulmonary vein → lungs → pulmonary artery → left atrium → mitral valve → left ventricle → aortic valve → aorta
Explanation: This question tests the precise sequence of blood flow through the heart and pulmonary circuit. The correct path is: Right atrium, through the tricuspid valve to the right ventricle, through the pulmonary valve to the pulmonary artery, to the lungs, back via the pulmonary vein to the left atrium, through the mitral (bicuspid) valve to the left ventricle, and finally through the aortic valve to the aorta. Option A incorrectly places the pulmonary artery before the pulmonary valve. Option B mixes up all the valves and vessels. Option D incorrectly has the pulmonary vein leading to the lungs instead of away from them.

Question 17

Lignin is a key component of xylem tissue. Which properties are conferred to the xylem vessel by the presence of lignin?

  1. Flexibility to allow for bending and a selectively permeable surface for osmosis.
  2. An adhesive surface for water molecules and a metabolic site for sugar synthesis.
  3. Increased tensile strength to withstand negative pressure and impermeability to water. (correct answer)
  4. A hydrophilic surface to maximize cohesion and living cytoplasm to repair damage.
Explanation: Lignin is a complex, rigid polymer. Its deposition in the cell walls of xylem provides two key features: 1) It provides significant mechanical strength, preventing the vessel from collapsing under the negative pressure (tension) generated during transpiration. 2) It makes the walls impermeable to water, ensuring that water is contained within the vessel as it moves up the plant. A is incorrect; lignin provides rigidity, not flexibility, and is impermeable. B is incorrect; xylem is non-metabolic. D is incorrect; lignin is largely hydrophobic, and mature xylem vessels are dead cells lacking cytoplasm.

Question 18

[HL] Which of the following describes a key event in the pressure-flow hypothesis of translocation?

  1. At the sink, active transport of water out of the sieve tube lowers the hydrostatic pressure.
  2. At the source, an inflow of water into the sieve tube by osmosis generates high hydrostatic pressure. (correct answer)
  3. The cohesion of sucrose molecules creates a pulling force from the sink to the source.
  4. Xylem vessels actively pump water into the phloem at the source to generate turgor pressure.
Explanation: The pressure-flow hypothesis states that active loading of sucrose into the phloem at the source makes the water potential in the sieve tube more negative. This causes water to move from the adjacent xylem into the sieve tube by osmosis. This influx of water generates a high hydrostatic (turgor) pressure at the source. At the sink, sucrose is actively unloaded, water follows by osmosis, and hydrostatic pressure is lowered. This pressure gradient drives the bulk flow of sap from source to sink. A is incorrect; water moves out by osmosis, not active transport. C is incorrect; it is a pressure gradient, not cohesion of sucrose, that drives flow. D is incorrect; water movement from xylem to phloem is a passive osmotic process, not active pumping.

Question 19

What is a key advantage of a double circulatory system, as found in mammals, compared to a single circulatory system, as found in fish?

  1. It allows deoxygenated and oxygenated blood to mix in the heart, increasing efficiency.
  2. It allows blood to be pumped to the body at a lower pressure, conserving energy.
  3. It allows for a slower rate of blood flow to the lungs, enhancing gas exchange.
  4. It allows blood to be re-pressurized after passing through the lungs, enabling higher metabolic rates. (correct answer)
Explanation: In a single circulatory system (fish), blood passes through the gills (gas exchange surface) and then directly to the rest of the body. This results in a significant drop in blood pressure, limiting the rate of delivery to tissues. In a double circulatory system, blood returns to the heart after passing through the lungs. The heart (specifically the left ventricle) then pumps this oxygenated blood to the body at high pressure. This high-pressure systemic circulation allows for rapid delivery of oxygen and nutrients, supporting the higher metabolic rates of mammals and birds. A is incorrect; a key feature is the separation of oxygenated and deoxygenated blood. B is incorrect; it allows for higher, not lower, systemic pressure. C is incorrect; the pulmonary circuit is a low-pressure system, but the primary advantage relates to the systemic circuit's high pressure.

Question 20

Xerophytes have adaptations to reduce water loss. The rolling of leaves, as seen in marram grass, is one such adaptation. How does this directly aid in water conservation?

  1. It reduces the total surface area of the leaf exposed to sunlight, lowering the leaf temperature.
  2. It traps a layer of still, humid air around the stomata, which are located on the inner surface. (correct answer)
  3. It directs water from rainfall more efficiently towards the root system of the plant.
  4. It increases the concentration of solutes inside the leaf cells, lowering the water potential.
Explanation: In marram grass, the stomata are located on the inner surface of the leaf. When the leaf rolls up, it encloses a small pocket of air. Water vapour that diffuses out of the stomata gets trapped in this space, increasing the humidity of the trapped air. This reduces the water potential gradient between the inside of the leaf and the air immediately outside the stomata, thereby reducing the rate of transpiration. A is a secondary effect but not the primary mechanism. C is incorrect as leaf rolling is not related to water collection. D is incorrect; leaf rolling is a physical, not a physiological, change to alter solute concentration.