IB Biology HL B3.2 Transport Questions

Practise IB Biology HL B3.2 by linking transport structures to pressure, cardiac cycles, xylem, phloem and mass-flow evidence.

123 questions in this syllabus scope, with question parts counted together.

Syllabus
First assessment 2025
Course
Biology HL
Level
HL

Exam analysis

HL · 2010–2025
Papers with this topic68 / 117in the analysed sample
Latest appearanceNovember 2025
Tagged question parts93
Paper types5

Most tested objectives

  1. B3.2.18 (HL)—Phloem adaptations23 papers
  2. B3.2.16 (HL)—Cardiac cycle stages18 papers
  3. B3.2.7—Water transport in plants16 papers
  4. B3.2.15 (HL)—Mammalian heart adaptations8 papers
  5. B3.2.2—Artery and vein structure4 papers

Common question formats

  • Definition or recall
  • Process explanation
  • Structured response
  • Diagram interpretation
  • Calculation
  • Graph interpretation
  • Experimental design
  • Comparison

Recent exam appearances

November 2025Paper 2 HL · TZ3Q4(b)(i)[ 2 ]
November 2025Paper 1B HL · TZ3Q2(f)[ 3 ]
November 2025Paper 1A HL · TZ3Q25[ 1 ]

117 papers analysed · Tagging incomplete

Exam points

  • Explain how thin, fenestrated capillary walls permit tissue-fluid formation and exchange.
  • Compare artery, vein and capillary structure to explain pressure, flow direction and exchange.
  • Measure pulse rate reproducibly by timing beats at the radial or carotid artery.
  • Compare single and double circulation, tracing blood flow and linking heart structures to pressure.
  • Interpret ECG, pressure or heart-sound data to identify cardiac-cycle stages and valve states.
  • Explain root-to-leaf water movement through xylem using transpiration pull and root pressure.
  • Identify vascular bundles and xylem/phloem positions in stem and root diagrams.
  • Explain phloem pressure-flow translocation using sieve tubes, companion cells and source-sink loading.

Covered syllabus points

B3.2.1—Capillary adaptationsB3.2.2—Artery and vein structureB3.2.3—Artery adaptationsB3.2.4—Pulse rate measurementB3.2.5—Vein adaptationsB3.2.6—Coronary artery occlusionB3.2.7—Water transport in plantsB3.2.8—Xylem vessel adaptationsB3.2.9—Stem tissue distributionB3.2.10—Root tissue distributionB3.2.11 (HL)—Tissue fluid in capillariesB3.2.12 (HL)—Exchange between tissue fluid and cellsB3.2.13 (HL)—Lymph ductsB3.2.14 (HL)—Single vs. double circulationB3.2.15 (HL)—Mammalian heart adaptationsB3.2.16 (HL)—Cardiac cycle stagesB3.2.17 (HL)—Root pressure generationB3.2.18 (HL)—Phloem adaptations

Exam points

  • Relate narrow capillary lumens to fitting between cells and greater exchange surface area.
  • Explain how one-cell-thick walls reduce diffusion distance and pores let plasma form tissue fluid.

Question 1

[Maximum number: 1]

Which small blood vessels have walls that are only one cell thick and are leaky enough to allow molecules carried by blood to diffuse into tissues?

A

Lacteals

B

Veins

C

Arterioles

D

Capillaries

Exam points

  • Distinguish arteries and veins by lumen size, wall thickness and elastic tissue.
  • Relate thicker artery walls and narrower lumens to pressure, and wider vein lumens to low-pressure return.
  • Interpret artery and vein stretch data to compare wall elasticity and recoil.

Question 1

[Maximum number: 1]

The light micrograph shows two blood vessels, an artery and a vein, in transverse section.

Figure for Question 1 — IB Biology HL

What explains the different shapes of these blood vessels?

A

Arteries do not have valves.

B

Muscle cells are found only in the walls of veins.

C

Arteries have a larger lumen-to-wall thickness ratio.

D

There are fewer elastic fibres in the walls of veins.

Exam points

  • Explain how thick artery walls and collagen resist high pressure and prevent rupture.
  • Explain how elastic fibres maintain arterial pressure when semilunar valves close.
  • Describe how the arterial lumen permits unobstructed blood flow during ejection.

Question 1

[Maximum number: 1]

In arteries, what are the functions of the lumen and the elastic fibres in the wall?

Lumen

Elastic fibres

Allows unobstructed flow of blood

Prevent excessively high blood pressure when
the semilunar valves in the heart are open

Allows unobstructed flow of blood

Maintain blood pressure when the semilunar
valves in the heart are closed

Regulates rate of blood flow

Increase blood flow to organs that are active

Regulates rate of blood flow

Decrease blood flow to organs that are inactive

Exam points

  • Outline how to measure heart rate during exercise by taking the pulse and counting beats per minute.

Question 1

[Maximum number: 2]

The graph shows the relationship between the maximum heart rate during exercise and a person's age.

Figure for Question 1 — IB Biology HL

Outline one method that the researchers could have used to measure heart rate in this study.

Exam points

  • Explain how venous valves prevent backflow and keep blood moving towards the heart.
  • Relate thin, flexible vein walls to muscle compression that assists low-pressure blood return.

Question 1

[Maximum number: 1]

What is a reason that veins have relatively thin walls compared to arteries?

A

Allows muscle contraction to assist in blood flow

B

Prevents a blood clot forming

C

Allows exchange of materials with tissue fluid

D

Easier attachment of semilunar valves

Exam points

  • Explain how evaporation from leaf mesophyll creates tension that pulls water up through xylem.
  • Explain how hydrogen-bond cohesion keeps the xylem water column continuous under tension.
  • Explain how adhesion to xylem walls helps water move upward against gravity.
  • Trace water movement from roots to leaves through xylem as a continuous transpiration stream.

Question 1

[Maximum number: 1]

The stem of a young plant is cut through and the cut end is immersed in water containing a red dye. The plant continues to transpire as normal. In what region of the stem would the red colour be visible soon after immersion?

Figure for Question 1 — IB Biology HL

Exam points

  • Explain how dead, hollow xylem vessels with absent or perforated end walls form continuous low-resistance tubes for water flow.
  • Explain how lignified xylem walls resist collapse under negative pressure and help waterproof and support the vessel.
  • Explain how pits or pores permit lateral movement of water between xylem vessels and surrounding tissues.

Question 1

[Maximum number: 2]

The light micrograph shows xylem vessels.

Figure for Question 1 — IB Biology HL

Outline two adaptations of xylem vessels for water transport.
1.
2.

Exam points

  • Identify xylem or phloem in a labelled dicot-stem micrograph and state its transport function.
  • Describe vascular bundles as a ring, with phloem outermost and xylem toward each bundle’s centre.

Question 1

[Maximum number: 1]

The micrograph shows part of the stem of the common sunflower (Helianthus annuus) in cross section.

Figure for Question 1 — IB Biology HL

What is the name and function of the structure labelled Z ?

Name

Function

xylem

transport water

phloem

transport water

xylem

transport sugars

phloem

transport sugars

Exam points

  • Label xylem and phloem in root vascular tissue, and identify phloem sieve tubes in a dicot-root micrograph.

Question 1

[Maximum number: 1]

The micrograph shows the cross-section of the vascular tissue in a dicotyledonous root. Which letter identifies phloem sieve tubes?

Figure for Question 1 — IB Biology HL

No public sample questions are available for this syllabus point yet.

No public sample questions are available for this syllabus point yet.

No public sample questions are available for this syllabus point yet.

Exam points

  • Compare bony-fish single circulation (heart→gills→body→heart) with mammalian double circulation, in which pulmonary and systemic circuits are separated.
  • Trace a red blood cell through the right and left heart sides, pulmonary artery/veins and aorta/vena cava to show two heart pumps in mammalian circulation.
  • Explain that separate circuits keep oxygenated and deoxygenated blood apart, maintain high systemic pressure for body tissues and lower pressure through the lungs.

Question 1

[Maximum number: 1]

The diagram shows a human heart.

Figure for Question 1 — IB Biology HL

After a red blood cell picks up oxygen in the lungs, which sequence shows the path it could take when passing through the heart during its circuit of the body?

A

I→II→III→IV\mathrm{I} \rightarrow \mathrm{II} \rightarrow \mathrm{III} \rightarrow \mathrm{IV}

B

II→I→IV→III\mathrm{II} \rightarrow \mathrm{I} \rightarrow \mathrm{IV} \rightarrow \mathrm{III}

C

IV→III→I→II\mathrm{IV} \rightarrow \mathrm{III} \rightarrow \mathrm{I} \rightarrow \mathrm{II}

D

IV→III→II→I\mathrm{IV} \rightarrow \mathrm{III} \rightarrow \mathrm{II} \rightarrow \mathrm{I}

Exam points

  • Identify heart chambers, septum, valves and major vessels on labelled diagrams.
  • Draw a labelled heart with connected chambers, valves and vessels, and a thicker left-ventricular wall.
  • Trace blood through the heart chambers and major vessels, including the oxygenated route from pulmonary veins to the aorta.
  • Explain how pressure opens and closes atrioventricular and semilunar valves to prevent backflow and maintain one-way flow.

Question 1

[Maximum number: 1]

The diagram shows the human heart.

Figure for Question 1 — IB Biology HL

After oxygen has been released from a red blood cell in the brain, which sequence shows the path taken by this red blood cell through the heart before it reaches the aorta?

A

I→II→III→IV\mathrm{I} \rightarrow \mathrm{II} \rightarrow \mathrm{III} \rightarrow \mathrm{IV}

B

IV→III→II→I\mathrm{IV} \rightarrow \mathrm{III} \rightarrow \mathrm{II} \rightarrow \mathrm{I}

C

II→I→IV→III\mathrm{II} \rightarrow \mathrm{I} \rightarrow \mathrm{IV} \rightarrow \mathrm{III}

D

IV→III→I→II\mathrm{IV} \rightarrow \mathrm{III} \rightarrow \mathrm{I} \rightarrow \mathrm{II}

Exam points

  • Trace the SA-node signal through atrial systole, AV-node delay and ventricular contraction.
  • Use pressure graphs to identify valve movements and link valve closure to heart sounds.
  • Interpret ECG, cycle timing and ventricular-area data to distinguish systole, diastole and filling.

Question 1

[Maximum number: 1]

What is the role of the sinoatrial (SA) node?

A

To produce epinephrine in response to vigorous activity

B

To stimulate the contraction of the walls of the atria

C

To send signals from the ventricles to the atria

D

To ensure that the heart rate does not respond to signals from the medulla

Exam points

  • Explain how endodermal ion pumping lowers xylem water potential so water enters by osmosis.
  • Link positive root pressure to upward xylem flow when transpiration is low, such as in humid conditions.

Question 1

[Maximum number: 1]

Which process and cause are responsible for water uptake by the roots?

Process

Cause

Simple diffusion

Solute concentration in the root lower than in the soil

Osmosis

Solute concentration in the root greater than in the soil

Osmosis

Solute concentration in the root lower than in the soil

Cohesion

Solute concentration in the root greater than in the soil

Exam points

  • Describe living sieve tubes, sieve plates, reduced organelles and plasmodesmata linking companion cells.
  • Explain companion-cell active loading of sucrose into sieve tubes using proton-gradient cotransport.
  • Link source loading, osmosis and sink unloading to pressure-flow of sucrose and amino acids.

Question 1

[Maximum number: 1]

How is the phloem adapted for transport?

A

Sieve tube elements have many mitochondria for active transport.

B

Plasmodesmata between companion cells and sieve tube elements aid transport between them.

C

Phloem tubes unload carbon compounds at sources by pressure flow.

D

Companion cells have reduced cytoplasm to enhance loading of carbon compounds.