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B3.2.5—Vein adaptations

Veins return low-pressure blood to the heart using valves, wide lumens and flexible walls that can be compressed by surrounding muscles.

Syllabus
First assessment 2025
Objective
B3.2.5
Level
HL

Exam analysis

Chance of appearing1%of analysed past papers
Latest appearanceMay 2025
Most common paperPaper1A
Typical marks1

Common command terms

  • Identify
  • State
  • Explain
  • Deduce

Scoring notes

Common mistake
Explaining venous flow without mentioning valves that prevent backflow.

Recent exam appearances

May 2025Paper1A ["HL"] · TZ324[ 1 ]B3.2.5—Vein adaptations
Practice this objective

Coverage 2025–2025 · Updated 15 Jul 2026

Veins Return Blood at Low Pressure

Veins use large lumens, valves and skeletal-muscle contractions to return blood to the heart despite low pressure.

A wide lumen reduces resistance, valves stop reverse flow and muscle compression raises local pressure. Breathing movements can also help draw venous blood toward the chest.

Follow one bolus of venous blood upward and identify how valves and muscle compression prevent reversal.

When calf muscles contract, a valve below the compressed region closes while the valve above opens, pushing blood upward.

Valves do not create the original pressure; they make one-way assistance effective.

Vein adaptations

Assessment in practice

1–2 marks
How it is assessed

This objective is assessed through structured response, commonly using Identify / State / Explain.

Command terms

Identify / State / Explain / Deduce

What earns marks

Build the answer around this relationship: Vein valves keep blood moving toward the heart.

Watch for

Explaining venous flow without mentioning valves that prevent backflow.

Representative question

Question 1

[Maximum number: 2]

Deduce what the experiment demonstrated about the circulation of blood.

Link Transport Structure To Function

Animal and plant transport answers should link structure to function. In animals, capillaries exchange, arteries maintain high-pressure flow, veins return low-pressure blood, pulse measures arterial pressure waves, and coronary occlusion blocks oxygen delivery to heart muscle. In plants, xylem transports water by transpiration tension and cohesion, while stem and root tissue plans show where xylem and phloem are arranged.

  • Blood vessel answers need structure plus pressure or exchange function.
  • Xylem answers need transpiration pull, cohesion, adhesion, lignin, pits, and hollow vessels when relevant.
  • Plant diagrams should identify tissue distribution: stem vascular bundles in a ring, root xylem cross with phloem between arms.

Concept essentials

  • Vein valves keep blood moving toward the heart.
  • Large venous lumens reduce resistance during low-pressure return.
  • Flexible vein walls can be compressed by skeletal muscles.
  • Veins have less elastic and muscle tissue than arteries.