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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
SL

Exam analysis

Chance of appearing4%of analysed past papers
Latest appearanceNovember 2025
Most common paperPaper1A
Typical marks1–2

Common command terms

  • Identify
  • State
  • Explain
  • Deduce

Scoring notes

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

Recent exam appearances

November 2025Paper1A ["SL"] · TZ115[ 1 ]B3.2.5—Vein adaptations
May 2025Paper1A ["SL"] · TZ115[ 1 ]B3.2.5—Vein adaptations
May 2019Paper3 ["SL"] · TZ13(b)[ 2 ]B3.2.5—Vein adaptations
November 2011Paper2 ["SL"] · TZ02(b)(i)[ 2 ]B3.2.5—Vein adaptations
May 2011Paper3 ["SL"] · TZ2B1(a)(i)[ 1 ]B3.2.5—Vein adaptations

Coverage 2011–2025 · Updated 15 Jul 2026

Valves and Muscles Return Low-Pressure Venous Blood

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

Two-state vein diagram showing a valve closed during backflow and open during forward flow while leg muscles squeeze the vessel.

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.

SL Summary: Flow Structures

Route Structural solution
artery elastic-muscular wall for high pressure
capillary one-cell wall + many branches for exchange
vein wide lumen + valves for low-pressure return
xylem hollow lignified tube for tension

Vein adaptations

[ 2 ]

Deduce what the experiment demonstrated about the circulation of blood.

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.