B3.2.7—Water transport in plants
Plant water transport depends on root uptake, xylem vessels, transpiration pull, cohesion, adhesion and lignified support against strong internal tension.
- Syllabus
- First assessment 2025
- Objective
- B3.2.7
- Level
- HL
Exam analysis
Chance of appearing12%of analysed past papers
Latest appearanceMay 2025
Most common paperPaper2
Typical marks2–7
Common command terms
- Identify
- Describe
- Explain
- Predict
Scoring notes
- Common mistake
- Explaining water movement as active transport through xylem rather than passive tension-driven flow.
Recent exam appearances
May 2025Paper2 ["HL"] · TZ24(b)[ 3 ]B3.2.7—Water transport in plants
May 2024Paper2 ["HL"] · TZ16(c)[ 7 ]B3.2.7—Water transport in plants
November 2020Paper2 ["HL"] · TZ07(b)[ 4 ]B3.2.7—Water transport in plants
November 2019Paper1 ["HL"] · TZ032[ 1 ]B3.2.7—Water transport in plants
November 2018Paper1 ["HL"] · TZ032[ 1 ]B3.2.7—Water transport in plants
Practice this objective
Coverage 2012–2025 · Updated 15 Jul 2026
Roots and Xylem Form a Continuous Water Path
Transpiration creates tension—a negative pressure potential—that pulls a continuous water column from roots to leaves through xylem.
Water evaporating from moist mesophyll cell walls draws replacement water through the wall by capillary action and out of nearby xylem. This lowers pressure in the leaf xylem and transmits tension down the vessel.
Cohesion from hydrogen bonding keeps water molecules joined so the pull is transmitted through an unbroken column. Adhesion to hydrophilic xylem walls assists capillary movement and helps stabilize the column.
When stomata open and evaporation increases, the leaf water potential becomes more negative, increasing tension in xylem and drawing water upward from roots.
The main long-distance force is tension generated at transpiring leaves, not an active pump in xylem. Cohesion transmits the pull; it does not create the initial gradient.
Water transport in plants
Assessment in practice
2–7 marksHow it is assessed
This objective is assessed through structured response, commonly using Identify / Describe / Explain.
Command terms
Identify / Describe / Explain / Predict
What earns marks
Build the answer around this relationship: Transpiration pull creates tension that draws water upward through xylem.
Watch for
Explaining water movement as active transport through xylem rather than passive tension-driven flow.
Representative question
Question 1
Explain the process of water uptake and transport by plants.
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
- Transpiration pull creates tension that draws water upward through xylem.
- Cohesion from hydrogen bonding keeps xylem water columns continuous.
- Adhesion helps water move through cell walls and xylem surfaces.
- Lignified xylem walls resist collapse under negative pressure.
- Root uptake begins with osmosis into root tissues or xylem.