Plant Transport
Water uptake, xylem transport, transpiration, stomatal control, phloem translocation and evidence for mass-flow models.
How to study A-level Biology
Move between scales deliberately: identify the biological process, trace matter or information, use quantitative evidence, then evaluate the method and conclusion.
Core concepts
Concept 1
Water moves across roots and leaves down water-potential gradients through apoplast and symplast pathways.
Exam cue: Track water potential from soil to root, xylem, mesophyll air spaces and atmosphere.
Concept 2
Transpiration and water cohesion create tension that pulls a continuous water column through lignified xylem.
Exam cue: Separate xylem's dead conducting tissue from phloem's living sieve elements and companion cells.
Concept 3
Phloem translocation moves assimilates between sources and sinks through pressure-driven mass flow supported by active loading or unloading.
Exam cue: Use experimental evidence and its limitations when evaluating translocation models.
Risk pitfalls and guardrails
Saying transpiration uses ATP to pull water up xylem.
Guardrail: Do not replace a mechanism with a vague purpose statement, or infer causation from an association without experimental support.
Assuming source always means leaf and sink always means root.
Guardrail: Do not replace a mechanism with a vague purpose statement, or infer causation from an association without experimental support.
Confusing translocation of assimilates with transpiration of water.
Guardrail: Do not replace a mechanism with a vague purpose statement, or infer causation from an association without experimental support.
Memory anchors
Transpiration
Transpiration is water loss by evaporation and diffusion from aerial plant surfaces.
Cohesion-Tension
Cohesion transmits transpiration-created tension through xylem water columns.
Xylem
Xylem vessels are lignified, hollow conduits for water and mineral ions.
Phloem
Phloem translocates assimilates between sources and sinks.
Mass Flow
Sucrose loading changes water potential and hydrostatic pressure, driving bulk flow in phloem.
Checkpoint rule
Do the check-up only after you can summarize each concept in one sentence and identify one dangerous pitfall from memory.
Knowledge Check (after reading)
Short check-up to confirm understanding of this module.
Check-up Questions
Why does water usually enter a root hair cell from moist soil?
Which description distinguishes the symplast from the apoplast pathway?
Answer all questions to submit.
Next step personalized recommendations
Continue learning
Move forward only after this module is stable.
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