What is Xylem and Phloem Transport?
Plants move water, minerals, and sugars through two specialized vascular tissues: xylem and phloem. Together they form the plant's transport system, keeping every cell supplied with what it needs to grow.
Xylem transports water and dissolved minerals upward from roots to leaves in one direction, while phloem transports sugars (food) made in leaves to all parts of the plant in either direction.
- •Transports water & minerals
- •Dead cells at maturity
- •One-way flow (roots → leaves)
- •Driven by transpiration pull
- •Thick lignified walls
- •Transports sugars (food)
- •Living cells (sieve tubes)
- •Two-way flow (source → sink)
- •Driven by pressure flow
- •Thin walls, sieve plates
Step-by-step worked examples
A tree loses a ring of bark (girdling) around its trunk. Predict what happens to the roots over time and explain why.
Girdling removes the phloem (located just under the bark). Without phloem, sugars made in leaves cannot reach the roots. Roots slowly starve and die, even though water still moves up through the xylem.
On a hot, sunny day, water evaporates rapidly from a plant's leaves. Explain how this affects xylem transport.
Evaporation from leaf stomata is called transpiration. This creates negative pressure (tension) pulling water upward through the xylem. More transpiration means faster xylem water flow — this is the transpiration-cohesion-tension mechanism.
A plant is given radioactive-labeled sugar at a leaf (source). Where will the label appear over time, and through which tissue?
The leaf is a 'source' producing excess sugar. Sugar loads into phloem sieve tubes and moves via pressure flow to a 'sink' (e.g., growing root or fruit). The radioactive label will appear in sinks, transported through phloem, not xylem.
Flashcards
Quick quiz
Q1.Which tissue transports water and minerals from roots to leaves?
Q2.Phloem transport mainly carries…
Q3.What is the driving force behind xylem water movement?
Q4.Which statement about phloem is true?
The full card deck, worked steps and AI-tutor support for “What is Xylem and Phloem Transport?” are in Notek — study by hand before your exam.
Common mistakes
Xylem and phloem both transport water. — Correct: Only xylem transports water; phloem transports sugars.
Phloem transport is always one-way (up). — Correct: Phloem flow direction depends on source and sink location — it can go up or down.
Xylem cells are alive and active pumps. — Correct: Mature xylem cells are dead; movement is passive, driven by transpiration pull.
Girdling a tree only affects the leaves. — Correct: Girdling removes phloem, cutting off sugar supply to roots, eventually killing the whole plant.
FAQ
What is xylem and phloem transport?
It's the process by which xylem moves water/minerals upward and phloem moves sugars between source and sink in vascular plants.
Is there a formula for xylem and phloem transport?
There's no single numeric formula — transport is described by mechanisms: transpiration-cohesion-tension for xylem and pressure flow for phloem.
What are examples of xylem and phloem transport?
Water rising in a tall tree trunk (xylem) and sugar moving from a leaf to a growing fruit (phloem) are classic examples.
How to calculate xylem and phloem transport rate?
Scientists estimate xylem flow rate using sap flow sensors (cm/hour) and phloem flow using tracer studies; there's no simple textbook formula for either.