What are the main functions of xylem and phloem in plants?

In the Cambridge IGCSE Biology curriculum, xylem and phloem are crucial components of the plant's vascular system. Xylem is responsible for transporting water and dissolved minerals from the roots to the rest of the plant, while phloem distributes the sugars and nutrients produced during photosynthesis from the leaves to other parts of the plant.

How do xylem and phloem differ in their structure?

Xylem and phloem have distinct structural differences. Xylem vessels are typically composed of dead cells that form long tubes, which are strengthened by lignin, allowing them to withstand the pressure of water transport. In contrast, phloem consists of living cells, including sieve tube elements and companion cells, which facilitate the transport of organic nutrients throughout the plant.

Why is the process of transpiration important for xylem function?

Transpiration is a key process in the Cambridge IGCSE Biology syllabus, as it drives the movement of water through the xylem. As water evaporates from the leaves, it creates a negative pressure that pulls more water up from the roots through the xylem vessels, facilitating the transport of essential minerals and maintaining plant turgor.

What role does phloem play in the process of translocation?

Phloem is integral to the process of translocation, which involves the movement of organic compounds, primarily sucrose, from the leaves to other parts of the plant. This process is crucial for distributing energy and nutrients to growing tissues and storage organs, ensuring the plant's overall growth and development.

How do environmental factors affect the functioning of xylem and phloem?

Environmental factors such as temperature, humidity, and soil moisture can significantly impact the functioning of xylem and phloem. High temperatures and low humidity increase transpiration rates, affecting water transport in xylem. Similarly, nutrient availability in the soil influences the efficiency of nutrient transport in phloem, impacting the plant's growth and health.

Why is "Saying xylem cells are alive." a common mistake in Xylem and Phloem?

Why it happens: Plant cells are usually alive. How to avoid it: Mature xylem cells are DEAD. Empty hollow tubes — much better for free water flow.

Why is "Saying phloem carries water." a common mistake in Xylem and Phloem?

Why it happens: Both are vessels in the plant. How to avoid it: PHLOEM carries SUGARS + amino acids, not water as its main job. XYLEM carries water.

Why is "Saying phloem only goes DOWNWARDS." a common mistake in Xylem and Phloem?

Why it happens: Sugars made in leaves and stored in roots → leaves are 'up'. How to avoid it: Phloem flow is BIDIRECTIONAL. Sugars go from any SOURCE (leaf, storage organ when broken down) to any SINK (growing tip, fruit, storage organ when filling up). In spring, sugars travel UP from roots to new shoots.

Transport in PlantsCambridge IGCSE Biology 0610 Extended

Xylem and Phloem

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Xylem and Phloem — Cambridge IGCSE 0610 Biology Extended (2026)

Plants have TWO transport systems. Xylem moves water UP. Phloem moves sugars EVERYWHERE.

What you’ll learn

Mapped to the Cambridge IGCSE 0610 syllabus (2026-2028).

8.2 — Identify the position of xylem and phloem in stems, roots and leaves.
8.2 — Describe the function of xylem and phloem.
8.2 — Describe the structure of xylem and phloem cells.

Xylem — the up elevator

Dead, hollow, lignified tubes. Water + minerals up from roots to leaves.

Function. Carry water and dissolved MINERAL IONS from the ROOTS UP to the rest of the plant — particularly the leaves.

Structure of xylem cells (vessels).

DEAD when mature — cytoplasm and nucleus break down.
Form long, HOLLOW tubes (cells join end-to-end, end walls dissolve).
Walls are LIGNIFIED — impregnated with LIGNIN, a strong waterproof polymer.
Lignin makes the wall WATERPROOF (water doesn't leak) AND STRONG (resists collapse from suction).

Why dead is best.

A hollow tube has the lowest possible resistance — water flows freely.
No cytoplasm or organelles in the way.
No need to feed the cells (saves the plant energy).

Direction of flow. ONE-WAY only — UP, from roots to leaves. Driven by transpiration pull (see Transpiration topic).

Worked qualitative. Why does cutting a ring of bark off a tree (girdling) eventually kill it?

Bark removal cuts the PHLOEM (which lies just inside the bark) but leaves the xylem deeper inside.
Water still flows up (xylem intact) → leaves keep photosynthesising.
But sugars can't get DOWN to the roots (phloem cut) → roots starve, plant dies over weeks/months.

Cambridge tip. Always include "lignified" when describing xylem walls. Cambridge marks the keyword.

Dead, hollow cells with dissolved end walls form one continuous lignified pipe.

Dead, hollow tubes.
Lignified walls.
Water + minerals UP.
One-way flow.

Phloem — the sugar courier

Living cells. Sucrose + amino acids in either direction. Source to sink.

Function. TRANSLOCATION — moving SUCROSE and AMINO ACIDS from where they're made/stored (a SOURCE) to where they're used (a SINK).

Structure of phloem.

Two main cell types:
- Sieve tube elements — long, narrow, LIVING cells. End walls have holes (sieve plates) for sap to flow through.
- Companion cells — alongside each sieve tube. Have nuclei + many mitochondria. Provide energy/management for the sieve tube.
Together: a continuous tube of living, energy-supported cells.

Direction of flow. TWO-WAY — wherever needed.

Living sieve tubes flow through perforated sieve plates; companion cells supply the energy.

Source vs sink.

Source: where sugars come from. Usually green leaves (just photosynthesised) OR storage organs being broken down.
Sink: where sugars go. Growing tips, developing fruits, expanding flowers, storage organs being filled.
A potato can be a sink in summer (filling up) and a source in spring (emptying).

What it carries.

SUCROSE — main transport sugar (more stable than glucose; doesn't react in transit).
AMINO ACIDS — going to growing tissues to build proteins.
Some hormones, mineral ions.

Worked qualitative. Why is sucrose the transport sugar (not glucose)?

Glucose is reactive (used in respiration, joins to make starch).
Sucrose is more stable → doesn't react with the cells while travelling.
At sinks, sucrose is split back into glucose + fructose for use.

Cambridge tip. TRANSLOCATION is the key term. Mark schemes credit "translocation in phloem from source to sink".

Living sieve tubes + companion cells.
Sucrose + amino acids.
Source to sink (any direction).
Translocation = the process.

Where xylem and phloem are in the plant

Stem: ring near outside. Root: cross in middle. Leaf: vein with xylem on top.

Stem (cross-section).

Vascular bundles arranged in a RING, near the OUTSIDE.
In each bundle: XYLEM toward the centre, PHLOEM toward the outside.
Often a layer of CAMBIUM between them — undifferentiated cells that can divide for growth.
Centre: PITH (storage of starch etc.).

Root (cross-section).

Xylem is in the CENTRE, often in a CROSS (X) shape (or star).
Phloem fills in the gaps between the xylem arms.
This central position helps the root resist BENDING forces (lignified xylem provides strength against pulling).

Leaf (cross-section through a vein).

Vein contains both xylem and phloem.
XYLEM on TOP (closer to the upper surface).
PHLOEM on BOTTOM (closer to the spongy mesophyll).
Surrounded by sclerenchyma fibres for support.

Vascular tissue is arranged differently in each organ to match its mechanical needs.

Why different in each organ?

Root: needs strength against pull (xylem central).
Stem: needs strength against bending (vascular bundles in a ring give a flexible, strong design — like steel rods in concrete).
Leaf: thin, branched veins reach every cell.

Worked qualitative. Why does a celery stalk in dyed water turn coloured?

Dyed water taken up by xylem (it carries water).
Visible "lines" of dye in the celery match the position of the vascular bundles.
Cutting the stalk shows the bundles in a ring.

Cambridge tip. Practise drawing both stem and root cross-sections — Cambridge sometimes asks you to label vascular tissues.

Stem: ring of bundles (xylem in, phloem out).
Root: xylem central (X-shape).
Leaf vein: xylem top, phloem bottom.
Position matches mechanical needs.

How it’s examined

Xylem and phloem appear Paper 4 (5-7 marks). Common formats: label a vascular bundle, compare structure/function. Examiner reports flag students saying xylem cells are alive, phloem carries water, or that phloem only flows down.

Sources: Cambridge IGCSE Biology 0610 syllabus 2026-2028 (8.2); 0610/42 May/Jun 2024 — Q7 (xylem structure); 0610 Examiner Reports 2022-2024. Last reviewed 2026-05-07.

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Step-by-step worked examples — Xylem and Phloem

Step-by-step solutions to past-paper-style questions on xylem and phloem, written exactly the way a tutor would explain them at the board.

1Compare xylem and phloem
Core• xylem, phloem
Question
Compare the structure and function of XYLEM and PHLOEM.
Step-by-step solution
1. Step 1
  Xylem: DEAD, hollow, lignified tubes. Carry WATER + dissolved MINERALS. Flow is ONE-WAY — UP from roots to leaves.
2. Step 2
  Phloem: LIVING cells (sieve tubes + companion cells). Carry SUCROSE + amino acids. Flow is TWO-WAY (TRANSLOCATION) — wherever sugars are needed.
3. Step 3
  Both form vascular bundles together (in stems, leaves, roots).
Answer
Xylem: dead, water/minerals up. Phloem: living, sugars/amino acids around. Both: transport tissues in vascular bundles.
2Position of xylem and phloem in a stem
Core• vascular bundles
Question
Describe the arrangement of vascular bundles in a typical herbaceous stem (cross-section).
Step-by-step solution
1. Step 1
  Vascular bundles are arranged in a RING near the OUTSIDE of the stem.
2. Step 2
  Each bundle: XYLEM towards the CENTRE, PHLOEM towards the OUTSIDE, with cambium between.
3. Step 3
  Centre: PITH (storage). Outside: cortex + epidermis.
Answer
Vascular bundles in a ring near the edge. Within each: xylem inner, phloem outer.
3Why are xylem cells DEAD?
Extended• Adapted from 0610/42 May/Jun 2024 Q7• xylem structure
Question
Explain how the structure of XYLEM is suited to its function.
Step-by-step solution
1. Step 1
  Hollow tubes: cells DIE and lose their cytoplasm + nucleus → empty inside → water flows freely.
2. Step 2
  End walls broken down: a continuous column of water from root to leaf.
3. Step 3
  LIGNIFIED walls: lignin is a strong, waterproof polymer → walls are STRONG (resist collapse from suction) AND WATERPROOF (water doesn't leak out).
4. Step 4
  No cytoplasm needed: dead cells don't waste space; not respiring → water can move passively, no energy needed for the bulk flow.
Answer
Hollow + lignified + open-ended → strong, leak-proof, frictionless tubes for water transport. Dead because no cell content needed.

Key Definitions and Keywords — Xylem and Phloem

Definitions to memorise and the exact keywords mark schemes credit for xylem and phloem answers — sharpened from recent examiner reports for the 2026 0610 sitting.

Xylem
Examiner keyword
Tissue made of dead, hollow, lignified cells that transports water and dissolved mineral ions from roots to leaves.
Phloem
Examiner keyword
Tissue made of living sieve tubes and companion cells that transports sucrose and amino acids around the plant.
Translocation
Examiner keyword
The movement of sucrose and amino acids in the phloem from sources (e.g. leaves) to sinks (e.g. growing tips, roots, fruits).
Lignin
Strong, waterproof polymer in xylem cell walls. Provides support and prevents water loss.
Vascular bundle
Group of xylem and phloem cells running together as a transport unit through stems, roots and leaves.

Common Mistakes and Misconceptions — Xylem and Phloem

The traps other students keep falling into on xylem and phloem questions — taken from recent Cambridge IGCSE 0610 examiner reports and mark schemes — and how to avoid them.

✕Saying xylem cells are alive.
Why it happens
Plant cells are usually alive.
How to avoid it
Mature xylem cells are DEAD. Empty hollow tubes — much better for free water flow.
✕Saying phloem carries water.
Why it happens
Both are vessels in the plant.
How to avoid it
PHLOEM carries SUGARS + amino acids, not water as its main job. XYLEM carries water.
✕Saying phloem only goes DOWNWARDS.
Why it happens
Sugars made in leaves and stored in roots → leaves are 'up'.
How to avoid it
Phloem flow is BIDIRECTIONAL. Sugars go from any SOURCE (leaf, storage organ when broken down) to any SINK (growing tip, fruit, storage organ when filling up). In spring, sugars travel UP from roots to new shoots.

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Xylem and Phloem

Short Study Notes in the form of Slides

Short Study Notes — Xylem and Phloem

Detailed Notes

What you’ll learn

How it’s examined

1Compare xylem and phloem

2Position of xylem and phloem in a stem

3Why are xylem cells DEAD?

Xylem

Phloem

Translocation

Lignin

Vascular bundle

✕Saying xylem cells are alive.

✕Saying phloem carries water.

✕Saying phloem only goes DOWNWARDS.

Practice questions

Past paper style quiz

Assess your understanding

Video lesson

Xylem and Phloem — frequently asked questions