8.1

Xylem and phloem

Cambridge IGCSE Biology (0610)  · Unit 8: Transport in plants  · 15 flashcards

Xylem and phloem is topic 8.1 in the Cambridge IGCSE Biology (0610) syllabus , positioned in Unit 8 — Transport in plants , alongside Water uptake, Transpiration and Translocation.  In one line: Xylem's main functions are to transport water and dissolved mineral ions from the roots to the leaves and other parts of the plant. Additionally, xylem provides structural support to the plant due to its rigid cell walls containing lignin.

This topic is examined in Paper 1 (multiple-choice) and Papers 3/4 (theory), plus Paper 5 or Paper 6 (practical / alternative to practical). Past papers from 2022 to 2025 confirm this is a high-yield topic: Cambridge has set 32 questions worth 451 marks here (about 6.8% of all Biology marks across those years).

The deck below contains 15 flashcards — 3 definitions, 8 key concepts, 1 application card and 3 identification cards — covering the precise wording mark schemes reward.  Use the 3 definition cards to lock down command-word answers (define, state), then move on to the concept and application cards to handle explain, describe and compare questions.

Key definition

The two primary functions of xylem

Xylem's main functions are to transport water and dissolved mineral ions from the roots to the leaves and other parts of the plant. Additionally, xylem provides structural support to the plant due to its rigid cell walls containing lignin.

Example: Water is transported upwards to supply the leaves of a tall oak tree.

What the Cambridge 0610 syllabus says

Official 2026-2028 spec

These are the exact learning objectives Cambridge sets for this topic. Match the command word (Describe, Explain, State, etc.) in your answer to score full marks.

  1. State State the functions of xylem and phloem: (a) xylem – transport of water and mineral ions, and support (b) phloem – transport of sucrose and amino acids
  2. Identify Identify in diagrams and images the position of xylem and phloem as seen in sections of roots, stems and leaves of non-woody dicotyledonous plants
  3. Relate Relate the structure of xylem vessels to their function, limited to: (a) thick walls with lignin (details of lignification are not required) (b) no cell contents (c) cells joined end to end with no cross walls to form a long continuous tube Supplement
Definition Flip

What are the two primary functions of xylem?

Answer Flip

Xylem's main functions are to transport water and dissolved mineral ions from the roots to the leaves and other parts of the plant. Additionally, xylem provides structural support to the plant due to its rigid cell walls containing lignin.

Example: Water is transported upwards to supply the leaves of a tall oak tree.
Definition Flip

What is the main function of phloem?

Answer Flip

Phloem transports sucrose (sugars) and amino acids, the products of photosynthesis, from source (e.g., leaves) to sink (e.g., roots, developing fruits) where they are used for growth or storage. This process is called translocation.

Example: Phloem transports sucrose from the leaves of a tomato plant to its developing fruit.
Key Concept Flip

In a non-woody dicotyledonous stem, where are xylem and phloem located relative to each other?

Answer Flip

In a non-woody dicotyledonous stem, xylem is located towards the center of the stem, while phloem is located towards the outside, closer to the epidermis. They are arranged in vascular bundles.

Example: In a cross-section of a sunflower stem, xylem occupies the inner portion of the vascular bundles, while phloem is on the outer side.
Key Concept Flip

In a non-woody dicotyledonous root, how are xylem and phloem arranged?

Answer Flip

In a non-woody dicotyledonous root, xylem forms a central core, often star-shaped. Phloem is located in patches between the arms of the xylem star.

Example: In a buttercup root, the xylem forms a central star-shaped structure, with phloem found in the spaces between the points of the star.
Key Concept Flip

In a non-woody dicotyledonous leaf, where are xylem and phloem found?

Answer Flip

In a non-woody dicotyledonous leaf, xylem and phloem are located within the vascular bundles of the leaf veins. Xylem is typically found on the upper side of the vein, while phloem is on the lower side.

Example: In a maple leaf, the veins contain xylem on the upper side and phloem on the lower side of the vein.
Key Concept Flip

How does the presence of lignin in xylem vessel walls relate to their function?

Answer Flip

The lignin in xylem vessel walls provides strength and rigidity, preventing the vessels from collapsing under the tension created by the transpiration stream. This allows efficient water transport and provides support to the plant.

Example: The lignified xylem walls enable tall trees, like redwoods, to maintain water transport up to great heights.
Key Concept Flip

How does the absence of cell contents in mature xylem vessels relate to their function?

Answer Flip

The absence of cell contents in mature xylem vessels reduces resistance to water flow, allowing for efficient and uninterrupted transport of water and mineral ions. This creates a clear, unobstructed pathway.

Example: Water can move freely through the hollow xylem vessels in celery stalks.
Key Concept Flip

How does the arrangement of xylem cells (end to end with no cross walls) benefit water transport?

Answer Flip

The arrangement of xylem cells joined end to end, without cross walls, forms long, continuous tubes. This allows for uninterrupted water flow from the roots to the leaves, facilitating the transpiration stream.

Example: The continuous xylem vessels in a rose stem enable efficient delivery of water to the petals.
Key Concept Flip

What property of xylem allows plants to grow tall?

Answer Flip

The lignin in the walls of xylem vessels provides structural support. This structural support enables plants, such as giant sequoia trees, to grow to great heights without collapsing.

Definition Flip

What is translocation?

Answer Flip

Translocation is the process by which phloem transports sucrose and amino acids from source (e.g., leaves) to sink (e.g., roots, developing fruits) throughout the plant.

Example: Translocation moves sucrose from the leaves of an apple tree to the developing apples.
Key Concept Flip

Compare the structure and function of xylem and phloem.

Answer Flip

Xylem:
• Transports water and mineral ions upward (roots → leaves)
• Made of dead cells with thick lignified walls
• Cells have no end walls — form continuous hollow tubes
• Also provides structural support

Phloem:
• Transports dissolved sugars (sucrose) both up and down (translocation)
• Made of living cells (sieve tube elements with companion cells)
• Has sieve plates with pores between cells
• Does not provide structural support

Key Concept Flip

Where are xylem and phloem found in a cross-section of a stem?

Answer Flip

In a dicotyledon stem:
• Xylem is on the inside (towards the centre) of the vascular bundle
• Phloem is on the outside (towards the surface)
• Vascular bundles are arranged in a ring around the edge of the stem

In a root: Xylem forms an X or star shape in the centre, with phloem between the arms of the X.

In a leaf: Xylem is on the upper side of the vein, phloem on the lower side.

Key Concept Flip

How does the structure of xylem vessels relate to their function?

Answer Flip

• No end walls between cells → forms a continuous hollow tube, allowing uninterrupted water flow
• Thick walls with lignin → provides strength and support, prevents the vessel from collapsing under tension
• No living contents (no cytoplasm, nucleus) → creates an empty tube with no resistance to water flow
• Narrow diameter → helps water rise by capillary action

These structural features make xylem ideal for transporting large volumes of water efficiently from roots to leaves.

Key Concept Flip

What is translocation and how does it differ from transpiration?

Answer Flip

Translocation is the movement of dissolved sugars (mainly sucrose) and amino acids through the phloem. It moves substances from where they are made (sources,

Example: leaves) to where they are needed (sinks,. roots, growing tips, fruits). It requires energy (active process).<br><br><strong>Transpiration</strong> is the loss of water vapour from leaves through stomata. It drives the movement of water through xylem. It is a passive process driven by evaporation.
Key Concept Flip

Why do plants need both xylem and phloem?

Answer Flip

Plants need two separate transport systems because they transport different substances in different directions:

• Xylem: water and minerals travel upward only (from roots to leaves), driven by transpiration pull
• Phloem: sugars travel both up and down (from leaves to any part that needs them), by translocation

A single system could not handle both — water transport is passive and one-directional, while sugar transport is active and bidirectional.

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7.5 Absorption 8.2 Water uptake

Key Questions: Xylem and phloem

What are the two primary functions of xylem?

Xylem's main functions are to transport water and dissolved mineral ions from the roots to the leaves and other parts of the plant. Additionally, xylem provides structural support to the plant due to its rigid cell walls containing lignin.

Example: Water is transported upwards to supply the leaves of a tall oak tree.
What is the main function of phloem?

Phloem transports sucrose (sugars) and amino acids, the products of photosynthesis, from source (e.g., leaves) to sink (e.g., roots, developing fruits) where they are used for growth or storage. This process is called translocation.

Example: Phloem transports sucrose from the leaves of a tomato plant to its developing fruit.
What is translocation?

Translocation is the process by which phloem transports sucrose and amino acids from source (e.g., leaves) to sink (e.g., roots, developing fruits) throughout the plant.

Example: Translocation moves sucrose from the leaves of an apple tree to the developing apples.

More topics in Unit 8 — Transport in plants

Xylem and phloem sits alongside these Biology decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.

8.2 Water uptake

8 flashcards
8.3 Transpiration

11 flashcards
8.4 Translocation

10 flashcards

Cambridge syllabus keywords to use in your answers

These are the official Cambridge 0610 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.

xylem phloem vascular bundle transport water mineral sucrose translocation transpiration stream root stem leaf lignin dead cells living cells sieve tube companion cell

Key terms covered in this Xylem and phloem deck

Every term below is defined in the flashcards above. Use the list as a quick recall test before your exam — if you can't define one of these in your own words, flip back to that card.

The two primary functions of xylem
The main function of phloem
Translocation

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