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B3.2.10—Root tissue distribution

Dicot roots contain central vascular tissue, with lignified xylem, phloem between xylem arms, surrounding cortex and a protective outer epidermis.

Syllabus
First assessment 2025
Objective
B3.2.10
Level
HL

Exam analysis

Chance of appearing1%of analysed past papers
Latest appearanceNovember 2018
Most common paperPaper3
Typical marks2

Common command terms

  • Label

Scoring notes

Common mistake
Confusing the central root xylem arrangement with the ring of vascular bundles in stems.

Recent exam appearances

November 2018Paper3 ["HL"] · TZ02(a)[ 2 ]B3.2.10—Root tissue distribution
Practice this objective

Coverage 2018–2018 · Updated 15 Jul 2026

Roots Combine Absorption with Selective Entry

A transverse section of a young dicot root has an outer epidermis, a broad cortex and a central vascular cylinder containing xylem and phloem.

Root hairs extend from epidermal cells to increase absorption area. The endodermis forms the inner boundary of the cortex, surrounding the central vascular tissue and controlling entry to xylem.

In the centre, xylem commonly forms a star or cross; phloem occurs in groups between its arms. Draw these tissue regions in their correct relative positions with clear outlines rather than individual cells.

A suitable plan diagram runs epidermis/root hairs → cortex → endodermis → central xylem cross with phloem between the arms, with annotations for uptake and transport.

Root vascular tissue is central rather than arranged as a ring of separate bundles like a young dicot stem. A plan diagram records tissue distribution, not detailed cell anatomy.

Root tissue distribution

Assessment in practice

1–2 marks
How it is assessed

This objective is assessed through structured response, commonly using Label.

Command terms

Label

What earns marks

Build the answer around this relationship: Dicot roots have central vascular tissue rather than a ring of separate bundles.

Watch for

Confusing the central root xylem arrangement with the ring of vascular bundles in stems.

Representative question

Question 1

[Maximum number: 2]

Label tissues X and Y .

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

  • Dicot roots have central vascular tissue rather than a ring of separate bundles.
  • Xylem commonly forms a central cross or star in dicot roots.
  • Phloem occurs between the arms of the root xylem.
  • Lignin is found in xylem vessel walls.