Q BankQuestion BankDocsDocuments

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

Root hairs increase surface area for water and mineral uptake, while the endodermis controls entry into the vascular cylinder.

Thin root-hair walls shorten diffusion distance. The endodermal barrier forces water and ions through selective membranes before they reach xylem, helping regulate the internal supply.

Separate increased surface area from selective entry: where do transport proteins and the endodermis matter?

A mineral ion can enter a root hair by a transporter, move through cortex cells and be checked at the endodermis before xylem loading.

More root hairs increase potential uptake but do not remove the need for concentration gradients and transport proteins.

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.
ConceptIB Biology HL