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4.1.4Unit 4: Energy, Environment, Microbiology and Immunity

Properties of Cellulose and Plant Fibres — IAL Edexcel Linear Revision Notes & Topical Questions

5 min read 4 parts Lesson 11 of 28 Unit quiz

📚 IAL Edexcel Linear Hub / Topical Revision
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Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
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Part 1 of 4What Plant Fibres Are

Sclerenchyma fibres and xylem vessels are long hollow cells with very strong walls.

Hollow cells
  • Hollow cells The cell contents have died, often because lignification of the wall prevents substances entering or leaving the cell.
Sclerenchyma fibres
  • Sclerenchyma fibres Bundles of dead, elongated cells whose thick walls give support to stems.
Xylem vessels
  • Xylem vessels Long dead cells with lignified walls that form tubes carrying water and mineral ions.
Human uses
  • Human uses Fibres from plants are used to make rope and fabrics, and cotton and hemp are two examples.

Part 2 of 4Sources of Strength

Sources of Strength
Microfibril mesh
  • Microfibril mesh Cellulose microfibrils are arranged in a mesh-like pattern, so the wall resists forces from many directions.
Secondary thickening
  • Secondary thickening A thick secondary wall is laid down inside the primary wall, increasing the amount of strengthening material.
Lignin
  • Lignin This tough substance is deposited in the secondary wall and makes the wall extremely rigid and waterproof.
Hydrogen bonding
  • Hydrogen bonding Many hydrogen bonds between cellulose chains bind them into microfibrils with high tensile strength.

Part 3 of 4Strength and Uses

The structure of the fibre explains both its advantages and limitations.

1
The mesh of microfibrils and the thick lignified wall allow a fibre to bear a large load before it breaks.
2
Because the fibres are long and flexible, they can be twisted together into ropes and woven into cloth.
3
Plant fibres are renewable and biodegradable, unlike many oil-based plastics.
4
However, ropes from plant fibres are typically not as strong as plastic ones, so there is a trade-off.

Part 4 of 4Exam Checklist & Tips

4.1.4 – Key Points for the Exam

  • Sclerenchyma Plant tissue of dead cells with thick lignified walls that provides support.
  • Lignin A strong, waterproof polymer that stiffens secondary cell walls.
  • Secondary thickening Deposition of a thick extra wall inside the primary wall of a cell.
  • Tensile strength The maximum pulling force a material can bear before it breaks.

Common Mistakes

  • Saying plant fibres are strong because they contain living cytoplasm; the fibre cells are dead and hollow.
  • Attributing the strength to cellulose alone, without mentioning microfibril arrangement, secondary thickening and lignin.
  • Confusing tensile strength (resisting stretching) with compressive strength (resisting squashing).
  • Claiming plant fibre ropes are stronger than plastic ones, when they are typically weaker.

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Cambridge 9700 AS Biology Core Formula

Magnification Triangle & Unit Conversion

Formula: M = I / A  ⇔  A = I / M  ⇔  I = M × A

Units: 1 mm = 1,000 μm = 1,000,000 nm.
Rule: Convert Image size (ruler mm) to μm by ×1,000 before dividing by Actual size.

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