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LearnYBI11WBI12 · Unit 2: Cells, Development, Biodiversity and ConservationPlant structure and function, biodiversity and conservationPlant fibres, starch and drug testing
Plant structure and function, biodiversity and conservation · Subtopic 2 of 4

Plant Fibres, Starch and Drug Testing

Plant cells have a cellulose cell wall, middle lamella (calcium pectate), plasmodesmata, amyloplasts (starch storage), chloroplasts and a large vacuole with tonoplast. Sclerenchyma fibres are dead, elongated cells with thick lignified walls: high tensile strength, used for rope, textiles and composites (more sustainable than oil-based plastics). Measure tensile strength by hanging masses until a fibre breaks. Mineral ions: nitrates (proteins, DNA), calcium (middle lamella), magnesium (chlorophyll). Plants make antimicrobial substances (e.g. garlic, tea tree); test with discs on bacterial lawns. Drug testing: William Withering's foxglove trials (digitalis, 1785) were early dose–response studies. Modern trials: preclinical (cells, animals) → phase 1 (small healthy group, safety) → phase 2 (patients, effectiveness and dose) → phase 3 (large, randomised, double-blind, placebo-controlled).

Edexcel YBI11 WBI12≈ 45 minRevision 1 · updated 2026-11-02
Section 1 of 14

Learning objectives

  • Describe plant cell ultrastructure.
  • Relate fibre structure to strength and uses.
  • Describe measuring tensile strength.
  • Describe drug testing past and present.
Pause and think

Why is a double-blind trial better than one where doctors know who gets the drug?

Section 2 of 14

Core idea

Start hereRopes from plants

For thousands of years people have made rope, cloth and paper from plant fibres. Their strength comes from cellulose and lignin.

The big idea

Plant cell structures give strength and storage useful to humans; plants also provide medicines, tested in careful staged trials.

Modern drug trial phases

Each phase bigger than the last.

Worked exampleBreaking force

A fibre breaks with 0.60 kg hung on it.

Goal
Force.
Strategy
F = mg.
  1. F=0.60×9.8F=0.60\times9.8
    Weight.
  2. =5.9 N=5.9\ \text{N}
    Evaluate.
Answer5.9 N.
✓ CheckMasses in kg ✓.

Summary

  • Cellulose, lignin, middle lamella.
  • Tensile strength practical.
  • Trial phases.
Key words
Sclerenchyma
Dead, lignified supporting tissue.
Double-blind
Neither patient nor doctor knows who receives the drug.
HistoryWithering's foxglove. In 1785 William Withering published careful records of treating 163 patients with foxglove extract, adjusting the dose to avoid poisoning.
Fun factHemp cars. Some car door panels are made from plant fibre composites such as hemp and flax, which are lighter and renewable.
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