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2.2.62 · Biological Molecules

Cellulose — Cambridge AS & A Level Biology 9700 Revision Notes & Topical Questions

5 min read 7 parts Lesson 12 of 25 1 quiz

📚 Cambridge AS & A Level Biology 9700 Hub / Topical Revision
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Lesson summary

2.2.6 Cellulose — CAMBRIDGE AS & A LEVEL BIOLOGY 9700 — REVISION NOTES notes: Describe the structure of cellulose and explain how it suits its structural function.Monomer — beta-glucose joined by beta-1,4 glycosidic bonds in long unbranched chains.Inversion — consecutive beta-glu…

  • Straight chains
  • Cross-links
  • Microfibrils
  • Tensile strength
  • Permeability
  • Few digesters

Part 1 of 5Cellulose structure

Cellulose structure
Monomer
  • Monomer beta-glucose joined by beta-1,4 glycosidic bonds in long unbranched chains.
Inversion
  • Inversion consecutive beta-glucose molecules are rotated 180° to each other so the bonds can form.
Straight chains
  • Straight chains the inverted arrangement keeps chains straight, suited to building structures.

Part 2 of 5Hydrogen bonding and microfibrils

Cross-links
  • Cross-links many hydrogen bonds form between parallel chains.
Microfibrils
  • Microfibrils chains bundle into microfibrils and fibres of high mechanical strength.
Matrix
  • Matrix fibres and other molecules such as lignin form a matrix that strengthens the wall.

Part 3 of 5Function in the cell wall

Function in the cell wall
Tensile strength
  • Tensile strength walls can be stretched without breaking, so they withstand turgor pressure.
Support
  • Support strengthened walls support the plant.
Permeability
  • Permeability cellulose fibres are freely permeable, so water and solutes reach the cell surface membrane.
Insoluble
  • Insoluble cellulose does not dissolve in water.

Part 4 of 5Cellulose in the diet

Few digesters
  • Few digesters few organisms have cellulase to hydrolyse cellulose.
Dietary fibre
  • Dietary fibre it therefore acts as a source of fibre.

Part 5 of 5More from the specification

More from the specification
Molecular Structure of Cellulose in Plant Cell Walls
  • Cellulose is an unbranched structural polysaccharide formed from β-glucose monomers linked by β-1,4-glycosidic covalent bonds,
  • where alternating glucose molecules are inverted 180°;
    • parallel chains form numerous intermolecular hydrogen bonds, aggregating into high-tensile microfibrils.
Starch and Glycogen as Storage Polysaccharides
  • Unlike cellulose, starch and glycogen are storage polymers formed from α-glucose; their compact, coiled structure and insoluble nature allow extensive glucose storage without exerting osmotic pressure on cell water potential.
    • (comprising branched amylopectin and helical amylose)
Structure and Properties of Triglycerides and Phospholipids
  • Triglycerides are formed by condensation of one glycerol molecule with three fatty acids via ester covalent bonds for long-term energy storage;
    • phospholipids have two hydrophobic fatty acid tails and a hydrophilic phosphate head, self-assembling into the lipid bilayer of biological membranes.
Condensation
  • A reaction that joins molecules and removes water.
Lipids
  • Concentrated energy, insulation, cell membranes.
Sucrose
  • The sugar mainly transported in phloem.
Covalent bond
  • A shared electron pair linking monomers.
Non-reducing sugar
  • A sugar that cannot reduce Benedict's reagent until hydrolysed.
Condensation reaction
  • A reaction that joins two molecules by a covalent bond and releases water.
Starch
  • An insoluble polysaccharide of glucose used by plants for energy storage.
Triglyceride
  • A lipid made of glycerol and three fatty acids.
Polysaccharide
  • Many sugars joined, such as starch, glycogen, cellulose or chitin.
Polymer
  • A large molecule made of many repeating monomers.
Phospholipid
  • Glycerol, two fatty acids and a phosphate group, which is amphipathic.
Monosaccharide
  • A single sugar unit such as glucose, fructose or galactose.
Hydrophobic
  • Water-hating; non-polar and unable to dissolve in water.
Carbohydrate
  • A molecule of carbon, hydrogen and oxygen, including sugars, starch, glycogen and cellulose.

Key terms

TermMeaning
CelluloseAn unbranched polymer of beta-glucose forming plant cell walls.
MicrofibrilA bundle of parallel cellulose chains linked by hydrogen bonds.
Tensile strengthThe ability to resist stretching without breaking.
Turgor pressureThe pressure of cell contents pushing on the cell wall.
CellulaseThe enzyme that hydrolyses cellulose.
Beta-glucoseThe glucose isomer with –OH above carbon 1.

Avoid these mistakes

1
Saying cellulose is made of alpha-glucose — it is beta-glucose.
2
Forgetting the 180° rotation of alternate residues — it allows the beta-1,4 bond.
3
Saying cellulose is strong because of covalent cross-links — the strength comes from many hydrogen bonds between chains.
4
Saying cell walls control entry of substances — cellulose is freely permeable.

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