Explain how the structure of a triglyceride makes it suitable for energy storage in animals.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Triglycerides consist of a glycerol backbone esterified to three fatty‑acid chains, giving a very high proportion of C–H bonds per unit mass.
The long hydrocarbon chains of the fatty acids are highly reduced; oxidation of these C–H bonds during respiration releases a large amount of energy per gram, far more than carbohydrates.
Because triglycerides are non‑polar they do not interact with water; they can be stored anhydrously in cells, avoiding an osmotic load.
They are stored as compact, insoluble droplets in adipocytes, providing a dense, long‑term energy reserve and an internal source of metabolic water when oxidised.
The long hydrocarbon chains of the fatty acids are highly reduced; oxidation of these C–H bonds during respiration releases a large amount of energy per gram, far more than carbohydrates.
Because triglycerides are non‑polar they do not interact with water; they can be stored anhydrously in cells, avoiding an osmotic load.
They are stored as compact, insoluble droplets in adipocytes, providing a dense, long‑term energy reserve and an internal source of metabolic water when oxidised.
Examiner tips
- Use the word ‘esterified’ to show the bond type; mention the high C–H ratio; link non‑polarity to anhydrous storage; note the compact droplet storage and metabolic water.
- Structure the answer in four clear points matching the four marks.
Common mistakes
- Confusing triglycerides with phospholipids; writing that they are polar; omitting the high C–H bond content; not linking non‑polarity to lack of osmotic load.
Mark scheme (4 marks)
- Triglycerides are composed of one glycerol molecule bonded to three fatty acid chains via ester bonds, giving a high ratio of C–H bonds relative to molecular mass.
- The long hydrocarbon chains of the fatty acids are highly reduced (rich in C–H bonds), so oxidation during respiration releases a large amount of energy per gram compared with carbohydrates.
- Triglycerides are non-polar / hydrophobic and therefore do not associate with water molecules, so they are stored anhydrously, adding no osmotic load to cells.
- Triglycerides are stored as compact, insoluble droplets in adipocytes, insulating the organism and acting as a metabolic water source when oxidised, making them well-suited for long-term energy reserves.
Key terms in this question
Related
- All IB DP Biology Higher Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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