B1.1.11—Triglycerides functions

Triglycerides store concentrated long-term energy because they are insoluble, stable, compact, and rich in energy-yielding carbon-hydrogen bonds within adipose tissue.

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Chance of appearing3%of analysed past papers

Latest appearanceMay 2024

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Common mistake: Saying lipids are more efficient because they are easier to transport than carbohydrates.

Recent exam appearances

May 2024Paper2 ["HL"] · TZ23(a)[ 1 ]B1.1.11—Triglycerides functions

May 2023Paper1 ["HL"] · TZ17[ 1 ]B1.1.11—Triglycerides functions

May 2014Paper1 ["HL"] · TZ17[ 1 ]B1.1.11—Triglycerides functions

Coverage 2014–2024 · Updated 15 Jul 2026

Storage property	Triglyceride consequence
highly reduced C–H-rich molecules	more than twice the energy per unit mass of carbohydrate
insoluble in water	stored without lowering water potential
oxidised completely	yields ATP, carbon dioxide and substantial metabolic water

Glycogen and triglyceride entering respiration, comparing rapid carbohydrate use with higher energy yield and metabolic water from fat.

Adipose triglyceride also provides:

thermal insulation beneath the skin
cushioning around organs
buoyancy when stored as low-density blubber

Triglyceride is compact long-term fuel, but it is mobilised less rapidly than branched glycogen and its oxidation requires more oxygen. Storage suitability depends on the biological timescale and demand.

Structure seen	Property predicted	Main biological outcome
3 fatty-acid tails on glycerol	hydrophobic, highly reduced	dense long-term energy store
more cis C=C bonds in tails	poorer packing, lower melting point	greater fluidity at a given temperature
phosphate head + 2 tails	amphipathic	self-assembled bilayer barrier
4 fused carbon rings, mostly non-polar	lipid-soluble	diffusion through bilayer core

Ester condensation joins fatty acids to glycerol. The components retained in the product determine whether it behaves as a hydrophobic store or an amphipathic membrane molecule.

Across carbohydrates and lipids, use the same reasoning chain:

atoms and functional groups → bonds → molecular shape and polarity → interactions with water and other molecules → biological function

[ 4 ]

Outline the use of lipids to store energy in humans.

Concept essentials

Triglycerides store more energy per gram than carbohydrates.
Adipose tissue is a major long-term lipid store in humans.
Insolubility prevents triglyceride stores from causing strong osmotic effects.
Stored lipids can also provide thermal insulation and cushioning.