B1.1.10—Fatty acids
Fatty acids vary in chain length, double-bond number, and cis-trans arrangement, affecting molecular shape, saturation, melting point, and physical properties.
- Syllabus
- First assessment 2025
- Objective
- B1.1.10
- Level
- HL
Exam analysis
Chance of appearing5%of analysed past papers
Latest appearanceMay 2024
Most common paperPaper1
Typical marks1
Common command terms
- Outline
- State
- Draw
- Distinguish
- Compare
- Identify
Scoring notes
- Common mistake
- Calling saturated fatty acids unsaturated because they contain a carboxyl group.
Recent exam appearances
May 2024Paper1 ["HL"] · TZ15[ 1 ]B1.1.10—Fatty acids
November 2019Paper2 ["HL"] · TZ04(a)(ii)[ 1 ]B1.1.10—Fatty acids
May 2019Paper1 ["HL"] · TZ210[ 1 ]B1.1.10—Fatty acids
May 2018Paper1 ["HL"] · TZ17[ 1 ]B1.1.10—Fatty acids
May 2016Paper2 ["HL"] · TZ02(b)[ 2 ]B1.1.10—Fatty acids
Practice this objective
Coverage 2012–2024 · Updated 15 Jul 2026
Fatty-Acid Double Bonds Change Chain Shape
Fatty acids are long hydrocarbon chains with a carboxyl group; double bonds in the chain change its shape and affect packing.
A cis double bond introduces a bend, preventing neighbouring chains from packing as tightly. Less tight packing generally lowers the temperature at which a lipid becomes fluid.
Compare fatty acids by checking:
- chain length
- number and position of double bonds
- whether a bend interrupts packing
Two chains of equal length can differ in melting behaviour: the chain with a cis double bond bends and packs less efficiently, so it tends to remain fluid at a lower temperature.
Unsaturation is not the only factor: chain length and the type/position of double bonds also affect packing. Do not equate ‘more double bonds’ with a universal numerical change.
Fatty acids
Assessment in practice
1–2 marksHow it is assessed
This objective is assessed through structured response, commonly using Outline / State / Draw.
Command terms
Outline / State / Draw / Distinguish / Compare / Identify
What earns marks
Build the answer around this relationship: Saturated fatty acids have no carbon-carbon double bonds in the hydrocarbon chain.
Watch for
Calling saturated fatty acids unsaturated because they contain a carboxyl group.
Representative question
Question 1
Distinguish between the structures of the different types of fatty acids in food.
Structure To Function
B1.1 becomes easy when every answer follows structure -> property -> function. Carbon skeletons and functional groups create molecular diversity. Condensation builds larger molecules and hydrolysis breaks them. Alpha-glucose stores energy as starch and glycogen; beta-glucose forms strong cellulose. Surface carbohydrates enable recognition. Lipids are hydrophobic, triglycerides store energy, phospholipids self-assemble into bilayers, and steroids cross membranes because they are mostly non-polar.
- Carbon bonding and functional groups explain molecular diversity.
- Condensation releases water; hydrolysis uses water.
- Carbohydrates can store energy, build cell walls, and mark cell surfaces.
- Lipids are hydrophobic and not true polymers.
- Triglycerides store energy; phospholipids form membranes; steroids signal across membranes.
Concept essentials
- Saturated fatty acids have no carbon-carbon double bonds in the hydrocarbon chain.
- Unsaturated fatty acids contain at least one carbon-carbon double bond.
- Monounsaturated fatty acids have one double bond, while polyunsaturated fatty acids have multiple double bonds.
- Cis double bonds bend fatty acid chains, whereas trans double bonds keep them straighter.