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
A saturated fatty acid has no carbon-carbon double bonds, a monounsaturated fatty acid has one, and a polyunsaturated fatty acid has more than one.
Cis double bonds introduce bends that prevent close packing and weaken intermolecular attractions, generally lowering melting point. Straight saturated chains pack more tightly and tend to melt at higher temperatures.
| Type | C=C bonds | Packing and usual state |
|---|---|---|
| Saturated | 0 | Straighter, tighter packing; common in solid fats |
| Monounsaturated | 1 | One cis kink; lower melting point |
| Polyunsaturated | 2 or more | Multiple kinks; often liquid oils |
Plants commonly store energy in oils rich in unsaturated fatty acids, which remain fluid at typical plant temperatures; endotherms can store more saturated fats while maintaining body temperature.
Double-bond number is important but not the only influence: chain length and cis/trans geometry also affect packing and melting point.
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.