Final answer:
Cis-fatty acids have hydrogen atoms on the same side of the double bond, creating a bent structure, while trans-fatty acids have hydrogen atoms on opposite sides, resulting in a more linear structure.
Step-by-step explanation:
The difference between cis- and trans-fatty acids lies in the configuration around the double bond. A cis fatty acid has two hydrogen atoms on the same side of the double bond, creating a bent structure, while a trans fatty acid has the two hydrogen atoms on opposite sides, resulting in a more linear structure. This difference in configuration affects the physical properties of the fatty acids, such as their melting points and whether they are liquid or solid at room temperature.