Final answer:
A fatty acyl chain is saturated if it contains only single bonds, but unsaturated if it has one or more double bonds. Saturated fatty acids have hydrocarbon chains connected by single bonds only, while unsaturated fatty acids have one or more double bonds.
Step-by-step explanation:
A fatty acyl chain is saturated if it contains only single bonds, but unsaturated if it has one or more double bonds. Saturated fatty acids have hydrocarbon chains connected by single bonds only, while unsaturated fatty acids have one or more double bonds. The double bond in unsaturated fatty acids may be in a cis or trans configuration, which affects the structure of the fatty acid chain.