This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
All are essential unsaturated fatty acids except 
Select and explain. 
A. Linoleic acid, B. Linolenic acid, C. Arachidonic acid, D. Palmitoleic acid
D: Palmitoleic acid
Answer: D: Palmitoleic acid 
Explanation: Palmitoleic acid, oleic acid, linoleic acid, linolenic acid and arachidonic acid are the five unsatured fatty acids.
Among them palmitoleic acid, oleic acid are mono unsaturated fatty acids. linoleic acid, linolenic acid and arachidonic acid are essential unsaturated fatty acids.
Arachidonic acid becomes essential, if its precursor, linoleic acid is not present in the diet. It is considered as the precursor for the synthesis of prostaglondins.