Short answers, pulled from the story.
Michel Eugène Chevreul introduced the concept of fatty acid in 1813. He initially used terms like graisse acide and acide huileux to describe these oily acids before the terminology evolved into modern scientific names.
Scientists later standardized the definition to include any carboxylic acid with an aliphatic chain. Most naturally occurring examples contain unbranched chains with even numbers of carbon atoms ranging from four to twenty-eight.
Chemists categorize fatty acids by counting their carbon atoms and checking for double bonds. Short-chain fatty acids possess tails of five carbons or fewer while medium-chain variants range from six to twelve carbons and long-chain types span thirteen to twenty-one.
Animals synthesize fatty acids primarily from carbohydrates inside the liver adipose tissue and mammary glands during lactation. This process involves glycolysis converting carbohydrates into pyruvate before decarboxylation forms acetyl-CoA in the mitochondrion.
Humans require essential fatty acids that cannot be made sufficiently from other substrates so they must come from food. Linoleic acid and alpha-linolenic acid represent two critical examples widely distributed in plant oils.