Expert: John Locke - 11/4/2009

Question
Can you please define 'preformed,'as applies to heterotrophs...obviously we can't convert sunlight and water into complex carbohydrates and other organic molecules that support life. So does preformed mean that we're getting carbs, proteins, lipids or nucleic acids by ingesting them directly, we're not creating them, we're just eating them?? So preformed means that another animal or plant or fungi has already created them, 'preformed,' them so to speak?

Answer
Your interpretation is correct: heterotrophs are defined by their consumption of complex organic carbon as a substrate for growth. Those complex organic molecules have been made already by plants, bacteria, fungi, or other animals; they are "preformed," so to speak, by those other organisms. As you probably know, autotrophs are capable of synthesizing organic carbon molecules directly using sunlight and carbon dioxide. Heterotrophs cannot do this, and depend upon autotrophs or other heterotrophs for their carbon source. Describing those carbon sources as "preformed" only suggests that they have already been manufactured by something else. The heterotroph that consumes these preformed molecules will then use them for other reactions--the manufacture of DNA from nucleic acids, the manufacture of proteins from amino acids--but those building blocks were already formed by another organism.