Living organisms use 20 standard amino acids to build proteins, so from the options 2, 5, 10, 20, the correct answer is 20.

Quick Scoop: The 20 Amino Acids

  • Proteins in almost all known life forms are constructed from a set of 20 common amino acids.
  • These 20 are often called the “standard” or “canonical” amino acids used in the genetic code.

Why the Confusion? 20, 21, or More?

  • In nature, there are hundreds of different amino-acid–like molecules, but only 20 are routinely used to make proteins in most organisms.
  • A few organisms can incorporate rare extras like selenocysteine and pyrrolysine, which is why some sources mention 21 or 22, but exams and textbooks usually expect 20 as the answer.

For your question “how many amino acids are found in living organisms? 2 5 10 20” the single best-choice answer is: 20.

Information gathered from public forums or data available on the internet and portrayed here.