Question 7
What makes an amino acid an essential amino acid?
The right answer is the one marked above.
Some amino acids cannot be produced inside the body at all. They have to be obtained through food, and that is what "essential" means here.
The word is about supply, not about importance or quantity — every one of the 20 is needed. Meat, fish, egg white and pulses such as mung bean and cowpea are the foods that carry them.