Simplify the following text for a Grade 11 native English-speaking person.
Original: Biochemically derived from tryptophan , serotonin is primarily found in the gastrointestinal ( GI ) tract , platelets , and in the central nervous system ( CNS ) of animals including humans .
Simplified: It is derived from Tryptophan . Serotonin can mainly be found in the gastroinstestinal tract , platelets and central nervous system of certain animals including humans .