Plethora would be the collective noun because it is a group.
The serotonin is a chemical neurotransmitter in the brain responses to keep the "happy mood" in humans, so-called, the "the molecule of happiness". Low levels of serotonin may produce serious problems like depression, anxiety, memory low-self esteem, irritation and so on. When a lover has a low serotonin level in his brain, his mood and general behavior can be affected in great ways. Young people may not be aware of the great-negative consequences of the decreased levels of serotonin and a treatment should be carry out. Depression and anxiety can lead to terrible outcomes in someone's life.
Scannable resumes are a brief account of a person’s education, qualifications, and previous experience, that can be scanned electronically into an employer's database.
Hope this helps
