The document discusses biological explanations and treatments for obsessive compulsive disorder (OCD). It outlines the biological approach, including genetic and neural explanations for OCD. Genetically, twin studies have found OCD has a hereditary basis, though no single gene is responsible. Neurochemically, abnormal levels of serotonin in the brain are linked to OCD symptoms. Treatment focuses on drug therapy like selective serotonin reuptake inhibitors (SSRIs) to raise serotonin levels and reduce symptoms, though drugs can have side effects.