1. What are endorphins, and what causes cells in the brain to release them? 2. Why do endorphins have effects similar to those of drugs like morphine and heroin? 3. What is the effect of endorphins?...

1. What are endorphins, and what causes cells in the brain to release them?

2. Why do endorphins have effects similar to those of drugs like morphine and heroin?

3. What is the effect of endorphins?

4. Rank the following from the smallest to the largest level of organization: organ, organ system, tissue, cell.