Welcome to Symbiosis. This site deals mainly with subjects related to technology, but if you came here to look up things about symbiosis for a homework, I can offer you its definition:

"Symbiosis is a close, permanent, deep, intentional cohabitation of two living organisms, and it's beneficial for both parties (symbionts). Symbionts are, for example, lichens, fungus roots and some bacteria genera."

- Tasku-Fokus 1967 (book)