Here are all the episodes he kisses her ! Coming Together-Kisses her before he leaves leaving only a Note. Summer's End-kisses her in the Rain while dating Kit and Amy wants him back but he rejects her..
Symbiosis occurs when two different species benefit from living and working together. When one organism actually lives inside the other it's called endosymbiosis. The endosymbiotic theory describes how a large host cell and ingested bacteria could easily become dependent on one another for survival, resulting in a permanent relationship. Over millions of years of evolution, mitochondria and chloroplasts have become more specialized and today they cannot live outside the cell.
Usually organisms living that close together will be symbiotes of some kind. What kind it is depends on how each of the organisms is affected by the relationship-for example, if you had a tapeworm, it'd be a parasitic relationship, because the tapeworm feeds off of you, potentially at the expense of your health.